Hydrology and Water Resources, UO

Geography 4/525

Exercise 7: Evaluating dam impacts on runoff with the

Indicators of Hydrologic Alteration (IHA) model

authored by Paul Blanton and W. Andrew Marcus

In previous labs on runoff you focused exclusively on estimating the probability of peak flood discharges. But in nature, the peak discharge is a rare event. The probability of low flows, the duration of flows of a certain magnitude, and the variability of flow from day-to-day are often more important to organisms, water supply, and modifying physical habitat than are peak flows. This exercise introduces you to a technique for characterizing some discharge metrics other than peak flow– and the impacts of a dam on those measures.

You will be using the Indicators of Hydrologic Alteration (IHA) model developed by the Nature Conservancy to examine thevariations in discharge. Although IHA was initially developed for understanding the ecological impacts of dams, it is an excellent model for documenting and understanding both natural and altered discharge regimes of streams. The IHA model is available for free from the Nature Conservancy.

The exercise takes you through the following specific activities:

Learning about the IHA model through an introductory article, the manual, and an article that evaluates dam impacts using IHA.

Downloading IHA onto your computer (see us if you do not have access to a computer on which you can download programs).

Using IHAto document components of the discharge regime for the BillWilliamsRiver in Arizona and changes in those components due to dam operations.

The materials you will turn in are:

Annual graphs of average monthly flows and daily flows, an environmental flow metrics graph, and graphs of 30 day duration minimum discharges for October and 1 day maximum flows for October.

Typed answers to the questions at the end of the lab

Please turn in your tables, graphs and answers by the time posted on the class web site. Late assignments will be penalized 15% per day, unless you have a documented excuse. Answers to the questions must be typed to receive credit.

1. Learning about the IHA Program (NOTE: IHA requires a Windows-based platform)

Before starting the exercise, you should read the description of IHA in the Conservation Ecology article that officially introduced the IHA model (Richter et al., 1996). Brian Richter, the lead author, was the person at the Nature Conservancy who led the development of the IHA model. Also look at the IHA manual to get guidance about the model and some of its potential outputs. Both the article and the manual are available on our password protected website, or at the site you will visit to install your software.

In addition, read the article by Magilligan and Nislow (2005), who used IHA to conduct a nation–wide assessment of the impacts of dams on the hydrologic regime. This article has rapidly become one of the most widely cited articles regarding the nature of dam impacts of river flow. Not only does it provide important insights on how reservoirs affect stream flow in different climates, but it also is an excellent example of how models can be an important tool for scientific investigation.

2. Downloading and Installing the IHA Program

You will need to download the IHA model onto a computer (visit me if you do not have access to a computer where you can do this). The total size of the downloads is ~5 meg, so download it from a high speed connection.

To download the model, go to:

The Nature Conservancy asks you to fill out a brief registration form (they only use this to see what kinds of folks are utilizing the model – it is not used for tracking you). Also download the manual from this site. I suggest you create a folder call IHA in your Program Files folder (e.g. C:\Program Files\IHA\) - save the download files to this folder. Once it is downloaded, follow the instructions for installing the program.

Once it is installed, start the IHA model.

3. Running the IHA Program

Once installed, you can start IHA using windows commands:

Start → Programs → Indicators of Hydrologic Alteration is where it all happens…

Start the IHA tutorial, and start the IHA program. The tutorial and the ‘wizard’ will guide you through an example of using the IHA model to analyze the impacts of a dam on the Bill Williams river in Arizona. (Note: If the wizard doesn’t appear when you start the IHA program or if you accidentally cancel out of it, you can make it reappear by clicking on ‘IHA’ at the top of the IHA model, and choosing ‘wizard.’)

Work your way through part I of the tutorial (up through page 10). Part II shows you how you can tinker with the inner guts of the model, rather than accepting the default settings.

Questions Name:

Exercise 7, IHA modeling of dam impacts

Type your answer the following questions, limiting your answers to one to two paragraphs.

  1. Under the “Other Graphs” tab, select “Monthly Flows.” Save the graph. How has the dam altered the annual hydrograph of average monthly flows? (i.e. what seasons are higher, which are lower, which are the same?). Why would the dam operation alter flow in this way?
  1. Also under the “Other Graphs” tab, select “Daily Data.” Save the graph. What is the big difference you see between the daily data before and after the dam was installed? Why is this?
  1. Also under the “Other Graphs” tab, select “Hydrologic Alteration.”Print out the graph. What kind of information is this graph showing you, and what is it telling you about particular types of impacts this dam is having on the river? (consult the IHA help menu or the Richter article, if need be).
  1. Under the “Annual Data Graphs” tab, select the month of October. Then select the “Minimum Flows” tab and the “30-day minimum.” Print out the graph. How has the dam changed the magnitude of the 30-day minimum flow? What are the implications of this for riparian and aquatic ecology along the river?
  1. Now make a graph of maximum 1 day flows for October. This will show you the pre and post dam distribution and magnitude of big flood events (remember that the 1-day flood is the biggest 1 day event in a given year). Given what you know about dam effects on hydrology in general, does this graph make sense?Why?
  1. Play around with the model and create some graphs of you own choosing to explore the dam impacts on stream function. What do you perceive as strengths of this model? What are some potential weaknesses?

Please turn in your graphs and answers by the time posted on the class web site. Late assignments will be penalized 15% per day, unless you have a documented excuse.

References:

Magilligan, Francis J. and Nislow, Keith H., 2005. Changes in hydrologic regime by dams.Geomorphology 71: 61-78.

Richter, Brian, Baumgartner, Jeffrey V., Powell, Jennifer, Braun, David P., 1996, A Method for Assessing Hydrologic Alteration within Ecosystems. Conservation Biology 10:1163-1174.