# What is the unit hydrograph method

The dataset provided here is representative of what you will generally get from a rainfall gauge.

## Derivation of Unit Hydrograph

The scatter plot hence obtained depicts the direct runoff hydrograph and the derived unit hydrograph of 2. Now this unit hydrograph can be used to derive runoff hydrographs from rainfall data! Computing Excess Rainfall using Phi Index. To do this, add all direct runoff values, and multiply the sum of all the direct runoff flows by the time interval in seconds of the series as shown below.

This spreadsheet based step demonstrates the derivation of unit hydrograph by using the excess rainfall and direct runoff data from a single historical storm event. The first step is to compute the total volume of direct runoff.

Your Account. Last Modified: The approach presented here should be applicable to any gauged watershed that has data for at least one storm event that satisfies the assumptions of the Unit Hydrograph theory.

This step uses the data for Hall Creek in Indiana. Derivation of Unit Hydrograph Introduction This spreadsheet based step demonstrates the derivation of unit hydrograph by using the excess rainfall and direct runoff data from a single historical storm event. Additional Activities and Variants. Area of Hall Creek Watershed: So, the ordinates of required UH can simply be obtained by dividing the ordinates of Direct Runoff Hydrograph by the equivalent depth of total direct runoff as shown below.

The role of unit hydrograph in hydrology is to provide an estimate of direct runoff hydrograph resulting from given excess rainfall hyetograph.

The following figure demonstrates this concept.

Unit Hydrograph Examples - Engineering Hydrology

Unit hydrograph is a direct runoff hydrograph resulting from one unit one inch or one cm of constant intensity uniform rainfall occurring over the entire watershed.

Do not forget to use appropriate conversion factors in calculations to have uniformity in the units of various quantities involved.

In the dataset for Hall Creek, excess rainfall occurs from 9: Numerical Values: