Estimation of annual runoff volume in Hydrological Region No. 10 (Sinaloa), Mexico, through regional frequency analysis

Abstract

One of the objectives of hydrological studies is the estimation of the annual runoff volume (VEA, for its name in Spanish) of watersheds without gauging. Such data is basic in the design of reservoirs. In this study, the estimation is provided through regional frequency analysis, based on the Runoff Index method. This approach was applied in the Hydrological Region No. 10 (Sinaloa), Mexico, for which 22 VEA records were processed, with amplitudes that varied from 24 to 57 years. Through the Discordance Test, three records were eliminated. Regional hydrological homogeneity was verified with the remaining 19 records and three statistical techniques: seasonality indices, linearity of ordinary moments, and linear regression between probability-weighted moments. The tests of loss of homogeneity of each record led to the elimination of four, due to their ascending linear trend. The 15 remaining records were processed in a dimensionless way, by dividing their data over their annual mean runoff volume (VEMA) and they were concatenated with the stations-years method, forming a series of 539 data. Three probabilistic models were applied to obtain the regional growth curve: Pearson type III, Log-Normal, and Potential Transformation; choosing the one with the smallest standard error of fit. The scaling of the regional Log-Normal distribution was achieved with a logarithmic relationship between the VEMA and the basin area of the processed records. In the Conclusions section, the established procedure is detailed and the importance of the results to generate synthetic sequences of VEA is highlighted (which are equally probable to occur). Therefore, the systematic application of the Runoff Index procedure as a method of estimating the VEA in other regions of the country is recommended.