Suitability of the SL index for the semi-automatic identification of mass movements affecting the drainage network

Abstract

Geomorphological indices, such as the Stream Length-Gradient (SL) index, have been demonstrated to be suitable for detecting anomalies in stream-profiles. These anomalies (knickpoints) are generally related to active tectonics, lithological changes and large mass movements. This study aims to detect drainage areas affected by mass movements using SL index in La Vall d’Àssua, Romadriu and La Vall de Tor basins (Central Pyrenees). The methodology used consists of computing the SL index using the Chi-Map script and then, applying two ArcGIS® tools, which are the Hotspot and Cluster Analysis (HCA) and Kernel Density (KD), to provide a better visualisation and location of the knickpoints. SL anomalies have been compared with the slope failure inventory of La Vall d’Àssua basin, indicating a good correlation between SL anomalies and slope failures. Additionally, this geomorphological index provided the identification of 13 mass movements which had not previously been described. To sum up, this geomorphological parameter is a useful tool for the identification of drainage network areas affected by mass movements.