A Coastal Dune Vulnerability Classification. A Case Study

Journal of Coastal Research 802-811 West Palm Beach, Florida Fall 2001

A Coastal Dune Vulnerability Classification. A CaseStudy of the SW Iberian Peninsula

M.R. Garcia-Morat,I.B. Gallego-Fernandez'], A.T. Williams+ and F. Garcia-Novo']

tDepartamento de BiologiaVegetal y Ecologia

Universidad de SevillaApdo. 109541080-Sevilla, SpainE-mail: [email protected].

:j: Air Terra Water Ltd21 Beach RoadPorthcawlSouth Wales, UKallan. [email protected].

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ABSTRACT .

GARCIA-MORA, M.R.; GALLEGO-FERNANDEZ, J.B.; WILLIAMS, A.T., and GARCIA-NOVO, F., 2001. A coastaldune vulnerability classification. A case study of the SW Iberian Peninsula. Journal of Coastal Research, 17(4),802811. West Palm Beach (Florida), ISSN 0749-0208.

A coastal Dune Vulnerability Index (DVI) has been proposed which incorporates the system's condition according togeomorphological (GCD) and ecological (VC) resilience levels, together with aeolian (AI), marine (MI) and anthrogenic(HE) factors. The index computation allows quantification of the coastal dune vulnerability as well as highlightingthe main source of imposed changes. The applied procedure in the SW Iberian Peninsula allowed spatial comparisonamong 30 dune systems and the zonation of coastal dune fields in contrasted management units. Cluster analysissuggested that four dune groupings could be differentiated for the case study area of the SW Iberian Peninsula. Thesewere Group I dunes (low vulnerability, DVI < 0.25); Group II dunes (low to medium vulnerability; DVI 0.25 to 0.5);Group III dunes (medium to high vulnerability, DVI 0.5 to 0.6); and Group IV dunes (High vulnerability; DVI > 0.6).The DVI algorithm was: DVI = (GCD+VC+MI+HE+AI) /5. The related procedure gives an integrated coastal dunevulnerability assessment which allows zonation of coastal dunes in suitable management units. The procedure helpsdune managers to focus management strategies at specific locations as it enables identification of both the potentialvulnerability and the main source(s) of imposed change.

ADDITIONAL INDEX WORDS: Integrated dune management; dune classification, dune vulnerability index, SW Iberian Peninsula.

INTRODUCTION

Species, communities or ecosystems likely to be damagedor become extinct because of human activities have oftenbeen called vulnerable, fragile or sensitive entities. Theseterms have been used interchangeably by some authors, butothers have defined each differently. Over the last few decades, habitats have been altered at accelerated rates andconservationists are repeatedly asked to assess the vulnerability or fragility of ecosystems (MYERS, 1990; NILSSON andGRELSSON, 1995). To answer these demands, many authorshave introduced subjective vulnerability assessment methods(e.g. SARGENT and BRADE, 1976; CLAUSMAN et al., 1984). Although there are no clear boundaries between what can beconsidered as stable or vulnerable ecosystems, the importantquestion regarding vulnerability is how much a particularecosystem is able to absorb displacement, can this be doneobjectively, and what action should be taken?

Coastal dunes are complex dynamic systems which respondrapidly to the driving forces which make them. These 'soft'landforms are the result of interaction between aeolian andmarine processes, vegetation, human pressure and the geomorphology of the system. Vulnerability of these coastaldunes is the outcome of integrating the above interactions.

98278 received 30 December 1998; accepted in revision 25 April 2001.

The aim of this paper is to describe a Dune VulnerabilityIndex (DVI) which encompasses the coastal dune conditionaccording to the various environmental changes that occur,both natural and human. By assessing the vulnerability leveland identifying the main source of system displacement at alocal scale, the index may assist in coastal dune managementon local, regional and even national scales.

There is no agreement on how many variables must bepooled into any vulnerability index. DAL CIN and SIMEONI(1989), stated that the more numerous the variables, themore robust the index. Such assertions might be debatableaccording to other authors such as COOPER and McLAUGHLIN (1998) who considered that a good index would bebased on the minimum amount of necessary information.However, removal of 'redundant variables', may underestimate coastal dune vulnerability in that the variables mayhave similar effects but be displayed discontinuously along acoastline.

METHODOLOGY

After a through literature review by dune workers (bothacademic and ranger staff) from the UK, France, Spain andPortugal, a list of proposed morphological and response variables concerning coastal dune systems was complied. Checking the list against field observations on SW Spain and Por-

A Coastal Dune Vulnerability Assessment 803

tuguese coasts, a selection was made of a set of variables thatallowed dune system vulnerability to be assessed in a quantifiable form. Five groups of variables were identified basedupon geomorphological, marine, aeolian, vegetation, and anthropogenic activities. Each selected variable was transformed to a semi-quantitative form and put into identifiedvariable groups considered to be vulnerability classes (Table1):

The Groups

Geomorphology Condition of the Dune System(GCD; 8 variables):

The resilience capacity of the system will depend on thetypology and extent of the coastal dunes (length, width,height, etc.i, The larger the sediment budget in coastal dunes,the more effectively they act as a buffer to extreme wavesand wind (CARTER, 1995). In coastal dune systems, landwardlosses of sand also influence the sediment budget. In thissense, wet slacks are important features, decreasing thewithdrawal rate of aeolian sand due to increasing humidityand vegetation cover. BROWN and McLACHLAN (1990)stressed that the most important feature in dune formation,morphology and development is sand particle size. Aeoliantransport and therefore potential deflation effects are muchgreater for fine than for coarse sands at any wind speed.

Marine Influence (MI; 9 variables):

Apart from sand supply, the main direct influence of thesea as a cause of dune vulnerability relates to marine erosionprocesses. Key marine factors affecting coastal dune erosionare wave action variables (i.e. height, length, energy), tidalrange, coastal exposure, beach slope and particle size(BROWN and McLACHLAN, 1990; CARTER, 1995). Fetch isused here as an indirect estimate of the importance of waveaction along the coast (KLIJN, 1990). Seaward developmentof a dune system is limited by storm tide height that maycause undercutting of the the dune face or washovers. Witha wide backshore zone dissipating wave energy, less marineerosion occurs and the greater will be the potential seawarddevelopment of the coastal dune.

Aeolian Influence (AI; 9 variables):

Wind exerts a strong influence on foredune development.Depending on wind activity and the predominance of eitherdepositional or erosional processes, the shape and volume ofcoastal dunes change through time (ARENS and WIERSMA,1994). The role of aeolian processes in coastal dune vulnerability largely depends on the ratio between sand supply anddeflation. For a given wind regime, sand supply relies on theamount of suitably sized sediment on the beach and on surface roughness. The presence in the upper beach of litter,shells or pebbles both alter the sediment boundary layerthrough increased roughness, and seal the underlying sediment from further deflation which decreases sand transportto the dunes. Embryo dunes develop on the backshore undera steady sand supply on prograding coasts. These embryodunes supply the bulk of the sediment for accretion to the

coastal dunes. Aeolian activity on poorly vegetated surfaces,dune gaps, corridors or erosional hollows influence the sediment budget, letting sands be blown inland, thereby increasing vulnerability due to deflation.

Vegetation Condition (VC; 10 variables):

Vegetation plays a major role in coastal dune formationand development (CARTER 1995). Interaction between windand vegetation is a key process for dune development (RANWELL, 1972) and differences in plant cover induce differentmorphological patterns in coastal dunes (SHORT and HESP1982). Vegetation performance in trapping and stabilisingwind-blown sands depends on some plant morphological andphysiological traits. GARCIA-MoRA et al. (1999) identifiedthree plant functional types in the coastal dunes of SW Spain.Type I species consisted mainly of winter annuals of smallsize with soft leaves, showing no morphological adaptation tothe dune environment. Type II species were mostly perennials with a below-ground spreading root. Their leaves presentspecific traits which may afford some advantages to coastalenvironmental stress. Type III species included those able towithstand sand burial and being dispersed by sea-water. Thethree plant functional types co-exist in almost every foredunebut the relative proportion of each type depends on prevailingenvironmental conditions. Persistent natural disturbances favour Type II and Type III species; their relative proportiondepending on the dominance of erosion/accretion processes,respectively. Stability, soil enrichment and compaction favours Type I plants over Type II and III. Type I plants aremore susceptible to salt spray dieback, are more vulnerableto wave damage and less stable under wind disturbance. Consequently, dunes which are dominated by Type I plants aremore susceptible to erosion, blowout development and hummock formation. The spread of neophytes, either introducedor escaped from gardens such as Carpobrotus edulis, Hippophae rhamnoides, etc., may displace the original vegetation.Neophites often develop into monospecific stands at the expense of native species which is detrimental to long termcoastal dune stability (CHAPMAN, 1989).

