“7th AGILE Conference on Geographic Information Science” 29 April-1May 2004, Heraklion, Greece Parallel Session 7.3- “Decision Support Systems / Risk Management II” 635

Monitoring Coastal Erosion Natural Resilience by Indexing Coastal Dunes State

Valpreda Edi, Gragnaniello Simona & Rotunno Michele

ENEA- PROT PREV- Bologna, I- valpreda@bologna.enea.it

SUMMARY The paper describes the results outcoming from a study done inside a Life Environment SELSY Project.

Along Puglia littoral (southern Italy) the coastal susceptibility to erosion and dune state have been quantitatively evaluated, A complex complex database has been built and this will be available to local Public Administrations. The database contains, and relates, information that make possible, through multivariate analyses inside GIS, to define priorities in coastal risk mitigation. The analyses are based on spatial indexes that express and related (for defined time intervals) the potential consequence and harm (referred to erosion), with the dunes presence and conservation state (as coastal system capacity to cope that). On these bases a resilience evaluation has been derived, where the relating database can be, easily, queried and updated. The beaches use, the socioeconomic relevance of the inner lands have also been considered to derive the elements at risk.

KEYWORDS: Coastline, erosion, hazard, susceptibility, morphological resilience, coastal dunes

INTRODUCTION Coastal erosion for European Mediterranean countries, and for Italy in particular, is a very significant

problem that, also for its economic and social relevance, is more and more highly perceived. Considering the different methodologies that have been proposed in the international literature to evaluate all conceptual steps that preface the coastal erosion risk assessment, and also considering the specificity of littorals in Italian regions, this work aims to suggest a possible proper way to use the available knowledge and derive a set of priorities on which focusing intervention precedence.

The coastal erosion problem management goes across the capability to apply an ICZM (Integrate Coastal Zone Management) process that lies private and public sector. A good knowledge of in progress phenomena, acting in coastal areas, only allows applying this process with the required transparency. Moreover there are some mismatches between the researches at national and international level on these topics (that propose and, in limited areas, test methodological guidances) and the normal, wide approach, used by Local Administration to manage their littoral zones. In Italy, only in some cases, the coastal planning background is referred to consistent dataset directly managed by Local Administration technical offices. When an external definite research is ordered by a Local Administration generally it is not usable besides the moment context. This creates a static result, difficult to modify. In reality, a local Administration has not much interest in applying a particular method rather than another. Generally the method is chosen, by its external advisers. Its interest is, mainly, to have the results of studies. The data use during the time, nowadays, is a need not fully perceived by Public Administrations, because their capability to elaborate the data by yourself, is not so usual. Consequently, generally, lack the habit to supply the Public Administration of these kinds of data. In fact, in Italy, the governmental levels are very distributed and shared among a very great number of local Administrations: from Regions (20), to Provinces (119), to Municipalities (about 8,000). A consequent great fragmentation of land planning tasks happens. So, it can be more difficult to improve, everywhere, technical resources in terms of equipments and expertises.

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The present paper presents an attempt to exceed the more usual way to do a research on coastal risk for a public local Administration. The realised work approaches both, the necessity to classify the littoral, (applying the international methodological approaches for the natural risk and resilience), and to set up a qualified and usable geo database, easy to use and, moreover, functional by Local Administrations internal technical offices. The work involves three Provinces, to which concern a large part of Puglia region littoral.

A great effort was done, both, in set up the database structure, as in its full implementation. The result is a large georeferred database for the whole three provinces littoral zones, at great accuracy (1.10.000), with many information that can support a primary assessment, of erosion susceptibility, at risk elements, and coastal system resilience; moreover the database allows also the application of some other methodologies, or complex queries, to analyse the whole coastal risk theme. A same attention was done building a database structure easily to update and to be used as tool for coastal state monitoring.

THE STUDY AREA The present paper refers to researches done inside a Life Environment Project (SE.L.SY.) in the littorals

of Taranto, Lecce and Brindisi Provinces of Puglia Region. The larger part of the regional coasts, belong to these authorities (about 700 km long), both in the Ionian and Adriatic Sea side. The studied coastal features are very different but, in a broad way, it is possible to distinguish four main coastal type The first type is with low fine sandy beaches, edged by coastal dunes, with a circa straight coastline shaped in a clayey substrate and nourished by a standing river network. This is usual in the Adriatic as in the Ionian Sea side. Remaining of considered littorals are shaped on a limestone bedrock where no surface river network exists; some difference in coastal type are nevertheless present: partially is a rocky coast with a complex morphology done by high discontinued tracts, pocket beaches and bays, remaining southern part is a continuous high rocky coast. The southern part of Adriatic Sea side, depicts a low sandy coast, edged by coastal dunes, where the sediments are generally coarser, with an important organogenic part (Viel. M., Zurlini G. 1986) (Figure 1).

