Peak flood discharge (PFD) for a given return period is considered as one of the most important parameters for planning and design of hydraulic structures, river protection works, and development of integrated water resources management projects. This can be achieved by adopting various methods such as flood frequency analysis, rational formula, envelope curves and Synthetic Unit Hydrograph (SUH) approach. Out of which, rational formula is applied for estimation of PFD for ungauged catchments with catchment area less than 25 km2 while SUH approach is adopted for ungauged catchments with catchment area more than 25 km2. This paper aims to investigate the study on intercomparison of probability distributions for estimation of extreme (i.e., 1-day maximum) rainfall for computation of PFD by adopting rational formula and SUH approach for the Vadhavan Port Project (VPP). The annual 1-day maximum rainfall series is extracted from the daily rainfall data observed at Dahanu site during the period 1969 to 2019 and also used for estimation of rainfall. The probability distributions viz., Extreme Value Type-1, 2-parameter Log Normal and Log Pearson Type-3 (LP3) adopted in extreme value analysis of rainfall is evaluated through diagnostic test using root mean square error and accordingly LP3 is adjudged as the best fit for estimation of rainfall. The 1-day maximum rainfall obtained from LP3 is considered to compute the rainfall intensity by applying one-third rule of IMD (India Meteorological Department) and also used for computation of PFD through rational formula. In SUH approach, the areal rainfall, physiographic and SUH parameters of the ungauged catchments are considered for computation of PFD. The study suggests the 25-year, 50-year and 100-year return period PFDs at six locations within the study area using rational formula and SUH approach could be considered for design purposes while designing any civil and hydraulic structures in the VPP.

Evapotranspiration is a vital parameter for irrigation planning and management, and for hydrological and climatological studies. This can be estimated by using Blaney-Criddle (BC), Thornthwaite (TW), Hargreaves (HG) and Penman-Monteith (PM) methods. Out of these methods, BC and TW are known as temperature based whereas HG is radiation based and PM is based on Food and Agriculture Organization (FAO) report on crop water requirements. This paper illustrates a study on comparison on estimates of reference evapotranspiration (ETo) obtained from temperature, radiation and FAO based methods for Surat region. The meteorological data such as air temperature, relative humidity and sunshine hours observed at Surat region for the period 2001 to 2016 is used. In addition, the wind speed and solar radiation data is downloaded from the International Water Management Institute website and used in estimation of ETo using PM. The performance of the methods used in estimation of ETo is evaluated through regression analysis by developing a linear regression between the observed and estimated values of ETo using BC, TW and HG, and FAO based PM. The results of linear regression analysis indicated that there is a good line of agreement between the observed and estimated ETo using PM with CC of 0.968 when compared with those values of BC, TW and HG. The study show that the PM is better suited amongst four methods applied in estimating the ETo for Surat region, Gujarat.

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