A GIS-based tool for automatic extraction of drainage anomalies. A case study of enfidha (North-East of Tunisia)

Abstract

It is particularly useful to analyze drainage anomalies for morphostructural interpretation of low relief areas. In basins and sub-basins, these anomalies may be due to local changes resulting from lithological discontinuities or tectonic activity caused by subsidence or uplift. Indeed, drainage anomalies are the most revealing geomorphological evidence of active faults. We present a new method to extract the drainage anomalies in watershed. The adapted methodology is therefore based on the drainage anomalies extraction in the Enfidha plain, indicating that the area is potentially tectonically active. Our objective in this article is to develop an automatic extraction tool, using the model builder technique in the ArcGIS environment, to extract drainage anomalies. To use this tool, a Digital Elevation Model (DEM) and drainage networks are required. In order to obtain the desired results, several tools are used: filtering of the DEM, generation of the summit surface, extraction of the slope orientation, calculation of the stream direction, etc. Based on the Automatic Drainage Anomalies Extraction Tool (ADAET), the relationship between drainage anomalies and tectonics was studied in the Enfidha sector of north-eastern Tunisia. The sub-watershed selected for this study is drained by numerous rivers and occupies the northeastern part of the Enfidha plain. This plain is known for its relatively high seismicity. Therefore, the method of automatic extraction of drainage anomalies in a GIS environment based on a global DEM (SRTM), detailed in this paper, appears very promising and can be of great utility in morpho-structural and morpho-neotectonic studies. This method allows to discover a high concentration of drainage anomalies on the Oued El Boul river and in the plain. Correlation with existing tectonic models shows that parts of the selected drains are located near the subsurface fault. Therefore, the drainage anomalies prove the existence of neotectonic deformation in the terrain. The activity of this fault has been proven by several authors. In this region, the extraction of drainage anomalies is most often used and reflects neotectonic activities.