Human Effect (HE; 17 variables):

Coastal dunes have been extensively altered over time byhuman processes, causing extensive ecological and geomorphological changes. Traditional dune-based activities included agriculture, afforestation, grazing of sheep and goats, sandextraction, military training and both active and passive recreation. At the present time, other factors have caused evenmore severe impacts on coastal dunes such as the development of touristic resorts, urbanisation, the spread of industrial states and urban areas, construction of airports, seaports and marinas (MAYER, 1995). Human impacts on coastaldunes may be sorted into two categories: temporary vs. permanent damage to geomorpholopogy and natural vegetation.To the first category belong pedestrian and vehicle trampling,horse riding, grazing and seasonal outdoor facilities, litterand beach cleaning. The latter items are frequently overlooked with respect to dune stability but litter can and doform the basis of embryo dunes and beach cleaning regimes

Journal of Coastal Research, Vol. 17, No.4, 2001

804 Garcia-Mora et al.

Table 1. Variables considered in the dune vulnerability classification procedure.

1. Geomorphological Condition of the Dune System

1. Length of homogeneous active dune system (km) DO D1 D2 D3 D4>20 >10 >5 >1 >0.1

2. Width of dynamic dune system (km) DO D1 D2 D3 04>2 >1 >0.5 >0.1 <0.1

3. Width of frontdune as % of active dune system DO D1 D2 D3 04<5% <25% <50 <75 >75

4. Average height of secondary dunes (m) 00 D1 D2 D3 04>25 >10 >5 >1 <1

5. Average height of frontal dunes (m) DO D1 D2 D3 04>25 >15 >10 >5 <5

5a. If any ridges, n° of major ridges 00 D1 02 D3 D4>10 >4 >2 2 1

5b. If plastered to slope, slope steepness DO 02 D4Moderate Gentle Steep

5c. If perched on cliff-cliff height (m) DO D2 04<2 2-5 >5

6. Relative area of wet slacks measured from map (%) DO 02 04Moderate Small None

7. Degree of dune system fragmentation DO 02 04Low Medium High

8. Particle size of the frontal dune-Phi sizes 00 D1 02 D3 04<-1 0 1 2 3

Total score/percent:

2. Marine Influence

1. Orthogonal fetch (km) DO 01 02 D3 04<25 <100 <250 >500 >1000

2. Berm slope (degrees) DO D2 04Moderate Gentle Steep

3. Width of intertidal zone (km) DO D1 D2 D3 04>0.5 >.2 >.1 >.05 <.05

4. Tidal range (m) DO 02 D4>2 2-4 >4

4. Coastal orientation to wave direction (degrees) DO D2 0410-45° 0-10° 0°

5. Width of the zone between HWSM and dune face (m) DO D1 D2 D3 D4>75 <75 <25 <10 0

6. Breaches in the frontal dune due to wash over, relative DO 01 D2 D3 04total area 0% <5% <25% <50% >50%

7. % frontal dune cliff by the sea or with only ephemeral DO 01 D2 03 04dunes as % of dune height 0 <25% >25% >50% >75%

8. Particle size of the beach: Phi sizes DO D2 04<0 0-2 >2


4. Aeolian Effect

1. Sand supply input DO D2 04High Moderate Low

2. % Cover of embryodunes along the seaward edge. DO 01 02 D3 04>50 >25 >5 <5 None

