Table of Contents

## What is the value of runoff coefficient?

Runoff coefficient is a dimensionless factor that is used to convert the rainfall amounts to runoff….Definition.

Type of area | Runoff coefficient |
---|---|

Commercial and industrial | 0.70–0.90 |

Parks and pastures | 0.05–0.30 |

Pavements and roads | 0.70–0.95 |

Flat agriculture | 0.10–0.50 |

## 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.

## What is the runoff coefficient of water bodies?

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 C in rational method?

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 does a low runoff coefficient mean?

The percentage of rainfall that appears as stormwater run-off from a surface is called the run-off coefficient. This means that only 11% of the rain falling onto pervious surfaces on this site would be stormwater run-off. The remaining 89% of the rainfall would be absorbed into the soil.

## What affects runoff coefficient?

Meteorological factors affecting runoff: Rainfall intensity. Rainfall amount. Distribution of rainfall over the watersheds. Direction of storm movement. Antecedent precipitation and resulting soil moisture.

## What is drainage coefficient?

The drainage coefficient is the design capacity of the drainage system and is typically expressed as a depth of water removed in 24 hours (inches/day). A drainage coefficient should be chosen that will economically remove excess water from the top part of the root zone within 24 to 48 hours.

## 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.

## How is water runoff calculated?

To calculate the runoff from any given rainfall:

- Take the dimensions of the footprint of your roof and convert them to inches. (So, a 50′ x 20′ roof is 600″ x 240″.)
- 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.)

## What is rainwater runoff coefficient?

The fewer the annual rainy days or longer the dry period, the more the need for rainwater collection in a region. (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).

## 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.

## How do you calculate drainage?

Another way to calculate the drainage is find a weighted “C” value for the whole area contributing to the low spot. To calculate the weighted average, you take the multiply the area of each part for the zone by its corresponding “C” value. You then add these factors together and divide that by the total area of the contributing parts.

## What is the normal range of C value for vegetation?

0.75 – 0.95 *Note: The designer must use judgement to select the appropriate “C” value within the range. Generally, larger areas with permeable soils, flat slopes and dense vegetation should have the lowest “C” values. Smaller areas with dense soils, moderate to steep slopes, and sparse vegetation should assigned the highest “C” values.

## How big of a drainage area do I need to divide?

For drainage areas greater than 200 acres, other methods can be used, or the drainage area can be divided into zones less than 200 acres.

## What are the values of runoff coefficient (C)?

Values of Runoff Coefficient (C) for Rational Formula Values of Runoff Coefficient (C)for Rational Formula Land Use C Land Use C Business: Downtown areas Neighborhood areas 0.70 – 0.95