Application of innovative trend analysis methodology and distribution fitting: Study on annual peak inflow into Ukai Dam, Gujarat, India

Trends in annual peak inflow into Ukai reservoirs, Gujarat has been detected using innovative trend analysis methodology recently proposed by ^aen (2012)^[1[, which is independent of the trend in time-series, pre-assigned significance level, magnitude of trend, sample size and the amount of variation within the time series. Annual peak inflow (in m^3S-1) into the reservoir, from commencement of Ukai dam in year 1972 to 2009 (38 years), were collected and used in present study to explore the possibility of any change in extreme flow in the recent past. The statistical parameters of the said time series have been worked out. Also, theadequacy of data for flood frequency analysis has been checked for their serial correlation (data independency) and computation of threshold values of high and low outliers. The Gumbel Extreme Value (GEV) distribution has been fitted for the said data using maximum likelihood method through X2 as evaluation criteria. Also, the Gringorten plotting positions have been obtained to find the suitability of fitted distribution. Flood event with higher return period can be obtained by extrapolating said GEV distribution. The maximum annul peak inflow into Ukai reservoir after commencement of Ukai dam occurred in year 2006 has been found to have a return period of 70 years.