Low stream flow Analysis for Damanganga basin, South Gujarat

Abstract

This study of Low stream flow intends to analyze the low-flow hydrology of River Damanganga at Valsad
District, South Gujarat. Flood and Low Flow are two extreme hydrologic events. Low Flow Hydrology is a discipline
which deals with minimum flow in a river during the dry period in summer season of the year. The discussion starts
with the analysis of low-flow generating mechanisms operating in natural conditions and it is imperative for
anthropogenic factors which directly or indirectly affect low flows, health of aquatic life, water supply and Waste water
allocations. For Damanganga river basin, 172 days on an average there is no flow at all. 47% of times it remains in dry
state. In this study, a statistical – probabilistic approach is utilized to predict the magnitudes of future low flow event.
The Low flow 7Q (7th Minimum) design data statistic is generated by analyzing data manually and finding Seventh
minimum low flow value 7Q (Mean discharge value from lowest flows for continuous seven days, a week) for each
years for 30 years. The generated low flow discharge data is fit to various probability distribution functions i.e. Log
Normal, Gumbel, Log Pearson Type III etc. and future low flow event is predicted. The most appropriate distribution
function is then tested with Goodness of Fit test i.e. Chi-square test, Root Mean Square Error (RMSE) test manually.
The parameters of the various probability distribution function is found out from statistic software EasyFit.
Kolmogorov smirnov Test and Anderson Darling Test Goodness of fit Test carried out with use of EasyFit. This is
followed by the generation of Flow duration curves (FDC) and determination of various flow characteristics (Low Flow
Indices) and its practical significance is discussed. The study is largely based on the research results reported during
the last thirty years. For this study, Last 30 years Discharge data (Year 1985 to 2014) of Damanganga Basin from
NaniPalsan Gauge station is collected from Central Water Commission (CWC), India.