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Abstract
In the broad sense, the term hydrological modeling implies rainfall-runoff modeling, which helps in simulating and forecasting the flow from a catchment and in determining the inflow series for the ungauged catchments. Efforts have been made for the spatial distributed nature of the watershed properties by introducing GIS for spatial discretisation of watershed into interlinked systems of triangles (TIN) and development of a physically based rainfall-surface runoff model for simulating flood hydrographs in a user-friendly interface (GUI). The model is compatible with both the Geographical Information System (GIS) database and the Remote Sensing (RS) data, although interactive option is provided to the user for modifying the database, if necessary. GIS has also been used to describe the various thematic layers such as physiography, Landuse, soil etc. in the present study. Terrain modeling is a pre-requisite to hydrologic simulation of the rainfall-runoff process. Algorithms have been used in the present study to extract watershed features such as overland flow cascades, channel network, confluence points, ridges etc. for a given digital elevation data using Triangulated Irregular Network (TIN). The overland flow is modelled as one-dimensional sheet flow over cascades of overland "flow planes" contributing as lateral inflow to the channels flowing in the valley. Both the overland and channel flows are simulated using the kinematic wave approximation of fluid flow and solved through explicit finite difference routines. The main input to the watershed is taken as the rainfall. The usage of the model for regional level planners is demonstrated for tasks such as determination of waterways for small bridges and culverts, design of spillways of small dams, construction of flood protection levees, agriculture, site planning for micro hydels etc.