General

Process models

• Rainfall/Runoff 

• Flow routing 

Routing method

• Dynamic Wave 

To simulate the 2D flood model, always Dynamic Wave routing option is selected. It solves the complete one-dimensional Saint Venant flow equations and therefore produces the most theoretically accurate results. These equations consist of the continuity and momentum equations for conduits and a volume continuity equation at nodes. With this form of routing it is possible to represent pressurized flow when a closed conduit becomes full, such that flows can exceed the full normal flow value. Flooding occurs when the water depth at a node exceeds the maximum available depth, and the excess flow is either lost from the system or can pond atop the node and re-enter the drainage system. Dynamic wave routing can account for channel storage, backwater, entrance/exit losses, flow reversal, and pressurized flow. Because it couples together the solution for both water levels at nodes and flow in conduits it can be applied to any general network layout, even those containing multiple downstream diversions and loops. It is the method of choice for systems subjected to significant backwater effects due to downstream flow restrictions and with flow regulation via weirs and orifices. This generality comes at a price of having to use much smaller time steps, on the order of a thirty seconds or less (SWMM can automatically reduce the user-defined maximum time step as needed to maintain numerical stability).

Infiltration model

• Green-Ampt 

Green Ampt is often preferred over Horton method because it is more physical based. The choice of the method often depends on the availability of the soil parameters in the modeled area.

Miscellaneous

• Allow ponding 

• Minimum conduit slope (%): 0 

• Flow units: based on project  

Checking “Allow Ponding” will allow excess water to collect atop nodes and be re-introduced into the system as conditions permit. In order for ponding to actually occur at a particular node, a nonzero value for its Ponded Area attribute must be used. This option is checked so that no water can loss from the calculation and to determine flood water volume properly.