How do you calculate rainfall intensity?

How do you calculate 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.

How do you calculate rainfall intensity from time of concentration?

Equation 4.1 Q = I *A *0.00278 Where Q = peak discharge (m3/s) I = rainfall intensity (mm/hr) A = area (ha). of concentration and ARI. Equation 4.1 can be applied to any ‘catchment’ if it is assumed that all of the rainfall resulted in runoff.

How is Q in CiA calculated?

Calculate peak flow using Equation 4A-5_1: Q = CIA = 0.95 × 6.12 × 0.09 = 0.52 ft3/s 3) Combined area. To calculate peak flow for the combination of the lawn and the paved area, use the flowpath associated with the longest Tc.

How do you calculate rainfall volume?

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.

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.

In which unit rainfall is measured?

The most common rainfall measurement is the total rainfall depth during a given period, expressed in millimeters (mm).

What is intensity of rainfall?

The intensity of rainfall is a measure of the amount of rain that falls over time. The intensity of rain is measured in the height of the water layer covering the ground in a period of time. We say things like: 30 millimeter of rain fell today or it rained 20 millimeter in two hours.

What is design rainfall intensity?

The design rainfall intensity is the intensity of a constant intensity design storm having the specified design return period and duration equal to the time of concentration for the drainage area.

What is C in rational equation?

c = Rational method runoff coefficient. i = Rainfall intensity, inch/hour. A = Drainage area, acre.

What is the rational method formula?

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. The peak runoff is sustained until the event duration has elapsed, and then decreases linearly to zero.

Can rainfall intensity be negative?

Effective rainfall cannot be negative and where this may occur reset it to 0. l note that in water balance soil moisture can be zero when calculated during dry episodes but the soil will be having quantifiable moisture deficit – which negative in value.

How to calculate the design rainfall intensity in Excel?

The next section presents and discusses an Excel spreadsheet for calculating the design rainfall intensity, i, based on rainfall intensity duration frequency data for the design location, and then calculating the design storm water runoff rate, Q.

How to calculate rain water runoff in Excel?

The Rational Method Equation and Parameters. A is the area that drains to the design point of interest (the drainage area) in acres (for SI units: ha ) C is the runoff coefficient for that drainage area, that is, the fraction of rainfall on the drainage area that becomes storm water runoff.

How to calculate the precipitation intensity ( IDF ) curve?

(IDF) Curves Basic Method The Precipitation Duration-Frequency-Depth (DFD)1 curves can be used to derive rainfall intensities for the Rational Method. The rainfall intensity can be determined using the following steps: 1. Determine the Mean Seasonal Precipitation from the District isohyet map. (Dwg. No. B-166). 2.

Where do I enter storm intensity in Excel?

There is also provision in the spreadsheet for entering data points for storm intensity (in/hr) vs storm duration (min) for the specified design return period. This data must come from a rainfall intensity duration frequency graph or table for the design location.