Runoff Coefficient For Roof

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.

Runoff coefficient for roof.

Rational method runoff coefficients. Typical values are given below. Rational method runoff coefficient applications. The american society of plumbing engineers data book suggests that initially there will be some friction along the drainage path but it will quickly go to zero.

There are two ways you can find the runoff coefficient. And q the peak storm water runoff rate due to a storm of intensity i on. 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.

Using the runoff coefficient scientists and hydrologists can calculate how much water passes over a given area per second. The runoff coefficient describes the percentage of rainfall which runs off a particular surface during a storm event. Measure along the length of the house or building and along the width of the house or building in feet. Count the number of downspouts coming from your roof.

On a low slope fully adhered epdm roof with slope of 1 4 per foot one could justify a coefficient of 95 to 99. Tot per per tot imp impa a c a a. Divide 100 by the number of downspouts in order to obtain the percentage of water collected from each downspout. C v using datafit 9 1 32 model selection criteria.

The formula for calculating this flow is called the maming formula. The other parameters are a the area of a watershed. 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 possible to calculate the average runoff coefficient for non homogeneous areas considering.

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. Step 1 determine the footprint of your structure f in square feet. 1 predicted c v must increase or remain constant for 0 p 100 mm 2 predicted c v 1 for 0 p 100. 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.

Why is it important. The higher the value the greater the quantity of water which will need to be dealt with by the drainage system. One of the parameters in the rational method equation q cia is the runoff coefficient c.