HYDROGEOLOGICAL INVESTIGATION TO MAINTAIN AN … · 2013. 8. 13. · represents a groundwater expression in spring through summer, as long as groundwater levels remain above the lake-bed

HYDROGEOLOGICALINVESTIGATION TO MAINTAIN AN

ADEQUATE BODY OF WATER INLAKE JUALBUP

NOVEMBER 2012

REPORT FORCITY OF SUBIACO

(Report No. 317.0/12/01)

City of Subiaco

Hydrogeological Investigation to Maintain an Adequate Body of Water in Lake JualbupPage i

Rockwater Pty Ltd317.0/12/1

EXECUTIVE SUMMARY

The City of Subiaco is proposing to apply a polymer additive to the base of Lake Jualbup in

Shenton Park to reduce the lake-bed permeability and thereby maintain “adequate” water

levels in the lake throughout the summer months. The lake is primarily a compensating basin

utilised by the Water Corporation to accept and infiltrate local stormwater flow from the

Shenton Park catchment. Currently it acts as a groundwater recharge point in winter and

represents a groundwater expression in spring through summer, as long as groundwater levels

remain above the lake-bed surface. For the purposes of this investigation, an adequate body

of water has been assumed to be one in which the minimum lake-water depth is 0.5 m over

most of the lake area, or a minimum water level of 4.0 m AHD.

This investigation utilised numerical groundwater modelling techniques to assess the

hydrogeological impact on the lake and environmental surrounds for varying reductions in

lake-bed permeability. It further considered the effects of installing local infiltration

soakwells throughout the lake catchment to offset reduced infiltration from the lake to the

superficial aquifer, and considered the potential impact of raising the overflow-drain outlet

from the lake to reduce the likely increase in outflow from the system to ocean out-fall

resulting from reduced infiltration rates. In conducting the study, Rockwater examined

relevant information on Lake Jualbup and the City’s drainage network and compensating

basins, and water-table response as observed in the seven monitoring bores installed around

the lake in 2009.

Information provided by the distributors of the proposed polymer additive to the City of

Subiaco indicated that the polymer could only be applied in such a way as to completely seal

the lake bed in the area to which it is applied. The distributors suggested application in strips

to achieve the desired percentage reduction in lake bed permeability. During calibration of

the model, it was found that a reduction in permeability in one area simply led to an increase

in infiltration rates in any area where the permeability remained unchanged, and only very

small increases in lake-water levels were achieved under most circumstances. It was also

found that horizontal flow increased significantly when the lake bed permeabilities were

reduced, and it was concluded that the perimeter wall would need to be rebuilt and sealed if

the desired minimum water levels are to be obtained.

Given the constraints identified above, preliminary modelling investigated the reduction of

the lake-bed permeability by 25%, 50% and 75% assuming the application of the polymer

additive over 25%, 50% and 75% of the lake floor, sealing the lake bed progressively from

the south-west to north-east. The results indicated that the minimum water-level requirement

could only be met with a 75% reduction in lake bed permeability and so the scope of work

focused on this scenario.

City of Subiaco

Hydrogeological Investigation to Maintain an Adequate Body of Water in Lake JualbupPage ii


With a 75 % reduction in lake-bed permeability and installation of low permeability walls

(modified lake conditions) the modelling indicates that minimum summer lake-water levels

would be about 4.2 m AHD under long-term average rainfall conditions (about 0.7 m higher

than for an unmodified lake system). Groundwater levels in the superficial aquifer would

only be affected immediately down-gradient of the lake where the polymer had been applied,

with maximum groundwater levels in this area being about 0.4 to 0.7 m lower, and minimum

groundwater levels being about 0.1 m lower. There would be no measureable effect on the

superficial aquifer regionally. Outflow from the lake to the main drain might increase by 2.7

to 4.4 times, which could be reduced by about 20% in the long term if the drain outlet was

raised by 0.3 m to 5.37 m AHD.

During an extended summer period with no rain, in a year where winter months have received

the long-term average rainfall, the modified lake would maintain water levels at greater than

0.5 m depth for about 9 weeks longer than under unmodified conditions. After this time,

water levels would fall below the desired minimum level and the eastern side of the lake

would dry up after another eight weeks with no rain. If the drain was raised, the period the

lake remained wet might be increased by an extra week or so. The modelling results suggest

that between 340 and 430 m3/d of groundwater would need to be pumped to the lake to

maintain water levels at 4.0 m AHD under these dry summer conditions.

It was found that at least 75% of the current lake inflow needed to be maintained to achieve

the desired minimum lake water levels. If the excess 25% of rainfall runoff from Shenton

Park was infiltrated via local infiltration soakwells, outflow from the lake could be reduced by

approximately 40%. This saving would increase to 60% if the drain outlet was raised by

0.3 m. Field monitoring of existing infiltration soakwells, however, raised questions as to the

practicality of infiltrating a significant proportion of runoff via soakwells, and further

hydrological investigation may be required.

Reducing the permeability of the lake-bed has implications for the risk of flooding that are

beyond the scope of this investigation. However, modelling suggests that maximum monthly

water levels may reach about 6.2 m AHD in a year of average rainfall and 6.9 m AHD during

a wet cycle; this does not allow for outflow to the main drain which may lower lake water

levels by up to 0.5 m/d. During a dry cycle, lake-water levels might still be maintained near

the desired minimum level in the modified lake.

This investigation has found that to maintain an adequate water-body in Lake Jualbup, it is

likely the polymer additive will need to be applied to at least 75% of the lake-bed surface,

working from the south-west back to the north-east. If practicable, application to 50% of the

lake might be trialled as a preliminary measure to test the modelling results. In addition, it is

recommended that the drain outlet elevation be raised 0.3 m to 5.37 m AHD to increase water

storage, increase infiltration outside the lake perimeter at times of high rainfall, and reduce

outflow to the main drain; thereby contributing to the maintenance of higher water levels in

the lake. Lake water levels, groundwater levels and lake water quality should continue to be

City of Subiaco

Hydrogeological Investigation to Maintain an Adequate Body of Water in Lake JualbupPage iii


monitored and assessed to validate the modelling results and provide ongoing review of the

modified conditions at the lake.

Disclaimer: Numerical groundwater modelling results and other calculations herein are

necessarily approximate because of the nature of natural systems. It is never possible to

obtain and extrapolate exact aquifer parameters. However, the modelling has used ‘state of

the art’ techniques, and has been calibrated to good data on lake and groundwater levels.


TABLE OF CONTENTSPAGE

EXECUTIVE SUMMARY I

1 INTRODUCTION 1

2 HYDROGEOLOGICAL SETTING 1

3 LAKE WATER QUALITY 3

3.1 Current Lake-Water Quality Conditions 3

3.2 Discussion on Current Lake-Water Quality Conditions 5

3.3 Potential Changes to Water Quality 6

3.4 Conclusions on Water Quality 7

4 STORMWATER RUNOFF AND INFILTRATION 7

4.1 Description of Stormwater Drainage System 7

4.2 Calculations of Volume of Surface-Water Runoff 8

4.3 Discussion of Rainfall and Runoff 9

4.4 Maximum Lake-Levels and Ocean Outflow 10

4.5 Soakwells 10

4.5.1 Infiltration Monitoring 11

4.5.2 Discussion 11

5 NUMERICAL MODELLING OF LAKE WATER LEVELS 12

5.1 Model Description 12

5.2 Model Calibration and Adopted Parameters 13

5.3 Model Operation 15

5.4 Preliminary Results of Modelling 17

5.4.1 Water Levels 17

5.4.2 Water-Flow Budget 17

5.4.3 Implications for Model Operation 19

5.5 Modelling Results 19

5.5.1 Impact on Groundwater Levels in the Superficial Aquifer 20

5.5.2 Lake Outflow 20

5.5.3 Raising the Drain Outlet 21

5.5.4 Maximum Lake Levels 22

5.5.5 Maintaining Lake Levels above the Desired Minimum during

Summer Periods of No Rainfall 22

5.5.6 Reducing Lake Inflow 23

5.5.7 Infiltration via Soakwells 24

5.5.8 Changes to Climatic Conditions 25

6 CONCLUSIONS AND RECOMMENDATIONS 25

REFERENCES 28


TABLE OF CONTENTS(Continued)

Tables

Table 1 : Stormwater drainage infrastructure – Shenton Park catchment area 8

Table 2 : Average annual runoff per 0.1 ha of shedding area for various rainfall intensities– based on calculations from Sim (1995) 9

Table 3 : Average rainfall and volume of runoff per month in the Shenton Park catchment 9

Table 4 : Adopted values of aquifer parameters 15

Table 5 : Modelled water flow budget 18

Table 6 : Lake outflow volume calculations 21

Table 7 : Estimated water requirements to maintain minimum desired water-levels 23

Table 8 : Calculated volumes of outflow for model simulations with and without soakwellinfiltration 24

Figures

1 Locality Map

2 Locality Map of Drainage Installations

3 Lake Jualbup Water Level Contour Map September 2011

4 Lake Jualbup Water Level Contour Map March 2012

5 Hydrograph Monitoring Bore GE4

6 Hydrograph of Monitoring Point LJ Lake (Rainfall Data from Bureau of Meteorology)

7 Hydrographs for Monitoring Bores LJ1 to LJ5

8 Stormwater Catchment Infrastructure Locations Shenton Park

9 Local Topography for Lake Jualbup and Surrounds

10 Water Levels in Stormwater Infiltration Wells with Daily Rainfalls from Shenton Park

Treatment Plant

11 Numerical Model Grid

12 Comparison Between Modelled and Measured Water Levels in Lake Jualbup

13 Comparison Between Modelled and Measured Groundwater Levels at Lake Jualbup

Monitoring Bores LJ1 and LJ5

14 Comparison Between Modelled and Measured Regional Groundwater Levels

Monitoring Bores HS1, CS1, MT1, GE4 and KS1

15 Comparison Between Modelled and Measured Lake Water Level Decline February

2008

16 Modelling Results for 25%, 50% and 75% Reduction in Lake Bed Permeability

17 Modelling Results for Simulated Changes to Lake Levels Resulting from 25%, 50%

and 75% Reduction in Lake Bed Permeability

18 Modelling Results for 50% and 75% Reduction in Lake Bed Permeability and New

Perimeter Wall


TABLE OF CONTENTS

(Continued)

Figures (cont.)

19 Simulated Groundwater Levels Calibrated Model and with 75% Reduction to Lake-

Bed Permeability Monitoring Bores LJ1 to LJ5

20 Simulated Groundwater Levels Calibrated Model and with 75% Reduction to Lake-

Bed Permeability Regional Monitoring Bores

21 Lake Water Drain Outflow Assessment

22 Summer Water Level Decline Calibrated Model, Lake-Bed Permeability Reduced

75% and with Reduced Permeability and Raised Drain Elevation

23 Simulated Lake Levels for a Period of No Summer Rainfall

24 Results for Modelling with Reduced Lake Inflow and Infiltration Via Soakwells

25 Drain Outlfow Comparison 75% Lake-Bed Permeability Reduction with Reduced

Lake Inflow

26 Lake Jualbup Modelled Maximum Groundwater Levels in a Wet Cycle : Perth 1961-

1966 Ave Annual Rainfall 927 mm

27 Modelling Results for 75% Reduction in Lake Bed Permeability – Wet Cycle

28 Modelling Results for 75% Reduction in Lake Bed Permeability and a Drying Climate

– Assumes 15% Reduction in Long Term Average Rainfall

Appendices

I Head-Discharge Relationship for Shenton Park Drain Outlet

II Peak Water Levels in Monitored Stormwater Infiltration Wells 16 July – 28 August

2012

III Monthly Recharge to Shenton Park Compensating Basins for Calibrated Model

IV Water Quality Assessment Figures for Lake Jualbup

City of Subiaco

Hydrogeological Investigation to Maintain an Adequate Body of Water in Lake JualbupPage 1


1 INTRODUCTION

The City of Subiaco commissioned a study, commencing July 2012, investigating the

hydrogeological implications of maintaining adequate water levels in Lake Jualbup by

reducing the permeability of the Lake bed utilising a polymer additive. The lake is primarily

a compensating basin utilised by the Water Corporation to accept and infiltrate local

stormwater flow from a number of drains; it acts as a groundwater recharge point in winter

and represents a groundwater expression in spring through summer, as long as groundwater

levels remain above the lake-bed surface. This investigation considers the hydrogeological

impact on the lake and environmental surrounds for varying reductions in lake infiltration

rates. It further considers the effects of installing local infiltration soakwells (“soakwells”)

throughout the lake catchment to offset reduced infiltration from the lake to the superficial

aquifer, and assesses the potential impact of raising the overflow-drain outlet from the lake to

minimise the likely increase in outflow from the system to ocean out-fall resulting from

reduced infiltration rates.

