Assessment of Soil Erosion and Sediment Yield for Prioritization of Watersheds Using Soil and Water Assessment Tool (SWAT)

Abstract

Deposition of sediment is a natural phenomenon of any storage structure or reservoir by which the reservoir’s storage capacity is lost year after year thus affecting the very economy of the community for whom the reservoir is intended to serve. It is required to take sufficient restoration measures to arrest the sedimentation, otherwise, the storage capacity of the reservoir will be reduced at a faster rate. This thesis provides the analysis of the field studies using the hydrographic surveys conducted on the Wyra, a medium irrigation reservoir built across Wyra, a tributary of river Krishna. Conducting of the survey during the period of good rains would give good results. The objectives of the study are to assess status of sedimentation, rate of annual sedimentation in the reservoir and to arrive at the trap efficiency (Te) of the reservoir. ‘Te’ is very useful for estimating the remaining useful life span of the reservoir, the deposition of the sediment pattern in the reservoir. The rate of sedimentation was about 6.86 ha.m/100km2/year, which is greater than that considered at the time of construction of the project. The thesis also presents the analysis of the results obtained by the SWAT model programming, for estimating the runoff and the sediment yield by using the data collected at the Konijerla hydrometric station of Wyra reservoir for the period of 1991 to 2019. To calibrate, the data from 2011 to 2016 is used and to validate, the data from 2017 to 2019 is used by the SWAT model. The watershed of Wyra basin consists of 26 sub-basins. and47 HRUs. From the study, it can be noted that the sub-basin 5 is yielding about 18.8% of the sedimentation. Two other sub-basins, though less in area, were generating more sediments. It is further noticed that through the seasonal sediment analysis, the sedimentation was increased by 12% in the month of August for wet years. On the whole, the sedimentation had increased by 10.60% in the wet years and it was decreased by 18.78%, in the dry years. The calibration and the validation of the SWAT model for the periods for the various parameters used had shown satisfactory results. It can be concluded that the SWAT model can be very useful for the analysis of both the runoff and the sedimentation including the management of reservoir capacity.