Model of Flood Attenuation by Combining Dry Dam and Retention Pond Distribution

Abstract

This research aims to find the most optimum condition for the position and capacity of the retention pond for decreasing the design flood and increasing the time concentration. This research was conducted in the Ciawi and Sukamadu dams-Indonesia. Based on the design, the Ciawi and Sukamadu dry dams only can reduce the flood peak to amount of 13%, so it is still needed the supporting infrastructure for increasing the efficiency in reducing flood. The combination of high- and low-intensity rainfall-runoff management methods can support the performance of dry dams in making an effort to reduce the design flood. The methodology consists of collecting the primary and secondary data, conducting the analysis based on the concepts of flood control and low impact development, then analyzing by using the HEC-HMS software. The results show that by adding the Ciawi and Sukamahi dams that have a storage capacity of 15 million m3, there is success to decrease the flood peak to 13% and the additional time concentration (Tc) is during 20 min. The additional retention pond will be able to reduce the number of flood peaks. The results show that the additional retention pond that is combined with the Ciawi dan Sukamahi dams can increase the performance of the Ciawi and Sukamahi dams with the percentage flood reduction is 19% and the additional time concentration is 50 min. The formulation that illustrates the flood reduction in the downstream of the Ciliwung watershed was proposed.