Figure 1- Coastal types in Taranto, Lecce and Brindisi Provinces littorals

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The former studies on the coastal erosion (at broadest scale) (CNR-MURST, 1997) outcome that in Puglia Region, 48% of 308 km of sandy beaches is retreating, 5% advancing and 47% steady (or be steady by at sea defence works).

Since the Greco-Roman age the Puglia Region littoral was interested by human interventions and this induced changes in the natural coastal evolution. In the last decades the human pressure is greatly increased: hydraulic works, dams, landslides settlement, river-beds sediments taking from, have been done in all the basins affluent the Puglia littorals. All this has extremely reduced the sediment supply for the beaches. Moreover harbours and sea walls impede the littoral sediments drift; urban settlements and road and railroad networks, built in the inner side of the beach, many times on the coastal dunes, hamper the natural evolution of the littoral systems. From all that become a greater weakness of the coastal zones where, also little changes in the relationships among local features, can now induce enormous effects. The outcome is that prograding beaches till to 50thies, in the last 40 years have reversed their tendency and, nowadays, have enormously increased their retreating. That happens also if the changing climatic conditions, in the affluent basins, induce a resistasy condition that, theoretically, makes more sediment available.

The economic relevance of the coastal use, in this region, requires a better management of this problem.

METHODOLOGY Assessing vulnerability or susceptibility and risk mitigation priorities, in the Italian littorals, requires the

necessity to know (and manage) a very large dataset of information, with both, a large scale approach and a very high accuracy. The first, allows considering the whole littoral tract in which the morphodynamic processes are homogeneous; the second, to generate results helpful to identify the coastal changes and morphologies sizes (net to errors due to source maps, digitization and data conversion).

The strategy adopted to make all that, is analysing the whole littoral, of three provinces limits, at maximum possible high accuracy, and building a vector database based on lines and polygons. The analysis is focused on sandy beaches and on two main topics: the first is the potential coastal erosion occurring and its consequences, together with the possible induced harms; the second is the coastal dunes presence and conservation state (as expression of coastal system capacity to cope that). Referred to data availability, as oldest accurate map is used the 1954 I.G.M.I. national cartography. From this basis was extracted the previous coastline to match with most recent shoreline position extracts from orthoimages, at 1.10.000 scale, updated at 1997. These maps are used by GI offices in Local administration as referring map and from these provided. Spot on field surveys have been done to validate the data extract from images.

The relevant features extracted for the sandy beaches are: the coastline positions (in the past and nowadays), the actual dry beaches width, the presence of permanent bathing establishments, the variety of beaches inner bounder, the dunes bulking and preservation state, the vegetation type on the coastal dunes. The work purpose is to consider the coastal system as a whole. In the coastal system there is, in fact, a sub environments sequence, from the submarines littoral, to submerged an emerged beach, to coastal dunes, to inner lands, natural or human settlements. The coast line position is, in the paper, used as geoindicator to assess the beach trend in a wide period, as expression of a more complex system in which many variables can interact (Morton, 1996).

The trend of the shoreline results from latest 43 years changes of dry-beach/wet-beach boundary coming from image analysis. The changes between two subsequent coastal line positions have been calculated (by a GIS routine) within transects, crosswise to present coastline, at 50 meters equidistance. For each transect, the consequent average speed values (m/year) have been estimated. So, the susceptibility assessment has been evaluated trough the coastal trend mathematical ratio with the nowadays beaches size. Quantitative index results (S-Index), which expresses the present beaches amount of erosion in the

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future, based on the assessment done in the period to which is referred the analysis. On this result the future coastline retreating could be evaluated, based on linear interpolation of these changes rates.

The coastal dunes presence and state are analyzed as natural resilience factors counterbalancing erosion. The applied methodology allows to link these to the coastal susceptibility.

The particular attention, given to coastal dunes, derives form the perception that, these frails coastal morphologies have a very important role as natural mitigation factors for the coastal erosion susceptibility. In the coastal dynamic the role of coastal dunes is expressed by their capability in counterbalancing both, back sea level raising or storms effects, and coastal erosion increasing. While the first aim is linked to their natural morphological contrast, the second is connected to natural dynamic sediments exchange between dunes and beaches. All that considered, the database makes easily to highlight spatial relationships among coastal dunes features, coastal susceptibility classification and beaches and inner lands current exploitation.

