Storm water is water that falls as rain, snow or ice. Most of it seeps into the ground. If the ground is saturated, frozen or has paved surface, the water flows on the surface and is called stormwater runoff. stormwater runoff depends upon:
- type of precipitation
- intensity of rainfall
- duration of rainfall distribution
- soil moisture deficiency
- climatic conditions
- shape, size and type of catchment area
Storm water flow is also known as Wet Weather Flow (WWF).
When rainfall takes place, a part of it infiltrates the ground surface while the remaining flows over the land depending upon permeability of the ground, its surface slope and other factors
The amount of water flowing over the ground surface, pavements, house roofs etc is called 'runoff' or 'stormwater'
The stormwater must be drained through sewers otherwise streets, roads, etc would be flooded
The stormwater flow also depends upon:
Stormwater flow depends on the imperviousness of the surface on which the rainfall takes place
The percentage of rainwater that is available in the form of run-off is known as impermeability factor or run-off coefficient.
Intensity depends upon frequency and duration of storm.
The value of rainfall intensity can be determined using rainfall intensity curves.
In case the catchment area is more than 400 ha, the following empirical formulae are used:
When rainfall takes place, a part of it infiltrates the ground surface while the remaining flows over the land depending upon permeability of the ground, its surface slope and other factors
The amount of water flowing over the ground surface, pavements, house roofs etc is called 'runoff' or 'stormwater'
The stormwater must be drained through sewers otherwise streets, roads, etc would be flooded
The stormwater flow also depends upon:
- Ground slope
- Permeability of the ground and
- Extent of impervious area (Buildings, Paved areas, non-absorbent road surface, etc)
- Extent of vegetation
- Condition of ground prior to rainfall
- Climatic conditions such as wind, humidity, temperature, etc
Stormwater flow depends on the imperviousness of the surface on which the rainfall takes place
The percentage of rainwater that is available in the form of run-off is known as impermeability factor or run-off coefficient.
Intensity depends upon frequency and duration of storm.
The value of rainfall intensity can be determined using rainfall intensity curves.
In case the catchment area is more than 400 ha, the following empirical formulae are used:
- Dicken's formula
- Ryve's formula
- Inglis's formula
- Talbot's formula
- Fanning's formula
- Metcalf Eddy's formula
- McMath formula
- Burkli-Zeiglar formula
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