Applying Gis To Coastal Erosion And Hazards Environmental Sciences Essay

The coast is the area where marine and terrestrial processes meet and interact. Limits of their respective actions are not well known, as processes which are characteristic of each of these environments are interrelated. This particular characteristic makes the coastal zone highly complex and vulnerable to human actions, which in many cases, cause permanent damage to the natural environment.

Coastal Erosion has turned out to be one of the most crucial socio-economic and environmental problems facing authorities in charge of coastal hazard management. Irrespective of the major causes of this hazard, which could be human or anthropogenic, it has caused economic losses, social problems and ecological damage. The problem of coastal erosion can extend hundreds of kilometres along the shore line or it might be localized to small areas affecting surrounding communities or the tourism industry.

Coastal Erosion has been defined as a natural process by which coastlines adjust to different sea levels, energy levels, sediment supply and existing topography. It poses a problem when it threatens to destroy human life and property.

In identifying the problems of erosion, human value judgements come in as erosion does have many societal and natural benefits. Coastal Erosion is usually judged as problematic wherever the rate of erosion, considered in conjunction with economic, recreational, agricultural, demographic, ecological and other relevant factors, indicates that action to remedy erosion hazard may be justified and required.

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The coast is used for several purposes and based on this fact, it is important to devise ways of attaining compatibility among these various uses while at the same time attempting to preserve the natural environment. Faced with the threat of climate change and possible sea level rises, it is necessary to put in place elaborate coastal management scenarios that will consider all elements for planning and sustainable development.

Many recent studies done on Coastal Erosion have approached the problem within an integrated framework. This integrated approach takes into consideration the need for deep knowledge of the physical environment and the relationships between processes of involved elements and acceptable coastal management plans. These physical factors are also conditioned by legal, environmental and social factors (Barragan, 2003).

The frequency of occurrence of coastal erosion is expected to rise and has become an issue of great concern to scientists and authorities in charge. Broad scale modelling of coastal morphology has been a major challenge for scientists and authorities alike. Several studies have been carried out in order to address this issue and its determinants (Townsend and Burgess, 2004; Burgess et all, 2002). More detailed analyses of risks and responses in coastal hazard management are affected by little knowledge of the magnitude and location of erosion hazard zones for different shoreline changes and management situations.

GIS AND COASTAL HAZARD MANAGEMENT

The coast is unique because of several marine and terrestrial processes that occur there. As result of this, there is need for integration of data relating to different aspects and factors of the coastal environment in policy development and planning.

GIS provides the right platform for data collection, analyses, and storage and information dissemination. It has the ability to display spatial and temporal evolution of processes and factors that control them in order to analyse them better and evaluate their impact on the coastal environment (Hamada, 2004). It also able to identify spatial connections between different data layers leading to the development of models for geomorphologic evolution and coastal change prediction.

Several studies using GIS applications and methodologies in coastal hazard management have been carried out in several parts of the world. These studies have lead to the development of GIS applications or models and a few of these include:

BALTICSEAWEB (Latinen and Neuvonen, 2001)

Oceanic Bigeographic Information Systems (OBIS) (Zhang and Grassel, 2002).

Coastal Erosion and Shoreline Development Regulation (Miller et all, 2003).

SCAPEGIS (Walkden and Hall, 2005).

Dune Hazard Assessment Tool (NOAA Coastal Services Centre, 2003)

These applications have been developed for specific coastal areas as each area requires its own peculiar management strategies and therefore its own GIS application for planning and policy development.

Recent studies in this area have advocated an integrated approach (ICZM) which promotes sustainable development of coastal areas by blending the use of natural resources in ways that limit damage to the environment. In using this approach GIS is useful as it aids data integration, storage, analyses and visualisation.

GIS AS A TOOL FOR COASTAL HAZARD MANAGEMENT

For the application of GIS to coastal hazard management to be carried out, there is need for data required for the different task to be available and accessible. The data requirements for this include slope, lithology, vegetation, drainage, structural conditions, coastal erosion and human action etc.

In the coastal environment GIS is being increasingly used as a tool for collection, integration of required information and storage in a database with a view to accessing data, generating thematic maps and performing spatial and geo statistical analyses (Latinen and Neuvonen, 2001). During the process, relevant information is sourced and collected, compiled into a geo database, converted into relevant units and introduced into the GIS platform. This is useful in the integration and analysis of parameters used in coastal vulnerability assessments resulting in coastal risk maps (Doukakis, 2005).

This is advantageous because it provides a flexible system. Data can be accessed and used through the database model system. It also allows data automation, visualisation, editing, mapping, spatial analyses, geo statistical analyses etc.

The flexibility and versatility allows GIS to be used in many planning tasks in different situations for example in the area of maps, aerial photographs, statistics, tables and graphs that give details of the environmental conditions and their spatial distributions can be displayed.

Fig 1. An example of a cartographic information prepared using GIS for coastal Management. Maps, aerial photos, tables and graphs that show spatial distribution of environmental conditions are displayed for visualisation. (Rodriguez et all, 2009)

APPLICATION OF GIS TO COASTAL EROSION ESTIMATION

GIS has been useful in studies of prediction and estimation of coastal erosion. The datasets required for this include topographic data, bathymetric data, recession rate data, historical maps and time series data as they describe the vulnerable state of the coastal environment and coastal erosion. Some of the applications of GIS include:

GIS allows comparison between cartographic or map information that has been geo-referenced and this is very important for coastal change analyses.

