Runoff in cumec by the Rational method

The Rational method is a widely used hydrologic method for estimating peak runoff rates from urban watersheds. It is a simplified approach that provides a quick estimation of the peak discharge for a given storm event. The runoff in cumec (cubic meters per second) by the Rational method is defined by the equation:

Q = K * A * I * R

Where:
Q = peak discharge (runoff) in cumec
K = runoff coefficient
A = drainage area in hectares
I = rainfall intensity in mm/hour
R = time of concentration in hours

Explanation:

The equation Q = K * A * I * R represents the runoff in cumec by the Rational method. Let's break down each component and understand its significance:

1. K (runoff coefficient): The runoff coefficient represents the fraction of rainfall that becomes direct runoff. It depends on the land use, soil type, and other factors that influence the runoff response. The value of K ranges from 0 to 1, with 1 indicating that all rainfall becomes direct runoff.

2. A (drainage area): The drainage area is the total area that contributes runoff to a specific point. It is usually measured in hectares. The larger the drainage area, the more runoff it generates.

3. I (rainfall intensity): Rainfall intensity refers to the rate at which rainfall occurs. It is usually expressed in millimeters per hour. The intensity of rainfall is an important factor in determining the peak runoff rate.

4. R (time of concentration): The time of concentration represents the time it takes for runoff to travel from the farthest point in the watershed to the outlet. It includes the travel time within the channels, overland flow, and any other flow paths. The longer the time of concentration, the more time it takes for the runoff to reach the outlet.

By multiplying these four factors (K, A, I, and R) together, we can estimate the peak discharge (Q) in cumec for a specific storm event. The Rational method provides a simplified approach to estimate runoff, but it is important to note that it may not be suitable for all types of watersheds and storm events. Other methods, such as hydrologic models, may be necessary for more accurate estimations.

To summarize, the runoff in cumec by the Rational method is calculated using the equation Q = K * A * I * R, where K is the runoff coefficient, A is the drainage area, I is the rainfall intensity, and R is the time of concentration. This method provides a quick estimation of the peak discharge for a given storm event in urban watersheds.