An existing numerical groundwater model representing the shallow aquifer system at Subiaco

and adjoining areas (Rockwater 2009) has been reconstructed in Visual Modflow and

recalibrated to simulate the observed lake water levels and groundwater data collected from

monitoring bores in the area since 2009. The model is used to estimate the lake-level and

groundwater-level response to reduced infiltration through the base of the lake, the

widespread installation and operation of soakwells, and response to a raised drain outlet. It

will contribute to determining the optimal operating conditions for the lake and surrounds.

In conducting the study, Rockwater has examined relevant information on Lake Jualbup and

the City’s drainage network and compensating basins, and water table response as observed in

the seven monitoring bores installed around the lake in 2009 (Rockwater 2009) and several

regional monitoring bores. This report contains the results of these evaluations. We

acknowledge the assistance provided by the City of Subiaco and the useful data and

discussions provided by the Water Corporation and Subiaco resident Dr Geoffrey Dean. The

latter made available his many measurements of water levels in Lake Jualbup collected

between 2005 and 2010.

Locality maps showing the surface-water catchment and relevant infrastructure are presented

in Figures 1 and 2.

2 HYDROGEOLOGICAL SETTING

Subiaco is located within the Perth Basin, with the uppermost strata in the area being sand and

limestone of the Tamala Limestone formation. About 6 m or more of sand overlies

City of Subiaco



interlayered limestone and sand extending to 24 – 35 m below sea level. Collectively, these

and other shallow strata are referred to as the superficial formations.

The hydrogeology of the Perth Basin is described by Davidson (1995). Investigations of the

Subiaco/Lake Jualbup hydrogeology have been reported by McFarlane (1983), Sim (1995),

and Rockwater (2005a, 2005b and 2009). Groundwater in the superficial formations is

recharged by rainwater infiltration, and locally it flows westwards to the ocean and

southwards to the Swan River. Lake Jualbup, and other lakes and wetlands in the

metropolitan area, are topographic lows that receive water by groundwater flow and surface-

water runoff.

Aquifer permeability (= hydraulic conductivity in this report) of the limestone material in the

superficial deposits is very high (100 – 1000 m/d), resulting in high rates of groundwater flow

and low hydraulic gradients. Sands have intermediate permeabilities of generally 10 to

50 m/d while local swamp deposits have low (horizontal) permeabilities of commonly 0.1 to

2 m/d depending on the amount of clay, silt, peat, and cementation. In the vertical direction,

aquifer permeability of sedimentary strata is very much lower than the permeability in the

horizontal direction. The thickness and lithology of the swamp deposits at Lake Jualbup have

not been determined because of lack of access. Natural deposits have been partly altered by

one or more episodes of excavation and waste-dumping. Of the monitoring bores installed

during the previous investigation, only one (LJ3), near the north-eastern edge of the lake

(Fig. 2), intersected clayey material: 0.25 m of black organic sandy clay at 1.5 m depth

(Rockwater, 2009).

Maximum (post-winter, September 2011) and minimum (post-summer, March 2012) water-

table contours in the vicinity of the lake are presented in Figures 3 and 4. The water levels

were measured in monitoring bores installed for the City of Subiaco in 2009 or obtained from

data supplied by the Department of Water (DoW). Regular historical water levels are

available from one monitoring bore in the City of Subiaco - bore GE4 (in Rosalie Park about

600 m south-east of the lake) - and are plotted in Figure 5; measurements are taken

biannually, close to summer minima and winter maxima.

In September 2011 (Fig. 3) the water table was mounded beneath Lake Jualbup, sloping

downwards most strongly to the south (with a hydraulic gradient of 0.006) but also to the

north, east and west; its elevation was close to 4.5 m AHD near the Lake. With water levels

in the lake at about 4.7 m AHD, the lake is evidently acting as a recharge point to the

superficial aquifer following the winter rains. In March 2012 (Fig. 4) the water table near

Lake Jualbup sloped downwards to the south-south-west with a hydraulic gradient of 0.002;

its elevation was close to 3.2 m AHD near the Lake. The small pool of water at the western

end of the lake during summer is apparently connected to the shallow aquifer, with

groundwater flowing into the lake from the north (where the water table is higher), and out to

the south (where the water table is lower).

City of Subiaco



Groundwater levels in the Subiaco area generally fluctuate by 0.5 to 1 m annually in response

to recharge from winter rainfall and depletion in dry months, as illustrated by the hydrograph

for monitoring bore GE4 (Fig. 5). The data show a generally declining trend in regional water

levels averaging 0.03 m/yr between 1994 and 2008, although water levels have stabilised

somewhat since 2006. This reflects the rainfall trends over this time.

Groundwater discharges from the aquifer by subsurface flow to the coast and the Swan River,

by evaporation and transpiration at lakes and areas of shallow water table, and by pumping

from bores for the watering of parks and domestic gardens. Historically, groundwater levels

rose as a result of urbanisation, which led to a greater percentage of rainfall infiltration, but

they have subsequently declined since the 1970’s because of lower rainfall and to a lesser

extent an increase in groundwater pumping from bores.

The hydrographs for Lake Jualbup and surrounding bores are shown in Figures 6 and 7,

respectively. The lake-stage hydrograph is based mainly on measurements provided by

Shenton park resident Dr Geoffrey Dean. The lake water level responded to individual

rainfall events and rose by a maximum of 2.1 m, being limited by flow to the outlet to the

Shenton Park branch drain (at 5.07 m AHD). The water ultimately discharges as ocean

outfall. Because the lake receives run-off water from surrounding stormwater drains and

water pumped from the Aberdare compensating basin (CB) at QEII hospital, its water level

rises by more than double the seasonal fluctuation of the regional water table. Similarly,

groundwater levels immediately surrounding the lake fluctuate by up to 1.8 m in response to

the local recharge from the lake, and in 2010 and 2011 peaked higher and over a longer period

in response to additional water being pumped into the lake from dewatering operations at

QEII. The lake generally contributes water to the aquifer for around 6 months of the year.

3 LAKE WATER QUALITY

As part of the scope of work associated with the current hydrogeological investigation,

Rockwater has been requested to provide an indication of the minimum lake-water level

required to provide an “adequate” body of water in the lake, such that visual appeal and

suitable water quality is maintained. A minimum depth of 0.5 m over most of the eastern side

of the lake was proposed, and this has been assessed based on historical data. Advice is also

provided regarding potential changes to water quality in the lake resulting from the reduction

in lake bed permeability and the establishment of a permanent body of water at the Lake

Jualbup site.

3.1 CURRENT LAKE-WATER QUALITY CONDITIONS

In its current state, Lake Jualbup undergoes a wetting-drying cycle with maximum capacity in

winter, between July and September, and the lake commonly drying out in summer, between

January and March.

City of Subiaco



The bed of the lake is estimated to lie at between 3.0 m AHD (western side) and 3.5 m AHD

(eastern side) over most of its area. Its banks slope to a little over 5 m AHD at the eastern end

and at a vegetated island. The lake has a wall and path around three quarters of its perimeter,

constructed to about 5 m AHD. Its length (east to west) is about 180 m and width is about

130 m, giving a surface area of about 2.3 ha. The island sits off-centre to the west, and

supports a mixture of Australian native and introduced species trees. Some grasses occur

around the fringe of the island. The lake is situated in grassed park-land and native vegetation

has recently been established on its eastern bank.

In winter, the lake generally fills for short periods to the elevation of a water outlet at

5.07 m AHD, giving a water depth of about 1.6 to 2.1 m. In low-rainfall winters, the lake

does not fill. In summer, the lake becomes almost or completely dry, with only a few stagnant

pools of water remaining.

Full mixing of the water column can be expected to occur during winter months by the effects

of wind, rainfall, and inflow of stormwater runoff. In summer, mixing is effected by wind,

council-operated fountains (when water-depth is sufficient), and to a small extent by

groundwater through-flow. Because of its shallow depth, stratification is probably minimal.

Key water quality parameters, as provided by the City of Subiaco, are presented in Figures

App IV – A to D in Appendix IV.

The figures show the lake water is very fresh, with an average salinity of about 250 mg/L

TDS and maximum salinity of about 575 mg/L TDS in late summer months. The water

temperature ranges from between about 15 oC in winter to about 25 oC in summer,

occasionally reaching above 30 oC. The median pH of the lake water is neutral at 6.8;

however, values can vary widely, from one very low value of 4 to as high as 9.5. It is

possible that some of the very high values are in error, although flow through concrete pipes

and/or water pumped from the dewatering operations at QEII may be contributing to the high

alkalinity. The one-off value of 4 in May 2007 is from a small area of water and is associated

with some high metal readings (particularly zinc) and may be real, possibly resulting from

rewetting of previously dry lake-bed deposits.

Dissolved oxygen (DO) levels in the lake frequently fall below 5 mg/L (the level where fish

will become stressed, ANZECC 2000), particularly to the east of the lake, and are generally

below the optimum 90% saturation level, averaging 4 mg/L in the east and 6 mg/L in the

west. Nutrient concentrations vary widely, with total nitrogen (TN) ranging from 0.07 mg/L

to 4.2 mg/L and total phosphorous (TP) ranging from 0.02 mg/L to 0.69 mg/L. Average TN

values (1.26 and 1.17 mg/L for east and west respectively) fall below the ANZECC 2000

guideline value for wetlands (1.5 mg/L). Average TP (0.22 and 0.17 mg/L for east and west

respectively) is above the guideline value for wetlands (0.06 mg/L).

City of Subiaco



Average values for the heavy metals copper, lead and zinc (Data supplied by CoS) are above

the ANZECC 2000, 80% protection trigger values.

The water quality plots show no evident correlation between water quality conditions and the

depth of water in the lake, with elevated nutrients and depleted oxygen levels occurring under

both high and low water level conditions, and vice versa.

Field notes recorded during sampling between 2008 and 2012 indicate stagnant water is

common during summer months, usually in small pools. There are also occasions, when water

levels are higher, up to 4.0 m AHD, when some stagnant water has been noted (November,

2008, May 2010, November 2010 and February 2011), although this appears to be in isolated

pools and is worse when water levels are lower (3.5 to 3.8 m AHD). There are occasional

references to midge and mosquito breeding associated with these pools. Algal blooms do not

appear common, although algae were noted in February 2011 and there was a likely bloom in

February 2012. The only notable difference in water quality at the time algae was present is

the unusually high water temperatures (> 30 oC), which may have triggered algal growth.

3.2 DISCUSSION ON CURRENT LAKE-WATER QUALITY CONDITIONS

A brief review of available reports for the site (see bibliography in References) suggests the

following processes may be contributing to current water quality conditions:

Stormwater inflow – the lake is primarily a compensating basin, receiving surface

water runoff from a highly urbanised environment. Nutrients (especially TP) and

heavy metals are likely to be introduced into the lake via the stormwater inflow,

particularly during “first flush” events (i.e. initial runoff following an extended dry

period);

Phosphorous and heavy metals input to the lake via the stormwater are likely to be

assimilated into the lake-bed sediments;

Degradation of vegetable matter – during the dry periods significant amounts of

vegetation, including “copious amounts” of grass and weeds cover the lake bed. As

the lake re-fills the vegetation dies and dissolved oxygen is likely consumed as the

organic matter is degraded. This is potentially a major contributor to depleted oxygen

levels in the lake;

Low DO levels may remobilise phosphorous into the water column.

Rewetting of dry, oxidised lake-bed sediments may release previously assimilated

heavy metals into the water column;

Small pools that remain in the drying lake-bed have been noted to be stagnant. It has

been reported that groundwater at the site is anaerobic, and therefore any through-flow

will not improve DO concentrations;

Old landfill – the lake is situated on an old landfill site, and it is possible that

groundwater containing elevated TN and ammonia is contributing to higher summer

City of Subiaco



nutrient concentrations. Similarly, the landfill may be the source of some heavy

metals.

3.3 POTENTIAL CHANGES TO WATER QUALITY

The proposed reduction in lake-bed permeability for Lake Jualbup is aimed at establishing a

permanent water body at the site. This represents a significant change in hydraulic conditions

and will necessarily have some impact on the water quality of the lake. The change from an

ephemeral water body to a permanent water body may justify a reclassification of the

ecosystem from a wetland to a constructed lake, which could potentially require more

stringent water quality control under the ANZECC 2000 guidelines.

A recent study on constructed lakes in the Perth metropolitan area (ENV Australia, 2008)

found that the most common problem associated with constructed lakes is eutrophication

(excess nutrients) and associated problems such as algal blooms, odour and midge

infestations. Other problems include invasion of feral fish and exotic flora and infrastructure

and maintenance issues. One key finding of the investigation was the absence of any

correlation between design features of the lake and problems such as eutrophication, with no

particular type of lake showing any greater susceptibility, or lack thereof, to eutrophication

than others. Instead, it was concluded that the best predictor for the effective performance of

a constructed lake is the water-nutrient balance. The lakes most susceptible to eutrophication

are those where residence time for the water is long (>30 days) and nutrient loads (TN and

TP) are high. Older lakes, where nutrients have had time to accumulate, appear to be more

susceptible to eutrophication.

