Confluence dynamics in an ephemeral gully basin (a case study at Rangamati, Paschim Medinipur, West Bengal, India)

Abstract

Despite many efforts over the last decades to understand confluence angles of rill or gully, they remain unclear. This paper presents the results of gully confluence angles developed at Rangamati ephemeral gully basin of Paschim Medinipur District, West Bengal in India. The confluence angles are monitored for 3 years (2007-2009) and gradient, discharge and stream power of both parent and tributary stream are measured at each junction. Calibrating the data to existing models shows that Optimal Confluence model (Roy, 1983) is better applicable to the present study where average value of symmetry ratio becomes, 0.300 and the value of exponent 'x' becomes -0.20. The plot experiment at laboratory under simulated rain shows the tendency of Tran's link development and downward migration of the lower most junctions due to availability of maximum discharge under constant slope condition. In the situation of homogeneous soil resistance, equal distributed rain and general gradient, local variation of energy is observed due to localized erosion or deposition and associated local variation of gradient in micro scale. Angles of junction are changed in response to the variation of gradient (S), discharge (Q) and Sediment Yield (SY). These changes are episodic in nature and so no average rate can be estimated. The junction migrates both upstream and downstream depending on the relative importance of deposition, erosion and associated change in junction angle. © Maxwell Scientific Organization, 2013.