Frequency analysis of annual one day to five consecutive days maximum rainfall for Gandak river basin

Abstract

The present study has been conducted for rainfall intensity and frequency estimation for the Gandak basin, a region prone to high floods with an unrealized and unexplored hydro-potential. The two popular gridded precipitation datasets i.e.: (1) APHRODITE, and (2) IMD, for the years 1969-2005, has been used to calculate the mean basin precipitation through the Thiessen polygon method on the ARC-GIS interface. This computed data was used to find out the 1-day, 2-day to 5-day consecutive maximum precipitation series and hence fitted into various well-known probability distribution functions viz., Normal, Gamma, Exponential, etc. According to the best fit data in these functions, the quantiles were determined corresponding to a return period of 2, 10, 20, 25, 50 and 100 years. The two widely used tests: Chi-square Test and Kolmogorov-Smirnov Test were employed to further check the goodness of fit of the series in the distributions. The results reveal that the best fit for 1-day was achieved with the normal distribution, for 2-day with GEV and with GPAR for the remaining maximum consecutive days rainfall. Such studies have thus proven to be substantially facilitative in planning for the safe and economic design of various engineered structures such as bridges, culverts, levees, canals, irrigation and drainage works and effective reservoir management.

Flood Frequency Analysis Using Participatory GIS and Rainfall Data for Two Stations in Narok Town, Kenya

“…The last method involves the use of statistical distribution function to fit the data. Peak discharges are used for flood frequency analysis, but in the absence of a long record of discharge gauge data for any watershed, rainfall data series is used [2]. One of the reasons why rainfall data are more likely to be used for flood frequency analysis is that rainfall data are stochastic [3].…”

“…Since there is nothing inherent in the series to indicate whether one distribution is more likely to be appropriate than another [5], goodness-of-fit test, which indicates how much the considered distributions fit the available data [6] is used to select the appropriate distribution. For instance, knowing that a major flood may be due to the accumulation of rain in the soil over several consecutive days, analysis of successive days of maximum rainfall can become an important tool for use in economic planning and for the design of hydraulic structures [2]. Such an analysis has been done by several researchers [2,7,8].…”

“…For instance, knowing that a major flood may be due to the accumulation of rain in the soil over several consecutive days, analysis of successive days of maximum rainfall can become an important tool for use in economic planning and for the design of hydraulic structures [2]. Such an analysis has been done by several researchers [2,7,8]. This study used the PGIS approach to spatial analysis in collecting data on past flood events and to identify major flood events.…”