The establishment of a permanent water body in Lake Jualbup could potentially have both

positive and negative impacts on the water quality:

It is unclear as to the nature of the polymer additive proposed for application to the

lake-bed, however it is possible that it may decrease the adsorptive capacity of the

lake-bed sediments, thereby increasing soluble concentrations of heavy metals and TP

in the water column;

With the lake-bed permanently inundated, there will no longer be the opportunity for

very large quantities of terrestrial vegetation to grow up during the dry season; this

should reduce the amount of organic matter degradation that occurs as the lake fills,

potentially reducing DO consumption and improving oxygen levels in the lake;

Improved oxygen levels may prevent remobilisation of TP from the sediments,

potentially reducing TP concentrations;

Without the drying cycle, lake-bed sediments will not become oxidised, minimising

the potential for acidification and re-mobilisation of metals;

The lake will no longer be in hydraulic connection with the groundwater during

summer, potentially decreasing TN, ammonia and/or heavy metal concentrations, if

City of Subiaco



these do in fact exist at higher levels in the groundwater at this site.

Through-flow and outflow to the groundwater system will be restricted, increasing

residence time for the water in the lake, potentially increasing the risk of

eutrophication of the lake;

If groundwater is high in TN, using it to maintain water levels in the lake could

contribute to water quality problems.

3.4 CONCLUSIONS ON WATER QUALITY

There is no significant correlation between the key water quality parameters and water level

depth in Lake Jualbup, although notes taken during sampling tend to indicate more visually

pleasing conditions and less obvious water stagnation when lake levels are greater than

4 m AHD.

A number of water quality changes can be expected as the lake moves from an ephemeral

wetland to a permanent lake, and these have been summarised. As the processes are complex

and highly interconnected, water quality monitoring should continue at the lake to assess the

net effect of these changes.

The planting of native grasses and vegetation at the lakes edge may lower nutrient and heavy

metal concentrations, reducing the risk of eutrophication.

4 STORMWATER RUNOFF AND INFILTRATION

Lake Jualbup acts as a compensating basin within the Shenton Park catchment, with

stormwater directed to the lake via local stormwater drains that collect rainfall runoff from the

streets and pavements throughout the catchment. Most stormwater drains in the catchment

direct their inflow to the lake via piped drainage. However, upgrading of stormwater drains

from around 2006 to 2009 has led to a number of drainage pits being replaced with infiltration

soakwells, which enable the collected rainfall runoff to infiltrate directly to the water table at

that location; some overflow from these drains may still be directed to the lake following high

intensity rainfall events. The details of the catchment system in relation to the lake and direct

aquifer recharge are provided below.

4.1 DESCRIPTION OF STORMWATER DRAINAGE SYSTEM

Runoff from paved areas is collected predominantly in the City’s piped drainage system

which includes about 2000 export drainage pits, with water-entry at road pavement level at

local low elevations. The installations are termed “gullies” (with horizontal grill) and “side-

entry pits”. Locations and associated drainage infrastructure are shown in Figure 8. The

drainage pits in the Shenton Park catchment allow runoff water to enter the local drains which

City of Subiaco



are directed to the Lake Jualbup or Aberdare Rd compensating basins (CBs). Water from

Aberdare Rd is pumped into Lake Jualbup via a branch drain, and any overflow from Lake

Jualbup is directed to the Subiaco Main drain via a branch drain. Since August 2010,

additional water has been pumped from Aberdare Rd CB to Lake Jualbup as a result of

dewatering operations associated with building-excavations at QEII hospital. The drains are

all enclosed pipes. The main drains and associated compensating basins are operated by the

Water Corporation. The Subiaco main drain water eventually reaches the ocean north of

Swanbourne Beach.

All the drainage is by gravity, with the exception of water pumped from the Aberdare Rd CB

to Lake Jualbup when water levels reach a trigger value. The Shenton Park catchment covers

293 hectares and includes an area of about 80 ha in the City of Nedlands, south of Aberdare

Road. For its assessment purposes, the Water Corporation has assigned 81 sub-catchments

based on the pipe-network configuration and the types of land development affecting water

runoff.

A summary of drainage infrastructure for the Shenton Park catchment is provided in Table 1,

based on information provided by the Water Corporation (Rockwater, 2009) and City of

Subiaco. The table shows total catchment area and the assigned value for the impervious areas

connected to surface-drainage. The drainage system – comprising 764 drainage pits, 60 local

infiltration soakwells, two compensating basins and two branch drains – is designed to

prevent deleterious flooding arising from moderately severe rainfall events; i.e. 5 year ARI

storm and 10 year ARI storm runoff, for residential and commercial developments,

respectively. The drain capacity, therefore is designed for high flow conditions, and provides

no indication of total flow volumes under usual conditions. Rates and volumes of flow are not

measured in any of the drain pipes.

Table 1 : Stormwater drainage infrastructure – Shenton Park catchment area

Total area (ha) 293

Impervious Shedding Area (ha) 63

Drainage Pits 764

Infiltration Soakwells 60

Compensating Basins 2

Branch Drains 2

Drain Outlets into Lake Jualbup 11

Lake Outlet Drain to Branch Drain 1

4.2 CALCULATIONS OF VOLUME OF SURFACE-WATER RUNOFF

Using a quadratic function derived empirically for the Shenton Park catchment (Discharge

(m3) = 43.3 x daily rainfall (mm) + 1.61 daily rainfall2 (mm) – 33.1 for 7 ha shedding area)

(Sim, 1995)), and a range of daily rainfall values, Rockwater has previously estimated annual

City of Subiaco



runoff per 0.1 ha for the Shenton Park catchment since 1999. These calculations were

updated for the current investigation and are presented in Table 2.

Table 2 : Average annual runoff per 0.1 ha of shedding area for various rainfall

intensities – based on calculations from Sim (1995)

Rainfall/DayAdopted Value

Rainfall/Day

Calculated Runoff

per 0.1 ha

Average No. of

Runoff Days/Year

Average Annual

Runoff

per 0.1 ha

mm mm m3 d m3

3-5 4 2.4 13.6 33

5-10 7.5 5.5 19.1 105

10-15 12.5 10.9 11.3 123

15-20 17.5 17.4 5.2 92

20-30 25 29.4 5.2 152

30-40 35 49.4 1.5 72

40-50 45 73.9 1.2 85

*50+ 55 103.1 0.5 52

Total 714

*Average 2008 to 2011.

Calculations made for the 2009 report used a combined average for rainfall data from Perth

and Subiaco treatment plant stations. The updated calculations for 2009 to 2012 are based

on Subiaco rainfall data alone. The average values reported here are an average of the results

obtained for the 2009 report and the updated calculations. Rainfalls of less than 3 mm/d have

been assumed to produce negligible runoff, because very small and low-intensity rainfalls are

essentially all consumed by depression storage and evaporation. Average volumes of runoff

per month, calculated using runoff per 0.1 ha and are listed in Table 3. Ninety per cent of the

runoff takes place (on average) in the seven months April to October.

Table 3 : Average rainfall and volume of runoff per month in the Shenton Park

catchment

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year

Average Monthly

Rainfall - Subiaco11.7 13.9 18.2 37.1 83.7 142.7 148.0 105.2 72.9 40.8 23.4 9.5 707.1

Average No.

of Runoff Days in

Each Month

1.0 5.5 0.9 3.2 6.0 9.5 12.1 9.2 8.0 3.1 2.5 0.9 62

Runoff (calc.)

per 0.1 ha (m3)19 9 22 41 79 125 138 111 63 31 15 11 663

Shenton Park

Runoff (m3 x 103)11.7 5.4 14.0 26.0 49.7 78.6 87.0 69.7 39.9 19.6 9.7 6.6 418

4.3 DISCUSSION OF RAINFALL AND RUNOFF

Not all of the calculated volume of runoff for the Shenton Park catchment reaches Lake

Jualbup. A significant but unknown amount of the water collected at the Aberdare Road CB

City of Subiaco



infiltrates to the aquifer beneath the storage pond at that site, rather than being pumped to the

Lake.

In most years of average to high rainfall, the water level in Lake Jualbup rises to the level of

the outflow drain (at 5.07 m AHD) and overflow water passes to the Subiaco main drain via a

branch drain. This was observed in 2008 and 2009, when the annual Perth rainfall was 808

and 607 mm, respectively. It probably also occurred in 2011, when the annual Perth rainfall

was 861 mm; however, it was not measured due to less frequent lake-level monitoring. The

volume of water that leaves the Lake is not measured, and it would vary depending on the

timing and duration of high-rainfall events. In low rainfall years, such as 2010, it has been

observed that the water level in Lake Jualbup remains below the outflow drain, and all the

runoff is retained.

4.4 MAXIMUM LAKE-LEVELS AND OCEAN OUTFLOW

Once lake levels reach 5.07 m AHD, water flows into the branch-drain outflow at the north-

west side of the lake, and is directed to the Subiaco Main Drain and ultimately the ocean

(Fig. 2). The lake-level monitoring results show that water rose above the outlet level on at

least four occasions between January 2008 and May 2012 (Fig. 6). The daily lake-monitoring

data (Dean, 2011) show that water levels remained above the outlet for six days in

July/August 2008, for three days in July 2009 and for four days in August 2009. Lake water

levels did not rise above the outlet height in 2010, and only monthly measurements were

made in 2011 and 2012, so the duration of any outflow is not known.

The head discharge relationship for the outlet drain has been provided by the Water

Corporation (Appendix I). The values are calculated, not measured. For lake levels of about

5.2 m AHD, up to 13,740 m3/d might flow from the lake to the drain, equivalent to about

0.5 m of lake storage per day.

At the lake’s peak measured water level (5.22 m AHD on 31 July 2008) the water would have

remained contained well within the park boundary, which has a topographic low of about

6.5 m AHD on the western side, along Herbert Rd (Fig. 9).

4.5 SOAKWELLS

The soakwells are concrete cylinders of 1.2 m diameter and 2.0 to 2.4 m depth with an open

base and lateral slots. Runoff water enters via gullies or side-entry openings. Overflow water

from the soakwells discharges into drain pipes and thence to the local drains, or back to the

road pavement and thence to a downstream drainage pit. About 60 of the drainage pits in the

Shenton Park catchment, and over 200 in the City of Subiaco as a whole, were converted to

soakwells between 2006 and 2009, and there is potential for the remainder to be converted.

City of Subiaco



4.5.1 Infiltration Monitoring

Water levels were recorded in three soakwells (119 and 142 Keightly Rd and 5 Waverley St)

at one-minute intervals through the end of July and August 2012, with a total rainfall of

35 mm and 110 mm, for each month respectively. The overall results are provided in

Figure 10, with detailed plots shown in Appendix II. The findings are summarised below.

Daily rainfalls ranged from 0.4 to 20 mm.

Peak water levels in the soakwell in Waverley St reached a maximum depth of about

1.5 m, while those in Keightly Rd reached a maximum of about 1.0 m. These levels are

below the drain inlets and the soakwells do not appear to have overflowed.

Peak water levels in Waverly St declined to near the base of the soakwell in about two

hours from the cessation of rainfall, while peak water levels in the soakwells on

Keightly Rd declined to near the base within 30 minutes.

Infiltration rates (calculated from the average rates of water-level decline after the

water-level peaks) in Waverley St ranged from 11 to 43 m3/d, with volumes of up to 3.4

m3 infiltrated over approximately 5 hours for rainfall events in the order of 10 – 20

mm/d. In the Keightly Rd soakwells, infiltration rates ranged from 20 to 66 m3/d, with

total volumes of up to about 1.7 m3 infiltrated over approximately 90 minutes for a 12

mm/d rainfall event.

In August 2012, a total of 15 m3, 4.2 m3 and 1.8 m3 of stormwater was infiltrated

directly to the superficial aquifer via the three soakwells in Waverley St and 142 and

119 Keightly Rd, respectively, for total measured monthly rainfall of 110 mm over 11

rainfall runoff days (rainfall >3.0 mm).

It appears that the Keightly Rd soakwells receive less rainfall runoff than the

Waverley St soakwells, which may be related to their location and spacing. They have

small catchment areas. It is also possible, that the volume of water appears to be less

due to the higher infiltration rates in these soakwells.

The variability in the volume of water flowing into the soakwells over a relatively small

area indicates that careful siting of the soakwells is required to ensure optimum

interception of rainfall runoff.

The operational infiltration rates measured in these soakwells are similar to the values

obtained from average rates of water-level decline in the controlled infiltration test rates

measured in 2009 (18 to 57 m3/d).

