Coupling of Tennant Concept with Standardized Precipitation Index (SPI) for the Prediction of Environmental Flow Condition from Rainfall in Upper Narmada Basin

In this study, an effort has been made to describe the environmental flow condition of a watershed using standardized precipitation index (SPI), a drought index based on the precipitation. Mohegaon, Manot, Hridaynagar, and Sher are the four watersheds of upper Narmada Basin that have been taken for the analysis. The purpose of this study is to derive relationship between environmental flow condition and the corresponding estimates of standardized precipitation index which is used as measure of drought conditions. It is expected that these relationship will be useful in determining environmental flow conditions in ungauged sub-basins using rainfall data only. The study revealed an excellent relationship between SPI and percentage of average annual flow as the value of coefficient of determination are greater than 0.75. The analysis indicates that for each of the four watersheds, the percentage of average annual flow increases with the increase in the value of SPI. It can be concluded that the relationships presented in this paper will be useful for estimating the EF condition for ungauged watersheds.