MANAGEMENT AND REHABILITATION PLAN FOR THE HOUT … · hout bay dunes management & rehabilitation plan ii Given the high cost of the exercise, the City and one of team members (DvE)

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MANAGEMENT AND REHABILITATION PLAN FOR THE HOUT BAY DUNES

Report PO 4501955067 prepared for the City of Cape

Town

First Draft: November 2012 Second Draft: February 2013

Final report: March 2013

Volume 2

A. Barrie Low and J. Deon van Eeden

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the 2011 Rand Water Trophy for BEST WATERWISE PROJECT in SOUTH AFRICA!

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hout bay dunes management & rehabilitation plan

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EXECUTIVE SUMMARY1

An ecological assessment of the Hout Bay beachfront dunes has found the area to be extremely degraded. Chief causes have been a combination of unusually strong summer easterly and south-easterly winds and summer drought over the 2010/11 season, coupled with a lack of maintenance and damage from pedestrians. The latter has been the single most decisive factor in dune degradation, particularly as the planning programme recommended by the CSIR in 1989 was not sustained. Linked with this has been poor town planning, with much of the climbing-falling dune between Hout Bay and Sandy Bay rendered non-functional due to development in the mobile dune zone. Development encroachment onto the beach and Hout Bay River estuary has also severely compromised the dynamics of the mobile dune system and meandering of the river mouth.

Four Management Options are evaluated which present choices for the client, the City of Cape Town (CCT). Essentially these are to maintain the status quo (Option 1), basic sand removal, maintenance of some plant cover, and keeping pedestrians off the dunes (Option 2), reshaping, coupled with selected dune removal, revegetation of disturbed areas, keeping pedestrians off the dunes, and maintenance of the entire dune area (Option 3), and major earthworks and removal of sand, removal of all infrastructure within the dune area, re-profiling all dunes between the Promenade and Mariner’s Wharf car parks, intensive revegetation of all reshaped dunes, installation of new irrigation, keeping pedestrians off the dunes, and perpetual maintenance (Option 4). We have recommended the last Option as it is the only one which will effectively solve the problem of windblown sand in the long-term and has proven success in the Big Bay and Dolphin Beach areas.

Dune functionality was divided into 15 Sectors, with Sectors being combined into six Management Units (MU’s) for ease of maintenance.

Modelled on Option 4, each MU is addressed by describing its background, past management, prognosis for management, and a detailed rehabilitation/maintenance proposal presented. The latter entails removal of sand, re-profiling of dunes, kelp removal, volumes of sand to be removed, and costing for the operation.

Recommendations for Option 4, projected management costs are as follows (rounded off to the nearest R10 000):

Management Unit 1: R2 450 000

Management Units 2 and 3: R2 900 000

Management Unit 4: R110 000

Management Unit 5 (the bulk of the site): R11 250 000


Basic assessment and public participation: R500 000

Total: R19 860 000 (excl. VAT).

1 Quote as: Low, A B. and van Eeden J.D., Management and Rehabilitation plan for the Hout Bay Dunes. Volume

2. Vula Environmental Service, Vredenburg


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Given the high cost of the exercise, the City and one of team members (DvE) discussed ways in which the City could contribute in kind to the overall costing. This reduced the budget by a substantial R????, with the City contributing significantly for labour and plant.

The revised costing is as follows:

Although it is our recommendation that ALL interventions are implemented as one, i.e. over a

single season, management could be phased in as follows:

Year 1: MU’s 1 and 6 (these are the most intensively used by the public) (R5 100 000)

Year 2: MU’s 2, 3 & 4 (including Hout Bay River estuary) (R3 010 000)

Year 3: MU5 (this is the largest intervention, requiring removal of massive amounts of sand) (R11 250 000).

The public participation process (R500 000) should be undertaken during the first year.

Furthermore, a management plan should be drawn up for the Hout Bay River, which would include consideration of the interaction between the river estuary and mouth, with management of the dunes and river being integrated by the City.

However, priority work could be undertaken, whereby the City would contribute labour and plant worth some R7.567 million and funding R5.650 million in external contracting. A further R6.553 million would need to be re-evaluated.

The report ends with a section on Monitoring, an element which was sorely missing in previous maintenance attempts. Good management must be underpinned by thorough, predictive monitoring which is absolutely essential for recording the efficacy of dune management.

Urgency for management intervention on a perpetual basis is stressed, given the massive build-up of bare and mobile sand in the area and the increased nuisance value sand will have in the foreseeable future. To this end, a management plan should be drawn up for the Hout Bay River, one which would include consideration of the interaction between the river estuary and primary dunes, with management of the dunes and river being integrated by the City.


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CONTENTS

EXECUTIVE SUMMARY ................................................................................................ I

GLOSSARY .............................................................................................................. VIII

ABBREVIATIONS ....................................................................................................... IX

1. PREFACE TO VOLUME 2 ...................................................................................... 1

2. INTRODUCTION .................................................................................................... 1

3. TERMS OF REFERENCE ...................................................................................... 2

4. EXPECTED OUTCOMES ....................................................................................... 2

5. APPROACH ........................................................................................................... 3

Desktop review and GIS layers ..................................................................... 3 5.1

Evaluation of dune management programmes ............................................ 3 5.2

Field survey .................................................................................................... 3 5.3

Dune contour data .......................................................................................... 4 5.4

Dune transects................................................................................................ 4 5.5

Sand volumes ................................................................................................. 4 5.6

Management plan and estimates .................................................................. 5 5.7

6. BACKGROUND ...................................................................................................... 6

Context (from Low & Pond, 2004; Low, 2012) .............................................. 6 6.1

History of the Hout Bay-Sandy Bay climbing-falling dune ......................... 9 6.2

Source and dynamics of sand supply ........................................................ 10 6.3

Stability of coastline ..................................................................................... 10 6.4

Sand movement dynamics .......................................................................... 11 6.5

Dumping of rubble on beachfront ............................................................... 11 6.6

Climate .......................................................................................................... 11 6.7

Coastal setback line ..................................................................................... 14 6.8

Vegetation ..................................................................................................... 14 6.9

History of planning in area .......................................................................... 17 6.10

7. REVIEW OF BIG BAY AND DOLPHIN BEACH MANAGEMENT

APPROACHES ..................................................................................................... 20

Advantages of this approach ...................................................................... 20 7.1

Implications of this approach ...................................................................... 21 7.2


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8. EVALUATION OF SAND MOVEMENT AT HOUT BAY BETWEEN 2009 AND

2011 ...................................................................................................................... 27

Survey of dune contours ............................................................................. 27 8.1

Change in sand volumes ............................................................................. 27 8.2

9. MANAGEMENT OF HOUT BAY DUNES ............................................................. 32

Dune management options ......................................................................... 32 9.1

The prime drivers in determining the sequence: ....................................... 40 9.2

10. HOUT BAY DUNE MANAGEMENT UNITS ......................................................... 46

Management Unit 1 (Sector 1 - eastern activities beach) .......................... 46 10.1

Management Unit 2 (Sectors 2 & 3 – back dunes above eastern beach) . 54 10.2

Management Unit 3 (part of Sectors 2 and 4 – beach around Hout Bay 10.3

River lower estuary and mouth) ............................................................... 62

Management Unit 4 (Sector 5 – sandy embankment between Hout Bay 10.4

River estuary and HBBC) .......................................................................... 66

Management Unit 5 (Sectors 6 to 14 – beach and dunes between Hout 10.5

Bay Beach Club and the storm water outlet adjacent to the western

car park) ..................................................................................................... 71

Management Unit 6 (Sector 15 – beach and parking area at Mariner’s 10.6

Wharf) ......................................................................................................... 87

11. MONITORING OF HOUT BAY DUNE MANAGEMENT ....................................... 93

Monitoring Methods ..................................................................................... 93 11.1

Maintenance requirements .......................................................................... 94 11.2

12. SUMMARY OF COST ESTIMATES ..................................................................... 96

13. RECOMMENDATIONS AND CONCLUSIONS .................................................... 98

14. ACKNOWLEDGEMENTS ................................................................................... 100

15. REFERENCES ................................................................................................... 101


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FIGURES

Figure 1 Comparison of 1948 and 2011 aerial view of Hout Bay 7

Figure 2 Noordhoek monthly rainfall 12

Figure 3 Noordhoek wind patterns 13

Figure 4 Coastal setback line for study area 15

Figure 5 Cost of Big Bay Management options 22

Figure 6 Dolphin Beach 2001 23

Figure 7 Dolphin Beach 2009 23

Figure 8 Big Bay frontal dune scour 24

Figure 9 Big Bay frontal dune management prior to planting 24

Figure 10 Big Bay frontal dune management post planting 25

Figure 11 Erosion at Blaauwberg 25

Figure 12 Dune contours for Hout Bay Lidar May 2009 28

Figure 13 Dune contours for Hout Bay survey November 2011 29

Figure 14 Dune management sections for Hout Bay 30

Figure 15 Management Units for Hout Bay Dunes 34

Figure 16 Location of 13 transects 35

Figure 17 Typical dune management regime for Hout Bay 41

Figure 18 Proposed planting east 42

Figure 19 Proposed planting west 43

Figure 20 Schematic irrigation design east 44

Figure 21 Schematic irrigation design west 45

Figure 22 Schematic design of sand trap along promenade 51

Figure 23 Current and reconstructed Profile A (Sector 1 – eastern beach front and Promenade)

52

Figure 24 Current and reconstructed Profile B (Sector 1 – eastern beachfront, east of Hout Bay River mouth)

53

Figure 25a Current and reconstructed Profile C (Sectors 2 & 3 – eastern beach front and Promenade)

60

Figure 25b Current and reconstructed Profile C (Sectors 2 & 3 – back dunes in eastern section)

61


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Figure 26 Current and reconstructed Profile D (Sector 4 – beach around Hout Bay River lower estuary and mouth)

65

Figure 27a Current and reconstructed profile E (Sector 5 – section below Hout Bay Beach Club, west of the Hout Bay River estuary)

69

Figure 27b Remainder of profile E (no reconstruction) Sector 8 – section west of Hout Bay Beach Club)

70

Figure 28 Hout Bay Beach extent of planting in 2001 76

Figure 29 Detailed Profile 77

Figure 30a Current and reconstructed Profile F: front section of beach, high dunes and blowout directly west of HBBC (Sectors 6, 7 & 8)

78

Figure 30b Current and reconstructed Profile F: back section of high dunes directly west of HBBC (Sectors 6, 7 & 8)

79

Figure 31a Current and reconstructed Profile G: front section – main dunes between HBBC and Mariner’s Wharf (Sectors 6, 7 & 8)

80

Figure 31b Current and reconstructed Profile G: back section – main dunes between HBBC and Mariner’s Wharf (Sectors 6, 7 & 8)

81

Figure 32a Current and reconstructed Profile H: front section – main dunes south of Princess Road car park (Sectors 6, 7 & 8)

82

Figure 32b Current and reconstructed Profile H: back section – main dunes south of Princess Road car park (Sectors 6, 7 & 8)

83

Figure 33 Current and reconstructed Profile I: dunes immediately adjacent to (east) Yacht Club (Sectors 4, 5 & 8)

84

Figure 34 Current and reconstructed Profile J: dunes immediately west of Yacht Club (Sectors 13 & 14)

85

Figure 35 Current and reconstructed Profile K: directly east of Mariner’s Wharf car park (Sectors 13 & 14)

86

Figure 36 Schematic design of sand trap along Mariners Warf car park 90

Figure 37 Current and reconstructed Profile L: stormwater outlet just east of Mariner’s Wharf car park (Sector 15)

91

Figure 38 Current and reconstructed Profile M (Sector 15) – Mariner’s Wharf car park and beach, and bus parking area

92


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TABLES Table 1 Dune systems occurring within the City of Cape Town (from Low &

Pond, 2004) (modified in August, 2011) 8

Table 2 General characteristics of the Hout Bay-Sandy Bay climbing-falling dune systems on the Cape Peninsula (modified from Low & Pond, 2001)

18

Table 3 Chief flora and vegetation features of the Hout Bay-Sandy Bay dune system (modified from Low & Pond, 2001)

19

Table 4 Evaluation of artificial and managed dune profiles (drawn from experience at Dolphin Beach and Big Bay maintenance phase)

26

Table 5 Dune mobility in selected parts of the Cape Flats, Peninsula and West Coast determined by measuring movement of mobile dune front on sequential Google images

31

Table 6 Possible options for managing the dunes at Hout Bay 36

Table 7 Comparison of management costs 97

APPENDICES APPENDIX 1. WINDROSES FROM CAPE POINT FARMS, NOORDHOEK

APPENDIX 2. DETAILS OF ERVEN OWNERSHIP, ZONING AND LANDUSE IN THE HOUT BAY DUNES STUDY AREA APPENDIX 3. IMAGES OF THE STUDY AREA APPENDIX 4. DETAILED MANAGEMENT COSTS (submitted as a separate PDF file)


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GLOSSARY FOR VOLUMES 1 & 2

Back dune Dune towards the back of a succession, usually non-mobile and stabilised by perennial vegetation

Climbing-falling dune Coastal dunes form where waves cause sand to accumulate on beaches, and the sand is then blown inland by prevailing onshore winds. Vegetation, rocks and other obstacles trap the moving sand and gradually sand accumulates, forming a dune. The wind continues to shape and move the dunes by eroding sand on the windward side and depositing it on the leeward side. This causes the dune to ‘migrate’ inland. In some cases the mobile sand is blown up a hill or mountainside and is deposited on the other side, where it moves downslope. This is termed a climbing-falling dune

Coastal setback line The setback is designed as a buffer between the high water mark and a stable area inland of the HWM and is aimed at:

(i) protecting coastal property and public safety;

(ii) protecting coastal ecosystems, particularly those prone to degradation and destabilisation, e.g. mobile dunes;

(iii) preserving the aesthetic value of the coastal zone;

(iv) prohibiting or restricting the erection, alteration or extension of structures that are wholly or partially seaward of the coastal set-back line.

Frontal (fore) dune Dune at the front of a succession, generally located at or near the HWM. This is in a zone of maximum instability and frontal dues are generally un- or poorly vegetated

Headland bypass dune A dune which literally bypasses a (rocky) headland, usually following a low valley. The Hout Bay-Sandy Bay system is a HBD, historically moving between the Karbonkelberg and Little Lion’s Head

Hummock dune As its name suggests these are hummocks amongst the frontal or pioneering dunes and which migrate away from the prevailing wind. On the Hout Bay beachfront, hummock dunes migrate in a general north-westerly direction. Hummocks tend to be poorly vegetated with pioneering species

Monitoring The process whereby an element(s) of the environment, in this case rehabilitation and related work, is observed over a time period, and actions taken to ensure that rehabilitation work is effective

Rehabilitation A process where a degraded habitat/landscape is ameliorated, generally through modification of the substrate and planting of suitable pioneering and other species; rehabilitation is NOT restoration which aims at returning a habitat to original state

Transect Generally a line through a habitat or ecosystem along which information is collected or interventions undertaken


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ABBREVIATIONS FOR VOLUMES 1 & 2

DTM Digital Terrain Model. A DTM represents the topography (height above sea level) of the bare ground surface without any objects such as plants and buildings

GIS Geographic information system. The study used ARC GIS/ARC INFO for its mapping and analysis, for example calculating sand volumes and estimating changes in dune extent over time

HBBC Hout Bay Beach Club, a development situated on the Hout Bay beachfront and alongside the Hout Bay estuary

LIDAR LIght Detection and Ranging or Laser Imaging Detection and Ranging is an optical remote sensing technology that can measure the distance to, in this case, dune topography, by illuminating the target with laser light and analysing the backscattered light; from this is derived an accurate account of height at point scale, and therefore the topography and contours of a site.