4.5.2 Discussion

For rainfalls of 3 to 20 mm per day the soakwells appear to be efficient at infiltrating runoff

water: probably 100 per cent of water intercepted. For larger and very intense rainfalls, some

excess water will overflow the soakwells and pass into the piped drainage system. Rainfalls

City of Subiaco



of 20 to 40 + mm per day contribute about half the estimated annual runoff from the Subiaco

catchments (Table 2).

The condition (cleanliness) of the soakwells will have a strong bearing on their efficiency in

transmitting water to the underlying aquifer. Likely impediments include:

Debris inhibiting water entry to the Gully/SEP

Leaf and other debris on the floor of the soakwell

Siltation of the floor and underlying sand (aquifer)

The number of soakwells installed in each drainage basin will determine the average

pavement area draining to the soakwells. Small local catchments are less likely – than large

catchments – to give rise to excess water, and ‘overtopping’ of soakwells.

Given the undetermined elements affecting the amount of water that may bypass the

soakwells, calculations in this report allow for infiltration of up to 75 per cent of the estimated

runoff from rainfalls exceeding 3 mm per day. This is down slightly on the 80 per cent used

in previous investigations (Rockwater 2009). During periods of exceptionally intense rainfall,

and/or if there are significant siltation and debris effects, the soakwell efficiency could reduce

to lower percentages.

The low total volumes of water measured in the monitored soakwells (average 7 m3 total

volume per soakwell for a 110 mm rainfall month) raises some questions as to the practicality

of infiltrating a significant proportion of runoff via local soakwells. With 742 soakwells, this

would allow 5,200 m3 to infiltrate in a 110 mm rainfall month. Actual runoff is calculated to

be 73,000 m3 (August, Table 3). However, the 7 m3 per soakwell might not be typical, as the

catchments for the tested soakwells were quite small; also, the analyses of the data did not

allow for the amount of run-off water that might have entered the soakwells during the water-

level decline from the peaks. A catchment-wide hydrological investigation (including the use

of recording-pluviometers) would be beneficial prior to implementing management practices

based on assumptions of large volumes of local infiltration.

5 NUMERICAL MODELLING OF LAKE WATER LEVELS

5.1 MODEL DESCRIPTION

An existing numerical model (Rockwater 2009) was reconstructed to simulate the water levels

in Lake Jualbup and the surrounding shallow aquifer in relation to rainfall events and

estimated catchment runoff (lake inflow). The new model utilises Visual Modflow 2011.1

which has been developed from the industry standard, MODFLOW software (McDonald and

Harbaugh, 1988). The latest model replaces a previous PMWIN version to make use of

Visual Modflow’s “re-wetting” capacity, which allows cells that have become dry to be

City of Subiaco



resaturated thereby enabling more-accurate modelling of the lake water-levels and local

surrounds.

The model covers an area measuring 6 km north-south from Lake Monger to the Swan River,

and 9 km east-west from Kings Park to the coast (Fig. 11). It comprises a rectangular grid of

66 rows and 64 columns with cells sizes ranging from 14 mx14 m around the lake to 460 m x

350 m in outlying areas.

The model has two layers, both representing the unconfined superficial aquifer and has

identical input parameters over most of the model area. Layer 1, is used to model the lake,

with the top of the layer set at topographic elevation and the lake cells given unlimited

horizontal hydraulic conductivity and a storage value of one. Cells immediately adjacent to

the lake have been given a reduced horizontal hydraulic conductivity to simulate boundary

conditions between the lake and the surrounding aquifer cells. The permeability of the lake

bed is simulated by varying the vertical hydraulic conductivity of the lake cells.

Constant-head cells were set on the western edge of the model to represent the ocean, and in

the south-eastern area to represent the Swan River. Here, the assigned water-level elevations

are 0 m AHD. Groundwater flows into the modelled area from the north-east and out of the

modelled area to the south-south-west; this flow was simulated using constant-head cells with

water levels set at elevations conforming to measured regional values.

Initial water levels were set at average groundwater levels extrapolated from monitoring-bore

measurements, and aquifer parameters were assigned based on previous modelling

(Rockwater, 2009) and adjusted during calibration, as described below.

5.2 MODEL CALIBRATION AND ADOPTED PARAMETERS

The model was calibrated by adjusting recharge and evapotranspiration parameters to

simulate the observed fluctuations in lake-water and in groundwater levels recorded over the

period 2008 to 2011 at the site monitoring bores (LJ1 to LJ5) and representative regional

monitoring bores (MT1, HS1, CS1, GE4 and KS1) (Fig. 2). Monthly values of rainfall

recharge and estimated runoff to Lake Jualbup, Aberdare Rd CB and Mabel Talbot CB were

used. Additional recharge was also input to Lake Jualbup from August 2010 to December

2011 to represent pumping of dewatering water to the lake from QEII.

Regional rainfall recharge to the aquifer was simulated using 28 per cent of measured

monthly rainfall (Subiaco WTP). The installation of soakwells was simulated by infiltrating

75 per cent of measured monthly rainfall in locations where installation has occurred, from

the year of installation. Monthly runoff into Lake Jualbup was simulated by inputting

additional recharge to the cells representing Lake Jualbup (24,750 m2 area) based on the

calculated volume of runoff over the Shenton Park catchment area. The pumping inflow from

City of Subiaco



QEII dewatering was similarly input based on estimated additional pumping volumes from

Aberdare Rd. Inflows to the Mabel Talbot and Aberdare Rd compensating basins were also

simulated using the recharge package. Modelled runoff recharge volumes are provided in

Appendix III.

Evaporation from the lake and CBs was simulated using the mean of the monthly rate of pan-

evaporation from Armadale and Upper Swan (Bureau of Meteorology) multiplied by a pan

factor of 0.8. The adopted rates ranged from 606 mm/year (1.7 mm/d) in June to

3156 mm/year (8.6 mm/d) in January.

Comparisons between modelled lake and groundwater levels and measured values are

provided in Figures 12 to 14. The figures show a good to reasonable match between the

simulated and measured results.

Once the simulated lake-water and groundwater levels were reasonably matched to the

measured data, the model was run over a short time interval (54 days) to simulate summer

infiltration at Lake Jualbup. The modelled lake water-level response was compared to

measured water-level decline over the period 8 February 2008 to end of March 2008. The

hydraulic conductivity in the lake cells and the starting groundwater levels were adjusted until

simulated lake water-levels declined at a rate comparable to the measured lake-level decline

over a summer period without rain.

The calibration process showed that the infiltration rate and minimum lake water-level at the

end of summer are most sensitive to the prevailing groundwater conditions (i.e. surrounding

groundwater levels). The modelling was much less sensitive to changes in permeability,

which could be varied by an order of magnitude with little difference in results. The initial

groundwater levels were set to values near the summer minimum (taken from model

simulation results near the end of January), with starting lake levels input at the measured

3.98 m AHD. The full February 2008 recharge was input to the lake cells on the first day of

modelling (to simulate the large rainfall event that filled the lake on that occasion) with no

recharge thereafter. The results are presented in Figure 15 and show a good match between

the modelled and measured infiltration. The results from sensitivity model runs are also

shown in Figure 15 to illustrate how infiltration is affected by changes in lake-bed

permeability and prevailing groundwater levels.

Modelled infiltration rates for the lake over the period of calibration (2008 to mid-2012)

ranged between a minimum of 30 m3/d in summer to a maximum of 2,900 m3/d in winter,

with average values of 650 m3/d and 1,480 m3/d for summer and winter respectively, or an

overall average of 980 m/d. These values are consistent with those reported previously, based

on measured infiltration rates (Rockwater 2005).

The final adopted values for the model aquifer parameters are listed in Table 4. Horizontal

hydraulic conductivity (Kh) values range from 15 to 120 m/d, with the highest values

City of Subiaco



reflecting the increased proportion of limestone towards the coast. The lake cells were

allocated unrestricted horizontal flow (Kh = 1,000 m/d), with cells immediately surrounding

the lake assigned Kh values lower than the surrounding aquifer (1 to 5 m/d) to represent

reduced hydraulic conductivity due to lake deposits, the wall and surrounding vegetation.

The assigned vertical hydraulic conductivity (Kv) values are 0.1 x Kh m/d, except at Lake

Jualbup where Layer 1 is assigned values of 0.2 to 0.5 m/d. The values for Kv are higher than

used in previous models, but were necessary to simulate predominantly downward flow to the

underlying groundwater system, and were similar to values reported in previous sensitivity

analysis where recharge rates more closely matched the calculated runoff values (Rockwater

2009).

Table 4 : Adopted values of aquifer parameters

Parameter Layer 1 Layer 2

General Values Lake Jualbup General Values

Horizontal Hydraulic

Conductivity (m/d)15 – 120

1,000 and

1 to 5 at boundary15 – 120

Vertical Hydraulic

Conductivity (m/d)0.1 x Kh 0.2 – 0.5 0.1 x Kh

Specific Yield 0.2 1.0 0.2

Storage Coefficient N/A N/A 0.001

N/A = not applicable

5.3 MODEL OPERATION

The primary purpose of the modelling is to assess the efficacy of reducing the permeability of

the lake bed to reduce leakage and maintain an adequate water body in the lake throughout the

year, and to determine the subsequent effects on the surrounding environment, in particular

the potential increase in outflow to the ocean and the reduced infiltration to the superficial

aquifer.

The modelling investigated the effect on water levels in the lake under three different

scenarios:

1. Reduction of lake bed permeability by 25 per cent;

2. Reduction of lake bed permeability by 50 per cent, and;

3. Reduction of lake bed permeability by 75 per cent.

It was originally planned to run each scenario over a period of ten years and consider the

results in the context of each of two options:

1. Maximum lake water levels based on the current height of the drain outlet, and;

2. Maximum lake water levels based on raising the drain outlet by 0.3 m.

City of Subiaco



And address the following:

1. How long is the body of water maintained above the desired minimum water level

(4 m AHD) during periods of no rainfall;

2. By how much will runoff to the lake (i.e. lake inflow) need to be reduced to minimise

loss of water to the outlet drain (as a percentage of current inflow estimates);

3. What volume of water is estimated to flow to the ocean with and without soakwells,

and the potential volume of water saved from overflow through the installation of

local infiltration facilities;

4. What volume of water could potentially be infiltrated to the shallow aquifer via local

soakwells, and an estimate of the number and location necessary to achieve the

required reduction to runoff;

5. How much bore water may be required to supplement the lake and maintain water

levels in an average rainfall year during summer months, and;

6. How would groundwater levels respond in a cycle of higher rainfall. (Added to scope

subsequent to meeting with the Water Corporation).

The polymer application proposed for reducing the permeability of the lake-bed forms an

impermeable seal over the area to which it is applied. It has been advised by the suppliers of

the polymer that the degree of permeability of the seal cannot practically be adjusted by

varying the amount of polymer applied per unit area. Therefore, the percentage of reduction in

the total lake-bed permeability is to be varied by changing the area covered with polymer.

Consequently, the reduction of lake-bed permeability was modelled by making 25, 50 and 75

per cent of the lake cells impermeable (Kv = 0.0001 m/d) for each modelling scenario,

respectively. The modelled scenario is that the polymer was first applied to the south-western

25% of the lake, and then applied in 25% segments progressively north-eastwards. Reduced

permeability at the lake boundary was simulated by decreasing the permeability of the cells

by 50 to 90% (Kh to 0.5 m/d and Kv to 0.125 m/d).

For the predictive modelling runs, average monthly rainfall values for the Subiaco treatment

plant were used (to calculate groundwater recharge of 28% regionally and 75% in areas with

direct stormwater infiltration) along with the calculated values for average rainfall runoff

(Table 3), 90% of which was input to Lake Jualbup as recharge and 10% to Aberdare Rd CB.

The model predicts the water-level fluctuations for the next ten years with the assumption of

average rainfall each year.

For the purposes of modelling, an adequate water body is taken to be one where minimum

lake water-levels are maintained just below the current base of wall at 4.0 m AHD, providing

a minimum water depth of 0.5 m over most of the lake.

City of Subiaco



5.4 PRELIMINARY RESULTS OF MODELLING

5.4.1 Water Levels

Figure 16 shows the results of preliminary modelling, plotting simulated lake water-levels for

each of the three scenarios (25, 50 and 75% reduction in lake bed permeability) compared to

modelled lake levels obtained with no reduction in permeability, i.e. the calibrated model.

The figure shows that minimum lake water-levels could be expected rise 0.4 m from the 2009

and 2010 minimum levels, to 3.4 m AHD, solely as a result of an increase in annual rainfall to

the long-term average. It also shows that of the three scenarios, only a reduction in lake bed

permeability of 75% would achieve the desired minimum water level of 4.0 m AHD assuming

an extended period of average annual rainfall.

