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)Introduction to Hydrology (Geog 3511)
Fall 2012
Assignment 1: The Water Balance and Catchment Manipulation
| Section | Lab | Assigned | Due |
| 012, 013 | Tuesday | Tuesday, Sept 4 |
Friday, Sept 7 |
| 011 | Thursday | Thursday, Sept 6 | Monday Sept 10 |
Write Tuesday or Thursday at the top of your assignment depending on what lab you are in
40 possible points. Each of the four questions is worth 10 points.
WRITE THE QUESTION AT THE START OF EACH ANSWER.
SHOW ALL YOUR WORK.
MAKE SURE TO INCLUDE UNITS.
LIST ASSUMPTIONS. CITE SOURCES FOR EQUATIONS AND CONSTANTS.
WRITE NEATLY and LEGIBLY.
To introduce you to the concept of the water balance;
To apply that knowledge in an interesting situation.
The data (below) derive from the Wagonwheel Gap Experiment, a classic paired basin study of 75 years ago. These data come from the experimental basin only. The catchment is in the upper Rio Grande valley (between South Fork and Creede) at about 10,000 ft elevation. It has an area of about 200 acres and was studied in the period 1910-1926. In 1910, 25% of it was covered by uncut spruce-fir forest, 61% by aspen, and 14% by grass meadows. In 1919-1920, the forest was cut, all large timber removed and the slash burnt (Sept 1920 for the last). By 1926, aspen regrowth over the catchment had reached 3 ft to 6 ft in height.
| Year | Precip () |
Runoff () |
Year | Precip() |
Runoff () |
| 1911 | 21.5 | 8.4 | 1919 | 21.8 | 8.6 |
| 1912 | 19.7 | 5.3 | 1920 | 22.5 | 8.3 |
| 1913 | 21.9 | 5.6 | 1921 | 20.5 | 8.7 |
| 1914 | 19.8 | 5.4 | 1922 | 23.8 | 7.2 |
| 1915 | 21.1 | 4.5 | 1923 | 16.8 | 8.0 |
| 1916 | 22.8 | 9.9 | 1924 | 22.4 | 5.0 |
| 1917 | 18.8 | 3.5 | 1925 | 18.1 | 5.1 |
| 1918 | 21.2 | 6.0 | |||
Years are water years, i.e. October 1 - September 30. Precipitation and runoff values for each water year are in inches.
Estimate evapotranspiration (
) for each
year. Assuming there is not change in storage (
).,
you can estimate 
as the
residual difference between Precipitation and Runoff (i.e. using a
water balance model).
Estimate the catchment efficiency for each year (%). In terms of water as a resource available for use, efficiency can be defined as the percentage of precipitation that was converted to runoff.
Graph the changes in precipitation (
), runoff (
),
evapotranspiration (
), and
efficiency through time. Mark on your graphs the 1919 -1920 period when
conditions in the basin changed.
Use your results to answer the question "Did clear cutting have an effect on runoff or efficiency?" Briefly (ca. 5 lines), give reasons for drawing the conclusion you have.
Even with a small data set like this one, you will find that using a spreadsheet routine (e.g. EXCEL or QUATTRO-PRO) will prove more efficient than manual labor. By allowing you to copy operations across multiple cells and graph data as X Y Plots it will give you cleaner and more consistent results than your own calculator and pencil work.