The Evaluation of retention pond capacity under a series of rainfall occurrence and land development

Abstract

A retention pond with total volume of 80,000 m3 and total area of 1.5 ha was constructed within a residential area in Bandar Lampung in order to protect the area from inundation during high intensity of rainfall. On 24 January 2013 the embankment of pond was found collapsing and caused about 1 m inundation at downstream. This study is aimed at evaluating the reliability of available retention pond to control runoff that flows into it. HEC-HMS model is employed here to simulate the events. Based on the simulation results, it is found that the existing retention pond is able to control the 5 years flood. Another retention pond is necessary to be built at the upstream in case higher return period is considered. Otherwise, outlet with diameter 1 or 1.5 m must be installed to lower the water level within the pond. Moreover, a combination of new retention pond (432,000 m3) and two culverts with diameter 1 m may increase the capability of available retention pond to cope with 100 years rainfall. To prevent inundation occurs at downstream, construction of dike or normalization is therefore crucial.