A comparison is shown in Figure 17 between the calibrated lake-level simulation and the

results for each of the three scenarios between 2008 and 2012. It can be seen that for a

reduction in lake-bed permeability of 25%, minimum water levels would have been between

0.1 and 0.4 m higher; for a reduction in lake-bed permeability of 50%, minimum water levels

would have been between 0.2 and 0.6 m higher; and for a reduction in lake-bed permeability

of 75%, minimum water levels would have been between 0.3 and 0.8 m higher. In each case,

the eastern side of Lake Jualbup would have dried up during the summers of 2009 and 2010,

and, with the possible exception of the 75% reduced lake-bed permeability scenario, in 2011

and 2012 summer water levels would have fallen well below the desired 4.0 m AHD.

5.4.2 Water-Flow Budget

The water-flow budget was assessed for the calibrated model and the 75% reduction scenario

using the zone budget function in Visual Modflow to compare flow rates over the simulated

time period corresponding to 2009 (i.e. stress periods 13 to 24). The results are presented in

Table 5.

It can be seen that in the calibrated model, approximately 20% of simulated infiltration was

horizontal flow to the lake surrounds, with 80% of the infiltration downwards to the

underlying aquifer in the south-west portion of the lake to be sealed (Zone: SW area sealed).

Following the application of a polymer seal over the base of the lake, the horizontal flow

component increased to 45% of the total infiltration (assuming the sides of the lake are not

completely sealed). Overall, the model predicts a 20% decrease in horizontal flow and 60%

decrease in downward flow over the area sealed for 75% permeability reduction.

The water budget also shows that following the application of the polymer, water will be

mainly lost from the unsealed portion of the lake (Zone: NE area unsealed) with infiltration

rates in this area increasing to three times those simulated for the calibrated model (from a

monthly average of about 155 m3/d to about 490 m3/d).

City of Subiaco



Table 5 : Modelled water flow budget

Model ZoneRecharge to

Layer 1

Recharge to

Layer 2

Total

Recharge

Horizontal flow

to surrounds

Downward

Infiltration

Total

Infiltration

(m3/d) (m3/d) (m3/d) (m3/d) (m3/d) (m3/d)

NE to SW

(m3/d)

SW to NE

(m3/d)

Calibrated SW area to be sealed

SP 13 117 117 54 211 265 34

SP 14 0 0 22 50 72 7

SP 15 122 37 159 24 79 103

SP 16 60 21 81 20 42 62

SP 17 17 19 36 17 29 46

SP 18 315 355 670 49 193 242

SP 19 1223 120 1343 103 768 871 13 44

SP 20 2516 2516 332 1514 1846 231 178

SP 21 1483 1483 275 1194 1469 62 83

SP 22 816 816 178 785 963 54 38

SP 23 37 37 70 286 356 43

SP 24 196 196 57 219 276 36

Average 100 448 548 40 29

75% reduction SW area sealed

SP 13 117 117 57 125 182 180

SP 14 0 0 34 74 108 68

SP 15 158 158 31 69 100 63

SP 16 83 83 26 58 84 26

SP 17 33 2 35 19 48 67 4

SP 18 623 42 665 39 131 170 139

SP 19 1319 25 1344 81 241 322 765

SP 20 2516 2516 175 370 545 832

SP 21 1483 1483 179 360 539 780

SP 22 816 816 155 312 467 647

SP 23 37 37 101 212 313 382

SP 24 196 196 65 143 208 217

Average 80 179 259 Neg. 342

Calibrated NE area to be unsealed

SP 13 35 35 34 34 35

SP 14 0 0 14 14 7

SP 15 47 47 30 30

SP 16 24 24 10 10

SP 17 0 10 10 5 5

SP 18 1 195 196

SP 19 398 398 41 261 302 13

SP 20 744 744 117 506 623 232

SP 21 439 439 83 377 460 62

SP 22 241 241 42 227 269 54

SP 23 11 11 54 54 43

SP 24 58 58 37 37 35

Average 24 130 153 40 Neg.

75% reduction NE area unsealed

SP 13 35 35 35 269 304 180

SP 14 0 0 10 126 136 68

SP 15 47 47 8 109 117 63

SP 16 24 24 49 49 26

SP 17 9 2 11 14 14

SP 18 166 30 196 223 223 139

SP 19 398 398 88 622 710 765

SP 20 743 743 206 997 1203 833

SP 21 438 438 202 948 1150 781

SP 22 241 241 165 804 969 647

SP 23 11 11 88 511 599 383

SP 24 58 58 44 318 362 217

Average 71 416 486 Neg. 342

Flow between SW

Sealed and NE

Unsealed Area of

Lake

Note: Neg. refers to negligible

City of Subiaco



5.4.3 Implications for Model Operation

The results from the preliminary modelling indicated that application of the polymer to only

part of the base of the lake, without sealing the sides, is unlikely be sufficiently effective in

reducing infiltration rates to maintain lake water-levels at the desired minimum level. Of the

three scenarios modelled, only a reduction in permeability of 75% was able to raise minimum

lake water-levels to a level considered sufficient for the maintenance of an “adequate water

body” in the lake, assuming annual rainfall levels increase to their long-term average in the

immediate and ongoing future.

Given the uncertainty of any of the proposed management options being able to deliver the

desired objective, a meeting was sought with the City of Subiaco to discuss how to proceed

with the model operation. The meeting outcomes are summarised below:

Application of the polymer to 100% of the lake to form a complete seal is not an

option, based on community consultation and subsequent undertakings of the Council,

therefore it will not be modelled;

There are plans to restore the lake wall along the southern and western boundaries.

This should significantly reduce horizontal flow from the lake in these areas; therefore

the model will be re-run for the 50% and 75% lake-bed cover with hydraulic and

vertical hydraulic conductivities of the boundary cells in these areas further reduced to

0.001 m/d and 0.0001 m/d, respectively.

Detailed assessment of the further options with regard to raising the drain outlet and

increasing local stormwater infiltration through installation of soakwells etc. will only

be conducted for the 75% reduction scenario and the 50% reduction scenario if

modelling results from dot point 2 above indicate it is warranted.

Modelling runs will include an additional scenario to allow for “drying climate”

conditions.

5.5 MODELLING RESULTS

The 50% and 75% reduction scenarios were re-run assuming significantly reduced horizontal

and vertical flow along the southern and western lake boundary, as detailed in Section 4.4.3

above. The results are shown in Figure 18.

It can be seen that further reducing the permeability of the lake wall did not increase lake

water-levels sufficiently in the 50% reduction scenario to achieve the desired minimum lake

water-levels, which remain around 3.8 m AHD (approximately 0.3 m above base of eastern

lobe of the lake) under long-term average rainfall conditions. Reducing the permeability in

the lake wall increased simulated long-term lake water-levels in the 75% reduction scenario

by a further 0.2 m, giving an annual minimum water level of around 4.2 m AHD under long-

term average rainfall conditions (this is 0.7 m above minimum long-term water levels for the

calibrated model).

City of Subiaco



The modelling runs for the various management options detailed in Section 2.3 were

conducted for the 75% reduced lake-bed permeability scenario, and the results are presented

below.

5.5.1 Impact on Groundwater Levels in the Superficial Aquifer

Figure 19 shows a comparison between simulated groundwater levels for the calibrated model

and the 75% reduction model at Lake Jualbup. It can be seen that the impact on groundwater

levels at the site will be confined to those monitoring bores immediately down-gradient of the

sealed area of the lake, LJ1 and LJ2, where maximum (winter) groundwater levels will be

about 0.7 and 0.4 m lower, respectively, and will occur about one to two months later.

Minimum (summer) groundwater levels in both bores will be within 0.1 m of the pre-sealed

levels. In the monitoring bores up-gradient of the lake and adjacent to the unsealed area,

minimum and maximum levels will remain essentially the same with some small lag in when

maximum water levels are reached.

There will be no measurable impact on groundwater levels regionally (Fig. 20).

5.5.2 Lake Outflow

It is not possible to simulate the flow of water away from the lake via an enclosed drain using

a numerical groundwater modelling package, such as Visual Modflow. However, estimates

of the volume of water above the drain outlet can be made by multiplying the maximum head

above the outlet elevation (5.07 m AHD) by the lake area. (In reality the water levels would

not reach the modelled elevations as the water would spread over a larger area as the lake

walls are breached.) Comparisons between measured and simulated lake water-levels for

calibrated and reduced-permeability model runs are provided in Figure 21 and the results of

volume calculations for the model results, including values for a raised drain outlet (at 5.37 m

AHD) are shown in Table 6.

It can be seen in Figure 21 that modelled lake-levels generally peak higher and over a longer

duration than those measured. This is to be expected as the model does not simulate flow

away from the lake via the overflow drain, nor does it allow the water to spread over a larger

area beyond the lake walls. The impact of reducing the lake bed permeability on maximum

water levels and volumes of outflow can be broadly assessed by comparing the difference

between the calibrated model results and the 75% reduction model run for the years 2008 and

2009 (where the results are not further complicated by dewatering input to the lake) and into

the future assuming a long-term average rainfall.

City of Subiaco



Table 6 : Lake outflow volume calculations

Maximum Lake-

Level (m AHD)

Maximum Level

Above Drain

Outlet (m)

Calculated

Volume Outflow

(m3)

Maximum Level

Above Drain

Outlet (m)

Calculated

Volume Outflow

(m3)

% Water

Saved with

Higher Outlet

Calibrated Model

2008 5.86 0.79 19,553 0.51 12,623 35%

2009 5.41 0.34 8,415 0.05 1,238 85%

75% Reduction

2008 7.2 2.12 52,470 1.82 45,045 14%

2009 6.69 1.51 37,373 1.21 29,948 20%

Factor Increase in Modelled Outflow with Reduced Lakebed Permeabilty

2008 2.7

2009 4.4

Long Term - Ave. Rainfall

Calibrated Model 5.52 0.45 11,138 0.15 3,712 67%

75% Reduction 6.8 1.73 42,818 1.43 35,393 17%

Factor Increase in Modelled Outflow with Reduced Lakebed Permeabilty

3.8

Current Drain Outlet Elevation Raised Drain Outlet Elevation

In general, the modelling suggests that a reduction in lake bed permeability of 75% will

increase outflow to ocean outfall by a factor of between 2.7 and 4.4 (i.e. outflow will be about

3 to 4 times greater than with no reduction in lake-bed permeability). Raising the drain outlet

by 0.3 m could decrease ocean outflow by about 20 to 85% with the higher percentages

relating to situations where the lake-levels rise only small heights above the proposed raised

drain-outlet elevation.

5.5.3 Raising the Drain Outlet

To assess the effect of raising the drain elevation on summer water levels, the model was run

to simulate lake-water level decline over a summer interval with no rain and compared results

for different starting water levels. The model used to calibrate summer infiltration was first

run with lake-bed permeability reduced by 75% and then run again with starting lake-water

levels set 0.3 m higher; the results are presented in Figure 22. The modelling indicates that

lake water-levels would be about 0.7 m higher at the end of the summer period with the lake-

bed permeability reduced by 75%, and that this would increase a further 0.1 m (total 0.8 m

higher) if the starting water levels were 0.3 m higher.

An additional benefit of raising the drain elevation would be to provide more time and a

larger area over which water would be able to infiltrate, thereby increasing recharge to the

aquifer at the site.

City of Subiaco



5.5.4 Maximum Lake Levels

The maximum lake levels generated in the model runs are not representative of the true lake

levels that would occur at the site. This is because: (1) water in the model is confined to the

area of the lake cells, rather than spreading over a larger area as the lake walls are breached,

and (2) flow from the drain outlet is not accounted for.

Using the volumes calculated in Section 4.5.2, maximum water levels at the park can be

estimated using the Shenton Park compensating basin volumes provided by the Water

Corporation (Appendix I). For a maximum modelled lake-level of 6.8 m (based on long-term

average rainfall and a 75% reduction in lake-bed permeability), the volume of water above the

drain outlet is calculated by the model to be 42,820 m3. This corresponds to a maximum water

level at the park of about 6.2 m AHD, covering an area of about 42,500 m2 (1.7 times the area

of the lake). These estimates do not take into consideration the drain outflow, which could

lower water levels by around 0.4 m/d (based on the data available, this value is valid for both

the current and proposed drain outlet elevations).

5.5.5 Maintaining Lake Levels above the Desired Minimum during Summer Periods of

No Rainfall

The length of time an “adequate water body” would be maintained in the lake during a period

of no rainfall was assessed by running the 75% reduction model with no rainfall recharge

from December to March, and comparing the results with the calibrated model and the 75%

reduction scenario. The results for drought summer conditions are shown in Figure 23. The

modelling indicates lake levels would fall below the desired minimum (4.0 m AHD) after

approximately 9 weeks and would decline to a minimum of about 3.5 m AHD. Water levels

would remain below the minimum desired level for about 10.5 weeks, assuming average

rainfall in April. Water levels in the lake would remain above the minimum desired level for

about eight weeks longer than they would under the current conditions, and the lake would

retain water in the eastern side for an additional five weeks.

