MAXIMUM FLOW STUDY BY THE HYDROGRAM METHOD FOR A WATERSHED IN THE SOUTH OF SANTA CATARINA, BRAZIL

Abstract

Knowing the maximum flow and its return period is extremely important for safely dimension hydraulic projects for flood prediction and control and also water erosion prediction. Thus, this study aimed to evaluate Capivari river watershed maximum flow, located in south of Santa Catarina, that has a flooding history. The method used was The United States Soil Conservation Service (SCS) Triangular Unit Hydrogram method (current Natural Resources Conservation Service), and, for effective rainfall, the US Curve Number (SCS-CN) method is used. To estimate the maximum flow in the watershed, three background moisture scenarios (CNI, CNII and CNIII) and six empirical equations proposed for rural watersheds were adopted to calculate the concentration time. To evaluate the observed upstream flow, a 34-years historical series was used, measured at the São Martinho downstream fluviometric station (code 84598002), located in the outlet section of the study watershed. The results showed that the maximum flows estimated by the SCS-CN method for the conditions of CNII and CNIII had greater differences (-198% and -287%) compared to the observed flow. The smallest differences were verified for the CNI condition for all the analyzed return periods (2, 5, 10, 15, 20, 25, 50 and 100). Also, it was observed that, the longer is the return period, smaller the difference among the maximum observed and estimated flows, and, the smallest was verified for the 50-year period, indicating that this is the most appropriate for studies of extreme events in the study watershed.