Watershed Modeling

In this assignment, you will use a watershed model to investigate the impact of different types of human development on the potential for flooding and on water quality. Watershed models are computer programs which allow citizens, city planners, developers and scientists to analyze the impact of rural and urban development on the local and regional surface waters and groundwater. Watershed models can be used to predict the likelihood of flooding, investigate the causes of water pollution, and manage water resources in protected habitats.

Although this assignment is specific to the two watersheds into which Murfreesboro surface waters flow, it can be used for any watershed in the United States. Murfreesboro is ideal for this assignment because it is one of the fastest growing cities in the United States.  The models you will run use data from agencies such as the U.S. Geological Survey and the U.S. Department of Agriculture, and specifically address the issues of flooding potential and water quality. Please read Chapter 9 in your textbook before beginning the assignment and review the definitions of the underlined terms. Consider the following information in interpreting your watershed model data.

All answers must be typed in bold.

Watershed – An area of land that separates waters flowing into different rivers, basins, or seas. On a map, a watershed is defined by a drainage divide (watershed divide).

Importance – The surface water features and storm water runoff within a watershed ultimately drain to other bodies of water. It is essential to consider these downstream impacts when developing and implementing:

  • Water quality protection for drinking and other domestic purposes, as well as wildlife protection
  • Development of natural land into ‘structural landscapes’ (housing developments, shopping centers, office buildings, parking lots, etc.)
    • Most structural landscapes are impervious to the infiltration of water, resulting in an increase in storm water
  • Development of natural land into agricultural land
    • Different crop types have different evapotranspiration properties
    • Fertilizers, pesticides and herbicides may become concentrated in downstream areas of the watershed
  • Preservation of agricultural and forested lands
    • Agricultural and forested land allow more water to return to the atmosphere by evapotranspiration and to the groundwater by infiltration.

 

 

 

 

WikiWatershed is a web-based application that allows citizens to examine and analyze factors which affect water quality within their local watershed.

Examine factors which impact precipitation and storm water runoff in Murfreesboro. (The app can be used to do the same in any watershed in the United States.)

Wikiwatershed Instructions:

  • Go to org
  • Launch the App under ‘Model My Watershed’
  • Click on ‘Get Started’
  • Click on ‘Select Boundary’
  • In the dropdown box, click on ‘USGS Watershed Unit (HUC-10)’
  • The red lines on the map outline the watershed units. Your map should be of Murfreesboro. If it is not, type ‘Murfreesboro TN USA’ in the search box. The map will move to Murfreesboro.
  • Zoom out, and you will see that Murfreesboro is largely divided into two watershed units.
  • Click on the western watershed unit.
  • Turn on ‘streams’ in the Layers box (it may already be on).
  • Under Layers, click on ‘Continental US Medium Resolution Stream Network’
  • Open a separate window, and go through the above steps for the eastern Murfreesboro Stream Network.
  • Compare the two maps to answer questions 1 – 5.

Part 1 – Watershed Characteristics

  1. The city of Murfreesboro is divided into two watersheds. What are their names?

 

  1. Which watershed has the greatest amount of forested land? (You can find this by clicking on the ‘Land’ link at the top of the box on the left of the screen.)

 

 

  1. Which watershed has the greatest amount of developed land?

 

 

 

 

 

  1. What factor(s) do you think have resulted in the difference in the amounts of forested and developed land in the two watersheds? (In answering this question, think about why development preferentially occurs in one watershed versus the other.)

 

 

  1. Based upon the above analysis, in which watershed do you predict the likelihood of flooding is highest?

Why?

 

 

 

 

Part 2 – Strom Models

 

We also can predict the likelihood of flooding within a watershed using a simple 24-hour storm model. This model assumes average rainfall during a typical 24-hour storm event. Consider the following when answering the storm model questions.

 

  • Evapotranspiration – The amount of water that is evaporated and returned to the atmosphere by plants
  • Runoff – The amount of water which runs over the surface into streams and rivers
  • Infiltration – The amount of water which infiltrates the soil and enters groundwater
  • At the upper left window are the words ‘Analyze, Monitor, Model’. Click on ‘Model’.
  • Click on ‘Site Storm Model’ for each watershed.

 

 

  1. Run the 24-hour storm model for each watershed and fill in the following data.

 

  West Fork Stones River West Fork Stones River East Fork Stones River East Fork Stones River
  Water Depth (cm) Water Volume

(m3)

Water Depth

(cm)

Water Volume

(m3)

Runoff

       
Evapotranspiration

       
Infiltration level

       

 

  • Compare the two models and answer questions 7– 8.

