Runoff Coefficients

Values of Runoff Coefficient

 

The runoff coefficient is a function of the ground cover and the rainfall intensity. During a storm the actual runoff coefficient increases as the soil become saturated. The greater the rainfall intensity, the greater is the runoff coefficient due to the reducing relative amount of rainfall losses.Recommended values of C is given in  Table 2.11: Table 2.5 (MSMA, 2011) Recommended Runoff Coefficients

 

Table 2.11: Table 2.5 (MSMA,2011) Recommended Runoff Coefficients for Various Landuses

Note: The runoff coefficients in this table are given as a guide for designers. The near-field runoff coefficient for any single or mixed landuse should be determined based on the imperviousness of the area.

 

 

Runoff Coefficient for Mixed Development

 

Segments of different landuse within a sub-catchment can be combined to produce an average runoff coefficient as follows. For example, if a sub-catchment consists of segments with different landuse denoted by j=1, 2….m, the average runoff coefficient (Cavg) is estimated by:

 


where

 

Cavg     = Average runoff coefficient

Cj         = Runoff coefficient of segment i

Aj         = Area of segment i (ha); and

m         = Total number of segments

 

 

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