Methodology of identification of existing structures and potential sites for jessour
The use of soil and water conservation techniques, such as the construction and protection of jessour in southern Tunisia, increased during the 1980s (jessour is an ancient runoff water harvesting technique widely practiced in the arid highlands in the south-eastern region of Tunisia, particularly in the Matmata mountain chain). However, because of the small size of these structures and the limited access to their location, their inventory and monitoring are very difficult. Therefore, the development of a methodology, based on the use of geomatic tools and identification of existing and potential sites for these structures, would be very useful. Designed within a geographic information system (GIS), the developed tool is based on a limited number of data: a digital elevation model (DEM), and free satellite imagery available in Google Earth©. The analysis and calculations steps were automated to cover large areas. Calibration was carried out in the watershed of wadi Jir (Matmata, Tunisia), whereas the validation was done in the watershed of wadi Hallouf (Medenine, Tunisia). The application of the proposed methodology has identified 94% of jessour actually existing in the watershed of wadi Jir and 87% of those existing in wadi Hallouf. The percentages are relatively high. These errors of 6% and 13% are acceptable considering that the aim of the proposed methodology is to guide people involved in the management of jessour to potential areas and not to choose a final location.