Saturday, November 11, 2023

🌊 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 🌧️

ParameterTypical Effect on HydrographEffect of Increase on Runoff VolumeEffect of Increase on Runoff PeakComments
🌳 AreaSignificantπŸ“ˆ IncreaseπŸ“ˆ IncreaseLess effect for a highly porous catchment
πŸ™️ ImperviousnessSignificantπŸ“ˆ IncreaseπŸ“ˆ IncreaseLess effect when pervious areas have low infiltration capacity
πŸ“ WidthAffects shapeπŸ”½ DecreaseπŸ“ˆ IncreaseIncreasing 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
⛰️ SlopeAffects shapeπŸ”½ DecreaseπŸ“ˆ IncreaseSimilar to width but less sensitive, as flow is proportional to square root of slope
🌾 RoughnessAffects shapeπŸ“ˆ IncreaseπŸ”½ DecreaseInverse effect as compared to width
πŸ’§ Depression StorageModerateπŸ”½ DecreaseπŸ”½ DecreaseSignificant only for low-depth storms. Losses like evaporation, depression storage, and infiltration become less important as storm depth increases

πŸ” 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.

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