Assignment on the Hydrologic Cycle and Water Resources
For discussion in class on Tuesday, Oct. 31

Our topic is the hydrologic cycle and water resources, and for this assignment I would like to have you do two things.

1. First, I want you to look up real-time water data from the U.S. Geological Survey, which maintains a district office in every state that collects data at a series of gaging stations. Some states have only streamflow data online, but some also have precipitation data. I prefer that you find a stream gage for a site where precipitation data are also available, and to reproduce the plot that shows both precipitation and streamflow data. Among the states that post precipitation data are: Maryland, Indiana, Kentucky, Wisconsin, Illinois, Arkansas, Alabama, Louisiana, Mississippi, Texas, Oklahoma, South Dakota, and the Puerto Rico office which includes stations from the Caribbean and several countries in Central America.

It might make sense to check recent weather and find a place where it seems to have been raining. Once you've decided on a state, click on that state on the map at the site referenced above. This will take you to a page where you have the option of going to that state's Water Resources page; you should take this option. Once you've arrived at the Water Resources Division's district office home page for that state, look for the real-time data and in particular look for the list of stations with rainfall data. You can look up both rainfall and streamflow data at the same time. You should also be able to get a table with the data used in the graph.

Compare the trend in the streamflow graph with the trend in the rainfall graph - i.e. discuss how streamflow or runoff appears to be related to the pattern of precipitation. Bear in mind that (1) some rivers are regulated by dams and may show relatively little response to short-term precipitation trends; and (2) depending on the size of the watershed, there may be a substantial time lag between a precipitation event and any rise in the hydrograph. In fact if the watershed is fairly large, you may not see much impact on the hydrograph unless the precip is fairly intense.

Try to find out how much time elapsed between the peak of the precipitation event and the peak of the hydrograph. Also find the drainage area for the stream gage at this site. We will combine results in class to see if we can find any relationship between drainage area and the time lag or elapsed time.

2. Next we will relate the annual cycle of runoff to the climatic regime for one of the rivers described in "Water balance in major rivers of the world." Visit this site and pick a river after first checking to see where it is; post your choice of river to the discussion board so we make sure that we get a sample of rivers from different climatic regions. The upper part of the plot you will get when you click on your river name is a bar graph showing monthly precipitation and evaporation estimated for the site. (The rest of the plot is hard to read.) Print out this plot and save it.

Next visit the Global River Discharge Database and click on "Geographically Referenced Data" and then click on the area of the world where your river is located. You may need to look up the geographic coordinates of the river station you have chosen in order to figure out where on the map to find it. Once you click on the world map, this will bring up another map with 5x5 degree grid squares, and you will need to choose the one where your station is located. Inside those squares you will see red targets representing river gages. Click on one of these and you will get a station name with geographic coordinates and upstream drainage area (upper left-hand corner) as well as a time-series plot and a view of the data file with mean monthly discharge for every year in the record. Look around until you find a station on your river at the location you chose previously. If you click on "Site Time Series Data" you will get a text file that you can save and import into a spreadsheet. Save the file as a text file under the station name, then import it into Excel. The "Text Import Wizard" will format it for you if you just keep clicking "Next" until you get to "Finish".

What you want to do now is to calculate the mean discharge for each month (leave out the missing values of -9999, otherwise they will mess up your results). If you don't know how to do this, we'll do a demonstration in class. Finally you will prepare a bar graph illustrating the annual pattern of mean monthly discharge.

Next, using the chapter 10 links on global climate, either get a climograph that is already prepared, or look up a city or town name in the region where your river station is located and get tabulated average monthly temperature and precipitation data for that site, from which you can prepare your own climograph. (Note: not all stations have both precip and temperature, so you'll have to check this to make sure precip data are available.)

Using the climograph and looking at your world map of the Koppen climate classes, describe what you would expect to see in terms of the annual cycle of river runoff. Keep in mind that river levels are responding to the balance between precipitation and evaporation. Compare the data shown in the climograph with the patterns of precipitation and evaporation shown in the first plot you downloaded, and with the annual pattern of runoff that you generated in your spreadsheet. Use these climatic factors to explain the annual distribution of runoff. If there is a problem or a discrepancy, explain what you would expect to see and indicate how the actual runoff pattern is different from what you might have expected.