ABSTRACT
The Network Persistence and Development Index (IDPR) is a tool for national and regional vulnerability mapping. Based on an analysis of the drainage patterns (calculated from a Digital Elevation Model (DEM)) and the natural hydrological flow, it reflects the influence of the underlying geological formations toward surface-water runoff or infiltration. The concept provides an indirect approach to infiltration, knowledge of which is essential for drawing up any vulnerability map, and replaces many of the criteria usually employed in the methodologies for producing vulnerability maps.
The vulnerability map described here relates to an area supervised by the Seine-Normandy Basin Agency, and is the first that was compiled using the IDPR approach. The methodology was validated by a working group made up of representatives from the French Ministry of Ecology and Sustainable Development (MEDD), the Water Agency, the Regional Environment Division (DIREN), the Regional Department for Industry, Research and the Environment (DRIRE) and the French Geological Survey (BRGM). Since then, the same approach has been used for areas supervised by the Loire-Bretagne Water Agency, for areas in the Nord-Pas-de-Calais and Aquitaine regions, and also for the area supervised by the Rhone-Mediterranean-Corsica Agency where calculation of the IDPR was begun in 2003.
The method is not designed for large-scale vulnerability mapping; the precision of the DEM and river networks would not allow it. It is rather an indicator of a general state of vulnerability. The resultant map must be interpreted not as reflecting an absolute vulnerability, but as showing a hierarchy of the systems in terms of their vulnerability. It enables the targeting of priority areas in terms of protecting the resource. Its application to local pollution pressure points, such as those related to the BASOL sites, undertaken in 2005 in the Seine-Normandy Basin in partnership with MEDD and the Water Agency, has shown the value of such comprehensive maps in helping establish monitoring and intervention priorities. Potential uses are many, in particular for monitoring groundwater quality in vulnerable areas downstream from classified installations.