OEMP Operational management plan

TIN A Triangulated Irregular Network is a digital used in GIS for the representation of the physical land surface made up of irregularly distributed nodes and lines with 3D coordinates that are arranged in a network of non-overlapping triangles. Topographic data from LIDAR and manual surveys is converted to a TIN prior to calculating sand volumes (see Section 5.6 of the report)


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1. PREFACE TO VOLUME 2

The study of dune management of the Hout Bay dunes encompasses two reports. Volume 1

deals with the essential actions which will be required to manage the dunes in a satisfactory

way, but excludes most of the technical detail on which the study was based.

Volume 2 (this Volume) is basically the Technical report for the study and describes the

approach and results of the research and analysis, concluding with the recommendation that

three phases of operation need to be followed if dune management at Hout Bay is to be a

success. It also includes most of the Figures and Diagrams which underpin the work.

Whilst the two reports should ideally be read in conjunction with each other, Volume 1

provides sufficient information for officials to make a cogent decision on the three phases of

dune management described.

2. INTRODUCTION

Mobile sand has become a major problem above the beach at Hout Bay. Ever since

development compromised the functioning of the climbing-falling dune system between Hout

Bay and Sandy Bay, sand has, as it were, had no place to go, with development having

severed the link between the two Bays. Despite strong recommendations for windblown

sand (CSIR, 1989), management of the problem was eventually curtailed and then stopped

due to lack of funds, and dare we say, interest. The result is that the problem became

exacerbated and unwanted mobile sand, driven by the south-easterly winds, is now a major

issue in the Hout Bay development.

In March 2012, the City of Cape Town (CCT) called for tenders to address the issue. The

tender was won by VULA and Coastec, acting in partnership, with an appointment on 7 June

2012. The project seeks to provide a solution(s) for windblown sand emanating from the

beach at Hout Bay and to provide a workable basis from which the City can manage the

beach in an ecologically responsible way.

Initially a draft report was produced for the City to review. Following the review of the draft

report, and, whilst agreeing with the recommendations for interventive action and

rehabilitation on the Hout Bay beachfront, City officials found the costs for implementation to

be too high. Howard Gold, Amy Davison (City of Cape Town) and Deon van Eeden


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discussed the possibility of revising the initial cost estimate and splitting the costs between

potential “in house” cost and contract cost. The City was able to reduce much of the total

cost of the project through provision of labour and plant. This resulted in a second draft

(revised) which now included a revised cost structure.

Phasing of the project was considered and incorporated in the new revised cost estimate.

3. TERMS OF REFERENCE

Source and review the CSIR Report (Hout Bay Beachfront: Development Plan, 1989), and any other relevant material, detailing a previous dune management strategy at Hout Bay Beach;

Consider and evaluate alternative management approaches to the problem;

Conduct an assessment of the status quo, based on an on-site survey and inspection that will include a “per property” review and comment, and which will also tie in with a review of adjacent plots;

Consolidate a basic photo documentation and basic quantification per property for the Hout Bay Beachfront;

Compile and present an Assessment Report to the City;

Develop a detailed Long-Term Dune and Beachfront Management Strategy for Hout Bay based on the most appropriate and sustainable option(s), and which will include budgetary and capacity requirements;

The Management Strategy must consider viable, cost effective and legal mechanisms to deal with/dispose of any sand that will be in excess of the needs of the Strategy.

4. EXPECTED OUTCOMES

Progress reports to the City’s Project Steering Committee (PSC);

Consultation with key City functions during the project in sourcing of information;

Deliver a detailed Assessment Report to the PSC;

Present a final Dune and Beachfront Management Strategy to the PSC.


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5. APPROACH

Desktop review and GIS layers 5.1

Key reports consulted included the CSIR’s (1989) dune management plan and the Hout Bay

estuary account (Grindley, 1988). Several existing GIS layers were interrogated and these

included the coastal dune survey for the City (Low, 2004, and Low & Pond, 2007).

Legal aspects of coastal dune management were also included. Owing to the potential

impact of the proposed management measures, the detailed planning phase should comply

with the requirements as stipulated by the relevant legislation. This will include:

The National Environmental Management Biodiversity Act of 2004 (Act No. 10 of 2004);

National Water Act of 1998 (Act No. 36 of 1998);

National Environmental Management-Integrated Coastal Management (Act No. 24 of 2008);

National Environmental Management Act: Amendment of regulations for Control of use of vehicles in coastal zone, (G 33711 – GN. 1012)

Although much of the dune system at Hout Bay has been artificially manipulated, approvals

will need to be sought for a range of interventions including removal of sand and altering of

the river channel. Once a detailed plan for managing the Hout Bay dunes is developed, then

the various triggers which these Acts deal with would need to be addressed.

Evaluation of dune management programmes 5.2

Dune management initiatives at Dolphin Beach and Big Bay provided an essential backdrop

to approaches applied in the Hout Bay study. Both these studies give excellent accounts of

the do’s and don’ts of dune management along the City coast, particularly where mobile

sand and development are in conflict.

Field survey 5.3

The site was visited on 1 and 26 June, and 1 October 2012, to record the characteristics of

dune mobility, plant species and vegetation, and development, as well photographic records

of the state of the dunes in the various private and City Erven, and to make observations on

seasonal dynamics of the system.

http://www.environment.gov.za/sites/default/files/legislations/nema_amendment_g33711rg9404gon1012.pdf

http://www.environment.gov.za/sites/default/files/legislations/nema_amendment_g33711rg9404gon1012.pdf


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Dune contour data 5.4

Two sets of dune contour data were available for the study. In May 2009, the City undertook

a Lidar aerial survey of Hout Bay and this included most of the dunes in the study area.

Further, in November 2011 the City undertook a manual survey of the dunes but which

excluded the northern part of the study area. However, the key sand mobility routes were

included, enabling direct comparison of changes over the one a half year period between

contours. During this visit extensive photographic records were taken of the state of the site

in the various private and City Erven.

Dune transects 5.5

On 19 June 2012, one of us (ABL) visited the site with Mr John Coetzee, a surveyor with the

City, in order to survey dune profiles from the high water mark to development behind the

dunes (Harbour Road, Princess Road, Beach Road, Promenade). The transects were key to

reviewing current and desirable dune sections for the management plan, as well indicating

the amount of sand required to be removed from the site.

Sand volumes 5.6

Based upon the contours and using the sectors provide by the consultants, sand volumes

were computed for the two datasets. Digital Terrain Models (DTM) for the study area were

constructed for May 2009 and November 2011. Input for the 2009 DTM was a LIDAR mass-

point data set provided by the City; the 2011 DTM was supplied in a point elevation file

representing a 0.5 m GRID of the study area. The terrain data provided was converted into

TIN’s (triangulated irregular networks) in order to facilitate the volume calculations using the

following steps:

Step 1: the 2009 LIDAR mass-point data were converted to a 0.5 m DTM GRID using Global Mapper v13. Both the 2009 DTM and the 2011 DTM provided were then converted to TIN’s using ARCGIS 10.

Step 2: the ARCGIS "Polygon Volume Tool" was used to calculate the volume per each Hout Bay dune sector for the 2009 and 2011 TIN’s. This was undertaken by subtracting the 2009 volumes from the 2011 volumes to provide the net volume change over this period. This amount was then divided by the 2009 volume to give the percentage volume change per sector.

Equation: 2011 Vol - 2009 Vol = Volume Change

Volume Change/2009 VOL x 100 = Percentage Volume Change.


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Step 3: the GRID map of volume change was created as follows: "Surface Difference Tool" (ARCGIS) was used to generate a GRID (10 m x 10 m) showing the elevation differences between 2009 and 2011 TIN’s. This grid was multiplied by 100 to get a volume per cell.

Equation: Vol 2011-Vol 2009/Vol 2009 = Volume difference per 10 m x 10 m grid.

Management plan and estimates 5.7

The impact of human settlement in the Hout Bay valley and in particular the establishment of

an urban area between the Karbonkelberg and the back of Table Mountain has not only

compromised the climbing-falling dune system but also limited the management options

available. In determining the most suitable management approach to this severely modified

system, in particular to ensure ease of implementation, the study area was divided into six

management units.

The reasons for the failure of past interventions were explored as this has to be understood

in order to avoid a repeat of these failures. There are two key issues regarding past

interventions:

Limited scale of structured intervention exposed these managed areas to the impact of windblown sand that originated from un-managed areas, increasing the need and intensity of maintenance required

Failure of maintenance in areas where interventions were implemented.

Different management options are proposed and one recommended on the basis of the most

cost-effective approach in the long term.

Cost implications will be substantial for any of the approaches and were evaluated against

the experiences of similar management regimes at Big Bay and Dolphin Beach. Final costs

are provided only for our preferred management intervention and will require refinement once

the City has decided on the appropriate course of action.

A cost estimate, based on current rates has been prepared for the most suitable

management option, Option 4 (see Section 9.1 below for discussion of options) (Appendix 4).

Since a detailed design would be required, the estimate is a guideline to assist the planning

and budgeting phase.


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6. BACKGROUND

Much anecdotal information and scientific study exists for the Hout Bay valley. For this

section we draw on two main sources: Grindley’s (1988) account of the Hout Bay River and

estuary, and the CSIR’s (1989) report on the management of the dunes. Both tell a story of

a natural climbing falling and headland bypass dune which was mobile from the Hout Bay

beach to Sandy Bay. The functioning of the dune became gradually compromised with the

onset of ill-planned development which took no cognizance of the importance of this rare

system, nor of the consequences of such planning action. In short, by the late 1980’s, the

dune had ceased to function in its entirety, with the dune plume permanently severed by

residential development along its path. The chief result of this was that sand continued to

accumulate on the beach and inland, providing a major hazard to residential development

and services such as roads.

Context (from Low & Pond, 2004; Low, 2012) 6.1

The lot of the Hout Bay-Sandy Bay climbing falling dune system, as aptly illustrated in Ken

Tinley’s (1985) monumental work on South African dune systems, has not been a good one.

Of the nine such systems found on the Cape Peninsula, only one retains some semblance of

naturalness (Low, 2012). The rest have succumbed to development which has by and large

attenuated sand supply to these magnificent systems. The Hout Bay-Sandy Bay system has

been severely compromised by road development, and housing and industrial activities at

the Hout Bay harbour, with the system – presently 3.5 km long (maximum 130 m absl), 1.5

km wide and 202 ha in extent (mapped from 2011 aerial photography) - now rendered

impotent due to sand flow being blocked by this development. Comparison with old aerial

photos dating back to 1948 (Figure 1) indicates that once wide broad expanses of exposed

sand have now been unnaturally vegetated, mainly by introduced rooikrans (Acacia cyclops).

This has resulted in the loss – over six decades - of 80 % of the mobile dunes! But, some

parts are still unvegetated and this can be seen quite clearly above the Hout Bay urban area

where sandstone bedrock has now become exposed locally. This indicates the dune system

still has a propensity to move northwards in the direction of Sandy Bay, but the replenishing

sand from the south is no longer available.

Low & Pond (2004) described seven major dune systems occurring in the CCT area. These

were reduced to four and are listed in Table 1. These are climbing-falling, headland bypass,

rock barrier and transgressive inland, by far the largest in extent.


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The Hout Bay-Sandy Bay system incidentally can also be termed a headland bypass system,

as it cuts off the Karbonkelberg.

The report laments the reduction in sand supply to the climbing-falling dune systems but

proposes conservation measures which would enhance their already compromised status.

These include conservation action such as formal protection of key dune complexes,

establishment of coastal and inland linkages to ensure greater dune habitat viability, removal

and control of woody alien vegetation and, perhaps, even restoration of these ancient

systems.

Table 1. Dune systems occurring within the City of Cape Town (from Low & Pond, 2004) (modified in August, 2011)

Dune system Description Area (ha) (% of total)

Climbing-falling System “climbs” over a barrier, usually a mountain or hill, and descends on the other side. This is a complex system, embracing a number of dune types.

1 224.5 (5.9)

Headland bypass This system “bi-passes” a rocky headland

498.2 (2.4)

Rock barrier deposit

Where sand accumulates against a rocky outcrop/ mountain side.

16.5 (0.1)

Transgressive inland

A mobile to stable dune system, which is moving inland or has moved inland in the past

18 965.2 (91.6)

Total 20 704.4


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History of the Hout Bay-Sandy Bay climbing-falling dune 6.2

The earliest available aerial photograph for the area (1944) indicates sparsely vegetated

hummock dunes present to the west of the river mouth. The road to the harbour crosses the

southern part of the dune system but does not impede northwards movement of sand.

By 1968 the sediment pathway has been severely compromised by development and

stabilization of vegetation, and by 1989, the system has ceased to function as development

has permanently cut off sand supply from the south. The situation is severely exacerbated

between 1989 and 2000, with unprecedented development in the valley.

In 1979, hummocks are still visible west of the river mouth, but are now backed by a gravel

car park, presumably to reduce windblown sand. Brushwood barriers have been erected to

prevent windblown sand from encroaching on development to the north.

By 1987, the sand encroachment observed in 1979 has been arrested through the

establishment of vegetation on the mobile dunes. Sand trapping barriers have been erected

between the gravel car park in the east and the river mouth, and across the beach to the east

of the mouth.

A comparison of the 1948 and 2011 aerial photos (Figure 1) indicates a major loss of mobile

sand between the two periods. Losses are attributed to an exponential increase in the urban

footprint (2011) with 178.3 ha in 1948 compared with a mere 29.9 ha in 2010. However, a

year later when a major sand ingression occurred at Hout Bay (see below), the area of bare

sand had increased slightly to 30.2 ha.

A site visit to the area by the CSIR on 22 February 1989 reported the following (CSIR, 1989):

(i) Diagonally placed, unvegetated brushwood barriers have been constructed at the eastern end of the beach (1.5 to 3.5 m tall). Sand is periodically removed through bulldozing back onto the beach. A dune of 8 m tall is located inland of Beach Road

(ii) The beach is flat and wide in the vicinity of the river mouth, backed by degraded hummock dunes vegetated with marram grass

(iii) To the west of the river mouth, vegetated compound dunes rise to 13 m. Low, incipient foredunes are located at the base of the higher dunes. A deflation hollow occurs between here and the western car park, with several hummocks – this appears to be the path of the strongest winds and the main source of sand across the car park and into Princess St.