GIS allows collection of data showing temporal trends of shoreline positions for different dates. Such data can be derived from sources like satellite imageries, aerial photographs and cartography digitization. GIS allows integration of data from all these sources.

GIS allows shoreline positions corresponding to different year to be overlaid with a view to aiding the identification of areas that have experienced movements or changes.

GIS aids the calculation of erosion and accretion rates. It does this by calculating line lengths and perimeter of polygons.

GIS allows detailed analyses of evolutionary trends. It aids the definition of the system and prediction of likely occurrence allowing change anticipation and hazard preparedness.

GIS is advantageous because new data can be integrated and constant and dynamic follow up of coastal processes can be carried out. This allows continued development of models that can be useful in studying other aspects of the coastal environment (Sanchez et all, 2005).

GIS has also been used in dune evolution studies and it has been highly useful in the area the data requirements are wind transport data, swell, sediments, wind speed, topography, soil humidity, bathymetry etc are required. These datasets are needed for the determination of dune field evolution and aeolian transport rates. This in turn enables the characterisation of the sedimentology, geomorphology and meteorology of coastal zones.

Some other studies have made use of GIS as a tool for analyses and interpretation of coastal erosion model outputs. Making use of GIS to visualise predictions of coastal erosion provides a vital means of understanding coastal changes and their impacts locally and regionally (Brown et all, 2004). The intended target audience here are policymakers and planners interested in visualising erosion predictions and to carry out analyses of their implications so that proper mitigation measures can be set up by integrating other data sets for impact estimation and decision support.

This basically involves the use models developed specifically for coastal erosion and one of such has been (SCAPEGIS) which is a process based model that determines the reshaping and retreat of shore profiles along the coast (Walkden and Hall, 2005; Dickson et all, 2005).It was developed from soft cliff and platform erosion model. These models provide the input for SCAPEGIS. It has been used in integrated assessments of coastal erosion and flood risk for strategic planning of responses to flood and erosion hazards.

The SCAPE model was run for different climatic and management scenarios and the results were integrated into SCAPEGIS with other auxiliary data for detailed visualisation and impact analyses. The advantage of this GIS platform is that it allows importation of other erosion models developed with similar data output format.

Fig. 2. The Impacts Estimation dialog of SCAPEGIS. Source: (Koukalas et all, 2005)

Fig 3. An example of an Erosion Risk Map showing recession lines under certain climatic scenarios and management. The land after the yellow line towards the sea is assumed lost while the land between the yellow and blue lines is at risk. (Koukalas et al, 2005)

The constant rise in the degradation of coastal environments has led to the need to develop techniques of balancing the protection of people and the economy against the cost of coastal hazards. As a result of this, a multidisciplinary approach to coastal management has been proposed (Nicholls et all, 2007).

Coastal environments have become more vulnerable to the effects of climate change and rising sea levels. They also have high social, economic and biological value. In order put all this factors into consideration, the Integrated Coastal Zone Management Framework was proposed with a view to integrating all this factors while at the same time preserving the natural environment. Methodologies for the application of GIS within this framework have been developed by several institutions like UNESCO, European Union and several working groups (Olsen et all, 2003; IPCC, 2007) to mention a few.

Within this framework, GIS is useful because of its ability to collect, integrate and analyse the different data requirements within an integrated framework. It has been used for coastal dune system research projects and shoreline evolution studies (Hernandez et all 2007; Ojeda et all, 2005). GIS aids the integration of required data like dune perimeter, shore line position so that spatial analyses of these data layers can be carried out and some of its application in this regard include:

GIS aids integration, organisation and structuring of required data sets.

GIS aids the development f Digital Elevation Models needed for the estimation of dune volume, volumetric evolution and dune migration.

GIS allows for determination of dune morphology, dune slope and orientation.

GIS allows for creation of possible dune predictions depending on sea level rise and waves. 3D GIS has proved to be very useful for this task (Sanchez et all, 2005)

The advantage offered by SCAPEGIS tools is made evident in the analyses of coastal erosion model results. It has been proposed that these models be linked with other models of environmental studies like land use models for better appreciation of coastal hazard management (Hall et all, 2005).

CONCLUSION

In coastal erosion and hazard management, modelling spatial and temporal dimensions of dynamics of the coastal environment have proven to be some of the most challenging tasks in marine and costal GIS. The shift from the regular line and polygon data structure to digital shoreline is as a result of the need to develop technology for shoreline change detection and spatial modelling.

GIS is being increasingly used in the development of policy and planning in coastal erosion and hazard management. This is due to the fact that in management policy implementation there is need for a tool able to store, analyse and display spatial and temporal data. GIS provides an appropriate platform for this. It provides a suitable instrument for integration of territorial data, makes variable analyses easier, allows for future scene simulations and allows potentially hazardous area to be identified.

GIS is also use for evolutionary trend analyses and system characterisation which are important in the management of the coastal environment.

However, models used are not always accurate as there are errors and uncertainties and as such these uncertainties should be systematically looked into when the results are being analysed for planning and policy development.

There is also the problem data availability and accessibility. Data required may not always be available or accessible. In the developed world, access to such data is more reliable and available. In other parts of the world, required data can be unavailable and where they are, may be inaccurate.