GEOG 1011
LANDSCAPES and WATER
-----HYDROLOGY INTERNET LAB-----
SPRING 2008
INSTRUCTOR:
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Accessing Streamflow Data via the Worldwide Web
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OBJECTIVES: |
(a)
to use the worldwide web to access streamflow data; |
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(b)
to compare precipitation/runoff characteristics of rivers in different
regions. |
BACKGROUND: The National Weather Service (NWS), the US Geological Survey (USGS), and various other federal and state agencies in the US share the responsibility of collecting, reporting and maintaining hydrologic data. There are literally thousands of precipitation and streamflow-measurement stations across the country. Some of these stations have been in operation for over 100 years and they record data at frequent intervals (e.g. every 15 minutes). As you can imagine, vast amounts of hydrologic data are available, and these data can be used for a variety of purposes.
DATA: The USGS maintains a comprehensive web site that provides information on current streamflow conditions, summaries of recently published reports, and access to historic streamflow and water quality data. The address of the USGS water resources site is:
ASSIGNMENT:
You may print out this assignment and answer the questions in the spaces provided, OR to save paper, you may simply answer on a separate piece of paper, clearly identifying the question number, e.g. 1a) 1b) ..... 6a) 6b) and so on.
You will need graph paper to complete this assignment, or print the lab and use the graphs provided.
Be sure to include:
- your name
- your section & T.A.
HINT:
Open TWO WINDOWS in you web browser. Keep the assignment on one
page and use the other page as a base to access links. This will allow you to
have the questions available as you look at the reference sites.
1. Open the USGS water resources web site http://water.usgs.gov/
a) Select the small map of the US labeled WaterWatch http://water.usgs.gov/waterwatch/
b) List two general regions of the country where streamflows are presently above / below average:
above average:
below average:
c) Select the state of Arizona. You should see a map
showing the locations of gauging stations in Arizona. Locate the station
south of the northern border of Arizona (when you scroll over the dots the
station name appears). Carefully select the station marked with the
colored dot corresponding to the COLORADO RIVER at LEES FERRY (09380000).
Scroll down the page until you see a graph of streamflow (hydrograph).
How do you explain the oscillating pattern of streamflow at this location
(hint: this gauge lies 15 miles downstream of Glen Canyon Dam)?
d) Estimate the approximate time of the peak flow on March 15, 2008, to the
nearest hour: __________________
(If March 15th not displayed then select more
days on the tab above the graph then hit "get data")
e) Step back to the map of Arizona. Select the station located about 1 inch (on the screen) to the south-southwest corresponding to the COLORADO RIVER NEAR GRAND CANYON, AZ (09402500); this station is usually marked with a green or orange dot. This gauge lies 87 miles downstream of the Lees Ferry gauge. The same fluctuations that occur at the upstream gauge occur here, except the timing (phase) of the peaks is offset. (HINT: The peak on this gauge occurs the day after the same peak at Lee’s Ferry).
(i) Let's try to estimate the offset of the peaks, which is the time it takes for a 'flood' wave to move from the Lees Ferry gauge to the Grand Canyon gauge. To do this, select a peak at the Grand Canyon (downstream) gauge with a shape that is similar to a peak at the Lees Ferry (upstream) gauge. If all the peaks look alike, change the number of days to 8 or more, and you should see one peak that's lower/higher than the rest. Estimate the time between the two peaks, in hours, then convert to seconds:
wave period = ____________ hours
____________ seconds
(ii) Assuming the distance between the gauges is 87 miles, convert that distance to feet and estimate the speed of the wave, in feet per second:
wave speed = ____________ feet per second
e) Scroll up a little bit to the blue bar labeled Available data for this
site and select "Surface-Water: Field Measurements". This
table lists data obtained from streamflow measurements. Note that the
values of mean velocity range from about 2.5 ft/sec to 3.5 ft/sec. How do
the measured flow velocities compare with the wave speed estimated in (ii)
above. What do you conclude?
2. In addition to streamflow and water quality data, the USGS provides
information on drainage basin characteristics for many streams and rivers (e.g.
drainage area, average elevation, channel gradient, mean annual precipitation,
percent forest cover, etc.). These data can be used to develop relations for
streamflow and floods in basins where there are no gauging stations.
Table 1 below lists flow and basin characteristics for 12 high-elevation
streams in Colorado.
