UNDERSTANDING HYDROLOGICAL PROCESSES OF LESSER HIMALAYAN HILLSLOPES

Abstract

The understudied Himalayan region is susceptible to various natural calamities. Thus, a detailed understanding of the hydrology of the Lesser Himalayan region is the need of today's time. In developing countries like India, eld experiments for studying detailed hydrological processes (i.e., understanding runo generation processes, controlling parameters of runo and interaction between di erent hydrological processes in ne temporal and spatial resolution) are rare. The present study is the rst study in the Lesser Himalayan region to analyze the detailed hydrological processes at plot- and hillslope-scales. The study focuses on plot-scale hydrological processes using the HYDRUS-2D overland ow module, hillslope runo connectivity, and thresholds controlling hillslope runo processes. Moreover, the current study analyses the interaction between soil temperature, soil moisture, and rainfall intensity. The current research was carried out in Aglar experimental watershed. This watershed is located in thatyur region of Uttarakhand, India. In the rst phase, plot-scale process understanding was studied using the collected hydrological datasets, which was recorded under arti cial rainfall conditions using a portable rainfall simulator at an altitude of 1,230 m above mean sea level. The in ltration-excess was found to be the dominant overland ow mechanism as only a few layers of top soil get saturated during all of the rainfall-runo experiments. The runo , rainfall, and soil moisture data were subsequently used to calibrate the van Genuchten parameters of the HYDRUS-2D overland ow module to simulate the runo hydrograph and soil moisture. The kinematic wave equation is used in this module to describe the in ltration-excess runo mechanism. The components of hydrograph were evaluated in terms of peak discharge, runo volume, and time of concentration. The average NSE and RMSE of all the simulated hydrographs were found to be 0.84 and 0.03, respectively. Similarly, the RMSE of simulated soil moisture was observed to be less than 0.06. The model produced satisfactory simulation results of soil moisture and runo hydrograph for all of the rainfall-runo experiments. The HYDRUS-2D overland ow module was found promising to simulate the runo hydrograph and soil moisture in plot-scale research.