3. Blowouts: % of the system. DO D1 D2 D3 04<5% <10% <25% <50% >50%

4. Aeolian breaches in seaward face not induced by tram- DO 01 02 D3 04pling: % of the system <5% <10% <25% <50% >50%

4. If breaches-depth as % of dune height DO 01 02 D3 04<5% <10% <25% <50% >50%

5. Natural litter drift cover as % surface DO 01 D2 D3 040% <5% >5% >25% >50%

6. Pebble cover as % surface DO 01 D2 D3 040% <5% >5% >25% >50%

7. Shell cover as % surface on upper beach DO D1 D2 D3 040% <5% >5% >25% >50%

8. % seaward dune vegetated DO 01 02 D3 04>90 >60 >30 >10 <10

9. % of the system unvegetated DO 01 D2 D3 04<10 >10 >20 >40 >75



Table 1. Continued

Total Score/percent:

4. Vegetation Condition

1. % cover of Type III plants in the beach 00 01 02 03 04>50 >25 >15 >5 <5

2. % cover Type III plants in the seaside of the frontal dune 00 01 02 03 04>90 >60 >30 >15 <15

3. Relative proportion of Type II plants in the seaside of the 00 01 02 03 04frontal dune (% cover) <5 <15 <30 <60 >60

4. Relative proportion of Type I plants in the seaside of the 00 01 02 03 04frontal dune (% cover) <1 >1 >5 >10 >30

5. Relative proportion of exotic species in the seaside of the 00 01 02 03 04frontal dune (% cover) 0 <1 <5 <15 >15

6. Relative proportion of Type II & III plants in 100 m inland 00 01 02 03 04of the dune front >75 >50 >25 >10 <10

7. Relative proportion of vigorous plants or plants with nor- 00 01 02 03 04mal vitality in the seaside of the frontal dune (%) >75 >50 >25 >10 <10

8. Relative cover (%) of exposed roots in the seaside of the 00 01 02 03 04frontal dune <5 >5 >15 >25 >50

9. Relative proportion (%) of plants with obvious effect of 00 01 02 03 04physical damage <5 >5 >15 >25 >50

10. % Vegetation removal seaward of the frontal dune due 00 01 02 03 04to human disturbance <10 >10 >25 >50 >75


5. Human effect

1. Visitor pressure 00 02 04Low Moderate High

2. Visitor frequency 00 02 04Low Moderate High

3. Access difficulty 00 02 04High Moderate Low

4. On dune driving 00 02 04None Some Much

5. On beach driving 00 02 04None Some Much

6. Horse riding 00 02 04None Some Much

7. Path network as percent of the frontal dune 00 01 02 03 040% <5% >5% >25% >50%

7.1. Path width (m) 00 01 02 03 04<1 <2 <3 <5 >5

7.2. Paths incised as percent of the frontal dune height 00 01 02 03 04<5 <25 <50 >50 <75

8. Anthropogenic litter: cover as % surface cover 00 01 02 03 040% <5% >5% >25% >50%

9. Amount of sand (%) extracted for building etc. 00 01 02 03 040% <5% >5% >25% >50%

10. Summer beach cleaning frequency. (High is twice a day; 00 02 04medium, daily) Low Moderate High

11. % upper beach cleaned 00 01 02 03 040 <25 <50 <75 >75

12. % permanent infrastructure replacing active dunes 00 01 02 03 04(roads, houses, etc) 0 <25 <50 <75 >75

13. % ephemeral infrastructure replacing active dunes (out- 00 01 02 03 04door facilities, camping, etc) 0 <25 <50 <75 >75

14. Relative surface (%) forested in the system (200 m inland 00 01 02 03 04from the fored une) 0 <25 <50 <75 >75

15. Relative cover (%) of agriculture in the system (200 m 00 01 02 03 04inland from the foredune) 0 <25 <50 <75 >75

16. Grazing on the active system 00 01 02 03 04None Low Moderate High Intensive

17. Rabbit numbers 00 01 02 03 04None Low Moderate High Intensive



806 Garcia -Mora et at.

lAAlFA'D

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~ Active dune systems

•HP HP HP HP

AI

GCD vc GCD vc

MI AI

GCD VC

MI AI

GCD VC

MI

DVI <0.25 0.25 <DVI :s; 0.5 0.5 < DVI :s; 0.6 DVI ~ 0.6

Figure 1. Location map of the dune area s in the Gulf of Cadi z an d avera ge DVI's.