(iv) The sea wall in front of the gravel car park stops windblown sand

(v) The western end of the beach is flat; windblown sand is a problem for the harbour.


10

Source and dynamics of sand supply 6.3

Although Grindley (1988) claims the main source of windblown sand on the mobile dunes

was during the Pleistocene (1.5 my to 14 000 years ago when sea levels dropped to 100 m

below their present levels), she did not explain that sand ingression inland was a recurring

phenomenon, regardless of past exposure. Thus, although much of the Hout Bay-Sandy

mobile dune system has been lost to residential development, the tendency is for sand

supply from Hout Bay to continue.

Hout Bay is a minor, crescentic pocket embayment with a small beach which is protected

from the south-westerly winds, but exposed to those from the south-east. Sand deposition

on the beach is governed by the following factors: long-shore drift, on-off-shore transport (the

latter two due primarily to wave action), sand characteristics (grain size and mass), and wind

(direction, strength and seasonality. Under natural conditions these processes reach a

dynamic equilibrium; however this equilibrium is compromised by manmade interventions in

the area. These include:

(i) The harbour breakwater (400 m long in 1989), with a subsequent northern pier and other quays;

(ii) Construction of a revetment in front of the Yacht Club and parking area

(iii) Building of houses north of the beach;

(iv) Planting of vegetation around the houses;

(v) Possible dredging of the harbour mouth.

Stability of coastline 6.4

Studies have shown that the beach eroded between 1944 and 1979, but that the eastern

section accreted between 1979 and 1987 with the western section eroding during the same

period. The latter was due to the construction of the harbour wall and breakwater, between

1936 and 1966 (Fromme, 1985, in CSIR, 1989a). The main sediment transport is on-off

shore movement, with the potential for such movement increasing towards Flora Bay in the

east (i.e. below the start of Chapman’s Peak Drive). Of major significance is that sand blown

inland is no longer recycled to the beach.

Sand cannot be returned to the western beach by northerly winds due to stabilization of the

Hout Bay-Sandy Bay climbing falling dune. We would also argue that the damper sands in

winter would also greatly impeded southwards movement.

In summary, the CSIR predicted a 40 m3-1yr-1 net northwards movement of sand.


11

Sand movement dynamics 6.5

(i) Wind

Wind velocity ranges from 0 to 20 ms-1, but mostly between 0 and 6 to 8 ms-1.

(ii) Direction

Wind arises mainly in the south and south-south east, but there is also a north-north west to north-west component.

(iii) Sand

Grains are coarser in the east than the west. Finer sand will move more readily.

Using the method of Swart (1986), the following sand movement was computed:

S/SE/SW direction (mainly in summer): 30 + 40 + 11 = 81 m3-1yr-1

N/NW/NE direction (mainly in winter): 10 + 13 + 12 = 35 m3-1yr-1

In other words, a net northwards dominance of wind direction. Note that sand movement is

based upon short-term data and a long-term monitoring of wind velocity is needed.

Dumping of rubble on beachfront 6.6

Rubble has been dumped intermittently over the years on the section of the beach just west

of the Promenade and north of the artificial windrows. This has altered natural sand

movement substantially, with rubble often being exposed in the teeth of a strong south-

easterly, and natural flow of sand inland being impeded.

Climate 6.7

Wind strength and direction, and wetness of sand, are the two critical factors affecting sand

movement. Although sand movement is from the south-east along much of the beach,

where is also a strong northwards vector as one moves up the slope of the climbing-falling

dune. Episodic sand pulse activity is also responsible for major ingressions. The major

difference in sand volumes between May 2009 and December 2011 suggests a marked

change in weather patterns, at least for the period under review. Weather data from the

nearest coastal station, Cape Point Farms (Chapman’s Peak unfortunately lacks continuity

due to theft of their server) is shown in Figure 2 (rainfall) and Figure 3 (summer wind

behaviour over the period 2009 to 2011). Detailed windroses for this period appear in

Appendix 1 (Figures A1a – A1f). The results clearly indicate a major shift in rainfall with an

unusually dry period over 2010/11 (Figure 2) coupled with strong easterly winds in summer

(Figure 3 and Appendix 1).


12


13


14

Of concern, too, is that stronger southerlies and easterlies are predicted for the City (City of

Cape Town, 2011). If this prediction is true then this is highly likely to exacerbate the quality

and movement of sand inland at Hout Bay.

(iii) Beach erosion

Between 1944 and 1987, the CSIR ascertained a loss of 46 m of beach at the harbour wall

and 78 m at Beach Road (1989a). The CSIR at that stage regarded the beach to be in

equilibrium (i.e. erosion = accretion). The erosion setback line computed for the artificial

establishment of a dune along the beach was therefore static (see below).

Coastal setback line 6.8

The City’s coastal edge for Hout Bay is shown in Figure 4. For our purposes, this is not a

true coastal setback line as it excludes Erf 9194 and much of Erf no. 653, both which contain

an the important back dune behind the eastern beach. This line also excludes part of the

Hout Bay River estuary. We have used a modified coastal setback line which uses Harbour

and Princess Roads as a boundary, but which includes the above-mentioned dune and

estuary (Figure 4), and this then forms the study area boundary for the project.

Vegetation 6.9

Dune vegetation is described in both Grindley (1988) and the CSIR (1989a). There is a

succession of plant communities between the beach and the stable back dunes.

6.9.1 Tetragonia decumbens-Acacia cyclops Foredunes

Just above the beach foredunes are colonized by Tetragonia decumbens kinkelbossie,

Acacia cyclops rooikrans, and Ammophila arenaria marram grass. Important species include

Tetragonia decumbens, Morella cordifolia dune waxberry, Metalasia muricata blombos,

Seriphium (Stoebe) plumosum slangbos and Chrysanthemoides monilifera bietou.

6.9.2 Metalasia muricata-Restio (Ischyrolepis) eleocharis Dune Fynbos

This community is present east of part of the Hout Bay-Sandy Bay climbing falling dune and

acts as a buffer between development and the mobile dune. Dominant species include

Metalasia muricata, Passerina corymbosa (P.vulgaris) gonnabas, Ehrharta villosa pypgras

and Hellmuthia membranacea duinebiesie.


15


16

6.9.1 Searsia (Rhus) glauca-Salvia africana-lutea Dune Scrub

This community represents the transition between Dune Fynbos and Dune Thicket (see

below) and is found in the stable dunes east of the Hout Bay River and reaching from 1 to

4 m tall. Dominant species include: Searsia glauca bloukoeniebos, Euclea racemosa

seeghwarrie, Olea exasperata slanghout, Osyris compressa Cape sumach, Otholobium

bracteolatum (O.fruticans) skaapbostee, Muraltia (Nylandtia) spinosa skilpadbessie and

Restio (Ischyrolepis) eleocharis duinekatstert.

6.9.2 Sideroxylon inerme-Chionanthus foveolatus Dune Thicket

This provides a good example of dune climax vegetation in the valley, reaching some 8 m

tall. The single canopy community is dominated by Sideroxylon inerme milkwood,

Chionanthus foveolatus fine-leaved ironwood, and Cassine peragua bastersaffraan. Large

Olea europaea subsp. africana individuals are also found.

6.9.3 Riverine vegetation

Although not particularly related to the current study, it is worth noting that the Hout Bay

River supports large stands of Phragmites australis fluitjiesriet along the edges of its main

channel and especially in its floodplain. The river tends to block during summer (low flow

and sand build up at the mouth), with a lagoon which could reach 500 m in length and 30 to

40 m wide (Grindley, 1988). The presence of primary mobile dunes at the mouth is thus

crucial to maintaining the seasonal lagoon, with winter spates breaking through these dunes

and providing a seasonal outlet to the sea.

A semi-detailed account of the dune characteristics in the area is given for the Hout Bay-

Sandy Bay systems (Table 2), and is derived from Low & Pond’s (2004) qualitative

assessment of the dune vegetation of the Cape Peninsula. Table 3 depicts the dominant

flora and community types for the Hout Bay-Sandy Bay system and both provide a good

indication of the diversity in both dune type as well as botany found here.


17

History of planning in area 6.10

At this stage it is appropriate to briefly highlight the role of inappropriate historical planning

decisions and how these are linked to challenges we are currently facing in Hout Bay. Urban

development in Hout Bay has severely compromised not only the functioning of the climbing-

falling dune system between Hout Bay and Sandy Bay, but has also led to high pollution,

altered flow rates and artificial narrowing of the Hout Bay River, through developments too

close to the river banks, with major negative impacts on the beachfront itself, through

construction of housing within the primary dune system. Inappropriate development

includes:

(i) The Hout Bay Beach Club (Hout Bay River estuary and primary dunes)

(ii) Beach Road, Promenade, car park and associated development (dunes)

(iii) Hout Bay harbour (dunes, coastline)

(iv) Mariner’s Wharf car park (dunes)

(v) Yacht Club; law enforcement offices (dunes)

(vi) Guesthouse (dunes).


18

Table 2. General characteristics of the Hout Bay-Sandy Bay climbing-falling dune systems on the Cape Peninsula (modified from Low & Pond, 2004)

Name of system

Location Dune topography Dune types and

systems Soils

Adjacent geology

Vegetation quality (indigenous) and threats

1a. Hout Bay-Sandy Bay

Southern slopes of Karbonkelberg (neck between Karbonkelberg and Sentinel)

Moderate to steep S-SE facing slopes at toe of mountain

Deflated parabolics; Old climbing/falling dune system (now inactive)

Calcareous sands; neutral sands (calc./acid transition); acid sands (aeolian calcareous)

Table Mountain Sandstone (TMS)

Very good, but with local Acacia; threats: alien invasion; dumping

1b. Hout Bay-Sandy Bay

Between Hout Bay and Sandy Bay

Steep east-facing slope with gentle gradient over neck. SE/NW trending parabolics; Sand sheet with blowouts

Coastal and inland embryo dunes; Deflated parabolics; Barchans; More recent mobile climbing/falling system; headland bypass (now inactive)

Calcareous sands; acid sands (aeolian calcareous); acid sands (TMS/granite)

TMS; granite Fair- medium. Threats: alien invasion (acacias), fire; erosion


19

Table 3. Chief flora and vegetation features of the Hout Bay-Sandy Bay dune system (modified from Low & Pond, 2004)

System Plant community (approx. % cover) Dominant plant species

1a. Hout Bay-Sandy Bay system (Hout Bay-Karbonkelberg/ Sentinel neck)

Dune Thicket (30-40) Cassine peragua, Salvia africana-lutea, Olea exasperata, Euclea racemosa, Osyris compressa

Dune Fynbos (20-30) Passerina paleacea, Othonna coronopifolia, Muraltia (Nylandtia) spinosa, Diosma hirsuta, Metalasia muricata, Thamnochortus erectus, Leucadendron coniferum

Scrub Forest (5-10) Sideroxylon inerme, Olea capensis

Sand Plain Fynbos (0-5) Protea scolymocephala, Diosma hirsuta

Dune Thicket/Mountain Fynbos thicket (0-5) Searsia (Rhus) spp.

Sand Plain Fynbos/ Mountain Fynbos (0-5) Leucadendron salignum, Diosma hirsuta

Dune Fynbos/Sand Plain Fynbos (0-5) Trichocephalus (Phylica) stipularis, Thamnochortus erectus

1b. Hout Bay-Sandy Bay system (Hout Bay to Sandy Bay)

Bare sand (60-70) No vegetation (40% mobile dunes, 30% shifting sand sheets)

Primary – inland (0-5) Morella cordifolia, Ehrharta villosa, Chrysanthemoides incana, Psoralea repens, Pelargonium capitatum, Hellmuthia membranacea, Asparagus spp., Solanum spp., Trachyandra divaricata, Cynanchum obtusifolium, Metalasia muricata, Chrysanthemoides monilifera, Acacia cyclops*, A.saligna* (massive invasion of acacias in burnt/cleared areas)

Dune Thicket (20-30) Euclea racemosa, Searsia (Rhus) lucida, Leucadendron coniferum, Searsia (Rhus) glauca, Sideroxylon inerme

Dune Thicket/Mountain Fynbos thicket (5-10) Euclea racemosa, Searsia (Rhus) lucida, Leucadendron coniferum


20

7. REVIEW OF BIG BAY AND DOLPHIN BEACH MANAGEMENT APPROACHES

A review of coastal dune management at Big Bay and Dolphin Beach indicates a number of

positive and negative aspects. Despite poor planning approvals, which led to development in

inappropriate sites, success was most evident when management was applied

immediately after construction. Big Bay has demonstrated major successes in dune

management in the post-construction phase over the last seven years (Figure 5). On the

other hand, Dolphin Beach functioned very well during the first four years after construction,

until 1999, when maintenance was curtailed (Figure 5). The impact of reduced maintenance

resulted in the loss of frontal dune vegetation. This accelerated sand accumulation in the

buffer dune by 2001, with the dune system becoming unstable by 2009. Ad hoc

interventions, including sand removal, planting and brush wood fence placement, have been

ineffectual and the approach is currently under review in order to restore the management

and functionality of the dune system. A summary of management interventions along this

coastline is shown in Figures 6 and 7 (Dolphin Beach), Figures 8 to 10 (Big Bay) and

Figure 11 (Blaauwberg).

Advantages of this approach 7.1

7.1.1 Possible management permutations are reduced and impacts are mitigated.

(a) Known parameters and predictable outcomes (within a range of variables) allow for effective long-term planning and management.

(b) Detailed management strategies can be incorporated into OEMP’s that can serve as an institutionalized memory. These OEMP’s can be adjusted over time as management techniques improve.

7.1.2 Reduced long term cost

(a) It has been shown at all the reference sites that the initial cost of repair is far greater than diligent ongoing maintenance

(b) Once systems are in place, management and external consultation is restricted to preventative management approaches and costly, ineffective ad hoc crisis management is avoided

7.1.3 Solution to critical issues such as nuisance

7.1.4 Restore system balance to “designer state”, based upon the profile provided by the CSIR (1991)

7.1.5 Scheduled maintenance can be predicted and included in budgets as part of a timeline of management interventions


21

7.1.6 The City environment gains benefits from a more functional dune system and concomitant delivery of ecosystem services, especially in combatting storm surges and controlling wind-blown sand.

Implications of this approach 7.2

7.2.1 A basic assessment2 is required

7.2.2 Cost, and possible phased implementation because of this

7.2.3 Management required during planning, implementation and maintenance

7.2.4 Public must be informed and perceptions must be managed

7.2.5 Disposal of sand might require a mining license, whilst other disposal methods present major challenges and even difficulties.

Table 4 provides an evaluation of artificial and managed dune profiles at Big Bay and

Dolphin Beach.

