Saturday, November 11, 2023

Based on the information in Section 3.10.1 "Runoff Coefficient Method" from the SWMM User's Manual, here's a summarized table

Based on the information in Section 3.10.1 "Runoff Coefficient Method" from the SWMM User's Manual, here's a summarized table:

ParameterDescriptionImpact on Runoff (πŸ’§)Implementation in SWMM (πŸ–₯️)
Runoff Coefficient MethodUsed in preliminary models for generating runoff flows with minimal site-specific data.-Simplifies runoff computations.
Runoff Coefficient (C)Represents the fraction of rainfall that becomes runoff.Higher values lead to more runoff.Set subcatchment's percent imperviousness to 100 and its percent of imperviousness with no depression storage to 0.
Rainfall Rate (i)Rate of rainfall (ft/s).Higher rates increase runoff.Use with the runoff coefficient in the formula: Q = CiA.
Subcatchment Area (A)Area of the subcatchment (ft²).Larger areas increase runoff.Define in subcatchment settings.
Infiltration Rate (f)Rate at which water infiltrates into the ground (ft/s).Higher rates reduce surface runoff.Implement as a constant infiltration rate in SWMM.
Depression StorageVolume that must be filled before runoff occurs.Influences the delay in runoff initiation.Assign the same depression storage depth to both pervious and impervious areas.
Manning’s Roughness (n)Coefficient indicating surface roughness.Higher values indicate rougher surfaces, reducing runoff speed.Use 0 for pervious and impervious areas to simulate immediate runoff.

This table captures the key aspects of the Runoff Coefficient Method as outlined in the SWMM User's Manual. The method provides a simplified approach for estimating runoff, particularly useful in initial, screening-level analyses. 🌧️πŸ“ˆπŸ–₯️πŸ’»πŸŒπŸŒ±πŸš°πŸ“Š

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