Runoff Coefficient For Roof

And q the peak storm water runoff rate due to a storm of intensity i on.

Runoff coefficient for roof.

A runoff coefficient is a number that relates the rainfall rate and runoff rate. One of the parameters in the rational method equation q cia is the runoff coefficient c. Step 1 determine the footprint of your structure f in square feet. Rational method runoff coefficient applications.

Typical values are given below. Tot per per tot imp impa a c a a. Using the runoff coefficient scientists and hydrologists can calculate how much water passes over a given area per second. Runoff coefficient c this coefficient allows for the quantity of water which runoff a particular type of surfacing into a drainage system and discount the quantity of water which will soak into or through the surfacing.

It is possible to calculate the average runoff coefficient for non homogeneous areas considering. 1 predicted c v must increase or remain constant for 0 p 100 mm 2 predicted c v 1 for 0 p 100. The formula for calculating this flow is called the maming formula. C v using datafit 9 1 32 model selection criteria.

The rational method considers a runoff coefficient of about 0 7 0 95 for both concrete streets and roofs the most impervious and a runoff coefficient of about 0 05 0 35 for lawns areas the most pervious. Measure along the length of the house or building and along the width of the house or building in feet. I the design rainfall intensity for a storm of specified recurrence interval and duration equal to the watershed time of concentration. The runoff coefficient c is a dimensionless coefficient relating the amount of runoff to the amount of precipitation received.

Annual runoff generated roof area annual rainfall runoff coefficient 200 1000 0 9 180 000 litres or 47 520 gallons hence a storage capacity of 47 520 gallons is required to sail through the summer months with adequate water supply. It is a larger value for areas with low infiltration and high runoff pavement steep gradient and lower for permeable well vegetated areas forest flat land. Runoff coefficients paired rainfall p and observed runoff q obs from 21 living roofs volumetric runoff coefficient for each storm linear regression for paired p. Rational method runoff coefficients.

Why is it important. On a low slope fully adhered epdm roof with slope of 1 4 per foot one could justify a coefficient of 95 to 99. Multiply the two figures together to obtain the square footage of your roof step 2 determine the percentage of water collected from each downspout p. The runoff coefficient describes the percentage of rainfall which runs off a particular surface during a storm event.

The other parameters are a the area of a watershed. Divide 100 by the number of downspouts in order to obtain the percentage of water collected from each downspout. Count the number of downspouts coming from your roof.