2Basic Assessment is the level of environmental assessment applied to activities listed in Listing 1 of

the regulations. These are smaller scale activities, the impacts of which are generally known and can be easily managed. See: http://www.eiatoolkit.ewt.org.za Listing 1: http://www.eiatoolkit.ewt.org.za/legal/listing1.html

http://www.eiatoolkit.ewt.org.za/

http://www.eiatoolkit.ewt.org.za/legal/listing1.html


22


23


24


25


26

Table 4. Evaluation of artificial and managed dune profiles (drawn from experience at Dolphin Beach and Big Bay maintenance phase)

Benefits Implications

1. Provide protection of infrastructure Not ideal situation, development tolerated within inappropriate areas (new setback line excludes these)

2. Excess sand is removed from system, providing window period to establish management systems

Semi-natural dune system is deprived of sand input

3. Designed profile is established with earthworks equipment and is simple to instate

EIA required

4. Compact design requires small area to be managed intensely, liberating larger areas for alternative land use

Functional dunes are sensitive to uncontrolled access; fencing required

5. Manage impact of ecological processes on development Because development is poorly located, attempts to manage ecological processes and impacts of natural occurrences, e.g. sea level fluctuation, sand movement within mobile dunes are difficult

6. Sand accumulates seasonally in the frontal scour zone part of the dune system and removed to circulation by winter storms

Natural sand system is deprived of sand input

7. Sand that escapes the scour zone is caught in the buffer zone before it can cause damage

Sand becomes land-locked due to vegetation cover in the buffer dune system and thus does not feed the natural flow of sand onto the beach. Once land-locked, unstable (and unvegetated) dune profiles develop as sand continues to accumulate; this situation becomes too complex to manage and sand removal is expensive and cannot be carried out in isolation

Note that regardless of the benefits, there are simply no practical alternatives to this form of dune management


27

8. EVALUATION OF SAND MOVEMENT AT HOUT BAY BETWEEN 2009 AND 2011

Survey of dune contours 8.1

Accurate contour surveys of the Hout Bay dunes (Lidar in May 2009, and manual surveying

in December 2011) (Figures 12 and 13) provide an excellent snapshot of sand movement

over one and a half years. Coincidentally during this period there was massive sand

ingression, illustrating that sand movement from sea to land is not constant but is heavily

dependent upon the vagaries of the weather! Recorded weather data from the Chapman’s

Peak toll gate are unfortunately erratic for this period so we have been unable to substantiate

our thesis that this ingression, confirmed by examining time-lapse aerial photographs from

Google Earth, occurred during the summer of 2010, a summer we suggest experienced

below average rainfall after an abnormally dry winter, and above average strength south-

easterlies. A similar pattern is also apparent for this period in mobile primary dunes along

the False Bay coast at Macassar, Monwabisi, Kapteinsklip, Strandfontein Resort and

Strandfontein Sewage Treatment Works, where inland movement of mobile sand was

between 4 and 33 m per annum (Table 5). All these dunes were driven by south-easterly

winds; correspondingly, no major sand ingressions were found for dunes whose direction is

from the south or south-west (for example at Koeberg and Yzerfontein).

Change in sand volumes 8.2

To provide accurate data on sand movement at Hout Bay, and therefore a key basis for

developing steps to deal with unwanted sand in the area, sand volumes were compared

between May 2009 and December 2011. Based upon the accurate surveys discussed in

Section 8.1 above, DTM models were developed for both instances. These were then

converted to sand volume using base levels extracted from the topographic information.

From an evaluation of aerial photography (mainly March 2009 and March 2011, as well as

the latest available Google image (16 December 2011)), fifteen Sectors encompassing major

paths of dune movement were interpreted from the aerials and mapped; these are shown in

Figure 14.


28


29


30


31

Table 5. Dune mobility in selected parts of the Cape Flats, Peninsula and West Coast determined by measuring movement of mobile dune front on sequential Google images

Dif

f. (

m)

Mo

nth

s

Rate

(mo

nth

s)

Rate

(year)

Month/year

Sep 0

1

Sep 0

2

Dec 0

2

Mar

03

Jan 0

4

Mar

04

Jul 04

Mar

05

Jul 05

Nov 0

5

Nov 0

6

Dec 0

6

Jun 0

7

Aug 0

8

Feb 0

9

Nov 1

0

Sep 1

1

Nov 1

1

Dec 1

1

Feb-1

2

Cape Flats (SE-NW)

Macassar dune (resort)

0

36 153

195

195 81 2.4 28.9

Macassar dune (central)

0

23

73 141

176

176 77 2.3 27.4

Strandfontein sewage treatment works 0 26 78 124

149

184

184 72 2.6 30.7

Wolfgat 0

7 43

50

50 124 0.4 4.8

Cape Peninsula (SE-NW)

Hout Bay (west dune – left (1) 0

7

-8 21

43

41 102

108

108 123 0.9 10.5

Hout Bay (west dune – left (2) 0 -2 -14 18 51 79 100 108 108 123 0.9 10.5

Hout Bay (west dune – left (3) 0 -9 -8 5 21 43 53 59 59 123 0.5 5.8

Hout Bay (west dune – right (1) 0 23 8 18 28 75 91 88 88 123 0.7 8.6

Hout Bay (west dune – right (2) 0 19 -49 17 10 26 45 54 54 123 0.4 5.3

Hout Bay (west dune – right (3) 0 -45 -2 24 17 18 17 27 27 123 0.2 2.6

Platboom

0

41

240

240 88 2.7 32.7

Soetwater - right dune

0

41

103

165 165 96 1.7 20.6

A zero indicates start of measurement

Note: 1) Change indicates difference between commencement of initial measurement and position on previous Google image photo 2) Mobile dunes on the West Coast (all SSW-NNE or S-N trending) indicated little or no change in mobility 3) The dunes at Buffelsbaai (Peninsula) are busty stabilizing (i.e. vegetation cover is increasing)


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9. MANAGEMENT OF HOUT BAY DUNES

Based upon the past experiences of dune management at Hout Bay, particularly through the

work of the CSIR (1989), and more recently at Big Bay and Dolphin Beach (see above), we

have provided four possible scenarios for dune management at Hout Bay (Table 6). The site

has been divided into six Management Units (MU’s) (Figure 15) which are designed to

optimize implementation of the proposed interventions. In each MU, transects have been

drawn, based upon a field survey (Figure 16), to provide detail of current and desirable future

dune cross-sections or profiles, and response to current maintenance practices and past

interventions such as the implementation of the structured interventions in MU’s 4, and 5.

The re-profiled dune is crucial to the success of implementing the management

strategy for Hout Bay beach.

Dune management options3 9.1

Option 1 effectively is the business as usual approach (Table 6). The major advantages are

that it offers a low cost option in the short term, no environmental authorization and no

skilling of staff. However, the negatives are substantial and include long term cost in

repeated management interventions, continued impact on the Hout Bay River mouth,

continued ad hoc management interventions and ongoing damage by pedestrians. In

essence there is very little reduction in sand movement with significant volumes

accumulating in the area

Option 2 addresses essential removal of sand and the maintenance of some plant cover,

with some attempts at pedestrian control. Again this is a low cost Option, with no

environmental authorization required, no skilling of staff and very little increase in

management effort. The Option involves ad hoc removal of sand, continued impact on the

river mouth, and although the damage to the dunes by pedestrians is reduced, it is

nevertheless unchecked. As with Option 1, unwanted movement and accumulation of sand

continues.

3 The City is incurring significant costs as a consequence of the management status quo on the Hout

Bay beachfront. Under this scenario, these costs are expected to increase exponentially into the future


33

In Option 3, reshaping of the dunes is included, coupled with selective dune removal,

revegetation of disturbed areas and maintenance of the entire dune field on a long-term

basis, with pedestrians being kept off the dunes. This approach would lead to a reduction in

unwanted sand with chances of rehabilitation failure partially reduced. However, the

approach would require a Basic Assessment and is far more costly in the short term than the

above Options. This might result in a phased implementation of methods, with the whole

system not being managed as an entity. This Option requires a high level of management

during planning and implementation and sand disposal will be a challenge. The Option will

also require the reinstatement of water supply, re-profiling and revegetating of dunes, and

staff training will be needed for the more advanced management methods. Option 4 is

preferred as, in our opinion, it offers the best long-term and most cost-effective solution to

dealing with sand management and removal at Hout Bay, and stresses the need for

perpetual maintenance. It also requires the greatest intervention in that the whole dune

system needs major re-profiling, from the east to west, with removal of large volumes of

sand. Newly profiled dunes would need effective revegetating, with installation of new

irrigation and water supply. All infrastructure within the designated area should be removed.

Management interventions would be permanent and pedestrians would need to be kept off

the dunes at all times. This Option would allow the City to more successfully deal with

unwanted sand and should see the development of well-vegetated dunes with a subsequent

reduction in windblown sand, particularly during the dry summer months. Chances of

rehabilitation failure are substantially reduced, and, above all, costs are drastically reduced

(see outcome of business as usual versus long term intervention management for Big Bay

(see above). Negatives are the requirement of a Basic Assessment, relatively high costs in

the short term, and high level of management inputs. Disposal of high volumes of sand

would also be a major challenge and might require a mining licence.


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35


36

Table 6. Possible options for managing the dunes at Hout Bay (refer to detail in the text

OPTION PRO’S CON’S

1. Maintain status quo Low short term cost No environmental authorizations required No new-skilling of staff required

Immediate and long term cost of managing accumulative impact of non-stable sand

Indirect cost of mitigation borne by local landowners Management options limited Increased cost due to necessary and unplanned management

interventions Poor efficacy of emergency interventions Continued impact on river mouth and Hout Bay Beach Club Management actions not cost effective Ad hoc management actions not cost effective Unwanted sand movement significant Pedestrians continue to damage dunes Indirect costs such as reduction in tourism potential and associated

tourism derived revenue Frustrated local community Not a long term solution

2. Essential ad hoc sand removal; maintenance of some plant cover; attempts to keep pedestrians off the dunes; enforce non removal of kelp from all but two sectors

Low short term cost No environmental authorizations required No new-skilling of staff required No significant increase in management effort

required

Ad hoc sand management not a viable proposition Unpredictable behavior of old modified dune systems Limited success of ad hoc interventions along promenade Continued impact on river mouth and Hout Bay Beach Club Management actions not cost effective Management without predictable outcome Unwanted sand movement still significant Pedestrians continue to damage dunes Not a long term solution


37


3. Reshaping, coupled with selected dune removal, limited sand removal by pushing dunes back to sea, local cut to fill operations on limited scale; revegetation of disturbed areas and maintenance of the entire Hout Bay dune area, commencing from the east; perpetual maintenance; pedestrians kept off dunes

Reduction in unwanted sand Can be perceived by public to be a more “natural”

approach Less sand to be disposed of compared to option 4 Less dramatic impact on previously established

(planted) vegetation Chances of rehabilitation failure partially reduced Public must be informed and perceptions must be

managed Limited long-term tactical option

Basic assessment required Most costly option due to complex operation, restricted access, and

detail level of design and supervision/ management required Possible phased implementation due to cost and therefore slower to

implement full plan Management more complicated than first two scenarios and more

complex than option 4 High level of management required during planning and

implementation Disposal of sand a challenge and might require a mining license Gain only limited functional buffer capacity in the back dune areas due

to limited removal of accumulated sand Costs will rise for future phases; major interventions will still be

required Complex and costly re-instatement of part of existing (defunct)

services e.g. water supply and irrigation to portions of re-profiled dunes and disturbed areas

Increased need for training Opportunity for monitoring success of rehab limited due to complex

resulting land form


38


4. Major earthworks at inception, removal of all infrastructure (Yacht Club building, law enforcements offices, etc.), removal off site of excess sand, re-profile systems from east to west; major revegetation in functional bands; install new irrigation; perpetual maintenance; pedestrians kept off dunes

Preferred management option as variables such as uncontrolled sand deposition, impact of uncontrolled access and unpredictable plant mortalities are reduced and major impacts mitigated

Chances of rehabilitation failure substantially reduced

Increase in management skills Reduced long term cost Solution to critical issues e.g. presence of

unwanted sand Public must be informed and perceptions must be

managed Restore system balance to “designer, semi-natural

state” Scheduled maintenance can be predicted and

included in budgets Regain maximum buffer capacity to accumulate

incidental sand accumulation beyond scour zone thus reducing major maintenance intervention intervals

Monitoring likely to have positive outcomes predicting problem areas and reducing costs

Long-term solution

Basic Assessment required Costly in the short term Phased implementation likely to be less effective than simultaneous

implementation High level of management required during planning, implementation

and maintenance Disposal of sand a challenge and might require a mining licence Increased need for training


39

In short, the entire Hout Bay dune system must be managed as an integrated system

and NOT in piecemeal fashion, as has happened in the past. Management should be

phased in from the east and in the shortest possible timeframe. Part implementation of the

proposals would lead to inadequate management and more costly interventions at a later

stage (see Figure 5). It is for this reason that we have selected Option 4 (Table 6) as the

preferred approach to holistic management of this dune system. This has followed several

discussions with the project management team and the City, and represents an effort which

not only should save the City substantial costs in management in the long-term, but also in

developing a dune system which provides the lowest nuisance value with regard to

windblown sand.

For Option 4 to succeed, major earthworks, followed by dune reshaping and vegetating, are

required. The CSIR report (CSIR, 1989a) deals with four management zones, with an

additional area added when the Hout Bay Beach Club was developed. The review of the

sand volume movement between May 2009 and December 2011 has resulted in the division

of the dune system into 15 sectors (Figure 15) that reflect a net accrual or loss during the

period. In order to expedite more efficient management, some of these sectors have been

grouped together into “functional or management units” that can be implemented as a single

phase in a possible sequence of management interventions.

Six management units are recognized (MU 1 to 6 – see Figure 16). These are the eastern

beach, between Beach road and the first back dune system (MU1 – Sector 1 (see

Figure 15)); the beach above the high water mark, just east and west of the Hout Bay river

mouth (MU3 – Sector 3); the back dune system landward of this (MU2 – Sector 2); the Hout

Bay river estuary (this should be managed as part of MU’s 3 & 4, but the river requires its

own management plan); the artificial dunes just below Hout Bay Beach Club (HBBC) (MU4

– Sectors 4 & 5); the major primary and back dune systems between HBBC and the western

parking area (MU5 – Sectors 6 to 14); and the western parking area and beach at mariner’s

Wharf (MU6 – Sector 15) (see Figures 15 and 16).

Although not part of the scope of this study, it is absolutely critical that management on the

beachfront (dunes, river, stormwater) is aligned and that a CCT task force is set up to

facilitate this process.


40

The prime drivers in determining the sequence: 9.2

(i) the principle of addressing the problem at (or close to) source of impact

(ii) reduction of any management unit’s exposure to uncontrolled impact from upwind

(iii) systematic, sequential approach

(iv) addressing areas of greatest use first

(v) the HBBC, although severely exposed and affected, is managing the local footprint in front of the property by arrangement and per an approved OEMP4 providing opportunity to address primary problem areas and areas of source first.

Management should follow a set pattern as follows:

(i) remove inappropriate and derelict infrastructure

(ii) rescue usable indigenous plants

(iii) remove excess sand

(iv) re-profile systems from east to west

(v) install irrigation

(vi) vegetate dunes in functional bands using nursery grown material and seed. There are basically three bands of vegetation:

a) The Frontal Dune (an 8 to 10 m wide sacrificial area and foredune) that is exclusively marram grass

b) the marram grass frontal portion of the Buffer Dune, approximately 15 to 20 m wide marram grass/local plant species mix that forms the remainder of the Buffer Dune approximately 15 to 20 m wide

c) the Back Dune area approximately 50 to 60 m wide that is vegetated exclusively by local plant species and that covers the remainder of the dune area

(vii) translocate and establish the rescued plants from (ii) above (undertake as part of (vi))

(viii) erect fencing and establish controlled access points

(ix) ensure maintenance in perpetuity.

A typical managed dune profile appears in Figure 17, with the proposed planting programme

for the Hout Bay shown in Figures 18 (eastern beach) and 19 (western beach) as well as

irrigation plan. Included in Figure 18 is the proposed predisposal alignment of the river

mouth which should be trenched, together with management interventions on either side of

the channel. Schematic irrigation designs are shown in Figures 20 and 21. Note that back

dune and scour zone irrigation systems are separate.

4 The OEMP was due to have been submitted to DEA&DP for comment on 12 October 2012


41


42


43


44


45


46

10. HOUT BAY DUNE MANAGEMENT UNITS

Management Unit 1 (Sector 1 - eastern activities beach) - 10.1see Figures 15 & 16)

Ownership is by the City of Cape Town, with zoning as POS and use for beach activities (see Appendices 2 & 3 for details of Erven and images).

(i) Description and current status

The beach is flanked in the south-east by a rocky shore and inland by a low wall that forms

the foundation and edge of the Promenade. Periods of regression (receding) have been

shown by the beach in the past, with but sand input and loss appearing to be in equilibrium

by the late 1980’s (the CSIR (1989). According to the comparison between 2009 LIDAR data

and the 2011 survey conducted by the City of Cape Town, a net loss of 1% of the sand in

this sector occurred between May 2009 and December 2011. These figures are however

inaccurate as they do not take into account the management interventions that took place as

much of the accumulated sand was pushed back to sea during 2010 (Howard Gold,

pers.comm.). Correspondingly Sectors 13 and 14 experienced a 4% increase in sand

volume in the same period.

(ii) Past management

Ad hoc maintenance by the CCT and Hout Bay Ratepayer’s Association included the

erection of brushwood fencing at various angles, distances apart and intervals between 2006

and 2009) (DvE, pers.obs.). Coupled with this, no fences were erected during this period,

resulting in an increase in sand accumulation on the Promenade and in Beach Road.

The initial low vegetation cover on the remnant dunes that existed in the middle of and to the

west of the Sector gradually decreased from 2001 until 2008, with all vegetation having been

lost by 2009 (from examination of Google images). This resulted in unrestricted sand

movement towards the western section of the Promenade and onto the adjacent private

Erven 1126, 1128 and 9615, as well as into the Hout Bay River mouth and beyond.


47

(iii) Prognosis

It is clear that net sand deposition continues and that the narrow beach cannot retain the

sand that previously freely circulated and moved along the original dune system. Since the

flattening of the accumulated sand that formed localized hummock dunes in 2010 by the City

of Cape Town (Howard Gold, pers.comm.), sand has had a tendency to accumulate against

the foundation and low wall of the walkway, spilling over into the Promenade area. The

brushwood rows have further resulted in localized deposition of sand until the capacity of

these structures was reached. Once this happened, sand continued to move in unrestricted

fashion onto the Promenade, into the road and onto the private properties to the north of the

beach.

Within the western portion of Sector 1, in the vicinity of the storm water manhole, an area of

approximately 80 m x 20 m contains construction rubble, with an estimated volume of some

1 200 m3. The storm water outlet on to the beach creates an unmanageable situation. The

option of creating a back dune retention pond would consume a substantial portion of the

back beach. Since such a system would require protection against silting up from the

summer sand movement, the establishment of a dune system to the south would be the only

workable option. This would, however, be unpractical should the high use pattern of the

beach continue. It is thus recommended that the storm water is pumped via a rising pipeline

and discharged into the Hout Bay River at a suitable point west of the shopping centre along

Stream Road or Sentinel Street, south of the Princess Street bridge.

(iv) Detailed proposal

The high use pattern of this sector requires a management regime that is simple and

effective. The location of the Promenade restricts options and the narrow width of the beach

limits these further. Kelp removal from this sector is likely to continue as alternatives cannot

be managed in the confines. Brushwood fences are unlikely to be integrated into a

meaningfully long term scenario.

(a) Removal of sand from the beach and Promenade: construction of a purpose-built retaining wall

Accumulation of sand in a predictable manner in an accessible area for periodic

removal would be the most practical management option for this sector. The

deposition pattern against the low retaining wall of the Promenade is already

established and remains relatively stable each year. However, the wall was not


48

designed specifically to arrest sand movement and the existing foundations are

inadequate for this purpose.

The construction of a purpose build retaining wall 50 cm higher than the current

structure is strongly recommended (see schematic design in Figure 22). The wall

should be engineered to withstand possible inundation by the sea and should have an

adequate foundation. A Reno mattress, at least 2 m wide and 30 cm thick, should run

the entire length of the Promenade and define the sand maintenance level. Sand must

be allowed to accumulate against the wall for scheduled removal. Initial planning

should allow for monthly removal from October until April, and this should be sufficient

for the year as no significant accumulation is expected during the winter months (wet

sand and gentler winds). The volume data gathered during the first year should then

be used to refine the management and removal cycles for subsequent years.

A schematic cross-section of the intervention is shown in Figure 17. Detail will only be

provided for all sections at the implementation phase.

A D6 bulldozer would be required to push sand towards the north to a loading area.

Here a ramp would need to be constructed in order for a front-end loader to dispose of

sand in trucks. Sand disposal should be undertaken in keeping with the proposed sand

management regime

The sand management options that should be considered, discussed and decided

upon include two options that would require a mining license application:

1. Using the sand as a resource for City of Cape Town projects

2. Selling the sand to interested parties

The non-mining alternative would be to dispose of the sand

1. To a registered dump site5

5 Sand mined from the Hout Beach could well be used to replace the supplies now lost to the Hout

Bay-Sandy Bay climbing-falling dune system or to augment the supply of sand to the beach at Sandy Bay. Both of these options would require expert input and consultation with the public


49

After sand removal, reshaping of the activities beach should be completed. The final

profile of the activities beach should allow for a gentle slope from the intertidal zone to

the proposed retaining wall along the Promenade. This section of beach should be

kept clear of kelp and debris, and should be regularly maintained and cleared of litter.

Access to the beach from the Promenade would be in the form of a series of stairs

constructed from Poly-wood and that can hinge into position to allow free access by the

public to the beach. This would also permit unrestricted access to the cleaning teams

enabling maintenance of the Promenade and immediate beach.

It is recommended that Sector 1, together with Sector 15 (Figure 15), be developed

and utilized as the primary beaches for public use, concentrating people in these two

areas and relieving pressure on the dune systems between the two Sectors (see

below).

(b) Re-profiling of Sector 1 and construction of artificial dune (profiles A & B in Figures 23 & 24)

There should be no interference below the intertidal zone. The spring equinox is often

associated with exceptionally high seas and it is expected that the flat beach profile

would increase the reach of these events. Owing to the spring tides and the narrow

width of the beach on the eastern side of Sector 1, we recommend that managed

vegetated dunes should not be constructed to protect the Promenade.

(c) Kelp removal

In order to permit general stability and significantly reduce windblown sand, we

maintain kelp should be left on the beach in this Sector. However, we acknowledge the

“nuisance value” posed by seaweed to the general public and suggest kelp is removed

only from Sectors 1 and 15 (Figure 15), in accordance with CCT Kelp Cleaning Policy,

but not in-between these two areas. Kelp should only be removed to the east of the

management line demarcated for Sector 1 (MU1 - Figure 16). Removal of kelp from

MU1 should be by hand and placed in one pile along the newly constructed revetment

for collection.

(d) Volumes of sand to be moved

The extent of current sand deposits along the 380 m long Promenade is about 20 m in

width wide and on average 50 cm deep. The estimated volume of sand currently in the

system is approximately 3 800 m3.


50

Removal of the 1 200 m3 rubble discussed above and replacement with sand will be

covered in the handling cost (see Appendix 4). Unless the material can be used as fill

material elsewhere, allowance for dumping fees should be made.

(e) Detailed costing

Cost estimates (Appendix 4) are based on the conceptual design for formalized

management of the activities beach. Detailed designs should be re-priced in order to

refine the costing of specific requirements.

The cost estimate allows for detailed design and construction of a re-enforced shoulder

to the retaining structure along the promenade, removal of excess sand, installation of

access stairs between the Promenade and the beach, as well as for basic

maintenance. (see Appendix 4)

(v) Conclusions: implications of intervention

The current ad hoc management of MU1 has proven to be inadequate and ineffective,

resulting in uncontrolled sand spill over onto the Promenade and into the adjacent road and

adjacent properties. Ineffective brushwood fences and random kelp removal has not

contributed to resolving the problems and the quality of the beach has therefore not

improved. Since this eastern portion of the Hout Bay beach complex is crucial as part of the

public’s experience, as well as a significant influence to the dynamics to the west, a

structured management and maintenance option should result in a more predictable beach

profile and an improved experience for beach goers.

Although significant capital expenditure is required initially, the long term maintenance will be

substantially reduced and the functionality of the activities beach will increase and the

nuisance factors will be substantially reduced.

This would be one of only two key pedestrian access areas (each with several points of

entry), the other being from the Mariner’s Wharf parking area.


51


52


53

Figure 24. Current and reconstructed Profile B (Sector 1 – eastern

beachfront, east of Hout Bay River mouth)


54

Management Unit 2 (Sectors 2 & 3 – back dunes above eastern 10.2beach) - see Figures 15 & 16

Ownership is by the City of Cape Town (beach) and private (back dunes), with zoning as POS and beach activities in Sector 2, and unknown zoning for Sector 3 (see Appendices 2 & 3 for details of Erven and images).

(i) Description and current status

This section of the beach continues from Sector 1 to the west, as far as the Hout Bay River

mouth, and is bounded by the back dune of Sector 3 (Figure 15). Sector 2 is currently

characterized by a relatively flat profile with much of the vegetation of the original back dunes

being lost due to blowouts that formed as a result of a combination of pedestrian access,

vagrant activity, increased impact from the poorly managed Sector 1 (mainly between 2005

and 2008) (Howard Gold, pers.comm.) and the continual removal of kelp along the high

water mark. This has resulted in sand from this area spilling into Sector 3 and into the river

mouth in Sector 4, as well as into the narrow Sector 5 that forms the buffer for the Hout Bay

Beach Club (HBBC). These observations were made by one of us (DvE) during frequent site

inspections conducted in order to assist the HBBC with developing methods to prevent

mobile sand from accumulating within the building complex.


The beach forms a key component in the effective management of the Hout Bay dune

complex. After the flattening of the beach profile in Sector 1 during 2010, (Howard Gold,

pers.comm.) the amount of sand that blew onto Sector 2 was reduced and the buildup of

unconsolidated sand has consequently slowed.

(iii) Prognosis

Owing to its location and distinct lack of ongoing management, Sector 2 has been

instrumental in causing the instability and collapse of the eastern dunes constructed in 1990

(CSIR, 1989). In order to establish a meaningful and sustainable management regime to the

west of the Hout Bay River, Sector 2 must be stabilized. If Sector 2 is unstable, sand

accumulation in the river mouth during the low flow summer months results in the river

periodically opening up against the artificially re-enforced edge of the western embankment.

This is undesirable as it leaves no space to re-instate, manage and maintain the CSIR dune

management profile. It furthermore forms the buffer between the eastern activities beach

and the river mouth to slow down sand movement across the flat clean beach surface during


55

strong winds. MU2 must thus be able to withstand the edge effect that is likely to prevail

where the sand laden winds from across MU1 will have a more profound impact on the

eastern edge of the area. This can be achieved by increased planting densities, additional

irrigation and fertilization of the marram grass along the edge of the Unit, and following an

adaptive management strategy where intervention is available as a response to possible

variation in the behaviour of sand on the edge of MU2.

The unpredictable seasonal infill by mobile sand and the annual breakthrough of the Hout

Bay River presents a further challenge, complicating planned management. Given the

confines of the space available for addressing mobile sand in the Hout Bay system,

construction of a dune system to trap mobile sand would be favoured as this would help in

reducing the secondary and uncontrolled impacts from the adjacent area.


Owing to the importance of MU2 in the management of the Hout Bay dune complex, it is

recommended that the area be stabilized and treated in a manner that will accumulate sand

in the dynamic scour sector on the seaward side of the planned vegetated buffer dune. The

latter would accumulate excess sand with a stable back dune section.

(a) Re-profiling of Sectors and construction of artificial dune (profile C in Figures 25a & 25b)

Most of the sand that would accumulate on the site would be derived from the Sector 1

(MU1) beach and would need to be caught in a robust system of nets, brushwood

fences, vegetation, such as marram grass, or a combination of two or more of these.

Cost and ease of maintenance would favour a number of rows of custom made wind

nets placed perpendicular to the summer winds. The nets, supplied by both Allnet and

Nittex, come in 225 m long rolls, are 750 mm high, and have stitched sleeves spaced

every 2.5 m for 1.2 m x 10 mm steel droppers6 to be inserted and pushed into the

ground. These can be lifted and maintained after major wind storms and routinely on a

14 day cycle. The nets would be removed in autumn to allow bulldozing of the

accumulated sand to the loading platform described for MU1, with subsequent

reinstatement of the nets. Lifespan of the latter is estimated to be two years under

these conditions. The use of the nets in conjunction with the marram grass and

irrigation lines along the windward edges of MU2 would greatly reduce the negative

6 This is the only cost-effective option to use under these circumstances; the droppers are easy to

erect and to maintain


56

wind erosion edge effect on the Unit. This would result in a larger stable, vegetated

footprint, thus increasing sand accumulation in the longer term7.

The historical Google Earth images clearly show a much more stable vegetation

regime pre 2005. Since the pre-2005 vegetation cover has now been lost, it is

proposed that excess sand is removed and a managed dune profile constructed. It is

likely that once Sector 2 is stable, the vegetation in the Sector 3 back dunes would

progressively recover owing to protection from the impact of mobile sand.

