What is a runoff coefficient?

The runoff coefficient (C) is a dimensionless coefficient relating the amount of runoff to the amount of precipitation received. 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).

What is the formula for runoff coefficient?

A = catchment area (ha). The runoff coefficient (Cy) is defined as the ratio of the peak runoff rate of a given ARI to the mean rate of rainfall for a duration equal to the catchment ‘time of concentration’ and of the same ARI.

What is runoff coefficient adjustment factor?

Cf = Runoff coefficient adjustment factor to account for reduction of infiltration and other. losses during high intensity storms. C = Runoff coefficient to reflect the ratio of rainfall to surface runoff. i = Rainfall intensity in inches per hour (in/hr)

What is the Rational runoff coefficient?

The Rational method runoff coefficient (c) is a function of the soil type and drainage basin slope. The duration is usually equivalent to the time of concentration of the drainage area. The storm frequency is typically stated by local authorities depending on the impact of the development.

What is rainwater runoff coefficient?

(Runoff coefficient for any catchment is the ratio of the volume of water that runs off a surface to the volume of rainfall that falls on the surface).

How do you calculate runoff?

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.

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 are the 2 types of runoff?

Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or base runoff, and according to source as surface runoff, storm interflow, or groundwater runoff. 2.

What are examples of runoff?

Runoff is defined as excess water draining away from land or buildings. The overflow of water that drains off of your driveway is an example of runoff. Dissolved chemicals, etc, included in such water. The runoff of nitrates is poisoning the lake.

What do you mean by runoff?

Runoff occurs when there is more water than land can absorb. The excess liquid flows across the surface of the land and into nearby creeks, streams, or ponds. Runoff can come from both natural processes and human activity. The most familiar type of natural runoff is snowmelt.

What is rainfall runoff relationship?

the rainfall-runoff relationship for any rainstorm depends on the dynamic interaction between rain intensity, soil infiltration and surface storage. Runoff occurs whenever rain intensity exceeds the infiltration capacity of the soil, providing there are no physical obstructions to surface flow.

How are runoff coefficient and impervious fraction calculated?

The runoff coefficient, R V, is the runoff depth in inches divided by the rainfall depth in inches. The impervious fraction, I A, is the impervious portion of drainage area in acres divided by the drainage area in acres The design volume, DV, is the volume of runoff that must be controlled for the design storm.

What is the composite runoff coefficient in Table 1?

The composite runoff coefficient is the weighted average of all of the land uses within the drainage area. Table 1 presents values of runoff coefficients for various surfaces. The Rational Method is most applicable to drainage areas that are 20 acres or less.

How to calculate the volume of stormwater runoff?

The Simple Method was developed by measuring the runoff from many watersheds with known impervious areas and curve-fitting a relationship between percent imperviousness and the fraction of rainfall converted to runoff (the runoff coefficient). It uses a minimal amount of information to estimate the volume of runoff.

Is it possible to capture runoff from impervious roofs?

However, when pervious concrete is well designed and installed for most or all of the parking or access areas, there will be no runoff from that area. It is even possible, pending some limitations**, to capture most if not all of the adjacent runoff from impervious roofs or other impervious.