Assessment of reservoir sedimentation in arid region watershed of Gujarat

Abstract

This study aimed at sedimentation assessment in an reservoir, for the first time, in an arid region watershed located in Kukma village of Kachchh, Gujarat by performing aerial topographical survey. The topographical database was subjected to SURFER software to generate grid, contour map and three-dimensional digital model of the reservoir by interpolating reduced levels spatially using kriging technique. Storage volumes were computed for entire depth of the reservoir at 1 cm interval by using trapezoidal formula. The storage volume data were utilized to develop depth-capacity curve, which was fitted with three empirical regression models, i.e. logarithmic, power, and exponential, and the best-fit model was selected by applying five goodness-of-fit criteria, i.e. correlation coefficient (R), coefficient of determination (R2), root mean square (RMSE), modified Nash-Sutcliffe efficiency (MNSE) and modified index of agreement (MIA). Contour map of the reservoir revealed the maximum depth of 2.85 m corresponding to full storage capacity of 24879 m3. The three-dimensional view closely matched with the real outlook, which confirmed accuracy of the survey and data analysis. The depth-capacity curve was utilized to determine rainwater storage during years 2012 and 2013 as 925 and 24879 m3, respectively in response to 79.1 and 291.9 mm of rainfall, respectively. This finding suggests that reduction in monsoon rainfall causes significant reduction in the rainwater storage. The power regression model is considered as the best-fit in this study due to the lowest RMSE (293 m3), and highest R (0.98) and R2 (0.93) values. The values of MNSE (0.60) and MIA (0.83) further supported the selection of the best-fit model. It is revealed that capacity of the reservoir is reduced by 4305.5 m3 (14.75%) over a period of 12 years due to sedimentation occurred at average annual rate of 358.8 m3. Finally, it is emphasized that there is need for planning and implementation of appropriate soil conservation measures within the reservoir catchment.