Other collected features can be also representative (as if geoindicators) of shoreline erosion weakness. In a normal state the whole coastal system, can retreat as consequence of a sea progress status. Since, as consequence of coastal cementing (through holidays houses, buildings, roads and railroads), the largest part of the Italian coastal environments became stiff, the relationships among the coastal system features sequence and their peculiarities, (i.e. dunes vegetation presence and type, dunes continuity, etc), can highlight a prograding sea condition even where the coastline movements do not clearly detect this trend yet.

In addition the possibility to attempt many different and integrated analyses on littoral state and evolution, referred to sea erosion, the paper proposes a more complex coastal classification, joining coastal susceptibility and morphological resilience (Susceptibility & Resilience Integrated Index). Starting from the Timmerman, that, first, lies the resilience concept to vulnerability (Timmerman, 1981), as, recently, developed in disaster reduction works (ISDR, 2002), the idea that resilience is the key to sustainable ecosystem management (Chapin et al., 2000; Folke et al., 2002) is increasing.

This relationship is expressed by a semi-quantitative index that links the susceptibility degrees, with the coastal dunes width as morphological natural resilience factor. The index is calculated in correspondence of each transect element trough mathematical ratio among retreating value in a data time period and, nowadays, dry-beach plus coastal dune width multiplied by a code representing the dune conservation state. The four classes of the “dune state index” become values ranging from 1 to 4. Where there are not dunes, the width value is “0” and the Susceptibility & Resilience Integrated Index is equal to Susceptibility Index. While the Susceptibility Index values are directly proportional quantities to erosion susceptibility relevance, the R&S Index pull down the previous susceptibility classification values. The indexes values indicate the time in which the whole loss of the present beaches width will occur.

The subsequent steps will compare other database features, to consider the economic value of beaches and inner lands where the previous indexes highlighted critical conditions. So vulnerability and risk assessment could be done.

The system will be still implemented, to better estimate the value of beaches and inner lands current use.

DATABASE OUTLINE Built on a vector model, the database is based on two polygons and one linear entities related between

them.

The first polygon class (Coastal Changes Polygons) has been derived from the spatial intersection between coastlines position at two successive times. Shows the littoral areas lost or upgraded as result of coastal dynamic in latest 43 years. The second polygon class shows the real bulking area of Coastal Dunes and to each dune-polygon are linked all dune relevant distinguishing features. The transect polyline class, has information on shoreline changes, in the considered time, on beaches width,

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presence/absence of coastal dunes, and keeps the Susceptibility and Susceptibility & Resilience Integrated Indexes.

The database model, link all features of coastal system through logical connections based on common ID –field that is present in each database entities class. The relationships applied among geometrical entities is “one to many”. So, each dune polygon is related to transects entities placed in the outlooking beach.

This allows to know and map the present (and former) main relevant coastal features, acting in the littoral (i.e. former coastal lines, coastal dunes); contemporary, that makes easily possible integrated spatial queries using plain “joins” operations without needing other complex procedures.

Moreover, focusing the monitoring attention on coastal dunes, the database structure allows upgrading the information linked to dune-polygons, and verifying, during the next time, the changes in coastal system resilience. This could be achieved re-building a new Susceptibility & Resilience Integrated Index field.

Data directly collected plus data derived from database elaborations form the whole dataset framework. The gathered data for the Dunes polygon class are: dunes vegetation type and compactness, walkways and blowups presence (classified with codex from R1 to R4 to indicate, progressively, the lost of original form: R1-no opening evidence; R2-few natural blowups; R3-diffused human and natural openings; R4- large and diffused openings), dune width (crosswise the present beach), the inner land use, the presence, near the surface, of hard bedrock, the presence of many beach ridges. For the Coastal Changes Polygons the collected data are: the nearest beach uses, the present beach width, the inner land use, the presence/absence of coastal dune as internal bounder.

The database elaboration, yet done, in addition to all the needed spatial links between created features, are referred to susceptibility degree calculation, to retreating calculation foreseen in the next 80 years and to susceptibility plus resilience integrated index. These allow disposing of a first broad analysis level from which to start for more complex investigation (i.e. goods value on and behind the beaches).