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Table 1. Values of mean
annual flood (MAF), drainage area (DA), mean annual precipitation (MAP) and
average channel slope (SLOPE) for 12 streams in the Rocky Mountains of
Colorado. |
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RIVER |
USGS STATION
# |
MAF (cms) |
DA (km2) |
MAP (cm) |
SLOPE (m/m) |
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NF Michigan River |
6616000 |
5 |
55 |
66 |
0.040 |
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Clear Creek |
6716500 |
30 |
376 |
66 |
0.051 |
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S St. Vrain Creek |
6722500 |
7 |
37 |
76 |
0.051 |
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M Boulder Creek |
6725500 |
13 |
94 |
69 |
0.060 |
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Big Thompson River |
6733000 |
31 |
355 |
72 |
0.039 |
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Poudre River |
6747500 |
58 |
515 |
69 |
0.021 |
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SF Poudre River |
6748600 |
15 |
234 |
70 |
0.015 |
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Colorado River |
9011000 |
21 |
264 |
70 |
0.015 |
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Fraser River |
9024000 |
10 |
71 |
79 |
0.006 |
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SF Williams Fork |
9035900 |
8 |
71 |
83 |
0.037 |
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Williams Fork |
9036000 |
29 |
231 |
83 |
0.035 |
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Snake River |
9047500 |
15 |
149 |
91 |
0.051 |
a) Suppose you are hired by the Summit County Planning Department to develop
a simple relation for estimating the discharge of the mean annual flood (MAF)
on an ungauged stream near Breckenridge, CO. In the absence of streamflow
data, your can try to estimate the MAF on the basis of drainage area (DA), mean
annual precipitation (MAP), or some other variable, such as average channel
slope. Using the data in Table 1 and the graphs below, plot the relation
between DA and MAF, and MAP and MAF.
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b) On the basis of these graphs, which of the two variables- DA or MAP- is
better for predicting the MAF? Why?
3. Precipitation data are collected and maintained by the National Weather Service. Data from weather stations in Colorado can be retrieved from the Office of the State Climatologist in Fort Collins. These data can be accessed as follows:
http://ccc.atmos.colostate.edu/
This site provides a variety of information, including useful summaries of the state's climate, as well as information on extreme weather and drought. To retrieve weather data select Data Access.
a) Scroll down to the section headed Long Term Climate, and select Colorado. On the next page, select Web Resources. On the next page select Colorado Climate Summaries Prepared by the Western Regional Climate Center. You should see a map showing the locations of weather stations in Colorado
b) Scroll through the list of stations on the left, and select the link to Boulder.
Complete the table below using the information provided. Repeat this for
the Winter Park weather station.
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BOULDER |
WINTER PARK |
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STATION |
050848 |
059175 |
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AVE.
ANNUAL PRECIPITATION |
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AVERAGE
ANNUAL SNOWFALL |
c) The density of fresh snow is about 1/10 that of liquid water, thus 10 inches of snow is roughly equivalent to about one inch of water. Using this assumption, convert the depth of snowfall at both stations to an equivalent depth of water.
d) Calculate the percentage of total annual precipitation that falls as snow
at both stations. Show your work in the space to the right of the table.
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BOULDER |
WINTER PARK |
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STATION |
050848 |
059175 |
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SNOW-WATER
EQUIVALENCE |
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PERCENTAGE
OF ANNUAL PRECIPITATION |
4. Table 2 compares NWS measurements of annual precipitation in Nederland, CO, with
USGS measurements of discharge in Middle Boulder Creek near Nederland. On the
graph below, plot the values of MAQ and MAP for each year; use the scale along
the left axis to plot values of MAP and use the scale along the right axis to
plot values MAQ. You might want to use different colors or symbols for
each data set.
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a) Does there appear to be a trend (upward or downward) in precipitation or
streamflow during this period?
b) Does there appear to be a correlation between precipitation and
streamflow? If not, can you explain why?
5. The Natural Resources Conservation Service (NRCS) maintains a network of stations that are used to track snowfall and snow accumulation (snowpack) throughout the western US. Snow accumulation is measured periodically along established survey lines called snow courses; real-time measurements of snowfall and snow-water equivalence (SWE) are recorded at automated sampling stations called SNOTEL sites. Real-time and historical data from the SNOTEL sites can be retrieved from the following web site:
http://www.wcc.nrcs.usda.gov/snow/
Click on the state of Colorado on the map...You should see a map of Colorado with red and blue dots indicating SNOTEL sites. Select one of the sites in Boulder County (e.g. Lake Eldora, University Camp or Niwot – scroll through the list or click on the dots); for many of the sites a photo of the actual location will appear with a data table. Click on the “Daily Graph” link for Snow Water Equivalent under “Current Water Year”; the graph shows the trends in precipitation, snow-water equivalent (SWE), and temperature since October 1. The smooth orange and blue lines indicate the long-term "average" trends in precipitation and snow-water content, respectively, whereas the jagged red and blue lines indicate the trends so far this year.
a) How does the trend in precipitation and SWC this year compare with the long-term trend? Estimate the difference, in percent = (this year - long term)/ long term.
b) Step back to the map of Colorado and scroll to the Molas Lake station; Molas Lake is in the middle of a cluster of stations in San Juan County, in the southwest part of the state. How does the trend in precipitation and SWE at this station compare with the long-term trend? Estimate the difference, in percent = (this year - long term)/ long term
You might want to bookmark this site for future reference.