Modelling and interpretation of channel profile anomalies through stream length gradient (SL) indexes and GIS: A case study from the Vamanapuram River, Kerala, India

Abstract

Longitudinal profile of the Vamanapuram River and its five major tributaries was characterized to detect anomalies in terms of knick points through the calculation of stream length gradient (SL) indexes. Longitudinal profiles show presence of knick points in different reaches, indicating changes from the graded smooth concave profile to ungraded convex profile. The ungraded profile segments were confirmed by high SL indexes having sudden changes in values than the adjacent segments and those exactly fitted with the ungraded profile segments. The SL anomaly index is capable of expressing the stream profile anomalies in terms of its severity and to classify the river segments into different orders of anomalies. Higher order SL anomalies are mostly in the midland and lower regions than the headwaters region and are in uniform lithology and are unrelated to the map-scale structural features present in the river basin. The present study points to differential effect of geological process in the middle and lower reaches of the watershed in which the tributaries responded more than the major river. Past seismic events in the region confirm the role of neotectonic processes, which might have influenced the streams by changing the graded base level. Detailed field investigations of the anomalous stream segments can help to identify and understand the imprints caused due to neotectonic activity.