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Introduction
Watersheds may be modelled by a lumped model using basin average input data and producing total basin streamflow. Such a model may produce reasonable result but because of the distributed nature of hydrological properties like soil type, slope and land-use, the model cannot be expected to accurately represent the watershed conditions. For connection of topography, the computer-based methodology known as Geographic Information System (GIS) is quite good to cover the link between the topographic, land-use and other information related to geographical location. It is applied to a hydrologic system to assess the impact due to land-use change. Remote sensing technique because of its capability of synoptic viewing and repetitive coverage provides useful information on land-use dynamics. With the development of GIS, the hydrological catchment models have been more physically based and distributed considering spatial heterogeneity. The purpose of this study is to develop a spatially distributed hydrological model using remote sensing and GIS, which can be used to assess the runoff changes due to land-use changes.

Earlier Works
The SCS-CN method is the most popular method for computing of surface runoff for rainfall event. This approach involves the use of simple empirical formula and readily available tables and curves. It is only one method, which can incorporate the land-use for computation of runoff from rainfall. SCS-CN method provides a rapid means for estimating runoff change due to land-use change. The SCS-CN method continues to be most satisfactory when used for different types of hydrologic problems that were designed to solve evaluating the effects of land-use changes (The Task Committee, ASCE, 1985). The GIS and SCS-CN method were combined to the model rainfall-runoff relations and the watershed parameters were estimated while computation of other parameters required significant user interaction. (White, 1988; and Bhaskar et al, 1992). Purwanto and Donker (1991) proposed semi-distributed hydrologic modeling using SCS-CN method and assessed the effect of land-use change for hypothetical cases of reforestation and deforestation conditions. When hypothetical case of 5% reforestation or deforestation conditions considered, the peak flow was reduced by 14 % for reforestation and increased by 12 % for deforestation case for hydrologic soil group C when compared to normal land-use. Kite and Kouwen (1992) developed a lumped hydrologic model for computing rainfall-runoff and snowmelt processes separately from different land cover classes. They found that using a semi-distributed model result in better goodness of fit than the lumped basin approach. Schumann (1993) developed a conceptual semi-distributed hydrological model using GIS for a limited consideration of spatial heterogeneity described by area distribution function of the hydrological characteristics and successfully applied for estimation of model parameters.