TR(BR)-7/97-98 : Overland flow modelling for urban catchment considering random roughness coefficient and irregular land surface

Abstract

Urbanization is defined as the concentration of people in urban settlements and the process of change in land use occupancy resulting from the conversion of rural land into urban, suburban and industrial communities. The world growth of urbanization over the years is of logarithmic pattern. In more developed countries, about 75% of the population is concentrated in urban areas and in developing countries, like India, the rate of urban growth is very high. The rapid process of urbanization in India is a challenge for administrators, planners and research workers. This rapid process of urbanisation is causing heavy demand for water necessitating increase in the construction of water supply and drainage facilities. With increase in impervious area due to urbanization there has been increase in runoff peak and runoff volume and decrease in time to peak. Design of drainage facilities, which do not account for this increased runoff volume, are inadequate and thus needs to develop an overland flow model for urban catchment in order to estimate the exact runoff and time to peak.

In this study, a two-dimensional overland flow model has been developed considering random roughness coefficients and irregular land surface for the analysis of surface flow component. One-dimensional Richards equation for subsurface flow component has been used for calculating the infiltration from pervious area. The surface and subsurface flow models are linked explicitly at the ground surface through the processes of infiltration. These two models have been validated separately for surface flow and subsurface flow using earlier results. Present model is used to simulate a hypothetical urban catchment.