Assessment of hydrological safety of Mae Sruai Dam, Thailand

Abstract

Mae Sruai Dam was completed in 2003; it was built across Mae Sruai river in Chaing Rai province, Thailand. This study is done to assess the hydrological safety aspect of the dam for spillway adequacy of the dam to accommodate probable maximum flood inflow (PMF). The hydrological assessment was done by estimating the probable maximum precipitation (PMP) over Mae Sruai River Basin. The two approaches of PMP estimates namely (1) statistical approach and (2) storm maximization and transposition approach were adopted to calculate the 1-day, 2-day and 3-day PMPs. The 1-day PMP of the two approaches were compared with the regional 1-day PMP of Mekong River Basin estimated by U.S. Weather Bureau and U.S. Corps of Engineers in 1970. From the comparison, the storm maximization and transposition approach was finally selected and the 1-day, 2-day and 3-day PMPs were transformed to the continuous 4-day PMP by a regional approach. The HEC-HMS model was applied to transform PMP to PMF and to route the PMF through the reservoir to check if dam-crest had flow overtopping. The continuous 4-day PMP was transformed to PMF with peak reservoir inflow discharge of 1,013 m3/s and corresponding peak outflow of 886 m3/s. This outflow was less than the design spillway capacity of 1,160 m3/s. Thus, the dam safety in hydrological aspect was assured. Furthermore, flood routing study in the flood plain downstream of the dam indicated that flooding in Mae Sruai District floodplain especially in urbanized area would occur due to PMF inflow and hence flood control measures should be adopted.