Indicator of sensitivity of groundwater bodies (regions Brittany and Pays de la Loire)

L' mass sensitivity indicator of groundwater in the territory of the West IRD measures intrinsic vulnerability (“speed of pollution spread to [...] the groundwater table” and defense capacity of the water table) and is calculated from the crossing for each polygon (corresponding to the finest hydrogeological entity on a column of several hydrogeological entities) between the middle of the hydrogeological entity (porosity, crack, fracture, permeability), the nature of the hydrogeological entity (aquifer, semi-waterproof or impermeable unit), the state of the table (free, semi-captive, captive) and the effective rain (unspecified as data only collected at the departmental scale). __Origine__ The LISA BD was the main data used for the production of the Groundwater Mass Sensitivity Indicator. It is the hydrogeological reference at the national level (Metropolitan and 4 overseas departments). Its objective is to provide a breakdown of the national territory into hydrogeological entities (aquifer geological formations or not), according to 3 levels of national use (level 1), regional (level 2) and local (level 3). Only Level 3 was used for the construction of the indicator, considering the following fields: "Ordrerel_EH " (positioning of this entity relative to the other entities in a pile of hydrogeological formations), " State_EH " (the state of the table — discriminated in 3 classes and weighted by 3 notes: free (10), semi-captive (7), captive (1)), "Middle_EH " (the middle of the hydrogeological entity — discriminated in 5 classes: porosity, crack, fracture, permeability) and "Nature_EH " (the nature of the hydrogeological entity — discriminated in 3 classes: aquifer unit, semi-waterproof or waterproof). The BD LISA proposes layers of polygons in relative order (from 1 to 17), so it was necessary at first to redesign the layers (by intersection, difference and fusion) to obtain the desired stratigraphic succession of hydrogeological entities by polygon, for each of the orders. A cross between Milieu_EH and Nature_EH was made to establish an indicator of the infiltration capacity of the entities inherent in each polygon. This indicator has been referred to as the K index. A vulnerability score of 1 to 25 was assigned to the different cross-classes, with karst media associated with the highest scores and continuous porous media impermeable to the lowest scores. In addition, a lower score was given to entities associated with a continuous porous medium compared to those associated with a discontinuous medium, as the circulation of pollutants was faster in the latter. Since each battery is associated with a greater or lesser number of orders, it was chosen to average for each battery the value of the K indices associated with the different hydrogeological entities belonging to the same polygon. Effective rain data were obtained nationally and broken down by department and year. The intrinsic vulnerability was then calculated from the following formula: V_MESO = 0.7*V1+ 1,2*V2+ 0.4*V3 (V1: the condition of the tablecloth, V2: permeability, V3: effective rain). The data were then aggregated to the departmental table. __ Partner Organisations__ CEREMA [See this sheet on geo.data.gouv.fr](https://geo.data.gouv.fr/fr/datasets/0a8baa03192be051bcdb17a7427c1b6131dc5e16)