The current dune profiles in this area are unmanageable since sand accumulation has

occurred within land-locked areas where it is not exposed to occasional erosion. The

current dune profiles are at unstable angles as the dune footprint has remained stable

but the height has increased over time due to unnatural buildup of sand in the

vegetation. The accumulated sand between Sectors 2 and 3 further pre-disposes the

Hout Bay River to break scour close to the HBBC re-enforced embankment, limiting the

management options for Sector 4. The accumulated sand should be removed from the

corridor formed between Sectors 2 and 3, and 4 and 5 (the eastern river bank); the

profile should be flattened after the removal of plants that can be used in the re-

vegetation phase. Excess sand from this process should be reused as required in the

reconstructing of the dune profiles. The remaining sand should be removed via the

access ramp that should be constructed adjacent to the Promenade, and must be

disposed of as detailed under MU1.

The dune profile should have a setback line at +2MSL, with a sacrificial fence at this

point. This fence should be inexpensive and “disposable”, constructed on the seaward

side of the scour zone. This position, on the seaward side of the fence, is well within

the area that will be inundated by the spring equinox storms. A further 3 m back, a

more permanent fence should be erected (Figure 17). Ideally this fence should be a

post and rail type if funds are available but in the estimates, provision has been made

for the use of a simple treated timber post fence with two strands of Deltex Polywire,

the same specifications suggested for the sacrificial fence. The front 20 m behind the

latter fence should be irrigated and planted with marram grass. The marram grass strip

on the eastern and southern sides should be 20 m wide, but on the estuary side can be

reduced to 10 m, as less of sand accumulation is anticipated in that area. The dune

7 Netting would be subject to vandalism and theft, and the management authority needs to implement

security which would deter or hopefully prevent these activities


57

toe should be situated at +2MSL, with a 1:5 slope reaching 5 m inland, and this would

result in a buffer dune at +3MSL. The latter will vary from 30 to 50 m wide. The first

part of the buffer dune will fall in the irrigated marram grass planting zone, with the

remainder containing both marram grass and locally occurring vegetation.

Finally, the back dune should be vegetated with locally occurring species only. The

width of this zone will vary as it stretches from behind the buffer dune to the inland

edge of the dune management area.

It is important to note that the estimates given may vary from the detailed design

required at the time of implementation particularly if implementation were to be

delayed. The area is very dynamic, with sand volumes and dune profiles constantly

shifting thus influencing the detailed design and therefore the cost. Schematic cross

sections of the re-profiled system are shown in Figures 25a & 25b.

The irrigation of the sacrificial sector (the front 3 to 5 m of the dune) should be

standalone and operate independently of the irrigation serving the remainder of the

dune system. It should also run parallel with the coastline as opposed to the

perpendicular design of the main irrigation system. The frontal dynamic portion of the

dunes will require seasonal maintenance to ensure that the system functions effectively

and that most of the sand is trapped and recycled here. Excess sand that cannot be

contained in the dynamic zone is then accumulated in the buffer dunes (the first 30 m

from the sacrificial fence). It is envisaged that occasional re-profiling of these buffer

dunes would be required since their relatively narrow limited footprint would result in a

limited ability to absorb the influx of all mobile sand. The frequency of maintenance

would be determined by the effectiveness of management of the dynamic zone and, in

particular, the amount of rainfall and strength of on-shore winds.

(b) Kelp removal

An unmodified profile should be retained down to the mean high water mark, i.e. west

of Sector 1. Kelp should be allowed to accumulate (i.e. harvesting should NOT be

allowed in this Sector) and a fluctuating buildup of sand should be permitted for 30 m

inland but at below +2MSL. There will thus be a relatively flat beach profile below

2MSL that will accumulate kelp and pioneer vegetation (notably Arctotheca populifolia

sea pumpkin) on a seasonal basis. This “kelp section” should extend westwards and

be included in and on either side of the Hout Bay River corridor mouth area (MU3).


58

(c) Hout Bay River

Management of the Hout Bay River corridor8 should be integrated with that of the

dunes: the unpredictable movement of mobile sand and resulting random break-out

patterns of the river (if the mouth were to be silted up by windblown sand from the

east), tend to cause an increase in unnecessary beach scour. If the river breaks

through to the sea at the start of the rainy season in a position close to the western

embankment, excessive scour occurs that will undermine the stability of the engineered

embankment protecting the development to the west. With the removal of the infill on

the eastern bank of the river, along the junction of Sectors 4 and 2 (Figure 12), the

migration of the mouth to the east again becomes possible. This would then allow the

extension of sacrificial dunes in Sector 5; this is currently not possible owing to

inappropriate scour patterns that develop as the meander is deflected by the infill of the

sand from the activities beach to the east.

(d) Volumes of sand to be removed

Since the area is very dynamic, the current quantities will differ from those that will be

moved once re-profiling has taken place. Accurate volumes are therefore difficult to

quantify.


Cost estimates (Appendix 4) for MU 2 & 3 are based on the conceptual design of the

main catchment buffer of sand that will flow in from the east. Detailed designs should

be re-priced in order to refine the costing of specific requirements of this area at the

time of implementation.

The cost estimate allows for detailed design and construction of the managed dune

system. This includes the removal of excess sand from the river mouth and dune

areas, installation of irrigation and permanent as well as sacrificial fences and for 12

months of basic maintenance

88

There is currently no management plan for the river, least of all for the estuary. We see this as a top priority for the City to develop in conjunction with sand management along the beachfront


59


The current patterns of sand movement in MU2 are similar to those for MU1, above, and

have resulted in the degradation of this dune system, seasonal infill of the river mouth and

sand accumulations in MU4. With MU1 being optimized for active use by the public (see

above), less sand will be available for movement into MU2, apart from the smaller

accumulations against the proposed Promenade wall.

Good management of MU2 will improve the status of the degraded dune system in MU5 to

the west (see below). Being a small and compact area, MU2 is relatively cost effective to

manage and this will ease the impact on the adjacent areas.

.


60


61

Figure 25b. Current Profile C (Sectors 2 & 3 – back dunes in eastern section). Note there is no change to the back dune

profile


62

Management Unit 3 (part of Sectors 2 and 4 – beach around Hout 10.3Bay River lower estuary and mouth) – see Figures 15 & 16

Ownership is partly by the City of Cape Town (beach) and private, with zoning as POS and use for beach activities (see details of Erven and images in Appendices 2 & 3).

Although management of the river is not specifically part of this brief, some interventions are

discussed here, but fall mainly under Sectors 2 and 4 on either side of the river. It is

imperative that the CCT develop a plan for integrating river management with that of the

dunes in question.

(i) Current status

The river mouth changes its course on an annual basis and affects all adjacent areas

directly. From observation of previous aerial photographs, the unpredictable course is partly

the result of sand accumulation in Sectors 2 and 3 (MU2) that limits the river’s tendency to

meander to the east. The deflection of the river to the west (September 2011 Google image)

by the sand bank that formed as a result of the infilling from MU1 and MU2, has also caused

excessive scour of the western embankment below the HBBC. This erosion has frequently

exposed the Reno mattress and armor flex foundations that were installed to protect the river

embankment as part of the 1989 CSIR study that preceded the HBBC development

approvals in 1994. Such erosion is undesirable as it undermines the long term integrity of

these engineered layers.


As mentioned elsewhere, the river has no management plan (Howard Gold, pers.comm.) and

has been severely constrained by development on its banks and within its floodplain. The

latter is also compromised through the construction of levees along its banks, preventing the

functioning of the floodplain.

(iii) Prognosis

Failure to manage the infill of sand, in particular from Sector 2, will result in the river mouth

silting up on a regular basis, particularly during summer. In addition, buildup of sand along

the eastern edge of the mouth means that the river will tend to erode the embankment below

(western edge) the HBBC.


63


(a) Re-profiling of Sectors and construction of artificial dune (see profile D in Figure 26)

Excess sand should be removed as part of the management of MU 2, after vegetation

from the eastern embankment has been salvaged. Once the accumulated sand has

been removed and the eastern beach has been managed (see MU 2), less mobile

sand will be expected to infill the Hout Bay River mouth. Should the latter close up in

summer, and this is highly likely, the break-through point should be predetermined

early in the following winter. A narrow trench should be excavated so as to guide the

initial break-through of the river, roughly in the middle of the river corridor (see

Figures 27a (profile to west of river mouth) and 18 (planting programme)).

The management of MU 4 (see below) should result in a vegetated embankment to

the west of the river mouth. The river corridor is 25 m wide at the narrow inland area

and approximately 100 m wide at the wave sector.

(b) Kelp removal

Summer accumulation of kelp and sand should not be hindered and no collection

permitted in and around the mouth of the river.

(c) Opening of mouth

Allow for annual evaluation and establishment of a low point trench (see above) to

pre-determine the break-through alignment of the river mouth after silting up in

summer. This would be carried out by a team of supervised labourers for two days

per annum.


This has been discussed under MU2 above, but again the area is very dynamic, and

current quantities will differ from those that will be moved once re-profiling has taken

place. Accurate volumes are therefore difficult to quantify.

(d) Detailed costing

Provision has been made for the initial re-profiling of the area. The ongoing cost will

be reduced as the implementation of MU2 will result in a reduction of the sand infill

into the river channel. Without complex modeling, it is not possible to predict the

volume of sand infill and therefore no accurate estimate can be given for the annual


64

removal of sand. Budget provisions have however been included based on 10% of

current volumes.

(vi) Conclusions: implications of intervention

The management of MU2 to 4 is interlinked as the areas affect each other directly. The

earthworks associated with re-profiling MU2 will include the removal of the accumulated sand

that currently deflects the river westwards. Since sand will not be pushed back to sea it will

remain a potential source that will require removal in future. The excess material must be

removed via the loading ramp along the eastern edge of MU1. Implementation of the

management proposals detailed in MU2 will result in less sand being blown into the river

during summer. Siltation by river sediments will however still take place but are less likely to

completely close up the river mouth during this period. Should this happen, pre-determining

the point of breakthrough and management of the process is important to avoid the current

random and unmanageable scenarios associated with a westward position of the main

channel; this has had a knock-on effect on the management of MU4 and MU5, reducing

management options and increasing costs.


65


66

Management Unit 4 (Sector 5 – sandy embankment between Hout 10.4Bay River estuary and HBBC) – see Figures 15 & 16

The narrow strip of beach above the high water mark belongs to the CCT, with the dunes behind this under private ownership. Zoning for the area is POS and use for beach activities (see Appendices 2 & 3 for details of Erven and images).

(i) Current status

This sector contains part of the flood plain of the Hout Bay River and the eastern extreme of

the HBBC development, as well as the protective dunes to the south of the complex. The

status of this area is largely unpredictable as the sand deposition and river patterns are

dynamic.

This managed dune system is the last of the CSIR designed systems (CSIR, 1989) in the

Hout Bay dune complex that still remains partly functional.


Functionality was previously compromised due to inefficient maintenance that treated the

symptoms rather than the cause of windblown sand. This resulted in the need for major ad

hoc interventions, including the re-instatement of the designed profile following an arduous

18 month process embarked on by the HBBC that resulted in the issue of an Environmental

Authorization by DEA&DP on 7 October 2007. The approvals for on-going maintenance

nearly lapsed as the OEMP was not revised timeously. This was a precondition of the

Environmental Authorization and would have entrenched the maintenance options as rights.

The approvals for on-going maintenance nearly lapsed as the OEMP was not revised

timeously. As a pre-condition, the Environmental Authorization had to allow regular

maintenance of the dune system associated with the HBBC, and that the maintenance

methods be described in an amended OEMP.

The HBBC has now commissioned the Nature Conservation Corporation (NCC) to compile

an OEMP based on previously approved methods and interventions in order to maintain the

CSIR designed profile protecting the development. These methods were developed by Vula

Environmental for the HBBC and were amended during October 2012 to accommodate the

changes that took place during the period when the OEMP was being revised. The

principles proposed for incorporation in the OEMP are in keeping with the strategies


67

proposed in this document. Approval of the revised OEMP is expected during December

2012 (see footnote 2 on page 20)

(iii) Prognosis

The profile is characterized by a narrow flat slope east of the channel at +1MSL and an

extremely steep rise to +6MSL. This is an unsustainable profile and the situation is

worsened when the river meanders to the west and undercuts the toe of the dune. This

occurred during the winter of 2012, resulting in a vertical face of more than 3 m high directly

above the re-enforcing Armourflex layer. This profile is undesirable as due to its height and

slope angle; it severely restricts the buffer capacity of the dune to absorb windblown sand in

if it is not caught in the scour zone. Owing to inconsistent maintenance at the toe of the

berm, the narrow buffer zone has already reached its capacity and urgent intervention is

required.

The eastern edge of MU4 should form part of the Hout Bay River management plan, so that

the western embankment of the river remains protected from scour.


(a) Re-profiling of Sector and construction of artificial dune (profile E in Figures 27a & 27b)

Sand accumulation west of the embankment towards the river channel should be

encouraged in order to provide a more functional vegetated base on top of the

present engineered re-enforcement layers. The latter are currently exposed below

the HBBC.

The lost buffer capacity on the top and in front of the narrow embankment should be

regained, with a functional toe of the dune re-established. The latter should be

protected through the erection of a fence at the edge of the toe of the dune

Since the buffer dune has little remaining sand-trapping capacity, it is now necessary

to remove the marram grass in 2 m wide strips from the top down to the river, and

then to transport all the accumulated sand down to the toe of the embankment and,

on the same day, re-plant the marram and place under irrigation. This process needs

to start in the north (i.e. upstream) and follow the entire face of the development in

order to re-claim capacity for future sand accumulation in the buffer zone.


68

The river channel should be established 20 m to the east (see above), flanked by a

2 m edge and a gradual infill to +4MSL during the re-profiling of Sectors 2 and 3.

(b) Kelp removal

Kelp should not be removed from the section of the beach below the embankment

and on either side of the river mouth.

(c) Volumes of sand to be removed

No sand removal is required as the area has been severely eroded. Infill is not

suggested as it will reduce the ability of the area to absorb windblown sand.


Cost estimates (Appendix 4) for MU 4 is based on the current post storm scenario.

Due to inconsistent maintenance and the lack of maintenance of MU1-3, conditions in

MU4 are extremely dynamic. It is anticipated the conditions should become more

stable once the appropriate management interventions are in place.

The cost estimate allows for the installation of temporary wind nets to accumulate

sand in the eroded toe area of the dune, Repairs to irrigation and planting has been

priced. Maintenance is provided by the HBBC and has been excluded from the

estimate. The re-profiling of the interface between MU4 and Mu 2 & 3, including the

excavation of the excess sand accumulated in the river has been priced under

MU2 & 3.


As there cannot be uncoordinated shared responsibility for this zone by the different role

players, the operations of MU’s 2, 3 and 4 should be integrated to ensure successful sand

management. The HBBC has a vested interest in protecting its assets and should be

granted approval to maintain the adjacent areas directly affecting the development. The

CCT is however the custodian and owner of most of MU2 and MU3 (see Appendix 2). It is

therefore recommended that the CCT and HBBC enter into a formal agreement about the

protocols to be followed in sand and river mouth management, including detail regarding

both management and funding responsibilities.


