Initial Publication Date: May 26, 2015

Derivation and Application of Unit Hydrograph

Introduction

The objective of this lesson is to introduce students to the concept of unit hydrograph by allowing them to create the necessary data to develop a unit hydrograph and then apply it to a storm event to create a direct runoff hydrograph. This lesson contains steps that allows the students walk through the entire process of obtaining the necessary data, processing the data, and using the data for unit hydrograph derivation/application.

Intended Audience

This unit is intended for upper level undergraduate or lower level graduate students in hydrology, environmental engineering/sciences and geology/earth sciences.

Conceptual Learning Outcomes

Students demonstrate the understanding of total rainfall and excess rainfall
Students demonstrate the understanding of direct runoff and total runoff
Students demonstrate the understanding of unit hydrograph
Students can use unit hydrograph concept to derive runoff hydrograph from rainfall hyetograph

Practical Learning Outcomes

Students demonstrate the use of online data sources or web services for obtaining historical streamflow and precipitation data
Students can use MS Excel for computing excess rainfall and direct runoff
Students can use MS Excel for the derivation and application of unit hydrographs

Student Time

4-6 hours

Reference Documents and Files

Instructions

Get started by first getting the instantaneous streamflow data [Step 1] and 15-min precipitation data [Step 2] for a region that you are interested in. This will give you two text files with data in text format. Next convert these individual text files into a simple time series in excel [Step 3]. This will give you two excel files (call these rainfall and streamflow). From these time series, pick one storm event and copy the corresponding precipitation and streamflow data into one excel file. Convert the rainfall data into excess rainfall by subtracting losses [Step 4]. Next, convert the streamflow data for the storm event into direct runoff by separating baseflow [Step 5]. Use excess rainfall and direct runoff from steps 4 and 5, respectively to derive a unit hydrograph [Step 6]. Once you have the unit hydrograph, you can then use this to derive a runoff hydrograph for any event where you have the rainfall data. Next, pick another storm event from the rainfall excel file, and convert this rainfall to excess precipitation [Step 4] by assuming some constant loss. Use this excess rainfall and the unit hydrograph from Step 6 to create a runoff hydrograph [Step 7].

Steps within this lesson

Assessment

Unit Hydrograph Quiz: