Characteristics of a Mixed Bedrock-Alluvial Channel in a Plateau and Plateau Fringe Region: A Study on the Barakar River of the Chotanagpur Plateau, India

摘要

The rivers that bear the properties of both alluvial and bedrock character are considered as bedrock and alluvial mixed character rivers. They are characterised by stable planform, erosion resistant bank, rock outcrop, local variability in channel bed gradient and variable flow regime. The Barakar River in the Chotanagpur plateau and its fringe region of India has the distinctive features of bedrock and gravel mixed river with sinuous and braided nature in the upper and the lower sections of the river, respectively. To investigate and extract the geomorphic features of the bedrock and gravel mixed character of the Barakar River, planform view and behaviour of the sediments were considered. The sinuous bedrock and braided reaches have been analysed using the Sinuosity Index and the Braid-channel Ratio, respectively. The upper sinuous bedrock section is marked by a steep-sided, narrow valley with the presence of incised channel. In the downstream reach of the Maithon Dam, the river channel is a box-shaped bedrock channel with a low form ratio. Potholes and grooves of varying size and shape and inner channel are the main features at the mouth zone. While, in the lower section of the river, the wide and straight braided reach is characterised by higher form ratio and higher gradient than the sinuous reach. The riffle-pool sequence in the braided section is not developed significantly like in the alluvial channel. In the braided reach, the sediment grain size is continuously decreased towards the Maithon Dam and the sediment grains are well sorted. The lithology and hydraulic processes of the river determine the mixed character of the river that favours the fluvial system to maintain its lateral stability.