69


70

Figure 13b. Remainder of Profile E (no reconstruction) (Sector 8 –

section west of the Hout Bay Beach Club)

Figure 21b. Remainder of Profile E (no reconstruction) (Sector 8 –

section west of Hout Bay Beach Club)

Figure 27b. Remainder of Profile E (no reconstruction)

(Sector 8 – section west of the Hout Bay Beach Club)


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Management Unit 5 (Sectors 6 to 14 – beach and dunes between 10.5Hout Bay Beach Club and the storm water outlet adjacent to the western car park) – see Figures 15 & 16

Most of this MU is owned by the CCT, with some residential Erven near the beach. Present zoning is mainly POS, with the private Erven unknown (see Appendices 2 & 3 for details of Erven and images). It is crucial that this MU, by far the largest in the study, is managed as an integrated unit.

(i) Current status

Failure to implement the CSIR’s (1989) management plan in the long-term has resulted in an

unnaturally mobile dune system, with several blowouts. This has resulted in significant

quantities of sand moving north into the parking area off Princess Road, partly covering the

law enforcement offices, amenities buildings and the Yacht Club. All the pathways and

ramps that were provided as part of the formalized beach access have also been covered.

The fence demarcating the +2MSL setback line on the beach is once again visible after sand

migrated inland once the blow out positions had cut paths through to +3MSL. This resulted

in an unnatural dune field being created over the present parking area.


Dunes along the beach in this MU, as well as the adjacent inland areas, were re-constructed

according to the CSIR dune management module (CSIR, 1989), and see diagram of the

2001 planting intervention in Figure 28. Owing to the lack of timely and ongoing

maintenance (also see comments above), these areas are now completely nonfunctional

and, owing to their largely unvegetated condition, are arguably in a worse state than before

the original intervention (Figure 29).

The dynamic frontal zone was not re-instated after being eroded by winter storms in 1997.

This resulted in sand accumulation in the frontal buffer zone and not in the sacrificial zone as

per the design. The dunes grew higher as sand was trapped, primarily by fast growing

marram grass, as well as some of the indigenous woody species such as Brachylaena

discolor wild silver oak, Chrysanthemoides monilifera bietou and Searsia (Rhus) glauca

which were introduced in the back parts of the dunes. Once the mobile sand equilibrium had

been lost and the dune profile in the front had become too steep, blowouts began to occur.

The natural dune dynamics were compromised by the introduction of fast growing marram

grass with its strong root systems was introduced. The areas were initially irrigated by


72

automated systems and later on an ad hoc basis by hand, resulting in a 1:1 dune profile in

places. The blowout position and time frame of occurrence was influenced, among other, by

the removal of irrigation as well as human impact due to unrestricted access to the beach

and back dunes.

Based on the assessment of recent aerial photos and the major changes in dune topography

(see above), the loss of vegetation accelerated between 2008 and 2011. This was due to a

combination of factors including a marked reduction in annual rainfall and stronger than

average easterly and south-easterly winds at the end of this period. Combined with the drier

conditions, the height of the dune profile in relation to footprint size led to severe droughting

of the vegetation outside the winter months. Dunes with a large “height to basal width ratio”

(i.e. taller than +8MSL) are prone to faster water loss due to increased percolation through

the sand profile. The resultant die-back in vegetation results in lower cover and therefore a

lower ability to trap mobile sand. This is illustrated by the net loss of sand from Sectors 1, 4,

6, 7, 9, 10 and 15 that occurred between 2009 and 2011, and the corresponding

accumulation in Sectors 2, 3, 5, 8, 11 (by far the greatest), 12, 13 and 14. (see above).

(iii) Prognosis

Since the collapse of the CSIR’s (1989) proposed dune management regime, the bulk of the

sand has accumulated beyond the original 50 m buffer dune system (see Figure 28). In the

current situation, the sand is unstable and unnaturally mobile. This has presented a major

nuisance to residents and other users behind (to the north of) the back dunes. Without major

intervention and reshaping, stabilization of sand would be impractical as it would require

major earthworks followed by an elaborate re-vegetation process spanning at least two

winter seasons.

The current accumulated sand volume exceeds the buffer capacity of the back dunes and

cannot be accommodated in the current location. The impact of sand moving onto the

Sectors to the west of the Hout Bay River, coupled with uncontrolled pedestrian access, the

sand erosion patterns are severe and largely unpredictable.

The presence of disused buildings, paved and unpaved parking areas, defunct launch ramps

and uncontrolled sand movement makes this MU particularly difficult to manage adequately

and cost effectively.


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(a) Re-profiling of Sectors and construction of artificial dune (detailed profile in Figure 29; schematic profiles F to K in Figures 30 to 35)

The long term stability of the dune management complex depends on limiting the

influx of sand to the buffer zone by trapping it in the vegetated toe situated within the

scour zone from where it is seasonally recycled. Finer sand particles mobilized under

strong wind conditions are accumulated within the vegetated buffer zone. The

vegetation traps the sand and continues to grow, forming increasingly higher dunes.

The maximum stable dune height of a 60 m wide dune complex without irrigation to

the buffer area is between approximately +6MSL and +7MSL.

The dune profile should be re-instated in line with the original CSIR proposals (CSIR,

1989a) with some variation to address problems experienced with the old design.

This would include a larger buffer dune section and a more stable profile footprint that

would not be compromised by the position of existing buildings as these would be

removed

No provision should be made for direct beach access for either pedestrians or small

craft. The dune system would be stabilized with marram grass on the dynamic edge

and on the dune front face and crown, with local dune vegetation in the back buffer

area.

The dune complex should have an uninterrupted sand flow from east to west. The

entire system should be constructed, managed and maintained as a unit but only

once the dunes in MU2 & MU4 have been reconstructed. The system (MU5) would

not be able to successfully withstand the longshore impact of the unmanaged eastern

beach as this area is the source of sand that caused the buildup and collapse of the

current dunes in this area.

The entire managed dune complex should be fenced off as pedestrian access to this

fragile system has proven to be pivotal in the collapse of these artificial systems.

The dunes should be reconstructed to retain accumulated sand in the dynamic scour

zone with only excessive amounts of sand spilling over and entering the buffer zone

(Figure 29). It is however anticipated that the latter would accrue sand over time.

After this, the vegetation will be need to be harvested, accumulated sand removed

and the buffer area re-profiled and the vegetation reinstated. The time frame is not


74

clear and would greatly depend on the standard of maintenance, as well as the

variability of the easterly and southerly winds and rainfall. The time frames need to

be informed by ongoing monitoring.

During initial re-shaping, all excess sand should be removed in the proposed manner

described in MU1 above (Section 10.1).

The components of the profile are (Figure 29):

Setback line for the toe of the dune at +1-1.5MSL

3 to 5 m sacrificial zone with a height of +1.5 -2.5MSL

Dune face with a varied topography constructed at a predominantly 25 degree slope. Due to the mechanical construction methods likely to be used, the resulting linear shape can be softened to be aesthetically more pleasing.

Dune buffer zone with a stable base at +3MSL

Back dune with a varied topography, constructed up to +3.5MSL and allowed to increase to +6MSL

The back of the dune should have a minimum 34 degree slope.

The first three components are the most variable and require the most maintenance

due to the unpredictable influences of storm surges and sand movement. Their

integrity is fundamental to the preservation of the alignment and functionality of the

man-made dune system.

All infrastructure - launch ramps, boardwalks, derelict buildings and hard surfaced

parking areas - should be removed from the MU. Following this, the new dune profile

should be instated along with the required services such as irrigation (Figure 21) and

fencing.

(b) Kelp removal

Kelp should not be removed from this section of the beach

(c) Volumes of sand to be removed

The new profile should be instated and all the remaining sand must be removed.

Allowance has been made in the estimate to remove approximately 62 000 m3 sand

from the system.


75


The cost estimate (Appendix 4) for MU 5 is based on the conceptual design of the

main catchment buffer west of the river. Detailed designs should be re-priced in order

to refine the costing of specific requirements of this area at the time of

implementation.

The cost estimate allows for detailed design and construction of the managed dune system.

This includes the removal of excess sand from the areas of accumulation in the current

dysfunctional public areas, installation of irrigation and permanent as well as sacrificial

fences and for 12 months of basic maintenance, the cost of demolishing and making safe of

the existing infrastructure is excluded.


The re-profiling and management of MU 5 presents the greatest challenge to the success or

otherwise of the management plan. It is in this area that most of the sand ingression has

occurred and where stability will be crucial to reducing inland sand flow. The system must be

treated as an integrated whole, with all elements undertaken in concert, as recommended

above. Past management of this unit in isolation has been difficult given that the MU is

exposed to the impact of harsh summer winds from the east and south-east. The successful

stabilization of MU2 and MU4 will reduce the sand input into MU5 thus improving the

management capability of the area substantially. Removing infrastructure from MU5 will also

enhance the management success of the MU in the long term, reducing sand ingression into

the neighboring urban area.


76


77


78

Figure 30a. Current and reconstructed Profile F: front section of beach, high dunes and blowout directly west of

HBBC (Sectors 6, 7 & 8)


79


80


81


82


83


84


85


86


87

Management Unit 6 (Sector 15 – beach and parking area at 10.6Mariner’s Wharf) – see Figures 15 & 16

Ownership is mainly by the CCT, but also the Public Works Department and private, with one Erf unknown. Zoning is chiefly POS and beach activities, with the bulk of the private Erven unknown. Much of the site is currently used as a parking area to service restaurants in the Hout Bay harbour. See Appendices 2 & 3 for details of Erven and imgaes.

(i) Current status

The main activities beach in the west consists of a 120 m x 30 m beach and a parking area

flanked on the east by a storm water outlet and on the west by the vehicle access to the

harbour wall.

The parking area is currently edged by informal rock placement and sand spills through this

onto the parking area

The storm water outlet scours the beach in an unpredictable fashion resulting in a variable

and scoured topography in the area between the road and the high water mark

The flat profile of the beach and exposure to the summer winds has resulted in major erosion

of sand. Even the slight elevation of the parking area above the beach does not prevent

wind from moving sand across the parking area, into and across Harbour Road, to the bus

parking area behind this.


Sand accumulated in the bus parking area is periodically cleared by the City of Cape Town’s

Amenities department.

(iii) Prognosis

This Sector has the least movement of sand within the Hout Bay dune system and requires

minimum effort to manage sand arising from the beach.


(a) Re-profiling of Sector 15 and construction of artificial dune (profiles L & M in Figures 36 & 37)

Accumulation of sand in a predictable manner in an accessible area for periodic

removal would be the most practical management option for this sector. In essence

the proposal echoes that of Sector 1, the eastern beach and Promenade


88

The current profile should be retained. Removal of accumulated sand from a pre-

defined constructed edge would improve the current management. The construction

of a purpose built retaining wall 50 cm higher than the current parking area surface is

recommended (Figure 38). The wall should be engineered to withstand possible

inundation from spring equinox high tides and should have adequate foundations. A

Reno mattress, at least 2 m wide and 30 cm thick should run the entire length of the

parking area. Sand should be allowed to accumulate against the wall for scheduled

removal. A D6 bulldozer would be required to push sand towards the eastern end of

the parking area. Here a ramp would need to be constructed in order for a front-end

loader to dispose of sand in trucks. Sand disposal should be undertaken in keeping

with the proposed sand management regime (see options described in MU1). Re-

shaping and possible sand removal should be conducted in October. During April,

summer sand accumulation should be removed and the beach area re-shaped. After

sand removal, reshaping of the activities beach should be completed. The final

profile of the activities beach should allow for a gentle slope from the intertidal zone to

the proposed retaining wall along the parking area. This section of beach should be

kept clear of kelp and debris and should be regularly maintained and cleared of litter.

The parking area should be re-designed and extended to the east by 25 m, up to the

edge of Sectors 13 and 14, once the storm water has been re-routed (see below).

Access to the beach from the parking area should be in the form of a series of stairs

constructed from Poly-wood and that can hinge back onto the parking area for access

by the public and management teams (see Figure 38).

(b) Storm water outlet

The storm water outlet to the east of the parking area cannot be integrated into the

beach management plan. Rather, it should be ducted from the current position of the

culvert north of Northshore drive, along the bus parking area and then along the

vehicle ramp to the harbour wall. The outlet should be seaward of MSL.

(c) Kelp removal

Kelp removal from this Sector should continue as part of an overall kelp harvesting

programme which targets only this MU and MU 1 in the east.


89


Minimal sand removal is required outside of the scope of works of the re-development

of the parking area.


Cost estimates (Appendix 4) for MU 6 are based on the conceptual design for

formalized management of the activities beach. Detailed designs should be re-priced

in order to refine the costing of specific requirements.

The cost estimate allows for detailed design and construction of a formal parking area

with a re-enforced shoulder to the edge of the parking area, removal of excess sand,

installation of access stairs between the parking area and the beach and the re-

routing of the storm water outlet to the edge of the pier. Basic maintenance for a 12

month period has also been priced


It is recommended that the Mariner’s Wharf car park serve as one of only two pedestrian

access points to the beach, the other being the Promenade in the east. Managing these

easy access areas for high impact use will alleviate pressure from the functional dune

areas. Public participation and education will be key to the successful implementation of

the management strategy. Increased capacity through the re-development and

expansion of the car park will result in less ad hoc parking during peak periods. The

managed dune profile will have an increased user capacity and the area is compact and

can be maintained at a high standard making it more desirable for tourists.

Improved storm water management will result in less ad hoc damage to the beach. The

management of the adjacent MU5 will reduce sand build-up in the storm water catchment

culvert on the bus parking area, reducing maintenance and allowing for better

functionality.

.


90


91


92

Figure 38. Current and reconstructed Profile M (Sector 15) – Mariner’s Wharf car park and beach, and bus parking area


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11. MONITORING OF HOUT BAY DUNE MANAGEMENT

The purpose of monitoring the management programme for the Hout Bay dunes is several-

fold:

(i) To ensure windblown sand is kept to a minimum and is not a nuisance

(ii) To respond to windblown sand where it is causing a problem, particularly with the public

(iii) To ensure planned management interventions are undertaken timeously, within schedule, and in an adequate manner

(iv) To document plant cover and species presence and to re-establish plant cover where necessary

(v) To document changes in the weather in the area (using the Chapman’s Peak weather station as surrogate for Hout Bay) and to respond appropriately in severe wind and/or dry conditions

(vi) To monitor reconstructed dune profiles and to reshape where required

(vii) To monitor the impact of pedestrians on the dunes

(viii) To monitor the status of the river mouth in terms of closing in summer and breakout in winter; in particularly the effectiveness of manual methods of opening up the channel

(ix) To monitor the impact of kelp on dune building above the HWM and the success of “no kelp removal zones”

Monitoring Methods 11.1

A variety of monitoring methods would be required in order to obtain relevant information to

base an adaptive management regime on. The monitoring methods should be fully

developed as part of the detail design of the interventions.

