Modeling of surface runoff, infiltration and evapotranspiration – A research report by National Institute of Hydrology

In this study, a model has been developed considering surface flow component and subsurface flow component along with the evapotranspiration from the crop as the sink term for the Lokapavani area of KR Sagar command of Karnataka. The surface flow component is represented using one-dimensional St-Venant equations and the subsurface flow component is represented using one-dimensional Richards equation with the sink term for the evapotranspiration from crop.

The sink term is calculated considering the crop coefficient, potential evaporation, moisture content in the root zone and the distribution of root density along the root zone depth. The surface flow equations are solved by the second order accurate, explicit, essentially-non-oscillating (ENO) finite difference scheme. The advance and recession fronts are treated in the same way as regular interior points. The strongly implicit procedure is used to solve the subsurface flow equation. 

Two models have been developed, the first using the subsurface flow component with the sink term. The second model has been developed for all processes in a cropped field, such as surface flow and subsurface flow components along with the sink term for evapotranspiration from the crop and the return flow generated below the ground surface.

A hypothetical problem has been simulated with the synthetic data set. The first model has been used to simulate the subsurface flow component with the sink term by way of the ponded water depth at the surface with variable head (sugarcane) and with constant head (paddy). The second model has been used to simulate the surface flow and subsurface flow components along with the sink term for evapotranspiration from crop.

The results obtained from these models have been presented for the variable and constant heads and with and without the sink term. The effect of the sink term has been shown for the applicability of the model. The percentage of the return flow from the irrigation has also been provided.

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