Based on the information in Section 3.10.1 "Runoff Coefficient Method" from the SWMM User's Manual, here's a summarized table:
| Parameter | Description | Impact on Runoff (💧) | Implementation in SWMM (🖥️) |
|---|---|---|---|
| Runoff Coefficient Method | Used 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 Storage | Volume 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. 🌧️📈🖥️💻🌍🌱🚰📊
