Application of SWMM Model to analyze the effects of ponds on the runoff of a watershed – A case study on the upper watershed of Qiaotougang Bridge in Tainan

Abstract

With the increase in population and the transformation of industrial types the area of Pitang has gradually shrinked in recent years In order to explore the impact on the surface runoff in the catchment area due to the reduction of the pond area this study takes the upstream catchment area of Tainan Qiaotou Port Bridge as the study area using the SWMM model to analyze the impact on the surface runoff in the catchment area under different conditions In the study under the circumstances whether there are ponds or not with a 2-year return period of rainfall the peak values of outflow discharge of three sub-catchment areas (Jingpupi drainage Nandi drainage and Wayaopi drainage) whose parts of the ponds respectively account for 8% 9% and 12% of the catchment area can be respectively reduced to 34% 38% and 51% due to the existence of ponds; however for the 25-year return period of rainfall they are respectively 7% 19% and 30% The results show that the existence of ponds has a significant effect of flood detention Comparing to the SWMM-simulation results of the three sub-catchments with ponds in 2008 and 2018 under the condition of 25-year return period of rainfall the reduction of the pond area caused the peak value of discharge to increase respectively 18% 8% and 11% If the area of the pond in 2018 reduced another 20% the peak flow will increase to 5% 4% and 18% It shows that the changes of the pond area in different sub-catchments have different effects on the peak value of discharge Lowering the pond water level by 0 5 m in advance the SWMM-simulation results in 2018 showed that for the 25-year return period of rainfall the peak value of discharge of the three sub-catchment areas could be reduced by about 25% 36% and 50% respectively and the effects of flood detention would be significantly improved

Date of Award	2020
Original language	English
Supervisor	Chyan-Deng Jan (Supervisor)