Given that raising the drain outlet by 0.3 m may result in lake levels being about 0.1 m higher

at the end of an extended period with no rainfall (Section 4.5.1), it can be estimated that the

lake levels may remain above the minimum desired level for about a further one week if the

drain outlet was raised.

An estimate of the volume of water required to be pumped to the lake to maintain an adequate

body of water over the period in which levels fall below the desired minimum was obtained

by running the model from January to April 2016, with starting groundwater levels set at

those modelled for the end of January and lake levels held at 4.0 m AHD using a constant

head boundary. The zone budget package was used to calculate the water inflow to the lake

City of Subiaco



from the constant head boundary, which equates to the total net seepage and evaporation from

the lake. The results are presented in Table 7.

Table 7 : Estimated water requirements to maintain minimum desired water-levels

Month

Estimated

Water

Requirement Total Volume

(m3/d) (m3)

January 341 10,571

February 392 10,976

March 427 13,237

April 367 11,377

Total 46,161

The modelling results indicate that with the lake-bed permeability reduced by 75% during an

extended summer period of no rainfall in an otherwise average rainfall year, pumping rates of

between about 370 and 430 m3/d may be required to maintain lake levels at 4.0 m AHD.

While these values are considered to be realistic, they should be taken as approximations due

to the uncertainties inherent in groundwater modelling.

5.5.6 Reducing Lake Inflow

To assess by how much the runoff to the lake would have to be reduced to minimise water

outflow to the ocean, the model was run to simulate 25 %, 50 % and 75 % less runoff

recharge to the lake. The corresponding amount of runoff water not recharged to the lake was

assumed to be infiltrated via soakwells within the Shenton Park catchment. The resulting lake

water levels are shown in Figure 24.

Figure 24 shows that at least 75% of the current average inflow to the lake needs to be

maintained if the minimum desired lake-water levels are to be achieved. A comparison

between maximum modelled lake levels for 75% reduction scenario with and without 25%

soakwell infiltration is shown in Figure 25; it shows that maximum lake levels would be

about 0.7 m lower, corresponding to about 40% less outflow from the lake (Table 8). This

saving would increase to about 60% if the drain outlet was raised by 0.3 m.

City of Subiaco



Table 8 : Calculated volumes of outflow for model simulations with and without

soakwell infiltration

75% Reduction in Lake-bed

Permeability

Maximum Lake-

Level

Maximum Level

Above Existing

Drain Outlet

Calculated

Volume

Maximum Level

Above Proposed

Drain Outlet

Calculated

Volume

(m AHD) (m) (m3) (m) (m3)

Without Infiltration 6.8 1.73 42,818

With 25% Infiltration 6.1 1.03 25,493 0.73 18,068

Decrease in Modelled Outflow 17,325 24,750

Percentage Less Outflow 40% 58%

5.5.7 Infiltration via Soakwells

Comparison between modelled inflow via soakwells in the calibrated model and the values

measured in the field suggests the model significantly over-estimates soakwell infiltration

rates (e.g. for the Shenton Park catchment, soakwells in the calibrated model contributed the

equivalent to 156 m3 per drain for a month with total rainfall of 110 mm, whereas the

measured volumes of infiltration were between 1.8 and 15 m3 (average 7 m3) for August

2012, with total rainfall of 110 mm). The discrepancy potentially occurs because of the size

of the model cells to which the higher recharge rates are applied (minimum 15 m x 50 m), and

the more restricted flow conditions imposed on the concrete lined soakwells. In addition, it is

unclear from the field results as to how much of the measured rainfall actually fell in the areas

studied and how much runoff occurs in the catchment zone serviced by each of the soakwells,

and so the percentage of rainfall intercepted and infiltrated at the monitored sites is unknown.

The modelled recharge via soakwells has been allowed to stand in the calibrated model, and

simply represents slightly higher rates of overall regional rainfall recharge.

Given the noted limitations in the current model set-up and the uncertainty in the field results

(Section 3.5) no attempt has been made to quantify the number or specify locations for

soakwells at this time. There were reported to be a total of 742 ‘export drainage pits’ in the

Shenton Park catchment, and this would be the total number of soakwell sites currently

available; 60 of these have to date been converted to soakwells. A detailed field investigation

covering the whole catchment area would be needed to clarify the efficacy of soakwell

infiltration and optimum siting for the soakwells.

City of Subiaco



5.5.8 Changes to Climatic Conditions

Wet Cycle

The Water Corporation has requested that the model be run to simulate a “wet cycle” in order

to obtain background hydrogeological conditions for input into their surface-water modelling,

which investigates potential flooding conditions under a worst case scenario. The present

groundwater model was run using rainfall data from the Perth Airport (BOM station 9021)

over the period 1961 to 1966, when the average annual rainfall was 927.4 mm – 30% higher

than the Shenton Park long-term annual average of 707.4 mm. The runoff recharge to the lake

was also increased by 30%. The results are presented in Figure 26.

Figure 26 shows that maximum groundwater levels in the immediate vicinity of the lake may

reach 6 m AHD, which would bring the water table very close to ground level. Groundwater

mounding would centre on the north-east sector of the lake where the impermeable seal is

absent. Maximum modelled lake levels are 8 m AHD (Fig. 27). This corresponds to a

modelled volume of 72,520 m3 above the current drain outlet, which can be used to obtain an

estimated peak value of about 6.9 m AHD (using the plot in Appendix I). This does not

allow for the water-level decline of approximately 0.4 m/d that will occur as a result of water

discharging to the outflow drain and so actual peak levels would be significantly lower.

Drying Climate

It is generally considered that the climate in South Western Australia is likely to become drier

over time (Department of Water, 2009) and so the implications for management of Lake

Jualbup have been considered.

The model was run to simulate a drying climate, assuming a 15% decrease in rainfall and

associated runoff. The results are shown in Figure 28, and indicate that long-term average

minimum lake levels might be about 0.3 m lower, but would be maintained at about

3.9 m AHD, close to the desired minimum lake levels. Long term average maximum lake

levels would be about 0.5 m lower. Actual lake levels would probably be lower than

presented however, as the corresponding increases in evapotranspiration and local pumping

have not been considered.

6 CONCLUSIONS AND RECOMMENDATIONS

Numerical groundwater modelling has been undertaken to assess the hydrogeological

requirements for maintenance of “an adequate body of water” in Lake Jualbup throughout the

year. For the purposes of this investigation, an adequate body of water has been assumed to

City of Subiaco



be one in which lake levels are maintained at a minimum of 4.0 m AHD, providing a

minimum water depth in the lake of 0.5 m.

Preliminary modelling investigated the reduction of the lake-bed permeability by 25%, 50%

and 75% by the application of a polymer over 25%, 50% and 75% of the lake floor. The

results indicated that the minimum water-level requirement could only be met with a 75%

reduction in lake bed permeability (i.e. with 75% of the lake-bed, made impermeable) and so

the scope of work was modified, in consultation with the City of Subiaco, to focus on this

scenario. The reviewed model operation also assumes that a new wall will be built along the

southern and western boundary of the lake, to reduce horizontal flow of water out of the lake.

For a 75 % reduction in lake-bed permeability, the reviewed model indicates that minimum

summer water levels in the lake would increase by about 0.7m to 4.2 m AHD, assuming long-

term average monthly rainfall. Minimum summer lake levels of 3.8 m AHD (an increase of

0.3 m) could be maintained, assuming long term average rainfall, if 50% of the lake bed was

made impermeable.

If the lake-bed permeability was reduced by 75%, groundwater levels in the superficial

aquifer would only be affected immediately down-gradient of the lake where the polymer had

been applied, with maximum groundwater levels in this area falling by about 0.4 to 0.7 m and

minimum groundwater levels about 0.1 m lower. There would be no measureable effect on

the superficial aquifer regionally.

Outflow from the lake to the main drain might increase by 2.7 to 4.4 times for a 75%

reduction in lake-bed permeability. Outflow for this scenario could be reduced by about 20%

in the long term if the drain outlet was raised by 0.3 m to 5.37 m AHD. In addition, raising

the drain outlet could potentially increase the end of summer minimum water levels by a

further 0.1 m and provide increased opportunity for local infiltration of water to the aquifer

via the grassed area surrounding the lake.

During an extended (four month) summer period with no rain, the lake may still dry out over

the eastern side, with water levels falling to almost 3.5 m AHD. Modelled lake water levels

fell below the desired minimum after about nine weeks with no rainfall, and reached a

minimum of 3.5 m AHD after seventeen weeks with a 75% reduction in lake-bed

permeability. The lake levels remained above the desired minimum for about eight weeks

longer than they would under current conditions, and the lake remained wet for an additional

five weeks. If the drain was raised, the lake might retain water for an additional week or so.

The modelling results suggest between 340 and 430 m3/d would need to be pumped to the

lake to maintain water levels at 4.0 m AHD under these conditions.

Modelling of reduced lake inflow (for the 75% reduced permeability scenario), showed that in

order to achieve the desired minimum lake water levels at least 75% of the current inflow

needed to be maintained. If 25% of the rainfall runoff from Shenton Park was infiltrated via

City of Subiaco



local infiltration soakwells, outflow from the lake could be reduced by approximately 40%.

This saving would increase to 60% if the drain outlet was raised by 0.3 m. While the model

results are promising, field monitoring of existing infiltration soakwells raised questions as to

the practicality of infiltrating a significant proportion of runoff via soakwells and a

catchment-wide hydrological investigation would be appropriate prior to implementing

management practices based on the assumption of large volumes of local infiltration.

Reducing the permeability of the lake-bed has implications for the risk of flooding that are

beyond the scope of this investigation. What the modelling does suggest, however, is that

maximum monthly water levels may reach about 6.2 m AHD in a year of average rainfall and

6.9 m AHD in a wet cycle (extended period with 30% higher than average rainfalls). These

levels do not allow for outflow to the main drain, which could lower water levels by about

0.4 m/d. Groundwater level contours have been provided showing maximum groundwater

levels in a wet cycle for use by the Water Corporation in their surface water modelling.

Given the potential for average annual rainfall to continue to decline, the model was run to

simulate a dry cycle (15% less rainfall). The results indicate that for a 75% reduction in lake

bed permeability, lake water levels could still be maintained near the desired minimum level,

at 3.9 m AHD; however this is conservative and higher evapotranspiration rates and increased

local pumping might lower the level further.

It is unlikely that reducing the lake-bed permeability by anything less than 75% will achieve

the desired outcome of maintaining an adequate water body in Lake Jualbup, and so

application of the polymer seal to 75% of the lake-bed surface, working from the south-west

back to the north-east is recommended. If practicable, application to 50% of the lake might

be trialled as a preliminary measure to test the modelling results.

In addition, it is recommended that the drain outlet elevation be raised 0.3 m to 5.37 m AHD

to maximise infiltration outside the lake perimeter, reduce outflow to the main drain and

contribute to the maintenance of higher water levels in the lake.

Lake water levels, groundwater levels and lake water quality should continue to be monitored

and assessed to validate the modelling results and provide ongoing review of the modified

conditions at the lake.

Dated: 26 November 2012 Rockwater Pty Ltd

K. J. Johnston

Principal Hydrogeologist

City of Subiaco



REFERENCES

Davidson, W. A., 1995, Hydrogeology and groundwater resources of the Perth Region,

Western Australia: Western Australian Geological Survey, Bulletin 142

Department of Water, 2009. Perth-Peel regional water plan 2010 – 2030. Responding to our

drying climate. Draft for public comment, December 2009.

McDonald, M.G., and W.A. Harbaugh, 1988, MODFLOW, A Modular Three-Dimensional

Finite-Difference Ground-Water Flow Model. U.S. Geological Survey, Washington,

DC. (A:3980), open file report 83–875, Chapter A1.

McFarlane, D.J. 1983: Effects of urbanization on groundwater quality and quantity in Perth,

Western Australia. University of Western Australia, Department of Geology, PhD

thesis.

Rockwater Pty Ltd, 2005a Hydrogeology of Lake Jualbup, Shenton Park, and options for

maintaining water levels. Unpublished Report (317.0/05/01) for City of Subiaco.

Rockwater Pty Ltd, 2005b Water Requirements for maintaining lake level, Lake Jualbup,

Shenton Park. Unpublished Report (317.0/05/02) for City of Subiaco.

Rockwater Pty Ltd, 2009 Hydrogeological evaluation to guide stormwater management

principles in the City of Subiaco. Unpublished Report (317.0/09/01) for City of

Subiaco.

Sim, D.A., 1995 The impact of stormwater runoff on the hydrogeology and chemistry of an

urban lake. Dissertation for Degree of Bachelor of Science, Natural Resource

Management. Department of Soil Science, University of Western Australia.