Structured inside ArcGis 8.2 the database is linked with meta information, based on the European standard; this can hold up a qualified data exchange inside and outside the local Administrations.

RESULTS AND CONCLUSION

On the basis of achieved data, many different analysis have been done or are still in progress, also together with local Administrations to optimize the framework.

Some introductory analyses to assess the distribution of coastal regression trend in the whole Apulian littoral. It is also been calculated the littoral regression (or upgrade) entity (as squared meters), to assess, on these basis, the sedimentary budget in each important littoral tracts. The coastal trend polygon entities highlight these coastal movement outcomes.

The same has been done with the coastal dunes: the first wide analyses concerned their distribution related with conservation state degree and with retreating trend of the beaches; moreover the lateral continuity of these coastal morphologies, have been calculated, (as well as their size). All these elaborations are very interesting to make available a whole framework that is homogeneous among neighbouring provincial coastal perimeters. The advancing of coastline produces, in roughly 43 years, a growth of about 1.056.876 m2 and a loss of about 1.912.540 m2 of littoral. The retreating values ranges from 0,02 to 2,93 meters/year. The average retreating value is 0,48 meters/year while advancing average value is 0,3 meters/years. The sedimentary budget balance highlights that in each investigated province the balance is negative (Figure 2).

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Figure 2- Sedimentary balance in the considered Provinces: grey shades show the eroded littoral, white

dotted shades the prograding littoral

These data, used to draw thematic map, have been reclassified for Province boundary, for Adriatic or Ionian Sea side, and can be reclassified. Some elaborations are particularly significant to contribute to the littoral planning capability: the lateral continuity of coastal dunes that shows a great difference between provinces as their conservation degree (Table 1). This index value distribution, that depicts a feature related to dunes conservation state, shows a great correlation with the distribution and entity of coastline retreating and mainly with beach use and the presence of seaside resorts.

PROVINCE Sandy littoral length (km)

Dune polygons number

Lateral continuity Index

BRINDISI 75 17 4.400 LECCE 73 98 743

TARANTO 56 112 501 Table 1- Lateral continuity index for the coastal dunes of studied areas.

As the average width of the beaches is about 29 meters and the average dunes amplitude is about 56 meter, the data evidence a great predominance of retreating tendency. In the retreating littorals the Susceptibility Index shows results that range from 0 to 441. Because of the Susceptibility Index equal 1 means that the whole loss of the present emerged beach will happen in the next 43 year, the results show a very important crisis of littorals. Figure 3 it shows that only 33% of the whole littoral (about 66 km) could be considered without serious problems regarding coastal erosion (A), while 21% of littoral (corresponding to about 42 km) will be completely eroded in a time ranging from about 80 to 40 years; 23% of littoral (about 47 km) will be lost in a time span ranging from about 40 and 20 years; the 14% (about 28 km) of classified littoral (D) will be lost in a time from about 20 to 10 years while for 9% of littoral ( about 18 km of littoral) the time to be loss is minus than 10 years (E).

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589997

102568

963820

224742

723978

100%

80%

60%

40%

20%

0%TARANTO LECCE BRINDISI

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Figure 3- Susceptibility index values distribution:

A - 0 ≤SI ≤ 0.5 (yrs ≥ 86); B - 0.5 < SI ≤ 1 (43 < yrs ≤ 86 ); C - 1 < SI ≤ 2 ( 21,5 ≤ yrs < 43); D - 2 < SI ≤ 4 ( 10,7 ≤ yrs < 21,5) ; E - SI > 4 (yrs < 10,7)

Moreover the coastal dunes analysis shows a very poor presence of well preserved coastal dunes: classified with codex from R1 to R4 to indicate, progressively, the lost of original forms, the well preserved type only corresponds to 6.6% of the whole. More than 26% of present coastal dunes are quite completely obliterated, mainly due to human passages and activities.

Despite this, being a large dominance of beaches with highest classes for susceptibility to be eroded by sea in all provinces investigated, the study highlighted an important difference in the coastal susceptibility classification (to sea erosion) once the morphological resilience based on coastal dunes presence and state has been considered (Figure 4).

In the classification of the littoral based on Susceptibility & Resilience Integrated Index it is possible, in fact, appreciate that the percentage of littoral that can be considered without serious problems regarding coastal erosion move from 33 to 52% (about 100 km) (A).

