Results and Discussion
1) Impacts of backwater
I extract the flow time series at Node 7, which is the confluence of the East River and Willow Creek. We can see that the backwater attenuates the discharge by reducing the peak flow and delaying peak time. Also, there are fluctuations when the discharge is low. At downstream Node 4, there is also an attenuation, and the fluctuation is even greater. At the river mouth, we can see that the discharge oscillates during the whole event, which means that the impacts of backwater will become stronger from upstream to downstream.
2) Impacts of stormwater
18'' pipe
Maximum flow rate at flooded nodes
Hours flooded at flooded nodes
72'' pipe
Maximum flow rate at flooded nodes
Hours flooded at flooded nodes
I will show the impact of stormwater by comparing the urban flooding scenarios of stormwater systems with 18-inch pipe and 72-inch pipe. When the return period increases, the maximum discharge and hours flooded also increase. For the 18-inch pipe case, there are three nodes with longer flooded durations than others, which are all located upstream of the sewage system, indicating that the drainage conduits limit the flow transport capability at these nodes.
Then, I increase the pipe diameter to 72 inches. The flooded nodes reduce to two, and the flood durations are much smaller than those of the previous case. Overall, the stormwater can change the flow conveyance direction and capability at the watershed. A small pipe conduit will limit the outflow and cause flooding at the junction.