Assessment of Seasonal and Annual Dependable Flows for River Baspa at Kuppa Barrage using Flow Duration Curves

Assessment of flows at various dependable levels is considered as one of the important parameters for planning, design and management of various water related projects. For this purpose, the Flow Duration Curve (FDC) is considered by analyzing the available stream flow data at the site when adequate length of observed data is not available. This paper presented a study on assessment of seasonal (viz., monsoon, post-monsoon, winter and summer) and annual dependable flows for river Baspa at Kuppa barrage using FDCs wherein the probability of exceedance for each sample is determined by Weibull plotting position formula (PPF). The series of seasonal total discharge (STD) and annual total discharge (ATD) was generated from the observed stream flow data (1991 to 2016) of river Baspa at Kuppa barrage and used for construction of FDCs, which is evaluated through model performance indicators viz., correlation coefficient and Root Mean Squared Error (RMSE). From the results of data analysis, it was found that (i) the computed STD and ATD from the constructed FDCs with Weibull PPF are closer to the observed flow data; (ii) there is a good correlation between the observed and computed flows using STD and ATD series applied in constructing the FDCs, and these values vary between 0.928 and 0.937; and (iii) the RMSE in the computed seasonal and annual dependable flows through the constructed FDCs are 1810.5 cumecs for monsoon, 142 cumecs for post-monsoon, 89.7 cumecs for winter, 661.4 cumecs for summer and 2158 cumecs for annual. The 75%, 90% and 100% annual dependable flows were computed as 24468 cumecs, 28427 cumecs and 31417 cumecs whereas the monsoon dependable flows at 75%, 90% and 100% levels are 19528 cumecs, 22689 cumecs and 25075 cumecs. The study suggested that the irrigation, hydro power and drinking water projects at Baspa site can be designed based on the 75%, 90% and 100% dependable flows computed from the annual FDC. The study also suggested that the seasonal and annual dependable flows at various levels computed from the constructed FDCs with Weibull PPF can be used for design purposes and also for various hydrologic analyses at a site.