(i) Automated weather station and data logger situated in the Hout Bay dune complex, recording local wind and rainfall data. Management can be adjusted according to deviation from long term norms.

(ii) Dust fall out monitoring stations, situated at approximately 100 m intervals along monitoring transects of 1000 m. Three to four transects will be required. These should be installed prior to any management interventions as no data is available to determine the fall out patterns resulting from the unmanaged dune system.

(iii) Fixed sand level measurement posts, installed to 1.5 m below and 1.5 m above the sand level, marked at 10 cm intervals. Sand level measurements to be recorded every 14 days and after storm events and high wind periods.

a. Installed on activities beaches east and west, to visually gage short term sand profile changes. Posts should be situated approximately midway between the retaining structures and the high water level. Another series of level pegs should be positioned against the retaining structure at 50 m intervals.


94

b. Installed at right angles to the fence lines in all the managed dune areas, at 50 m intervals, in short 20 m transects starting at the sacrificial fence spaced 5 m apart

(iv) Landscape functional analysis transects

a. Permanent transects should be installed from the high water mark to the inland edge of the dune management area MU 2, MU4 and MU5 at 50 m intervals. These transects should be monitored at the end of summer and the end of winter to determine the dynamic state of the dune systems

(see http://www.csiro.au/en/Organisation-Structure/Divisions/Ecosystem-Sciences/EcosystemFunctionAnalysis.aspx#a1)

(v) Inspection of the scour zone and buffer dunes

a. The condition of the vegetation and status of the irrigation should be assessed every 14 days. Maintenance schedule should be adjusted should the inspections reveal dieback or disease in the vegetation. Repairs should be affected to irrigation should it be required.

(vi) Fixed point photography

Maintenance requirements 11.2

Maintenance forms an integral part of the management of the dune system. The discussion

in Chapter 6 illustrates the importance of adequate and preventative maintenance on a

perpetual and ongoing basis as the most cost effective management option. A detailed

Operational Environmental Management Plan must be developed as part of the detailed

planning for the interventions and should include the following maintenance requirements:

(i) Activities Beach (MU 1 and MU 6)

a. Weekly removal of kelp from beach and placement in kelp zones of MU3-5

b. Daily removal of rubbish

c. Monitor sand accumulation against retaining wall. Remove sand once accumulation reaches an average of 300 mm above the designed level (Figure 24 & Figure 38).

(ii) Managed dunes profiles MU2, MU4 & MU5

a. Allow kelp accumulation

b. Monitor and maintain sacrificial fence during summer. Once damage is imminent (winter), remove for safekeeping

c. Re-instate sacrificial fence after September spring high tide

d. Maintain signage and permanent fence

e. Monitor irrigation system every two weeks and maintain in working order. Adjust controller in response to weather and plant growth. Once buffer and back dune vegetation has been established, irrigation can be reduced. Independent frontal irrigation line must function throughout summer in order to ensure adequate growth of Marram to catch any sand accumulation

http://www.csiro.au/en/Organisation-Structure/Divisions/Ecosystem-Sciences/EcosystemFunctionAnalysis.aspx#a1

http://www.csiro.au/en/Organisation-Structure/Divisions/Ecosystem-Sciences/EcosystemFunctionAnalysis.aspx#a1


95

f. Remove for safekeeping, the entire scour zone irrigation system’s piping and sprinklers at the end of April.

g. Fertilize marram grass areas once every month during summer using 2:3:2 (22) @ 400 kg/ha and Bounce Back @ 600 kg/ha during year one. Maintain this level of fertilization for the dune toe area and adjust in response to growth.

h. Post September high-tide maintenance:

i. Re-profile dune as required

ii. Re-plant Marram that have been washed away

iii. Repair or re-instate sacrificial fencing

iv. Re-instate irrigation system

v. Install wind nets at the toe of MU4 if required and maintain. Remove in April for storage


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12. SUMMARY OF COST ESTIMATES

This section presents a summary of all costs9 associated with managing Option 4. A detailed

breakdown is shown in Appendix 4. Note that all costs are VAT exclusive.

Management Unit 1 R2 450 000

Management Units 2 & 3 R2 900 000

Management Units 4 R110 000



Basic assessment and public participation R500 000

TOTAL R19 860 000 (excl. VAT)

Although it is our recommendation that ALL interventions happen as one, i.e. over one

season, management could be phased in as follows:




Public participation (R500 000) should be undertaken during the first year.

The above cost estimates have not been escalated to allow for the phased implementation

and the additional management cost associated with the phased implementation has also not

been estimated.

However, based upon discussions between the City and one of the authors of this report

(DvE), a substantially reduced budget can be achieved through contributions from the City in

terms of labour and plant (Table 7). This would enable essential works to be undertaken,

with the City re-evaluating certain aspects of the proposed rehabilitation work (Table 7).

:

9 Calculated to the nearest R10 000


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Table 7. Comparison of first and second order costing, following discussions with City to reduce the budget

Management Unit Full costing (from this

report) Secondary costing Primary costing Re-evaluate

Management Unit 1 2 450 000 1 050 000 1 400 000

Management Units 2 & 3 2 900 000 1 207 000 1 200 000 493 000

Management Unit 4 110 000 110 000

Management Unit 5 11 250 000 5 400 000 3 950 000 1 900 000

Management Unit 6 2 650 000 2 646 000

Basic assessment and public participation

500 000 500 000

Total 19 860 000 7 657 000 5 650 000 6 553 000

Primary costing: Work that would require external contractors for implementation

Secondary costing: Work that can be undertaken internally by the City and with its own resources

Re-evaluate: Work that might require reconsideration as indicated by the City


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13. RECOMMENDATIONS AND CONCLUSIONS

It is clear from the review of past management strategies for Hout Bay that control of isolated

portions of the Hout Bay dune system has failed. Management intervention has been

severely compromised by poor planning, leading, among other, to development’s

encroaching on both the sensitive mobile primary dune systems as well as the Hout Bay

River estuary.

Limited implementation of the CSIR guidelines (1989a & b) for dune management, mainly

due to a lack of funding and a commitment to a systematic approach, has meant the

continual ingress of sand into the urban area. This has led to recurring costs for even

minimal management, with no solution to the current and severe mobile sand problem.

We strongly recommend that the interventions as detailed for Management Units 1 to 6 are

commenced without delay and that sufficient funding for such urgent intervention is sought

from the City. The implementation of works should preferably be conducted as a coordinated

project in a single phase. The latter offers the opportunity to reduce management variables

that would be associated with an extended implementation over a number of years, thus

reducing costs and increasing the efficiencies that would be experienced with large scale

implementation.

Based upon the recommendations for Option 4, projected management costs are as follows

(rounded off to the nearest R10 000):


Management Units 2 and 3: R2 900 000

Management Unit 4: R110 000

Management Unit 5 (the bulk of the site): R11 250 000

Management Unit 6: R2 650 000.

Basic assessment and public participation: R500 000.

This gives a total of some R22 million for a single phase intervention.

In the event funding is not forthcoming for the preferred single phase of implementation, we

have recommended three phases as follows:


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R500 000 to be used for the basic assessment and for public participation.

However, priority work could be undertaken, based upon the figures in Table 7, whereby the

City would contribute labour and plant worth some R7.567 million and funding R5.650 million

in external contracting. A further R6.553 million would need to be re-evaluated.

A management plan should be drawn up for the Hout Bay River, one which would include

consideration of the interaction between the river estuary and primary dunes, with

management of the dunes and river being integrated by the City.


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14. ACKNOWLEDGEMENTS

To the CCT project management team, particularly Howard Gold and Darryl Collenbrander, for useful discussion and comment on the report

To Johan Coetzee for surveying the dune transects

To Andrew Skowno for calculating the sand volumes

To the South African Weather Bureau for supply of wind and rain data.


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15. REFERENCES FOR VOLUMES 1 & 2

CSIR (1989a). Dune management plan and the Hout Bay estuary. CSIR, Stellenbosch

CSIR (1989b). Hout Bay beach front development plan. Report EMA-c 8996. CSIR, Stellenbosch

CSIR (1991). Dolphin Beach management plan and Post Construction Maintenance Manual. CSIR, Stellenbosch

City of Cape Town (2011). Climate change think tank: marine/freshwater theme – marine

inputs to Salt River flood model. Report No. 1063/1. September 2011. Prestidge Retief Dresner Wijnberg Pty) Ltd.

Grindley, S A (1988). Estuaries of the Cape: Part II: Synopsis of available information on individual systems. Report No. 29. Hout Bay (CW 27). Heydorn A E F & Morant P D (eds.). Stellenbosch, CSIR Research Report 428

Low, A B (2012). Dunes that climb and fall no more. Veld & Flora 98(3): 112 - 115

Low, A B & Pond, U (2004). Mapping of coastal dunes within the City of Cape Town metropolitan area. Coastec, Rondebosch

Tinley, K L (1985). Coastal dunes of South Africa. South African National Scientific Programmes Report no. 109. CSIR, Pretoria.


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APPENDICES


103

APPENDIX 1 – WIND ROSES FROM CAPE POINT FARMS, NOORDHOEK


104


105


106


107


108


109


110

APPENDIX 2 – DETAILS OF ERVEN OWNERSHIP AND LANDUSE


111

APPENDIX 2. DETAILS OF ERVEN OWNERSHIP, ZONING AND LANDUSE IN THE HOUT BAY DUNES STUDY AREA

ERF NO. DESCRIPTION OWNERSHIP ZONING PRESENT LANDUSE

MANAGEMENT UNIT 1

Sector 1 Eastern beach

2066 CPA Unknown Beach activities

3655 CCT POS Beach activities

MANAGEMENT UNIT 2

Sector 2 Back dunes to west of Promenade and north of the eastern beach


653 Private Unknown Unknown

7744 Private Unknown Unknown

MANAGEMENT UNIT 3

Sector 3 & 4 Beach, east and west of Hout Bay River mouth


7744

Private Unknown Unknown

MANAGEMENT UNIT 4

Sector 5 Narrow strip between Hout Bay Beach Club and Hour Bay River

7743

Private Unknown Beach activities; pedestrian access

7744

Private Unknown Beach activities; pedestrian access


112

MANAGEMENT UNIT 5

Sectors 6 to 14 Main beach and back dunes between Hout Bay Beach Club and stormwater outlet adjacent to western car park

153

Unknown Unknown Dune system; beach activities; occasional pedestrian access

154

CCT POS Dune system; beach activities; occasional pedestrian access

158


159

CCT Civic Dune system; beach activities; occasional pedestrian access

160

CCT Unknown Dune system; beach activities; occasional pedestrian access

162

Private Service station? Dune system; beach activities; occasional pedestrian access

165

CCT Unknown Dune system; beach activities; occasional pedestrian access

170


311


312


313


315


335


336


338


340


342


349


350


354


355


357

CCT RES Dune system; beach activities; occasional pedestrian access

547

Private Unknown Dune system; beach activities; occasional pedestrian access

548



113

MANAGEMENT UNIT 5 (contd.)

553


558


559

Private Unknown Dune system; beach activities; occasional pedestrian access

2386


2387


2401


2589


2699


2849

CCT Substation (Electricity) Dune system; beach activities; occasional pedestrian access

2999


3655


7807

Private RES Dune system; beach activities; occasional pedestrian access

MANAGEMENT UNIT 6

Sector 15 Western beach, and car and bus park

628

CCT RES Beach activities; car & bus park

629


630


1141

Private Unknown Beach activities; car & bus park

1142


1143


1144

CCT POS Beach activities; car & bus park

1145

PWD Unknown Beach activities; car & bus park

1147


5903



114


115

APPENDIX 3. IMAGES OF THE HOUT BAY DUNES STUDY AREA


116

1


117

2


118

3


119

4


120

5


121

6


122

7


123

8


124

9


125

Explanation of images

(1) eastern section of study area showing Promenade, private erven above Promenade, walkway along the Promenade, lack of plant cover on windrows and heavy use of beach area. The report proposes a solid wall built along the Promenade which would intercept windblown sand and make sand removal easier.

(2) Stormwater overflow onto beach – this will need re-routing to the Hout Bay River as part of the overall management plan; rubble in this area will also need to be removed; kelp collection should be restricted to the extreme eastern and western beaches, and allowed to accumulate in-between these two areas; back dune in MU2 showing gentle hummocks and taller back dune vegetation with good cover.

(3) Hout Bay River – siting of the Hout Bay Beach Club is totally inappropriate in that it impacts directly on the river mouth which in turn is not permitted to meander freely (as shown by historical records).. Although not part of the brief, river management should form an integral part of the dune management and rehabilitation programme. Note scouring of western bank, planting of marram grass as a key stabilizer and exposure of reinforcing Armourflex mattress; if implemented correctly, management should prevent mobile sand silting the river. Management within MU3 on either side of the river will also provide much needed protection for the mouth.

(4) MU5 complex. This forms the core of the management plan and must be managed as one entity. Most sand movement, particularly during the past summer, has occurred in this area and urgent intervention is required to reduce windblown sand moving onto the adjacent residential area to the north; note naturally forming dune hummocks but low plant cover over much of the primary dune area.

(5) Stable back dune vegetation of MU5. Note dominance of dune thicket species and the introduced Brachylaena discolor wild silver oak; also note major unnatural blowout zone; Erf 559 supports the only dune slack wetland in the area and this should be conserved as part of the overall management plan.

(6) MU5 car park off Princess Road. Impacts of sand ingression obvious and mainly caused by extreme south-easterly winds last summer (2010/11). All infrastructure should be removed from the area and the c park decommissioned (main pedestrian access from eastern and western car parks.

(7) Old CSIR fence line from 2001. Lack of maintenance has led to the loss of plant cover and major increases in mobile sand; stormwater outlet just to the east of the Mariner’s Wharf car park. This outlet interferes with natural dune movement and should be relocated to the harbour. Intensive use of beach below car park should be permitted to continue with minimal intervention. The last image is of a vagrant’s “skuilplek”. No pedestrian or other use should be permitted on the back dune complex between the two car parks.

(8) Rehabilitation species: Arctotheca populifolia sea pumpkin – a key pioneer species to be used in dune rehabilitation, together with Tetragonia decumbens kinkelbossie (hummock dune) and Senecio elegans wild cineraria

(9) Chrysanthemoides monilifera bietou – another key species to be used in back dune rehabilitation, with Searsia (Rhus) crenata duinekraaibessie, Chasmanthe aethiopica suurkanol and Sideroxylon inerme milkwood. Ammophila arenaria marram grass (last image) is the only non-indigenous species to be used in rehabilitation. This species is non-invasive and an extremely effective dune stabilizer under adverse conditions such as those at Hout Bay.


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APPENDIX 4 – DETAILED MANAGEMENT COSTS This is a separate PDF document, submitted with both Volume 1 & 2 of the report

Documents

MANAGEMENT AND REHABILITATION PLAN FOR THE HOUT … · hout bay dunes management & rehabilitation plan ii Given the high cost of the exercise, the City and one of team members (DvE)