Deep water aquifers constitute the strategic water reserve for Morocco, these natural resources are used in many activities such as irrigation and more importantly they are the source of fresh water for local population. However these resources are vulnerable to anthropogenic activities and natural phenomenon combined with the ongoing climate change and increasing population growth the problem gets more alarming. To contribute to the recent initiative of the protection of karstic environment of water springs in Tabular Middle Atlas of Morocco, the present research work intend to characterize different karst landforms in Jurassic carbonate rocks of Tabular Middle Atlas in the Causse of El Hajeb which are the origins of pollution identified in water samples of this this region. Using satellite imagery (Copernicus Sentine2, Landsat, Terra-ASTER, ASTER-GDEM), drone laser scanner and GIS tools, we delineate the extent of carbonate rocks which hold water reservoir and areas with intense human activities in the aim of enhancing the understanding of karst environment system in order to establish a roadmap of water vulnerability. We also want to explore the feasibility of modern technology combining aerial LiDAR/photogrammetry with satellite images and ground-based field works in karst environment studies. On satellite images, these carbonate rocks have high reflectances in shortwave infrared and are easily distinguishable from clay rich soil, vegetation and water. Using satellite image bands in visible, near infrared and shortwave infrared of electromagnetic spectrum portion we computed red, green, blue color composite; Normalized difference vegetation index (NDVI); Normalized difference moisture index (NDMI); and soil adjusted vegetation index (SAVI) to analyze land cover/use of the area. Principle component analysis technique has been used to maximize the information in few images bands which helped us compute Sobel operator filter to extract lineaments (faults and fractures) which can be the groundwater stream flow pathways, pathways for pollutant infiltration or karst landforms location in this karstic environment. Seismic and electrical resistivity tomography and self-potential geophysical methods and based-field works were used to validate pixel and object-based image classification. This led to the identification of new and existent faults system in two major direction Northeast-Southwest (NE-SW) and Northwest-Southeast (NW-SE), and model of some sinkholes. The first one, NE-SW, was identified as pathway for water infiltration and contribute to the chemical erosion of carbonate rocks hence the presence of many circular and elliptic karst landforms, while Northwest-southeast fault system has been identified as one which drain groundwater from the El Hajeb Causse to the Saiss basin this has been vindicated by the presence of numerous water springs located in the contact of Causse and the Basin,figure. The results of this study show that climatic variations and the increased water use in this region by farmers has contributed to the dramatic change of the landscape and has led to the instability of roof for some sinkholes, in some areas these karst landforms have been collapsing creating cavities. Farmers are unaware of the complexity of this phenomenon and their unintended activities are deteriorating the quality of this precious resource. Locating these sinkholes and following the hydrogeological pathways of this water will help us establish the protection perimeter for these karst landforms and minimize the effect of water pollution in this area.
Keywords: Karst environment 1, Causse of El Hajeb 2, Remote sensing/applied Geophysics 3, Water vulnerability 4, sinkholes 5
6d. Water and sanitation
