How do you find the runoff coefficient in rational functions?

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.

How do you find the composite runoff coefficient?

Composite runoff coefficient: C = (A1. C1+ A2.

What is meant by runoff coefficient?

Definition. Runoff coefficient is a dimensionless factor that is used to convert the rainfall amounts to runoff. It represents the integrated effect of catchment losses and hence depends upon the nature of land surface, slope, degree of saturation, and rainfall intensity.

What is C in Q CiA?

Q = CiA. where. Q= design peak runoff rate, cfs. C = runoff coefficient, dimensionless – defined as the ratio of the peak runoff rate to the rainfall intensity.

Why is rational method defined as an uncalibrated model?

Question: QUESTION 2 Why is rational method defined as an uncalibrated model? The peak discharge is not based on observed values from the project and or near the project. Intensity is based on the project site.

What is the rational method?

The Rational Method expresses a relationship between rainfall intensity and catchment area as independent variables and the peak flood discharge resulting from the rainfall as the dependent variable. It has been used for over 150 years, and known as the Rational Method for nearly 100 years.

How is stormwater runoff measured?

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.

Which of the following surface has a maximum coefficient of runoff factor?

5. Which of the following surface has a maximum Kuichling’s impermeability factor? Explanation: The water tight roof surface has maximum Kuichling’s impermeability factor with a magnitude of 0.7 to 0.95 while gravel road, unpaved surface and macadamized road ways have < 0.7.

What is peak runoff?

One of the key parameters in the design and analysis of soil and water conservation structures is the resulting peak runoff or the variations of runoff with time (hydrograph) at the watershed outlet. The maximum flow at outlet thus attained is called peak flow of runoff.

What is SCS method?

The SCS curve number method is a simiple, widely used and efficient method for determining the approxient amount of runoff from a rainfall even in a particular area. The curve number is based on the area’s hydrologic soil group, land use , treatment and hydrologic condition.

What is modified rational method?

Modified Rational Method. The Modified Rational Method is a somewhat recent adaptation of the Rational Method that can be used to not only compute peak runoff rates, but also to estimate runoff volumes and hydrographs.

How to calculate runoff coefficient?

How to Calculate Runoff Coefficient. Step 1. The Rational Method is used for areas less than 50 acres. If the area you are assessing is more than 50 acres, you will have to use a Step 2. Step 3. Step 4. Using a Runoff Coefficient Table .

What is rational method equation?

Rational Method Equation. The Rational equation is the simplest method to determine peak discharge from drainage basin runoff. It is not as sophisticated as the SCS TR-55 method, but is the most common method used for sizing sewer systems. Rational Equation: Q=ciA. The Rational equation requires the following units: Q = Peak discharge, cfs.

What is the coefficient of runoff?

Runoff coefficient is loosely defined as the ratio of runoff to rainfall, and is a function of watershed characteristics including land use, soil type, and slope of the watershed. The value of runoff coefficient ranges between 0.0 and 1.0.