Water Quality Bibliography

ENV Australia Pty Ltd, 2008. Constructed lakes in the Perth metropolitan area and South

West region. Literature review and interview project. Prepared for Department of

Water, Western Australian Local Government Association and Urban Development

Institute of Australia. November 2008.

Horticulture and Turf Diagnostic Services, 2008. Monitoring program of lake water and

sediment quality in the City of Subiaco. Prepared for City of Subiaco. February 2008.

City of Subiaco



JDA Consultant Hydrogeologists, 2007. WESROC total water cycle monitoring program

2004-2006. Prepared on behalf of Western Suburbs Regional Organisation of

Councils. January 2007.

Sims, D.A., 1995, The Impact of Stormwater Runoff on the Hydrology and Chemistry of an

Urban Lake. Dissertation submitted to Department of Soil Science, UWA, Western

Australia.


FIGURES

CLIENT: City of Subiaco

PROJECT: Hydrogeological Investigation - Lake Jualbup

DATE: July 2012

Dwg. No: 317.0/12/1-1

LOCALITY MAP

Rockwater Pty Ltd

Figure 1

317.0/Surfer/Fig 1 Subi Topo & Cadastral.srf

387000 387500 388000 388500 389000 389500 390000 390500 391000 391500

Eastings (m MGA)

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City of Subiaco

Catchment, Wembley-JolimontMain Drain (Mabel Talbot)

Catchment, Subiaco MainDrain (Cliff Sadlier)

Catchment, Shenton Park(Jualbup)

Main Drain

Branch Drain

Compensation Basin

Aberdere Rd CB

Lake Jualbup

Cliff Sadlier

Mabel Talbot

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LJ2LJ3

LJ4 LJ5

KS1

GE4

GD6

SW1

SW2SW3

Rockwater Pty Ltd

317.0/Surfer/Fig 2 Subi Locality Plan.srf


PROJECT: Hydrogeological Evaluation - Lake Jualbup

DATE: July 2012

Dwg. No: 317.0/12/1-2

Figure 2

SWAN RIVER

KINGS PARK



Catchment, Shenton Park(Lake Jualbup)

Compensating Basin

Main Drain

Branch Drain

Piezometer

Soakwell, Tested July/August 2012

Soakwell installed prior toApril 2009

LEGEND

317.0/Surfer/Fig 3 Lake Jualbup WLs Sep 11.srf

Figure 3

387550 387600 387650 387700 387750 387800 387850 387900 387950

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4.29 4.31

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Figure 4

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3.01

3.27

3.46

3.61 3.79

3

3.2

3.2

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3.6

3.8

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ate

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1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 20120

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1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 20120

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Bores about 100 m north of Lake Jualbup

Rockwater Pty Ltd

317.0/Surfer/Fig 8 Drainage Gullys.srf



DATE: July 2012

Dwg. No: 317.0/12/1-8

Figure 8

SWAN RIVER

KINGS PARK



Catchment, Shenton Park(Lake Jualbup)

Compensating Basin

Drainage Cell

Main Drain

Branch Drain

Gully Drainage Pit

Side-entry Drainage Pit

Soakwell, monitored July/August 2012

Soakwell installed prior toApril 2009

Drain Outlet

LEGEND

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Eastings (m MGA)

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18 20

387300 387400 387500 387600 387700 387800 387900 388000 388100

Eastings (m MGA)

646310

06463200

6463300

6463400

6463500

6463600

6463700

6463800

6463900

Nort

hin

gs

(mM

GA

)

LJ1

LJ2

LJ3

LJ4 LJ5

Rockwater Pty Ltd

317.0/Surfer/Fig 9 Local topograph.srf



DATE: September 2012

Dwg. No: 317.0/12/1-9

Figure 9

Compensating Basin

Topographic contour (m AHD)

Branch Drain

Piezometer

LEGEND

Herb

ert

Rd

Keightly Rd

Excels

ior

St

Evans St

Nicholson Rd

Lake Ave

Fig

ure

10

31

7.0

/Gra

ph

er/F

ig1

0S

oa

kwe

llsJu

lya

nd

Au

gu

st.grf

21-Jul-12 28-Jul-12 4-Aug-12 11-Aug-12 18-Aug-12 25-Aug-12 1-Sep-12

0.80

1.20

1.60

2.00

2.40Pre

ssu

reH

ead

notco

mpensa

ted

(m)

0

10

20

30

Daily

Rain

fall(m

m)

Rainfall (mm) Pressure head (m)

21-Jul-12 4-Aug-12 18-Aug-12 1-Sep-12

0.80

1.20

1.60

2.00Pre

ssure

Head

notco

mpensa

ted

(m)

0

10

20

30

Daily

Rain

fall(m

m)

Rainfall (mm) Pressure head (m)

21-Jul-12 28-Jul-12 4-Aug-12 11-Aug-12 18-Aug-12 25-Aug-12 1-Sep-12

0.80

1.20

1.60

2.00Pre

ssure

Head

notco

mpensa

ted

(m)

0

10

20

30

Daily

Rain

fall(m

m)

Rainfall (mm) Pressure head (m) 142 Keightly Rd

119 Keightly Rd

5 Waverly St

Rockwater Pty Ltd

317.0/Surfer/Fig 11 Model extent.srf



DATE: September 2012

Dwg. No: 317.0/12/1-11

Figure 11

Fig

ure

12

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig1

2M

od

elle

dL

ake

Le

vels

20

08

-20

12

.grf


Date

0

10

20

30

40

50

60

70

Rain

fall(m

m)

0

2x104

4x104

6x104

Modelle

dR

echarg

e(m

m/yr)

Perth Metro Subiaco Treatment Plant


Date

0

1

2

3

4

5

6

Wate

rLeve

l(mA

HD

)

Monthly lake levels - RW Daily lake levels - GD Modelled lake levels Modelled recharge

0

2x104

4x104

6x104

Modelle

dR

echarg

e(m

m/yr)

Fig

ure

13

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig1

3L

J1to

LJ5

.grf

Jan

-08

Fe

b-0

8

Ma

r-08

Ap

r-08

Ma

y-08

Jun

-08

Jul-0

8

Au

g-0

8

Se

p-0

8

Oct-0

8

No

v-08

De

c-08

Jan

-09

Fe

b-0

9

Ma

r-09

Ap

r-09

Ma

y-09

Jun

-09

Jul-0

9

Au

g-0

9

Se

p-0

9

Oct-0

9

No

v-09

De

c-09

Jan

-10

Fe

b-1

0

Ma

r-10

Ap

r-10

Ma

y-10

Jun

-10

Jul-1

0

Au

g-1

0

Se

p-1

0

Oct-1

0

No

v-10

De

c-10

Jan

-11

Fe

b-1

1

Ma

r-11

Ap

r-11

Ma

y-11

Jun

-11

Jul-1

1

Au

g-1

1

Se

p-1

1

Oct-1

1

No

v-11

De

c-11

Jan

-12

Fe

b-1

2

Ma

r-12

Ap

r-12

Ma

y-12

Jun

-12

Jul-1

2

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Wate

rLeve

l(mA

HD

)

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Wate

rLeve

l(mA

HD

)

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Wate

rLeve

l(mA

HD

)

Fig

ure

14

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig1

4M

od

elle

dW

Ls

Re

gio

na

lBo

res.g

rf

Jan

-08

Fe

b-0

8

Ma

r-08

Ap

r-08

Ma

y-08

Jun

-08

Jul-0

8

Au

g-0

8

Se

p-0

8

Oct-0

8

No

v-08

De

c-08

Jan

-09

Fe

b-0

9

Ma

r-09

Ap

r-09

Ma

y-09

Jun

-09

Jul-0

9

Au

g-0

9

Se

p-0

9

Oct-0

9

No

v-09

De

c-09

Jan

-10

Fe

b-1

0

Ma

r-10

Ap

r-10

Ma

y-10

Jun

-10

Jul-1

0

Au

g-1

0

Se

p-1

0

Oct-1

0

No

v-10

De

c-10

Jan

-11

Fe

b-1

1

Ma

r-11

Ap

r-11

Ma

y-11

Jun

-11

Jul-1

1

Au

g-1

1

Se

p-1

1

Oct-1

1

No

v-11

De

c-11

Jan

-12

Fe

b-1

2

Ma

r-12

Ap

r-12

Ma

y-12

Jun

-12

Jul-1

2

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

Wate

rLeve

l(mA

HD

)

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

Wate

rLeve

l(mA

HD

)

Fig

ure

15

31

7.0

/Gra

ph

er/H

ydro

inve

stiga

tion

/Mo

de

lling

Re

sults/F

ig1

5In

filtratio

nC

urve

.grf

7-F

eb-08

21-F

eb-08

6-M

ar-08

20-Mar-08

2.5 3

3.5 4

4.52

.6

2.7

2.8

2.9

3.1

3.2

3.3

3.4

3.6

3.7

3.8

3.9

4.1

4.2

4.3

4.4

LakeWaterLevels(mAHD)

Me

asu

red

Wa

ter

Le

ve

ls

Mo

de

lled

Wa

ter

Le

vels

Gro

un

dw

ate

rL

eve

ls1

mh

igh

er

La

keP

erm

ea

bility

(Kh

&K

v)

Re

du

ce

d1

0x

Fig

ure

16

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig1

6R

ed

uce

dp

erm

ea

bility

La

keL

eve

ls

Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13 Jan-14 Jan-15 Jan-16 Jan-17 Jan-18 Jan-19 Jan-20 Jan-21 Jan-22

3

4

5

6

7

8

Wate

rLevel(m

AH

D)

Lake Levels - no reduction in permeability Lake Levels - reduced permeability

75% Reduced Lake Bed Permeability

3

4

5

6

7

8

Wate

rLeve

l(mA

HD

)


3

4

5

6

7

8

Wate

rLeve

l(mA

HD

)


Minimum desired lake-water level

Calibrated intervalPredictive modelling

Calibrated interval Predictive modelling

Calibrated intervalPredictive modelling

Fig

ure

17

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig1

7R

ed

uce

dp

erm

ea

bility

La

keL

eve

ls

Jan-08 Jan-09 Jan-10 Jan-11 Jan-12

3

4

5

6

7

8

Wate

rLevel(m

AH

D)

Lake Levels - no reduction in permeability Lake Levels - reduced permeability


3

4

5

6

7

8

Wate

rLeve

l(mA

HD

)


3

4

5

6

7

8

Wate

rLeve

l(mA

HD

)



Fig

ure

18

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig1

8R

ed

uce

dp

erm

ea

bility

La

keL

eve

lsN

ew

Wa

ll.grf


3

4

5

6

7

8

Wate

rLeve

l(mA

HD

)


3

4

5

6

7

Wate

rLeve

l(mA

HD

)



Fig

ure

19

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig1

9L

J1to

LJ5

75

pcre

d.g

rf

2012 2013 2014 2015 2016 2017 2018 2019 2020 2021

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Wate

rLeve

l(mA

HD

)

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Wate

rLeve

l(mA

HD

)

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Wate

rLeve

l(mA

HD

)

Fig

ure

20

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig2

0m

od

elle

dW

Ls

Re

gio

na

l75

pcre

d.g

rf

2012 2013 2014 2015 2016 2017 2018 2019 2020 2021

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Wate

rLeve

l(mA

HD

)

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Wate

rLevel(m

AH

D)

Fig

ure

21

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig2

1W

ate

ro

utflo

wa

ssessm

en

t.grf

Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13 Jan-14 Jan-15 Jan-16 Jan-17 Jan-18 Jan-19 Jan-20 Jan-21 Jan-22 Jan-23

3

4

5

6

7

8

9

Wate

rLeve

l(mA

HD

)

Current Drain Outlet ElevationProposed Drain Outlet Elevation


Fig

ure

22

31

7.0

/Gra

ph

er/H

ydro

inve

stiga

tion

/Mo

de

lling

Re

sults/F

ig2

2In

filtratio

nC

urve

.grf

7-F

eb-08

21-F

eb-08

6-M

ar-08

20-Mar-08

2.5 3

3.5 4

4.52

.6

2.7

2.8

2.9

3.1

3.2

3.3

3.4

3.6

3.7

3.8

3.9

4.1

4.2

4.3

4.4

LakeWaterLevels(mAHD)

Ca

libra

ted

Mo

de

lWa

ter

Le

ve

ls

La

ke

-be

dP

erm

ea

bility

Re

du

ce

d7

5%

La

ke

-be

dP

erm

ea

bility

Re

du

ce

d7

5%

Ou

tlet

Dra

inR

ais

ed

0.3

m

Fig

ure

23

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig2

3N

osu

mm

er

rain

.grf

1-Dec-15 29-Dec-15 26-Jan-16 23-Feb-16 22-Mar-16 19-Apr-16

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Wate

rLeve

l(mA

HD

)

