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Project EDDIE: STREAM DISCHARGE Student Handout
This module was initially developed by Bader, N.E., T. Meixner, C.A. Gibson, C.M. O’Reilly, and D.N. Castendyk. 26 June 2015. Project EDDIE: Stream Discharge. Project EDDIE Module 5, Version 2. http://cemast.illinoisstate.edu/data-for-students/modules/stream-discharge.shtml
. Module development was supported by NSF DEB 1245707. Module was revised in October 2022 by N.E. Bader, C. Carey, and D. Richardson to repair data sources and update for the new USGS data distribution system.
Learning objectives
:
●
You will understand how to download, organize and analyze streamflow data.
●
You will learn about major climate impacts in their region.
●
You will analyze streamflow data to detect and quantify climate change impacts on water
quantity in their region.
●
You will learn about flood events and how to predict the likelihood of big flood events.
Why this matters:
Fresh water is a fundamental resource for our society. A synonym for streamflow is “discharge,” which is the volume of water passing by a point on a riverbank per unit time. Discharge is also a way to measure the quantity of water that is available for various uses. For example, water rights are often measured in units of discharge. Fish might require a certain discharge in a reach of stream in order to thrive or move through the reach. Conversely, the highest discharges result in floods that may harm people and structures. Discharge is fundamentally connected to our hydrologic cycle. Streams are fed by water that originally fell as rain and snow. Changes in the quantity of rain and snow, their distribution, and their timing, can be expected to cause changes in stream discharge. Clearly, it is important to be able to understand the way discharge varies. How can we measure these changes? We must start with data. In this activity we will use data from the United States Geologic Survey
(or USGS) network of stream gaging stations. The USGS is a governmental organization established in 1879, as part of the Department of the Interior. Originally tasked with the classification and mapping of United States public lands (and assessment of their mineral resources), the USGS has since expanded their role as a provider of impartial information on the status of ecosystems in the United States. (See http://www.usgs.gov
for more details.) Outline:
1.
Discussion of papers read for class and quick PowerPoint introduction
2.
Activity A: Variability in stream flow
3.
Activity B: Changes in discharge over time
4.
Activity C: Peak discharge and flood hazard
1
Activity A
: Variability in real stream data
Viewing and accessing data:
1.
Navigate to the USGS Water Dashboard, at
https://dashboard.waterdata.usgs.gov/
2.
Notice the colored dots, depicting real-time conditions at stream gages nationwide. The dots are colored to show you if the streamflow is unusually high or low for this day of the
year. Red colors are unusually low; blue colors are unusually high. You can click on “legend” at the upper right to see what the colors mean. For example, the dark blue color
indicates that the flow is at or above the 90
th
percentile, which tells you that at least 90% of the flows measured on this day in the past were lower. Put another way, flow is high enough to earn the dark blue dot only about 10% of the time.
3.
You can click on any of the colored dots to bring up a pop-up window with a plot of discharge over the past week. Try this now, then close the pop-up window when you are finished.
4.
Let’s look at a specific stream gaging station, on the Neversink River in New York. In the search box at the upper left, type “neversink,” then select the Neversink Reservoir in Sullivan County, New York. This reservoir is one of several that supply New York City with drinking water. You can scroll to zoom into the map and see the reservoir. Note the
gaging stations on the inflow and outflow of the reservoir. Click on the dot upstream (north) of the reservoir – you want the one called “Neversink River near Claryville, NY (Monitoring location USGS 01435000).” There are several similarly named gaging stations, so be sure you have the correct one. Click on the dot to open the popup window.
5.
Notice that there is a lot of data available for this gaging station. That is because it this station was formerly part of a smaller network of intensively monitored stations in relatively undisturbed locations. These monitoring sites are collectively called the Hydrologic Benchmark Network. (A “benchmark” is something against which other things are measured. In this case, an undisturbed stream is a benchmark against which we can measure a stream modified by human activity.) 6.
At the top of the pop-up window, click the link to open the Site Page, which is a more detailed description of the site. Take a look at the data available here: o
Notice that there is a camera view showing the river over the past few days, and even an infrared camera showing the relative temperature of the water and land.
o
The map shows the drainage basin for this gaging station, which means the area “upstream” where water that originally falls as rain or snow will eventually flow past the gaging station.
o
At the bottom, open the Location Metadata. You can see that the water draining past this point has been collected from a drainage area of 66 square miles (sorry, but the U.S. Government works in Imperial units. That’s 171 square km.)