frequently remove nutrients (sea weed etc.) that are important for sustained dune growth. To the second category belong hum an activities involving complete structural and ecological reshaping of the dune environment such as road building, housing, parking, agriculture, afforestation, etc.

Site selection

The coastal dunes of the SW Iberian Peninsula were initially divided into homogeneous segments based on theirmorpho-sedimentological, ecological and anthropogenic features. The first division, distinguished among accretional,st able and erosional foredunes (KLrJN, 1981) followed bywhether or not the coastal dunes were colonised by pioneerplant communities (H ESP, 1984). Sub sequent divisions weremade according to land use typ e: replacing/disruptive/nondisruptive human activit ies (CHAPMAN, 1989). From the

I

above classification, 30 coastal dune segm ents comprising allth e variabl es mentioned above were selected.

For each selected coastal dune site in th e SW Iberian peninsula (Figure 1), partial and tot al vuln erability indices werecalcul ated over a 100m longshore stre tch again selected randomly. For the index computa tion, each variable was associated to a five point sliding scale (Table 1) which ranged fromo (nil) to 4 (most vulnerable). The formal layout was basedon the clas sic work defining river aesthetic parameters byL EOPO LD (1969). For each vulnera bility class (i .e. GCD, MI,AI, VC, HE), th e sum of th e ranked variables divided by th esum of the maximum ranking attainable within each groupgave a partial vulnerability index expre ssed as a percentage.A matrix with all 5 var iables (partial vulnerability indicesobtain ed from GCD, MI, AI, VC, HE), and th e 30 species(sites) were subje cted to cluster ana lysis (UPGMA) in orderto group sites of similar characteristics (Figure 2). The total

Journ al of Coas ta l Research, Vol. 17, No. 4, 2001


Figure 2. Dendrogram of 30 SW Iberian Peninsula coastal dune sitesaccording to the five partial vulnerability indices: GCD, MI, AI, VC andHE.

P. Malandar

T. lalabar

T. Carbonero

Inglesillo

Carios de Meca

Faro

La Bota O.

Monte Gordo

Hoyo

P. Espada

Piedras Gordas

N. Umbria meridional

SaltE~s E.

Casita Azul

Alagoa

Saltes o.Areia

P. Umbria

P. Candor

La Antilla

La Bota E.

N. Umbria Occ.

Dunas Douradas

Tavira

La Redondela

EI Portil

Campo Soto

Enebrales

Cortadura

Taray

GroupI

GroupII

GroupIV

GroupUI

Dune Vulnerability Index (DVI) was computed as the unweighted average of the five partial vulnerability indices (Table 2). Each index ranged between 0 and 1, and as the indexincreases, the ability of a dune system to withstand furtherintervention decreases. WILLIAMS et al., (in press) haveshown via principal component analysis that utilisation ofsuch a methodology for assessing dune vulnerability is soundand robust. Results were presented graphically on a five-axisfigure, with each axis corresponding to a vulnerability class(Figures 3 to 6). Linking partial vulnerability indices definesa polygon whose area is positively correlated to the total DVIvalues; the larger the polygon, the greater the vulnerability.The DVI algorithm was:

DVI = (GCD + VC + MI + HE + AI)/5. (1)

RESULTS AND DISCUSSION

Total DVI and partial vulnerability indices for each sampling site are shown in Table 2. Cluster analysis revealed fourmain dune groups each showing a different DVI range (Figure 2).

• Group I dunes have a DVI below 0.25. This cluster (n = 4,dissimilarity value (d.v) = 0.05 ± 0.039), enclosed highlyresilient dune systems with low partial vulnerabilities(Figure 3). These systems, belonged to Dofiana NationalPark and are characterised by a series of inland, parallel,dynamic dune ridges up to 2 km long and 200-800 m wide.

