AN INNOVATIVE IMPACT ASSESSMENT
Coastal development is generally assessed subjectively, by considering the integration in the landscape of the reclamation, and pragmatically, by highlighting the economic advantages generated. A further type of assessment is called for: that of the impact on coastal ecosystems caused directly by reclamations from the sea.
The extent of of reclamations from the sea, compared to the original surface area and length of coastline, provides a basis for reliable quantitative assessment:
- of the main ecological impact of reclamations resulting in the irreversible destruction of the shallow bottoms concerned,
- of the landscape impact, taking into account the rate of artificialised coastline. Seen from the sea or the land, the coast offers a view of piles of blocks of rock, interlocking concrete tetrapods or vertical concrete jetties.
This process was initially undertaken in the 1970, but using manual calculations that were difficult to update. Assessments were also published for the Alpes-Maritimes (Meinesz, 1976 ; Meinesz et Lefevre, 1978), the Var (Meinesz et al. 1981), the Bouches-du-Rhône (Meinesz et al. 1982) and Corsica (Meinesz et al. 1980) with surveys for the Provence-Alpes-Côte d’Azur Region (Meinesz et al. 1990 et 1993). The data presented here is therefore an update of these data, extended to cover the whole of the French Mediterranean coast, including the shores of the Etang de Berre and the Principality of Monaco.
A new system for collecting data has been applied using a Geographical Information System (GIS) coupled with computer data processing with online access (Internet) to the data produced.
The data base designed by MEDAM (Meinesz et al. 2006) has been constantly updated (new reclamations identified) and improved over the years (Meinesz et al. 2010) by the addition of:
- an image bank of photos of reclamations or of the coast prior to redevelopment,
- historical data on redevelopments on reclaimed land (providing a basis for drawing histograms showing the progression of impacts),
- better online access to data at the new website: the database now uses opensource technologies (PHP/MySQL) allowing greater flexibility of use and ensuring the security of the original data,
- better cartographical presentation based on the IGN Geoportail database.
ECOLOGICAL IMPACT
Built-over areas
The built-over areas are the parts that are no longer submerged. This is the direct impact of construction on the sea bottom. The under-sea habitats that have been built over are thus irreversibly destroyed. The landward delimitation of the built-over area is based on the original coastline (natural). It should be pointed out that we have not taken into account submerged parts of constructions or pontoons built on piles.
The built-over areas
Enclosed water area
The enclosed water area corresponds to the body of water enclosed by construction (port, port of refuge, artificial beach). The delimitation of the enclosed water area is based (i) on the seaward side, by the ends of the seawalls (ii) on the landward side, by the inner contour of the jetties quays or rockfill. The enclosure of this water mass irreversibly upsets the enclosed ecosystems. The body of water, in particular in the case of harbours, is the receptacle of various kinds of pollution such as heavy metals (from anti-fouling paint on boats), hydrocarbons, macro-detritus and various organic substances (from waste water from inhabited boats). Given that the ecosystems originally situated on these spaces have been definitively enclosed by the constructions and have been irreversibly destroyed or disturbed, these areas are taken into account for calculation of the ecological impact rate.
Example of an enclosed area of water.
Area reclaimed from the sea
This is the sum total of the surface area of built-over areas and enclosed bodies of water.
Cross-section of a harbour showing the reclaimed area (built-over areas + enclosed bodies of water)
Particular cases
Areas of water in spaces excavated on land. When a construction has been built by digging part of the space for a body of water out of the land, we have dissociated the ‘excavated body of water’ from the ‘enclosed body of water’; only the ‘enclosed body of water’ has been taken into account for the ecological impact calculations
Accumulations of sediment caused by construction. This is the surface area representing the emerged part of the sediment accumulated against a construction because of alteration of the currents and local hydrodynamic forces. These surface areas are not taken into account in the impact assessment since they are mobile sediments that may have come from the erosion of another part of the coast (in cases where the marine domain is extensive).
Example of accumulation of sediment against harbour structures.
IMPACT ON THE LANDSCAPE
The landscape impact is an easy impact to assess pragmatically, by calculation of the rate of artificialisation of the coast.
First the outline of the original coastline : must be clearly determined: that of the originally natural coastline prior to any reclamation. This coastline is measured on 1/10 000 scale maps for all the administrative subdivisions.
Next, the outline of the original coastline which has been artificialised must be determined (harbour, landfill, breakwater constructed out to sea, etc.). This outline is not the same as the contour line of the limit of the reclamation, it is that of the natural coastline that has been artificialised. The rate of occupation of the coast can thus be calculated with precision for the coastal area of a municipal or rural district (commune), a "county" (département), a Region, an ECD water mass or the whole of the French Mediterraneean coast: it is the linear percentage of artificial coast / original coastline.