Study on optimal starting time of detention ponds and water resource reuse

Adopting the SWMM (Storm Water Management Model) developed by the U.S. Environmental Protection Administration, this study presumes the condition of a regional drainage system and simulates the starting of a detention pond in different time based on the change of water levels. Because the pattern of rainstorms is unpredictable, five types that have occurred most frequently in Taiwan are used for analysis normal distribution, logarithmic normal distribution; Pearson type III distribution, Log-Pearson type III distribution and Extreme-Value type I distribution. The purpose is to acquire the best timing for starting the detention pond, with the regional drainage system fully loaded, and the optimal value of water storage without causing a flood. Another goal is to recycle the water resource by planning the reuse of flood water. As the results of the simulation show, different rain types produce different solution sets. If the optimal solution can be located without the threat of a flood, we can prolong the duration to fill up a detention pond on its designed capacity and reduce the effects caused by the uncertain factors in a rainstorm. Moreover, the storms can be turned into excellent water resource. This study has demonstrated the procedures to strike the best timing of starting the detention pond. It has to be remembered, however, that the change of data on hydrology and underground hydrology in a specific region will definitely affect the results of simulation. To put it into practice, one should closely attend to the existing situation of the region.