NOEVA project study area and existing data
The first aim of NOEVA project is to improve the knowledge of the groundwater system which supplies the Greater-Cotonou. On that way and before starting hydrogeological and geophysical measurements, a huge work of data collection from many sources has been conducted. After a checking process of the reliability of the collected data, they have then be re-analyzed using appropriated and recent techniques according to their type. The following step has been dedicated to the setting up of a GIS using an open source software which has been helpful to locate and analyze all the existing data.
From several reports (Master, Bachelor and PhD thesis; project reports and other field activities reports) related to previous studies that have been done on the NOEVA project study area, many information and data have been collected. These data include longue duration pumping test data, borehole logging, chemical analysis and many more. In addition to that, groundwater level chronicles have been collected from 60 monitoring well monitored by the National Directorate of Water (DG-Eau) and the Laboratory of Applied Hydrology. Daily rainfall data from 15 rainfall stations ranging between 1950 and 2016 has also been collected from the meteorological agency of Benin.
In order to first improve our understanding of the hydrogeological dynamic of our study area and then prepare the input data of the future numerical model, all the collected data have been interpreted using recent and appropriated tools. For instance, previous interpretations of longue duration pumping test data were carried out using the Theis analytical solution, assuming a confined behavior of the aquifer. The re-interpretation of these data using Aqtesolv Pro software (www.aqtesolv.com) revealed leaky aquifers, partial wells penetration and unconfined or confined aquifers depending to the location of the test in the study area.
Finally, all these data and the results of their interpretation have been used to elaborate a GIS using the open source software of Quantum GIS V2.8.9-Wien (http://qgis.osgeo.org). This allow us having an overview of the partial distribution of the existing data and also carrying out some spatial analysis. This overview of the data also helped us identifying few documented areas were to drill new boreholes or to supply with new rainfall stations, dataloggers and even telemetry (Fig1).