Table 2. Partial and Total Vulnerability Indices for sampling site. For location see Figure 1.

Dune Sites Partial Vulnerability

Name GCD MI AI VC HP Total DVI

1 Dunas Douradas 0.62 0.66 0.38 0.60 0.20 0.492 Faro 0.90 0.37 0.46 0.38 0.35 0.473 Tavira 0.62 0.56 0.52 0.65 0.15 0.504 Alagoa 0.66 0.25 0.17 0.23 0.25 0.315 Monte Gordo 0.84 0.31 0.35 0.23 0.34 0.416 Areia 0.66 0.25 0.27 0.40 0.11 0.347 Punta de la Espada 0.81 0.22 0.40 0.33 0.34 0.428 Playa del Hoyo 0.81 0.25 0.42 0.38 0.34 0.449 Casita Azul 0.72 0.28 0.17 0.13 0.33 0.33

10 La Redondela 0.81 0.66 0.40 0.58 0.34 0.5611 Taray 0.78 0.97 0.69 0.6 0.47 0.7012 La Antilla 1.00 0.47 0.40 0.61 0.53 0.6013 N. Umbria occ. 0.66 0.69 0.40 0.53 0.09 0.4714 N. Umbria mer. 0.75 0.31 0.35 0.20 0.11 0.3415 El Portil 0.78 0.66 0.50 0.48 0.30 0.5416 La Bota O. 0.78 0.34 0.35 0.48 0.37 0.4017 La Bota E. 0.97 0.62 0.67 0.78 0.55 0.7218 Enebrales 0.72 0.53 0.50 0.48 0.34 0.5119 Punta Umbria 1.00 0.41 0.58 0.73 0.61 0.6720 Saltes O. 0.66 0.34 0.17 0.08 0.02 0.2521 Saltes E. 0.66 0.34 0.40 0.18 0.29 0.3722 Torre Carbonero 0.25 0.31 0.44 0.15 0.04 0.2323 Torre Zalabar 0.25 0.28 0.17 0.13 0.04 0.1724 Inglesillo 0.25 0.31 0.40 0.10 0.04 0.2225 Punta de Malandar 0.25 0.28 0.13 0.15 0.03 0.1726 Punta Candor 0.88 0.44 0.56 0.63 0.53 0.6127 Piedras Gordas 0.75 0.31 0.42 0.30 0.32 0.4228 Cortadura 0.84 0.41 0.52 0.48 0.42 0.5329 Campo Soto 0.81 0.66 0.52 0.64 0.27 0.5830 Canos de Meca 0.84 0.37 0.48 0.28 0.39 0.47



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Figure 3. Group 1 dune systems (DVI of 0-0.25). The axes are split into 5 black and 5 white segments. Each axis has a value of 100 % on whichrespective partial vulnerability indices are plotted-see Methodology section.

The foreshore shows low energy beach profiles with a variable berm width ranging from a few metres to about 200m. Maximum tidal range is 3.60m. The active dune systemincludes small embryo dunes, one to two metres high, andmassive transgressive dunes 4 to 30m high with advancingfronts, which may extend for over 2 Km. Dunes progressinland under the prevailing southwesterly winds with leeward slopes of 32° and windward slopes of 2-5° (GARCIANovo and MERINO, 1997). The foredune, with a 5m heightaverage, makes an almost continuous alignment over thewhole area (30 km). Seaward slopes of 20° occur on thenarrowest backshores, averaging 4° over the rest of thearea. Foredune vegetation is characterised almost exclusively by vigorous Type III plants (Ammophila arenaria,Euphorbia paralias and Eryngium maritimum) indicatingthe accretional character of the coastal dune. Inland vegetation, 70% cover, is largely composed by Type II plants(Lotus creticus, Helichrysum picardii, Armeria pungens andReichardia gaditana among others) and to a lesser extent

