Estimating Additional Water Yield from Changes in Management

• File Number: 8461.250
• Description: Water Issues
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 5/12/2000
• Author: Charles A. Troendle, James M. Nankervis
• Title: Estimating Additional Water Yield from Changes in Management
• Water Supply Pro - Doc Type: Report/Study

( _ ., .`..
.r>
800
? 700
w
?
0 600
u.
? 500
? 400
Q 300
a?
? 200
?
(U
¢ 100
0

N
r? ?
? •
.? '
•?
??.

0 100 200 300 400 500 600 700 800
Cumulative ELOLJI Seasonal Flow (in)

Figure 9: Cumulative d'ucharge from Fool Creek (harvested) plotted over the cumulative discharge for
East St. Louis Creek (control) at the Fraser Experimental Forest. A represents the beginning
of ineasurement (1943), B represenu the abrupt impact of harvest (1955), and C represenu 1996.
As an example of the problems associated with defining the response from
timber harvest at the landscape scale, Kircher et al. (1985) evaluated those
factors most responsible for influencing natural stream flow characteristics
in western Colorado watersheds. Based on analysis of the long-term record
from 123 USGS gauging sites in western Colorado, only drainage area and
mean basin elevatinn were found to be significant parameters in predicting
mean annual flow. Percentage of the total watershed area in forest, or
percentages of watershed area in other land use categories, were not a
significant parameter in predicting either annual mean flow or any other
stream flow characteristics Kircher et al. (1985) and others elsewhere have
been unable to show that the percentage of watershed in forest is corre at d
with stream ow at landscape scale. In landscape scale watersheds, such as
those gau eg d by the USGS, forested area is often only a portion of the total
area. If the actual amount of forest vegetation is not well correlated with
flow at this level, change in the density of vegetation is equally unlikely to
be related as well. One can assume that detecting the effect of subtle
changes in forest vegetation over time, even where they occur, would be
difficult. As part of ongoing work (unpublished) by C. A. Troendle to
develop improved, flood forecasting equations for western Colorado and
Wyoming, the percent of forested area in the watershed did not prove to be
significant in describing peak stream flow response at the landscape level;
i.e., using USGS stream flow data. At the landscape scale, many factors
influence stream flow generation, including the variance and errors
associated with monitoring flow at this scale and resolution; all of which
18