🌊 Table 3-6: Sensitivity of Runoff Volume and Peak Flow to Surface Runoff Parameters 🌧️ from the SWMM5 Hydrology Manual
🌊 Table 3-6: Sensitivity of Runoff Volume and Peak Flow to Surface Runoff Parameters 🌧️
| Parameter | Typical Effect on Hydrograph | Effect of Increase on Runoff Volume | Effect of Increase on Runoff Peak | Comments |
|---|---|---|---|---|
| 🌳 Area | Significant | 📈 Increase | 📈 Increase | Less effect for a highly porous catchment |
| 🏙️ Imperviousness | Significant | 📈 Increase | 📈 Increase | Less effect when pervious areas have low infiltration capacity |
| 📏 Width | Affects shape | 🔽 Decrease | 📈 Increase | Increasing width tends to produce higher and earlier hydrograph peaks, especially for storms of varying intensity. Affects volume only when reduced width on pervious areas allows more time for infiltration |
| ⛰️ Slope | Affects shape | 🔽 Decrease | 📈 Increase | Similar to width but less sensitive, as flow is proportional to square root of slope |
| 🌾 Roughness | Affects shape | 📈 Increase | 🔽 Decrease | Inverse effect as compared to width |
| 💧 Depression Storage | Moderate | 🔽 Decrease | 🔽 Decrease | Significant only for low-depth storms. Losses like evaporation, depression storage, and infiltration become less important as storm depth increases |
🔍 Additional Notes:
- In flooding scenarios, the land surface behaves increasingly like an impervious surface, hence urbanization has less impact on high-return period events than on common events.
- Ground saturation consideration may invoke groundwater routines to allow water table rise to the surface.
- For small storms, depression storage becomes crucial, although it is difficult to estimate and depends on initial conditions.