by Type III plants (Cutandia maritima, Pseudorlaya pumilla and Aetheorriza bulbosa among others). In the transgressive dunes, there are some thickets of mature forest,with dense groups of Juniperus phoenicea ssp. macrocarpa,in isolated stable areas. On the active dunes, Pinus pineaoccurs mostly in the dry slacks. Associated with the pines,dune slacks show different natural vegetation types according to water table depth. Presently, human influenceon this coastal sector is very low, limited to vehicle trafficbelonging to nature tours within the National Park, whichinvolves daily driving on both beach and dunes. The passage of vehicles (100-200 tracks/day) along the beach destroys bedforms, tidal litter lines and pioneer vegetation aswell as inhibiting seedling establishment. Foredune andinland dune driving causes minor disturbance since routesare restricted to a few paths created to guide visitors.

• Group II dunes have DVI ranging between 0.25 and 0.5,characterises (n = 13, d.v. = 0.099 ± 0.091). It enclosescoastal dunes where vulnerability is mainly due to the geo-

Faro

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Figure 4. Group 11 dune systems CDVI of 0.25-0.5). For explanation, see Fig.3.



maldulensis (e.g. Hoyo and Casita Azul). Some of these systems are cut by a road network built over the coastal dunesand as close as possible to the beachfront (i.e. Bota 0.,Monte Gordo and Casita Azul). Apart from the impacts derived from dune landscape fragmentation, low to moderateoutdoor recreation is the main human influence on thesedunes areas. Litter is regularly removed from the shore bycleaning machines which operate seaward of the High Water Springs position, enabling backshore vegetation to beestablished together with embryo dune.development.

• Group III dunes have a DVI ranging between 0.5 and 0.6(n = 8, d.v. = 0.077 ± 0.051). They are vulnerable due toboth the Geomorphological Condition of the System (GCDranging from 0.62 to 0.84), as for Group II, and the MarineInfluence (MI, ranging from 0.41 to 0.69; Figure 5). TheVegetation Condition, ranged from 0.48 to 0.65, and together with Aeolian Influences contributes greatly to theDVI of these systems. With high tides, the beach is completely covered by water and beach slopes are steep withno nearshore bar development. Lack of sand sediment input due to disturbance of the longshore sand sedimenttransport and high coastal energy place these systems under quasi-continuous marine erosion. Consequently, negative sediment budgets, overwash and bare cliffed foredunesoccur. In these recurrent marine erosional areas, the seaward face of the coastal dunes is almost bare, and thescarce vegetation present -Type II plants-show undermined roots. The effects of land use on these dune areasare similar to those dunes clustered on Group II. Few orno Type III plants survive under the shade of the foresttrees. When tidal erosion cuts back to forested zones e.g.at Redondela and Taray sites, viable rhizome fragments oftype III plants, such as marram, are no longer available tothe shore and fail to regenerate dune growth. A main anthropgenic dune feature in these areas is a network of fanshaped paths, spreading from inland access points towardsthe coast which form an array of blowouts and increase thepotential for overwash fans.

• Group IV dunes have a DVI > 0.6 characterises (n = 4,d.v. = 0.065 ± 0.032). This group (Figure 6) clusters dunesystems where the geomorphology condition displays highvulnerability values (GCD ranging from 0.88 to 1) mainlydue to the intense human pressure in replacing dunes byseaside resorts (HE ranging from 0.55 to 0.61). In theselocations, dune systems are restricted to a small narrowforedune ridge (1m height average) with a high shore-normal fragmentation dominated by Type I plants. Large sec-

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CampoSoto

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morphological condition of the system (GCD > 0.66; Figure4). These dune areas exhibit a relatively narrow littoralactive zone (25 m to 250m), due to either their location insand spit bars (i.e. Nueva Umbria mer., Faro, Saltes) orbecause of dune field loss due to forestation or habitat fragmentation by coastal roads. The coastal dunes are 2 to 6mhigh, with gentle windward and leeward slopes and no signof strong aeolian action. Erosion features are limited to anetwork of pedestrian paths. Nearshore topography ischaracterised by multiple parallel bars. The beach has agentle slope, wide surf zone and well-vegetated backshore.Foredune vegetation is dominated by Type III plants, asexpected in prograding coastal dunes (GARCIA MORA et al. ,1999). Landward dunes were forested by the end of the XIXcentury with the aim of preventing sand loss and increasing the productivity of a barren area. Just landward of theforedune ridge, dune dynamics are suppressed and vegetation cover reaches its highest value with dense scrubs ofRetama monosperma (e.g. Pta. Espada), Pinus pinea (e.g.Piedras Gordas, Hoyo, Casita Azul, etc.) or Eucalyptus ca-