 

 

 

  1. Do the results of the model support your prediction in question 5? Explain using data in the above table.

 

 

  1. Which of the three data types is most significant in assessment of your prediction, if any? Why?

 

 

 

Part 3 – Water Quality

We also can use a watershed model to examine the effect of a 24-hour storm on water quality by examining the following variables. These variables reflect the amount of solid and dissolved mater in our streams and rivers, much of which is the result of human development and activities.

  • Click on the ‘Water Quality’ link in the upper left window.
  1. Fill in the following data for both watersheds.

Load = the amount of the variable (solid, nitrogen, or phosphorous) in surface waters
Loading Rate = the rate at which the variable is being added to surface waters
Average Concentration = the mean of variable concentration in all surface waters

 

  West Fork Stones River West Fork Stones River West Fork Stones River East Fork Stones River East Fork Stones River East Fork Stones River
Quality Measure Load (kg) Loading Rate (kg/ha) Ave Concentration

(mg/L)

Load (kg) Loading Rate (kg/ha) Ave Concentration

(mg/L)

Total Suspended Solids

 

           
Total Nitrogen

 

           
Total Phosphorous

 

           

*kg = kilograms                 *kg/ha = kilograms per hectare                  *mg/L = milligrams per liter

  • Use the data to answer questions 10 and 11.

 

 

  1. In which watershed is the concentration of total suspended solids highest? Why do you think this difference occurs?

 

 

 

 

  1. What is a possible explanation for the similarities or differences in concentrations of dissolved nitrogen and phosphorous in the two watersheds? (In formulating your answer, think about/investigate the source(s) of nitrogen and phosphorous.)

 

 

 

 

 

 

Part 4 – Middle Tennessee State University Hydrologic Setting

 

  • In each watershed window, in the Layers box click on the ‘Basemaps’ icon on the lower right.
  • Choose ‘Streets’
  • Zoom in to find the MTSU Campus (between Greenland DR. to the north, and E. Main St. to the south).

If you have ever been on the MTSU campus during heavy rain or over several days of rainfall, you know that the streets, parking areas and even grassy areas do not drain well. Let’s explore the problem in questions 12 – 20.

 

  1. In which watershed(s) is/are the MTSU campus included? Does all water which falls on the MTSU campus flow into the same watershed?

 

  • In the ‘Layers’ box, click on the Coverage icon and then choose ‘National Land Cover Database’

 

 

  1. Compare the density of MTSU campus land development to the immediate surrounding areas. (Darker red colors indicate higher density land development.) Many MTSU students, faculty members and administrators think of the MTSU campus as being campus open with wide ‘green’ spaces. Is this really true with respect to the campus hydrologic setting? What is your evidence from the land cover database?

 

 

 

 

  • Locate Rutherford Boulevard on the east side of campus. On the east side of Rutherford Boulevard, next to the large parking lots, are two bodies of water.
  • Review text sections 9.9 – 9.11 on groundwater and then answer the following questions.

 

 

  1. What hydrologic term describes these two bodies of water? (Hint: Note that there are no streams leading to or from either body of water.)

 

 

 

  1. How do you think MTSU uses these bodies of water to manage water on the east and northeast side of campus?

 

 

 

 

 

 

  1. Since there are no streams leading from these bodies of water, where does the water they hold flow? (It does not all evaporate.)

 

 

 

 

  1. What are the potential environmental consequences of MTSU’s use of these water bodies on water quality in the East Fork Stones River watershed?

 

 

 

 

 

 

  1. Examine the southwest side of campus (that part of campus within the West Fork Stones River Watershed).

 

Are there major streams into which campus surface waters flow?

 

 

Are there water storage bodies, such as on the northeast side of campus?

 

 

What problem does this create for draining from the west and southwest part of the MTSU campus into the West Fork Stones River Watershed?

  1. Think about the residents living to the immediate west and southwest of the MTSU campus. What potential problems does campus high density development and lack of natural drainage features present to these residents?

 

 

 

 

  1. List three ways in which MTSU could do (have done) a better job managing surface water runoff as the campus develops(ed).

 

 

 

 

If you are interested in learning more about how MTSU handles stormwater runoff or volunteering to improve MTSU’s surface water environmental impact on surrounding communities and ecosystems, please take a few moments to explore the MTSU Stormwater website.

 

 

 
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