Field Investigation and Modeling of Rapid Subsurface Stormflow through Preferential Pathways in a Vegetated Hillslope of Northeast India

A conceptual model for rapid lateral subsurface flow under extreme storm events in wet vegetated hillslopes with a high preferential flow network is presented. The kinematic form of Darcy’s equation and a continuity equation with a sink term to account for lateral preferential flow are used to formulate a subsurface flow equation. The resulting equation is numerically solved using a finite difference approximation. The physical parameters of the model are derived from field experiments conducted in a hillslope in the Brahmaputra River basin of India. Apart from capturing the rapid buildup and recession of a saturated profile in the hillslope, the model gives an indication of hydrologically active lateral macroporosity and its dependency on the rate of recharge. The computed flow hydrographs showed that for the hillslope under investigation, the rapid subsurface storm response is primarily controlled by lateral preferential flow.