Current Drain Outlet Elevation

Proposed Drain Outlet Elevation


Fig

ure

24

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig2

4S

Win

filtratio

nm

od

ellin

g.g

rf


3

4

5

6

7

8

9

Wate

rLeve

l(mA

HD

)




Fig

ure

25

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig2

5S

Win

filtratio

nd

rain

ou

tflow

com

p.g

rf


3

4

5

6

7

8

9

Wate

rLeve

l(mA

HD

)




317.0/Surfer/Fig 26 Wet cycle.srf

Figure 26

387550 387600 387650 387700 387750 387800 387850 387900 387950

Eastings (m MGA)

6463400

6463450

6463500

6463550

6463600

6463650

6463700

6463750

Nort

hin

gs

(mM

GA

)

(LJ1)

(LJ2)

(LJ3)

(LJ4) (LJ5)

4.5

55

5

5.5

5.5

5.5

6

Fig

ure

27

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig2

7R

ed

uce

dp

erm

ea

bility

La

keL

eve

lsW

etC

ycle.g

rf


3

4

5

6

7

8

Wate

rLeve

l(mA

HD

)

Overflow Drain Elevation


Fig

ure

28

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig2

87

5p

cre

dd

rycycle

lake

leve

ls.grf

Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13 Jan-14 Jan-15 Jan-16 Jan-17 Jan-18 Jan-19 Jan-20 Jan-21 Jan-22 Jan-23

3

4

5

6

7

8

9

Wate

rLeve

l(mA

HD

)

Current Drain Outlet Elevation Minimum Desired Lake Level



APPENDIX I

HEAD DISCHARGE RELATIONSHIP FOR

SHENTON PARK DRAIN OUTLET

KJohnston

Typewritten text

Appendix I - Head Discharge Relationship for Shenton Park Drain Outlet

Ap

pI-

A

31

7.0

/Gra

ph

er/H

ydro

ge

olo

gica

lInve

stiga

tion

/Mo

de

lling

Re

sults/F

ig1

9W

ate

ro

utflo

wa

ssessm

en

t.grf

Plots generated using data provided by the Water Corporation.

5 6 7 8Elevation (m AHD)

0

20000

40000

60000

80000

100000

120000

140000

Volu

me

Above

5m

AH

D(m

3)

5 6 7 8Elevation (m AHD)

20000

30000

40000

50000

60000

Pla

nA

rea

Above

5m

AH

D(m

2)Modelled volume

Corresponding Water Level

Maximum lake levels:long term average rainfall.

Maximum lake levels:Wet cycle30% above long term average rainfall.


APPENDIX II

PEAK WATER LEVELS IN MONITORED STORMWATER

INFILTRATION WELLS 16 JULY – 28 AUGUST 2012

App

II-

A

31

7.0

/Gra

ph

er/H

ydro

inve

stiga

tion

/So

akw

ella

na

lysis/Ap

pII-

5W

ave

rlyJu

lyd

ata

.grf

0 120 240 360 480 600

Time (min)

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

2.00

2.10

2.20

Pre

ssure

Head

notco

mpensa

ted

(m)

0 60 120 180 240 300 360 420

Time (min)0 60 120 180 240 300

Time (min)0 60 120 180 240 300

Time (min)0 60 120 180 240

Time (min)0 180 360 540

Time (min)

31 July 2012 1 August 2012 1 August 2012 2 August 2012

(3.0 mm) (4.8 mm) (12.4 mm)(6.6 mm) (12.8 mm)

16 July 2012 2 & 3 August 2012

(20.0 mm)

App

II-

B

31

7.0

/Gra

ph

er/H

ydro

inve

stiga

tion

/So

akw

ella

na

lysis/Ap

pII

-5

Wa

verly

Au

gu

stDa

ta.g

rf

12 August 2012 14 August 2012 21 August 201227 August 2012 28 August 2012

(11.9 mm) (5.2 mm) (10.5 mm)(16.0 mm)

6 Aug 2012

(4.2 mm) (2.2 mm)

0 60 120 180

Time (min)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

2.00

2.10

2.20

Pre

ssure

Head

notco

mpensa

ted

(m)

0 60 120 180 240

Time (min)0 10 20 30 40 50 60

Time (min)0 10 20 30 40 50 60

Time (min)0 120 240 360 480 600 720 840 960

Time (min)

App

II-

C

31

7.0

/Gra

ph

er/H

ydro

inve

stiga

tion

/So

akw

ella

na

lysis/Ap

pII

-1

19

Ke

igh

tlyJu

lyd

ata

.grf

0 10 20 30 40 50 60

Time (min)

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

2.00

2.10

2.20

Pre

ssure

Head

notco

mpensa

ted

(m)

0 60 120 180 240 300

Time (min)0 60 120 180 240

Time (min)0 10 20 30 40 50 60

Time (min)0 180 360 540

Time (min)


(3.0 mm) (20.0 mm) (12.4 mm)(12.8 mm)

16 July 2012

(6.6 mm)

App

II-

D

31

7.0

/Gra

ph

er/H

ydro

inve

stiga

tion

/So

akw

ella

na

lysis/Ap

pII

-1

19

Ke

igh

tlyA

ug

ust

Da

ta.g

rf

0 30 60 90 120

Time (min)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

2.00

2.10

2.20

Pre

ssure

Head

notco

mpensa

ted

(m)

0 10 20 30 40 50 60

Time (min)0 60 120 180

Time (min)0 120 240 360

Time (min)0 120 240 360 480 600 720

Time (min)


(11.9 mm) (5.2 mm) (10.5 mm)(16.0 mm)

6 Aug 2012

(4.2 mm) (2.2 mm)

App

II-

E

31

7.0

/Gra

ph

er/H

ydro

inve

stiga

tion

/So

akw

ella

na

lysis/Ap

pII

-1

42

Ke

igh

tlyJu

lyd

ata

.grf

0 10 20 30 40 50 60

Time (min)

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

2.00

2.10

2.20

Pre

ssure

Head

notco

mpensa

ted

(m)

0 60 120 180 240 300

Time (min)0 60 120 180 240

Time (min)0 10 20 30 40 50 60

Time (min)0 180 360 540

Time (min)0 60 120 180 240

Time (min)


(3.0 mm) (20.0 mm) (12.4 mm)(12.8 mm)

16 July 2012

(6.6 mm)

3 August 2012

App

II-

F

31

7.0

/Gra

ph

er/H

ydro

inve

stiga

tion

/So

akw

ella

na

lysis/Ap

pII

-1

42

Ke

igh

tlyA

ug

ust

Da

ta.g

rf

0 30 60 90 120

Time (min)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

2.00

2.10

2.20

Pre

ssure

Head

notco

mpensa

ted

(m)

0 10 20 30 40 50 60

Time (min)0 60 120 180

Time (min)0 120 240 360

Time (min)0 120 240 360 480 600 720

Time (min)


(11.9 mm) (5.2 mm) (10.5 mm)(16.0 mm)

6 Aug 2012

(4.2 mm) (2.2 mm)


APPENDIX III

MONTHLY RECHARGE TO SHENTON PARK COMPENSATING

BASINS FOR CALIBRATED MODEL

Appendix III - Monthly Recharge to Shenton Park Compensating Basins for Calibrated Model

Date

Relative

time Measured WL

Total Runoff for

Shenton Park

Catchment

Dewatering

Recharge

Total Recharge to

Compensating Basins

(90% to Lake Jualbup,

10% Aberdare Rd)

(days) (m AHD) (m3/month) (m3/month) (mm/yr)

31-Jan-08 31 3 0 0 4

28-Feb-08 59 3.24 29460 0 14441

31-Mar-08 91 3.72 18501 0 9058

30-Apr-08 121 3.95 76800 0 37628

31-May-08 152 3.95 26526 0 13095

30-Jun-08 182 4.37 99469 0 48737

31-Jul-08 213 5.21 118929 0 58380

31-Aug-08 244 4.30 21237 0 10389

30-Sep-08 274 4.42 36696 0 18031

31-Oct-08 305 4.08 8330 0 4157

30-Nov-08 335 3.98 27912 0 13754

31-Dec-08 366 3.71 4933 0 2455

31-Jan-09 397 3.53 0 0 1

28-Feb-09 425 3.45 6837 0 3357

31-Mar-09 456 3.36 3440 0 1698

30-Apr-09 486 3.00 1493 0 742

31-May-09 517 3.68 28778 0 14088

30-Jun-09 547 4.47 57726 0 28422

31-Jul-09 578 4.70 109061 0 53367

31-Aug-09 609 4.63 63980 0 31416

30-Sep-09 639 4.65 34898 0 17245

31-Oct-09 670 4.37 1493 0 764

30-Nov-09 700 3.87 8330 0 4127

31-Dec-09 731 3.40 0 0 0

31-Jan-10 762 3.10 0 0 0

28-Feb-10 790 3.00 0 0 0

31-Mar-10 821 3.93 64968 0 31681

30-Apr-10 851 3.78 23434 0 11516

31-May-10 882 4.03 43178 0 21212

30-Jun-10 912 3.94 15210 0 7568

31-Jul-10 943 4.54 87510 0 42934

31-Aug-10 974 4.71 39056 7423 22766

30-Sep-10 1004 4.62 17157 36416 26120

31-Oct-10 1035 4.98 10320 35938 22487

30-Nov-10 1065 4.27 3440 23949 13312

31-Dec-10 1096 3.98 4933 23231 13720

31-Jan-11 1127 3.83 6880 28530 17222

28-Feb-11 1155 3.47 0 12145 5889

31-Mar-11 1186 3.3 0 9706 4706

30-Apr-11 1216 3.25 3440 7685 5466

31-May-11 1247 3.2 50761 2958 26340

30-Jun-11 1277 4.8 129632 6033 66392

31-Jul-11 1308 5.4 97463 11948 53641

31-Aug-11 1339 5.02 72068 11948 41092

30-Sep-11 1369 5.09 50002 11563 30160

31-Oct-11 1400 5.07 34393 11948 22676

30-Nov-11 1430 4.6 13305 8672 10753

31-Dec-11 1461 4.5 62184 5974 33278

31-Jan-12 1492 3.8 0 0 0

29-Feb-12 1521 3.5 14399 0 7070

31-Mar-12 1552 3.3 0 0 0

30-Apr-12 1582 5.04 76738 0 37516

31-May-12 1613 3.9 18607 0 9175

I:\317-0\Reports\Appendices\Appendix III - Modelled Runoff Recharge


APPENDIX IV

WATER QUALITY ASSESSMENT FIGURES FOR LAKE JUALBUP

App

IV-

A

31

7-0

/Gra

ph

er/L

ake

WQ

/Ap

pIV

aa

llda

ta.g

rf

0

100

200

300

400

500

600Tota

lDiss

olv

ed

Solid

s(m

g/L

)

4

5

6

7

8

9

10

pH

Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12

0

10

20

30

40

50

60

Da

ilyR

ain

fall(m

m)

0

2

4

6

La

keW

ate

rleve

l(m

AH

D)

0

10

20

30

40

50

60

Te

mpera

ture

(°C)

App

IV-

B

31

7-0

/Gra

ph

er/L

ake

WQ

/Ap

pIV

ba

llda

ta.g

rf

0.0

1.0

2.0

3.0

4.0

Tota

lNitro

gen

(mg/L

)

0.0

1.0

2.0

3.0

4.0

Tota

lPho

sphoru

s(m

g/L

)


0

10

20

30

40

50

60

Daily

Rain

fall

(mm

)

0

2

4

6

Lake

Wate

rlevel(m

AH

D)

0

2

4

6

8

10

12

14

Diss

olv

ed

Oxyg

en

(mg/L

)

App

IV-

C

31

7-0

/Gra

ph

er/L

ake

WQ

/Ap

pIV

ca

lldata

.grf

0

100

200

300

400

500

600Tota

lDiss

olv

ed

Solid

s(m

g/L

)

4

5

6

7

8

9

10

pH


0

10

20

30

40

50

60

Da

ilyR

ain

fall(m

m)

0

2

4

6

La

keW

ate

rleve

l(m

AH

D)

0

10

20

30

40

50

60

Te

mpera

ture

(°C)

App

IV-

D

31

7-0

/Gra

ph

er/L

ake

WQ

/Ap

pIV

da

llda

ta.g

rf

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Tota

lNitro

gen

(mg/L

)

0.0

0.1

0.3

0.4

0.5

0.7

0.8

0.9

1.1

1.2

Tota

lPho

sphoru

s(m

g/L

)


0

10

20

30

40

50

60

Daily

Rain

fall

(mm

)

0

2

4

6

Lake

Wate

rlevel(m

AH

D)

0

2

4

6

8

10

12

Dis

solve

dO

xygen

(mg/L

)

Documents

HYDROGEOLOGICAL INVESTIGATION TO MAINTAIN AN … · 2013. 8. 13. · represents a groundwater expression in spring through summer, as long as groundwater levels remain above the lake-bed