Redondela

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Figure 5. Group 111 dune systems (DVI of 0.5-0.6). For explanation seeFig. 3.

P. Umbria

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Figure 6. Group IV dune systems with a DVI of > 0.6. For explanation see Fig. 3.



tors of the original dune systems are now buried undertourist villages/seaside resorts and parking plots. As a result, not only are the vital geomorphology links betweenbeach, outer and inner dunes destroyed by fragmentationbut also significant losses occur on vegetation and morphological patterns, processes, zonation and the successionof coastal dune habitats. The beach and the first seawarddune line is used mainly for swimming, sunbathing andangling activities. Beach condition and backshore clean-upactivities have severe impacts on bedforms and vegetation,with sediment compaction and displacement, beach accumulation smoothing and rapid vegetation die-back.

Application of the methodology described in this paper toSW Iberian Peninsula dunes, suggested that only 13% of thesampled coastal dunes experience a low vulnerability (DVI <0.25; Figure 1». These areas correspond to large areas ofhighly resilient dunes where management should focus onexcluding these areas from any disruptive human activities.Vehicle driving on the beach should be restricted to the intertidal zone which would avoid destruction of beach vegetationaccumulations.

The remaining 87% of dunes sampled showed an increasedvulnerability due to low GCD resilience levels (GCD valuesranging from 0.61 to 1; Figure 1). These high GCD vulnerabilities are mainly due to either the dunes being located onnarrow sand spit bars (13%) or to disruptive human intervention (84%). In the former case, potential changes in thesystem were mainly imposed by natural factors and corresponded to a new equilibrium state being attained. In thelatter case, management decisions focusing on reducing dunesystem fragmentation and forestation replacement by natural vegetation will be needed for sustainable conservation ofthese coastal areas.

In addition to the high geomorphological dune vulnerability levels for 31% of the sampled foredunes, marine effectsincreased the system's vulnerability by threatening these areas with erosion. The dune systems were low in elvation dueto coastal exposure and a restricted sand supply resulting innarrow beaches. Over the last few decades, sediment supplyin the SW Iberian Peninsula coast has been refuced by damming tributaries, building of groins at river mouths, rivermouth dredging, and building on coastal dunes.

Coastal dunes persistence in these areas mainly dependson restoration of the offshore sand balance. Current management strategies are almost exclusively focused on beach nourishment and engineering solutions involving the use of rigidstructures to achieve shoreline stability. However, permanent fixing of the position of high water mark may be in conflict with natural cycles of shore and dune development (RAN

WELL and BOAR, 1986). From a socio-economic point of view,complete removal of the current infra-structure is virtuallyunfeasible but management plans should allow where possible, the natural response of the system to adjust to theseimposed modifications.

CONCLUSIONS

The procedures described above have produced an integrated coastal dune vulnerability assessment which allows zona-

tion of coastal dunes into suitable management units. The procedure helps dune managers to focus management strategiesat specific locations as it enables them to identify both thepotential vulnerability and the main sourcets) of imposedchange. Systematic application of the procedure on a temporalscale may allow assessment of progressive changes in the system as an aid to implementing preventive management strategies in advance of probable impacts, i.e. it is pro-active. Numerical estimation of coastal dune vulnerabilities enables spatial comparison among dunes systems to be made, as well asestablishing priorities in coastal management plans.

ACKNOWLEDGEMENTS

This work is a contribution to the European Union ELOISEProgramme (ELOISE No.59) in the framework of the'DlTNES' project carried out under contract ENV4-CT960215.

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A Coastal Dune Vulnerability Classification. A Case Study