Runoff Coefficient For Roof

The runoff coefficient c is a dimensionless coefficient relating the amount of runoff to the amount of precipitation received.

Runoff coefficient for roof.

It is possible to calculate the average runoff coefficient for non homogeneous areas considering. There are two ways you can find the runoff coefficient. For sample purposes a 55 gallon barrel will be used. The runoff coefficients from the field experiments were calculated using observed precipitation and runoff from existing green roofs in oslo trondheim sandnes and bergen norway.

Tot per per tot imp imp a a c a a 2. Related spreadsheets from civilweb. The runoff coefficient used as part of the rational method is a simple estimate of the amount of rainfall which will runoff the surface. Why is it important.

I the design rainfall intensity for a storm of specified recurrence interval and duration equal to the watershed time of concentration. 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. Using the runoff coefficient scientists and hydrologists can calculate how much water passes over a given area per second. One of the parameters in the rational method equation q cia is the runoff coefficient c.

Green roofs can help to reduce both storm water volume rate of run off entering the drainage system. A runoff coefficient is a number that relates the rainfall rate and runoff rate. Therefore green roofs have an important role to play in the urban realm. The other parameters are a the area of a watershed.

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. As with other green infrastructure interventions. For example it is 0 9 for metal or tile roofs and up to 0 3 for green roofs. Alternatively the runoff coefficient is the factor by which depending on the type of surface the effective impermeable area is calculated.

Events that had a cumulative precipitation comparable to the laboratory events but longer durations were selected. Typical values are given and the runoff coefficient is used in the civilweb rainfall runoff spreadsheet as part of the rational method. Colebrook white pipe design spreadsheet. Also outlined are the steps to build your own rain barrel to collect water from your roof and downspout for all outdoor uses like watering and cleaning.

Rational method runoff coefficients. 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. The system outlined below will walk you through the steps of determining your rain barrel sizes based on average roof runoff.