The study applies the methodology developed by United States Department of Agriculture’s (USDA), Soil Conservation Services (SCS) for the nine subwatersheds of the representative Dudhnai basin in Assam & Meghalaya and estimates the runoff volume on a daily basis for the period 1986-1991. The method is widely adopted for the estimation of runoff from rainfall depths and takes into account the important physical aspects of a basin on which runoff depends such as land-use, hydrological soil cover and antecedent moisture condition.
In many regions of the country, rainfall records are available for long periods but runoff records are inadequate in most of the cases particularly at the subwatershed level. Therefore, runoff estimation using suitable model that transforms the available rainfall into runoff forms an essential task in hydrological analysis.
SCS, an outcome of more than two decades of study of the rainfall-runoff relations has the advantage of being sensitive to changing land-use conditions and applicability to different types of basins, be it large or small. Land-use and land-cover are an important parameter of the SCS model and can be accurately delineated using remote sensing with the advent of its synoptic view, repetitive coverage and reliability.
The land-use conditions have been evaluated using IRS-IB, LISS II data through visual interpretation in 1:50000 scale. Interpretation has been carried out up to level II classification. Soil atlases available with the Soil Survey Organization of the region have been used to derive the runoff potential of the soil. Antecedent Moisture Condition (AMC) that affects the runoff has also been taken into account in this method.
The study recommends the following -
- The high yielding sub-watersheds can be given priority for water conservation measures like construction of check dams, percolation ponds and farm ponds
- Analysis of shape and geomorphological conditions of the subwatershed may indicate exact location of water harvesting structures
- Sediment yield of subwatershed can be determined by including erodibility factor and shape factors with basic parameter of SCS method
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