# how to calculate runoff from rainfall data

## How To Calculate Runoff From 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.Dec 28, 2020

## How do you calculate rain runoff?

To calculate the runoff from any given rainfall:
1. Take the dimensions of the footprint of your roof and convert them to inches. (So, a 50′ x 20′ roof is 600″ x 240″.)
2. 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 the formula to calculate runoff from a particular area after a rainfall?

Q = 16 P2 Q = 0.48 (P – 635), With discharge amount. also, runoff coefficient can be calculated as a= Q/P Regards.

## How is runoff measured?

Runoff measurements

The measurement of runoff, in the field, is generally carried out using current meters and calibrated or rated channel cross sections, flumes or standardized weirs, together with water level readings, often by automatic recorders, to give a continuous height record which can be correlated to flow.

## How is runoff ratio calculated?

Runoff ratio is the runoff for each watershed divided by the precipitation for that watershed. It is the proportion of rainfall that does not infiltrate and is not taken up by evapotranspiration, and thus ends up as runoff.

## How is peak runoff 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.

## What is the formula for rainfall intensity?

Formula Of Rainfall Intensity

The intensity of rainfall (p) in mm/hr is given by the following general formula: p = 254a / (t+b) mm/hr Where, t = Duration of storm in minutes, a and b are constants. a = 30 and b = 10 when t is 5 to 20 minutes.

## Which of the following method is used to calculate runoff?

1. Rational Method: This is a most common method used to compute the peak runoff rate from the small watershed. The peak runoff is defined as the maximum runoff to be used as capacity for design of a given structure that must carry the runoff.

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## What is rainfall runoff?

After a heavy rainfall you might see sheets of water running downhill… … When rain falls onto the earth, it just doesn’t sit there, it starts moving according to the laws of gravity. A portion of the precipitation seeps into the ground to replenish Earth’s groundwater. Most of it flows downhill as runoff.

## What are the methods of estimation of runoff?

The curve number method (SCS–CN, 1972) is an adaptable and widely used for runoff estimation. This method is important properties of the watershed, specifically soil permeability, land use and antecedent soil water conditions which take into consideration (Bansode et al.

## What is runoff in hydrology?

runoff, in hydrology, quantity of water discharged in surface streams. … Runoff also includes groundwater that is discharged into a stream; streamflow that is composed entirely of groundwater is termed base flow, or fair-weather runoff, and it occurs where a stream channel intersects the water table.

## What is runoff estimate?

There are several techniques to compute runoff volume or runoff depth, among them curve number (SCS-CN) technique is most widely used. … 6.1 SCS-CN Method. The SCS curve-number (SCS-CN) method was developed by the Soil Conservation Service for estimating runoff volume (SCS, 1969).

## What percentage of rainfall becomes runoff?

Despite dramatic flash flooding after big storms, studies of the fate of precipitation over long periods and large regions, show that only about 35% of it becomes runoff in streams and rivers. About 65% returns to the atmosphere as water vapor.

## 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 the value of runoff coefficient?

Normally, runoff coefficient is applied to storm events, but it can also be used for monthly and annual rainfall and runoff values.

Definition.
Type of area Runoff coefficient
Commercial and industrial 0.70–0.90
Parks and pastures 0.05–0.30
Flat agriculture 0.10–0.50

## 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.

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## How do you calculate rainfall frequency?

Then the rainfall intensity, I (in mm/h) for return period T is obtained from:(5) I t = P t T d where Td is duration in hours. The frequency of the rainfall is usually defined by reference to the annual maximum series, which consists of the largest values observed in each year.

## How do you convert rainfall depth to intensity?

In order to have the average rainfall intensity in m/s corresponding to that interval of time, you have to divide the rainfall depth for the number of seconds in the time interval or for mm/s you multiply for 1000/21600. If you want the intensity in m/h you divide for 6 hours.

## What are the most common runoff estimation method?

The most common method of calculating the amount of rainfall converted to runoff is the SCS Curve Number (CN) Method, originally presented in the National Engineering Handbook, Section 4 (NEH-4).

## What is the full form of SCS CN?

This research aims to determine the runoff depth using the Soil Conservation Service Curve Number (SCS-CN) method with Geographic Information Technique (GIS). … The curve number method was used to estimate the runoff depth for selected storm events in the watershed.

## What is AMC in hydrology?

The Soil Conservation Service curve number (CN) method commonly uses three discrete levels of soil antecedent moisture condition (AMC), defined by the 5-day antecedent rainfall depth, to describe soil moisture prior to a runoff event.

## How is runoff produced?

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. … Glaciers, snow, and rain all contribute to this natural runoff. Runoff also occurs naturally as soil is eroded and carried to various bodies of water.

## What is runoff unit?

A. cubic metre/sec.

## How many Litres is 1mm of rain?

With a rainfall of 1 mm, every square metre receives 1 litre of rain water. A rainfall of 1 mm supplies 0.001 m3, or 1 litre of water to each square metre of the field.

## How do you calculate rainfall over area?

Find the average volume of rain = Depth x radius x radius x 3.14. Find the area at the top of the bucket (this is the area over which the rain is collected). Divide the rainfall volume by this area to get the rainfall.

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## What does 10 mm rainfall mean?

Very heavy rain: Greater than 8 mm per hour. Slight shower: Less than 2 mm per hour. Moderate shower: Greater than 2 mm, but less than 10 mm per hour. Heavy shower: Greater than 10 mm per hour, but less than 50 mm per hour.

## What is the TR 55 method?

Technical Release 55 (TR-55) presents simplified procedures to calculate storm runoff volume, peak rate of discharge, hydrographs, and storage volumes required for floodwater reservoirs. These procedures are applicable in small watersheds, especially urbanizing watersheds, in the United States.

## How do you calculate CN?

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 C stands for in hydrology?

b) Total volume at that instant, as the area under hydrograph indicates the force of water during the duration. c) Rate of flow at any particular time during the duration period. d) Mean runoff for each month. Explanation: Mean runoff for each month is available.

## Is runoff and discharge the same?

The data in the reports of the Geological Survey on surface water represent the total fluids measured. Thus, the terms discharge, streamflow, and runoff represent water with the solids dissolved in it and the sediment mixed with it. Of these terms, discharge is the most comprehensive.

## What is rainfall frequency?

(Also called frequency curve.) The probability distribution specifying the exceedance probability of different rainfall depths for a given duration (such as 1 hour, The exceedance frequency is often reported as a return period (in years), which is the reciprocal of the annual exceedance frequency. …

## CE 433 – Class 9 (19 Sept 2017) Making an IDF Curve from Weather Station Data (no audio)

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