Preliminary Results of the Contribution of Marrakech High Atlas Watersheds to the Plioquaternary Aquifer of the Haouz Plain Recharge. A Primary Hydrological Study Based on Remote Sensing Technologies.

The region of Marrakech in Morocco is in an arid to semi-arid climate. The amount of water available is low and varies in space and time. In addition to the scarcity of water and its uneven distribution, because of climate change observed globally, the region is subsequently subject to a growing demand of water due to the increasing population and several needs leading in this context to the extreme need of a rational and wise management of groundwater resources which are of a great importance for sustainable development.The southern part of the Tensift basin is characterized by high altitudes that can exceed 4000 meters, while the northern part is occupied by the Haouz plain characterized by altitudes around 500 m and a very gentle slope. Rainfall in the mountains, is ranging between 300 and 900 mm/year, and in the plain, it is varying between 150 and 300 mm/year. Conversely, the need for water is much higher in the plain where temperatures are higher, and vegetation (agriculture) is more important. These two effects combined make it possible to rightly consider the High Atlas as the water main source of the Haouz plain.The transfer of water between these two compartments is accomplished by the capture of seguias at the outlet of mountain basins, the retention of water in large dams, as well as by the infiltration of runoff water towards the water-table. The objective of our study is to qualify the five watersheds of the Moroccan High Atlas and to quantify their water contribution to the Plioquaternary aquifer of the Haouz plain, as well as the estimation of groundwater recharge for an effective and sustainable groundwater management. To complete this study, we used a geographic information system to obtain all the geographical and physiographical characteristics of each watershed. Following this, we were interested in the piezometric map of the region, which revealed a regular spatial distribution of piezometric contour. Groundwater head range from 875.2 m to 313.03 m; the flow direction is oriented from south to northwest, with a high hydraulic gradient of about 2% in the south and a low value of about 1% in the north.The study of the hydropluviometric data over a period of 30 years (precipitation and flow) of the outlets associated with the five watersheds of the High Atlas, as well as the dynamics of the snow cover by remote sensing, confirmed that the flow depends mainly on the rain: the volume of water brought to the Haouz plain water table is nearly 500 million m3/year. The contribution of each watershed in this volume is 26,5% for the N'Fis watershed, 9,2% for the watershed of Rheraya, 32,7% for the watershed of Ourika, 18, 7% for the watershed of Zat and 12,8% for the watershed of R'Dat.Keywords: Arid to semi-arid area, Groundwater resources, Sustainable development, Water table, Plio-quaternary, Remote sensing.