What is C in Q CiA?

Q = CiA. where. Q= design peak runoff rate, cfs. C = runoff coefficient, dimensionless – defined as the ratio of the peak runoff rate to the rainfall intensity.

WHAT IS A in Q CiA?

The Rational method predicts the peak runoff according to the formula: Q=CiA, where C is a runoff coefficient, i is the rainfall intensity, and A is the subcatchment area. This formula is applicable to US or metric evaluation, as long as consistent units are employed.

How do you calculate rainfall depth and intensity?

Hi Mohamad, The first thing that you have to do is to convert the table of annual maximum (statistical) values of rainfall depth into Intensity Values (mm/hr) just divide the total depth (precipitation) by the rainfall duration (i.e. for 1971 during 1 hr you have a rainfall max.

What is peak runoff?

The flow at outlet starts with minimum flow called base flow (sometimes its value is zero) and attains the maximum flow after some times and then recedes to base flow again. This time variation of flow is called hydrograph. The maximum flow at outlet thus attained is called peak flow of runoff.

How do you calculate rainfall deviation?

Meteorologists do this by computing the Coefficient of Variation. The Coefficient Variation is simply the standard deviation divided by the average annual rainfall. For San Francisco’s average rainfall of 21.79″ for its period of record, the standard deviation is 7.63″. Dividing 7.63 by 21.79 gives 0.35.

How do you calculate rainfall intensity from annual rainfall data?

To convert a rainfall depth during a period of time into an intensity in mm/hr. The depth in mm is divided by the duration in hours : ie: 50 mm over 30 minutes. => 50 / 0.5 = 100 mm/hr.

What is SCS unit hydrograph?

The SCS (Soil Conservation Service) unit routing model uses a curvilinear unit hydrograph to calculate runoff resulting from subcatchment net rainfall. The SCS method uses a dimensionless unit hydrograph derived from the analysis of extensive measured data.

What is the formula to calculate the duration of a storm?

p = 254a / (t+b) mm/hr Where, t = Duration of storm in minutes, a and b are constants. a = 30 and b = 10 when t is 5 to 20 minutes. a = 40 and b = 20 when t is 20 to 100 minutes.

How do you calculate the intensity of rainfall?

The intensity of rainfall is greater when shorter periods are considered while it is lower when large periods are considered. The intensity of rainfall (p) in mm/hr is given by the following general formula: p = 254a / (t+b) mm/hr Where, t = Duration of storm in minutes, a and b are constants. a = 30 and b = 10 when t is 5 to 20 minutes.

What is the formula for stormwater flow?

Stormwater flow formula is used to calculate the amount of stormwater that has been collected due to excessive rainfall and is represented as Q = C*I*A or peak_runoff = Runoff coefficient*Average rainfall rate*Area.

What is a constant intensity design storm typically used with?

A constant intensity design storm is typically used with the Rational Method because short duration storms are appropriate for the relatively small drainage areas modeled with the Rational Method, and the effect of a short duration storm can be represented well as a storm of approximately constant intensity.