2
7.
Scroll back to the top to see the different types of data that we can show. Leaving the range at 7 days, select “Discharge, cubic feet per second” to see a plot showing how discharge has changed over the past week.
Questions
:
1.
Look at the discharge data. How variable was discharge over the past week? You can answer this in several ways. First, what was the range (the maximum minus the minimum) of the data? Another good way to think about variability is to think about percent change. First, estimate the mean value of the data by looking at the plot. Approximately how much higher (as a percent) are the highest discharges? 2.
Where you clicked the box to select discharge data, check the box that says “Select data to graph on second y axis,” and choose water temperature. Look at the temperature graph. Based on this graph, what probably drives temperature changes in the Neversink River? Do you think there is any relationship between temperature and discharge? If so, what do you think it might be?
[Aside: don’t try to calculate percent change using temperature data because your answers won’t be meaningful. Why does percent change work with discharge but not temperature? Because of what “zero” means. For both the Fahrenheit and Celsius scales,
zero is an arbitrary temperature. When it is three degrees C outside, that doesn’t mean that there is “50% more heat” than when it was two degrees C outside. In contrast, zero discharge really does mean that there is no water movement, and a discharge of three cubic meters per second really is
50% more water movement than a discharge of two cubic meters per second.]
3.
When discharge is high enough, flooding occurs. Is the discharge you observe here unusually high? Unusually low? Typical for the region? Can we answer these questions with only a week’s worth of data?
Seasonal variation in streamflow:
We might expect flow in a stream to change seasonally. After all, most (or all) of the streamflow that you observe originated as rain and snow falling in the watershed, and precipitation in most places is seasonally variable. Let’s take a look at how streamflow changes over an entire year to see what happens.
Still looking at both discharge and temperature data, go back to the top and change the time range to 1 Year. It may take a minute to load all of the data.
4.
Question
: Temperature is high in summer and low in winter, as you might expect – but what month was the warmest? What about discharge? Was it the same all year? What months had the highest discharge? The lowest?
3
Activity B: Changes in discharge over time
B.1: Change through time on the Neversink River
Let’s go back to an important question we had at the beginning of this activity. Is stream discharge changing through time? How might we answer this question, given the seasonal variability of the data?
One solution is to reduce the variability in our data by considering summer and winter data separately. In order to do this, we will need to manipulate the data ourselves using Excel.
1.
First, export the data. We are looking for historical data (going back farther than one year), which is not available from this page. To find historical data, return to the popup window that opened when you first clicked on the map, and click on the link at the top that says “Data.” (If you closed this popup window, that’s ok: simply click on the map again to reopen it - but be sure that you click on the correct dot.). From the statistics page you opened, find and select Monthly Statistics. In the new page, check the box next to discharge, Select discharge, and leave the date range blank to get the entire date range. Choose tab-separated data in YYYY-MM-DD format, and save to file. Once you click Submit, a text file called “monthly” will be saved to your computer.
2.
Now import the data into Excel. Open Excel, and select File > Import > Text file. Navigate to your “monthly” file and open it. (If it is grayed out, you may need to change “Text Files” to “All files” in the drop-down menu under the dialog box.) The text file is delimited by tabs, so check the appropriate boxes to tell this to Excel, accepting the remaining defaults.
3.
You only need three columns: year, month, and mean discharge. Take a close look at your columns to see if you can figure out which is which. When you are confident, type “Year”, “Month”, and “Discharge” in the cells above the appropriate columns. Now you can clean up by deleting the remaining columns, as well as the rows above your labels.
4.
Now is a good time to save your Excel spreadsheet. Call it something sensible such as “Neversink monthly discharge” and save it in a folder where you can find it again. You should periodically re-save your spreadsheet so that you don’t lose your work.
Plotting discharge by month
1.
Currently your data is organized by year, and within each year it is organized by month. In order to make a plot of a particular month, you should arrange your data by month instead.
Click one of the cells in the month column and use Sort and Filter > Smallest to Largest to sort by month - you will see all of the January data first, followed by February, etc.
Select all of the data cells from February, in all three columns. (Hint: you can click once to select the top left cell, then scroll down and shift-click on the bottom right cell to select the data you want.) 4
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