## How do you calculate the 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.

What is the value of runoff coefficient?

The variation of the runoff coefficient values was between 0.011 and 0.35.

How is Q in CiA 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.

### Is runoff coefficient the same as curve number?

The runoff coefficient is not equal to Curve number. but if you know CN, you can calculate S, from S and known initial loss, you can calculate the runoff and from that you can calculate the runoff coefficient. That you can calculate also. You have to know the value of initial loss.

What is water runoff coefficient?

The runoff coefficient is a factor dependent on the collection surface, by which the accumulated rainfall is multiplied to obtain the actual rainfall runoff introduced into the drainage system.

How do you calculate stormwater runoff volume?

Therefore, to assure that the first flush is captured and treated, the easiest method to determine the stormwater treatment volume is simply to multiply the project size or contributing drainage area times the treatment volume.

#### How is CN number calculated?

The weighted CN is calculated by taking the sum of each CN value multiplied by its fraction of the total subcatchment area. The sum is (usually) rounded to the nearest whole number, as described below.

What does runoff coefficient depend on?

How do you calculate stormwater drainage?

To calculate the volume of water that needs to be stored, multiply the amount of runoff from each drainage zone by 15. The runoff for each zone was in gallons per minute. Multiplying by 15 minutes leaves you with the amount of gallons to be stored.

## How do you calculate rain runoff?

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 do you calculate antecedents?

The Antecedent Precipitation Index is precipitation falling before, but influencing the runoff yields of, a given rainfall event is calculated using Antecedent Precipitation Index = Coefficient ‘a’*Precipitation in (i)th Year+Coefficient ‘b’ in Straight-line regression*Precipitation in (i-1)th Year+Coefficient ‘c’* …

Where can I get TR-55?

TR55

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### How do you find CN in hydrology?

What is CN value in hydrology?

The runoff curve number (also called a curve number or simply CN) is an empirical parameter used in hydrology for predicting direct runoff or infiltration from rainfall excess.

How do you calculate runoff coefficient?

c = Rational method runoff coefficient i = Rainfall intensity, inch/hour A = Drainage area, acre. Note that our calculation allows you to use a variety of units. The Rational method runoff coefficient (c) is a function of the soil type and drainage basin slope. A simplified table is shown below.

#### How do you calculate runoff?

How do you calculate runoff using rainfall data? 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 do you calculate runoff coefficient using rainfall data?

Roof plan and measurements

• Calculator
• Pencil
• Paper
• How to calculate runoff?

Q is the storm-water run-off in gallons per minute (GPM)

• C is the runoff coefficient,
• I is the rainfall intensity in inches per hour.
• A is the drainage area in sq. ft.
• 23 is a conversion factor when you want the flow rate in GPM and your drainage area is in sq. ft.