Simulation analysis of the influence of heavy rainfall on urban lake

Abstract

Urban lakes play a role in flood control and storage, they are also important urban landscape, which have certain requirements for water quality. In addition to the impact on the lake water quantity, the short-term heavy rainfall runoff carries a large pollution and has a great impact on the water quality, especially for urban lakes with relatively small reserves. However, there are few studies on the effects of heavy rainfall on lake hydrodynamics and water quality. In this paper, taking the rainfall of typhoon Fitow as an example, EFDC was used to simulate the hydrodynamic water quality process of West Lake in Hangzhou China during the Fitow period, the water level and water quality monitoring values were used to validate the model during this period. The simulation shows that the heavy rainfall had a great influence on the water level of the West Lake. Water level of West Lake crossed warning mark about 71 hours, with Sudi and Baidi Causeways were flooded about 57 hours. According to the simulation, as the TP concentration of early runoff was high, the TP concentration at the inlets of each sub-basin increased above 0.1 mg/L. After the early runoff, the TP concentration at the inlets began to decrease. The high concentration area gradually migrated to the downstream, and decreased gradually until it was discharged from the Shengtangzha Outlet, and water quality gradually returned to normal. Since the water level of West Lake increased significantly during the period, the influence of different drainage discharges was analyzed. The analysis shows that the highest water level of West Lake during Fitow period would fall below warning mark in case of increasing the flood discharge capacity to 46.8m3/s, which was 29m3/s more than current discharge. Otherwise there s little effect on the spatial distribution of TP with the increasing of flood discharge. In conclusion, the main threat of short-term heavy rainfall to urban lake is flood control and drainage, meanwhile the impact of the heavy rain on water quality cannot be ignored. A perfect drainage and diversion system would make the water quality back to normal quickly after the heavy rainfall.