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Estimation of Surface Runoff using Rainfall – Runoff Modeling of Warasgaon Dam Catchment - a geospatial approach
The altitude varies from 2100 feet above msl to 3200 feet above msl. The Warasgaon backwater lake is about 18 km in length on the river Mose. The depth of water varies from 50 to 60 feet. The climate is humid tropical with moderately warm summer. Since, mountains form a barrier from all side and enough backwater surrounds the area, the entire valley has a microclimate quite different from adjacent areas.
Climate is subtropical monsoon with moderately warm to hot summer, high monsoon rains and of cold winter season. Most of the rainfall in the study area is received from the months of June to October. The fifty percent of the study area is covered with forests of varying density with Tropical Evergreen, Tropical Semi- evergreen and Tropical Moist deciduous forest. The terrain consists of low-lying valley to highly dissected ridges forming ridge–valley topography. There are 23 villages, with a combined population of three thousand only. The people are poor and marginal farmers, depending heavily on traditional farming techniques called shifting cultivation by burning and clearing the forest. The area is very closed by two metro cities viz. Mumbai, Commercial Capital on India and Pune, second city of Maharashtra State. The proposed land is purchased by The Lake City Development Corporation, Pune and they are developing this site as Model Hill Station known as “Lake Town”. The work on the project has already started in phased manner. In the first phase slope stabilization work has been taken up for ecological development. Three small dams are also under construction on tributaries to stop flow of sediment to Lake and for water conservation for sustainable development of Lake Town. Materials and Methods: Satellite images of IRS – IC LISS III (4th February 2002) & IRS – IC PAN (30th January 2002) were used for land use/land cover mapping. The satellite data was visually interpreted and accuracy was checked on the ground. Digital Elevation Model (DEM) was created using contour map for deriving slope map of Mose river catchment in GIS domain. Using the DEM percent slope has been calculated. Classifying soil map in to its hydrologic groups has created HSG Map overlaid with the Land use/Land cover map together to create CN map. To create CN map, AMC conditions has been considered. Modified SCS Model also considers the Slope while estimating the runoff. The following equation is used for calculation of Modified CN II. (Fig. 4.12)
Modified CN II =(1/3)*(CN3-CN2)*(1-2*EXP (-13.86*SLOPEPT))+CN2 -----Eq. 4
Finally, the runoff is estimated with help of following equation no.5 as
Q=(P – Ia)² / [(P – Ia) + S)] -------Eq.5
Where,Q = Accumulated storm runoff, mm. P = Accumulated storm rainfall, mm. S = Potential Maximum Relation of Water by the soil.  Fig. 2 Methodology for Rainfall – Runoff Modeling Using above equation no. 5, modified weighted CN map has been created. |