How do you calculate runoff coefficient?

How do you calculate runoff coefficient?

The Rational Formula is expressed as Q = CiA where: Q =Peak rate of runoff in cubic feet per second C =Runoff coefficient, an empirical coefficient representing a relationship between rainfall and runoff.

How do you calculate runoff per year?

Simple, straightforward methods of calculating runoff can tell you the amount of water that storms bring to the earth. For a given surface area such as a roof or yard, multiply the area by the inches of rainfall and divide by 231 to obtain the runoff in gallons.

How is peak runoff rate calculated?

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.

What is the composite runoff coefficient?

The composite runoff coefficient, C, reflects the runoff potential of the drainage area. The range of runoff coefficients varies from 0.35 to 0.95, with higher values corresponding to greater runoff potential. The composite runoff coefficient is the weighted average of all of the land uses within the drainage area.

How do you calculate runoff volume?

To calculate the runoff from any given rainfall:

1. Take the dimensions of the footprint of your roof and convert them to inches. (So, a 50′ x 20′ roof is 600″ x 240″.)
2. Multiply the roof dimensions by the number of inches of rainfall. (In this example, 600″ x 240″ x 1″ = 144,000 cubic inches of water.)

How do you calculate weighted C Factor?

The weighted C for a drainage area is computed by dividing the sum of all subarea CAs by the total area, where CA is the subarea C value multiplied by the area of the subarea.

What is the runoff coefficient for Ari?

The runoff coefficient is for the 10 year ARI event (i.e. Y = 10). It can then be adjusted for events of other frequencies.

Where can I find runoff coefficient for eastern NSW?

Runoff coefficient for 10 year ARI event For eastern NSW the runoff coefficient is obtained from a map in Volume 2 of Australian Rainfall and Runoff . The map is shown in Figure 8-2 with an enlarged version for around Sydney in Figure 8-3.

How do you calculate runoff from a site?

Runoff volume = (0.005 inches/12 inches per foot)(2 acres)(43,560 sf per acre) Pervious area runoff volume = 36 cubic feet Total site runoff volume = 3775 + 36 = 3811 cubic feet(vs. 1089 cubic feet using weighted average CN)

What is the main factor that affects runoff?

Runoff volumes are influenced primarily by the total amount of rainfall. However, runoff rates resulting from a given rainfall, including the peak rate or discharge, are influenced primarily by the rainfall’s distribution, which is how the rainfall rate or intensity varies over a period of time.