SPRING 2005INSTRUCTOR:
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Accessing Streamflow Data via the Worldwide Web
| OBJECTIVES: | (a) to use the worldwide web to access streamflow data; |
| (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.
Be sure to include:
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: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, just below the year 2005. 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)?
below average:
d) The flow on March 13, 2005, is much lower than the other days shown, and there's a period of about 6 hrs. when the maximum flow is steady at about 8,000 cfs. Estimate the time, to the nearest hour, when the flow begins dropping from 8,000 cfs: __________________
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.
(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, 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: 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?
| RIVER | USGS STATION # | MAF (cms) | DA (km2) | MAP (cm) |
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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:
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.
| BOULDER | WINTER PARK | |
| STATION | 050848 | 059175 |
| AVE. ANNUAL PRECIPITATION (1948-2003) (inches) |
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| AVERAGE ANNUAL SNOWFALL (1948-2003) (inches) |
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.
| BOULDER | WINTER PARK | |
| STATION | 050848 | 059175 |
| SNOW-WATER EQUIVALENCE (inches) |
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| PERCENTAGE OF ANNUAL PRECIPITATION FALLING AS SNOW |
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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:
Select the link to Current
Observations and Forecasts...... then select SNOTEL Data..... then select SNOTEL Station Time Series and Graphs and
Listings.... then Colorado. You should see a
yellow map with purple dots. Select one of the sites in Boulder
County (e.g. Lake Eldora, University Camp or Niwot) and click on the
link to Graph and Lister; the graph shows the trends in precipitation,
snow-water content (SWC), and temperature since October 1. The
smooth green and blue lines indicate the long-term "average" trends in
precipitation and snow-water content, respectively, whereas the jagged
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 try to locate 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. San Juan County has a kind-of triangular shape. How does the trend in precipitation and SWC 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.