Figure 4- Susceptibility& Resilience Integrated Index values distribution:

A - 0 ≤S&RII ≤ 0.5 (yrs ≥ 86); B - 0.5 < S&RII ≤ 1 (43 < yrs ≤ 86 ); C - 1 < S&RII ≤ 2 (21,5 ≤ yrs < 43); D - 2 < S&RII ≤ 4 (10,7 ≤ yrs < 21,5) ; E - S&RII > 4 (yrs < 10,7)

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The Susceptibility & Resilience Integrated Index ranges from 0 to 87,4. The dune presence (although not in very good state) lowers to 18% the littoral (corresponding to about 36 km) that will be completely eroded in a time ranging from about 80 to 40 years (B); the same percentage of littoral will be lost in a time span ranging from about 40 and 20 years (C); the 8% (about 16 km) of littoral will be lost in a time from about 20 to 10 years (D), and, now, only for 4% of littoral (about 14 km of littoral) the time to be loss will be minus than 10 years (E). Appreciably reduced is the presence of classes corresponding to the greater expected erosion.

The work, aims to furnish a real improvement of coastal planning potential for the local administration. A specific attention was addressed to solicit the improvement of coastal dune keeping policies.

The dunes in the studied littoral are largely diffused although not well managed by local stakeholders. In the last decades many villages have growth in the inner part of costal dunes bodies; where those have been partially destroyed the sea induces flooding inside villages; where those retreating, as consequence of the landward coastline movement, the dunes growth inside the villages. Despite all this, the dunes bodies are still very important coastal morphologies (Figure 5) that greatly work as a natural mitigation factor for the coastal erosion. The possibility to improve the local coastal policies and to recover these important natural environments in the studied regions seems to be still possible.

The proposed classification underline the coastal dunes function as very determinative morphological resilience factor and can furnishes a simple way to estimate the real beaches susceptibility to be eroded.

Comparing these results with the beach use and the inner littoral features it will possible to achieve a preliminary risk assessment analysis. This part of research is in completion.

It is very important in Italy where citizens and stakeholders prove a feeble agreement in coastal dunes safeguard policies. Depending that also because the people widely ignore the great relevance and value of these environments for the coastal existence.

At the same time the coastal dunes rebuilding projects are till now mainly referred to their ecological safeguard rather than to coastal risk mitigation or management programs. The only exception since nowadays has been done in the northern Adriatic littoral by the Regional Civil Defence, inside the southern Po mouth. Here armed dunes have been used as barrier to sea flooding. Traditionally, coastal risk mitigation does not considers the dunes (with hard works building in the sea for example). When the interventions take them into consideration, most of the times they remodel the dunes in a wrong way (i.e., some defence enclosures that are build around them can stop “de facto” their interact with the beach and their possibility to grow up; the dunes are simply rebuilt by means of sandy-banks).

Aim of the present job has been also to avoid the abovementioned approaches improving an integrated coastal planning.

The geodatabase has been recently given to local Administrations involved in the Project as an open working tool: technical manuals and educational trainings are incoming.

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Fig.5- Coastal dune features in a retreating littoral tract of the studies area

BIBLIOGRAPHY

Chapin F.S , Zavaleta E.S., Eviner V.Y., Naylor R.L., Vitousek P.M., Reynolds H.L., Hooper D.U., Lavorel S., Sala O.E., Hobbie S.E:, Mack M.C. and Diaz S., 2000 Consequence of changing biodiversity. Nature, 405, 234-242

Morton R.A, Geoindicators of coastal wetlands and shorelines. In A.R. Berger & W.J. Iams (ed). Geoindicators. Assessing Rapid Environmental Changes in Earth Systems. A.A. Balkema, Rotterdam, 207-230, 1996.

Folke C., Carpenter S., Elmqvist T., Gunderson L., Holling C.S., Walker B., Bengtsson J., Berkes F., Colding J., Danell K., Falkenman M., Gordon L., Reid W., Rockstroem J., Savenije H, and Svedin U. Resilience and sustainable Development: Building Adaptive capacity in a word of transformation. Environmental Advisory Council, stockolm, Sweden, 2002, 73 pp.

ISDR Living with risk: A Global Review of Disaster Reduction Initiatives. Secretariat of the International Strategy for Disaster Reduction, Geneva, Switzerland, 2002, 382 pp.

Viel M.& Zurlini G., Conclusioni: Il sistema marino costiero Pugliese: ecotipologia e qualità ambientale. In ENEA (ed). Indagine Ambientale del sistema marino costiero della Regione Puglia. Roma, 1986, 277pp.