Impact of Forest Service Activities on Stream Flow

• File Number: 8461.250
• Description: Water Issues
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 5/22/2003
• Author: Charles A. Troendle, James M. Nankervis, Laurie S. Porth
• Title: Impact of Forest Service Activities on Stream Flow
• Water Supply Pro - Doc Type: Report/Study

Troendle/Nankervis/Porth Page24 5/22/2003
Table 4: The nine stream gauges retaineci as Reference sites.
Site No Name of Stream a e
06710500 BEAR CREEK AIC MORRISON, CO.
06733000 BIG THOMPSON RI VER AT ESTES PARK, CO.
0675200(1 CACHE LA POUDRE R A MO OF CN, NR FT COLLINS, CO.
06620000 NORTH PLATTE RI VER NEAR NORTHGATE, CO
0672400G ST. VRAIN CREEiK AT LYONS, CO.
06623800 ENCAMPMENT RIV AB HOG PARK CR NR ENCAMPMENT WY
06625000 ENCAMPMENT RIVER AT MOUTH, NEAR ENCAMPMENT, WY
06659500 LARAMIE R AND PIONEER CANAL NR WOODS LANDING, WY
06622700 NORTH BRUSH CREEK NEAR SARATOGA, WY
SUmmary
This phase of the Plattt-I R.iver analysis had 3 outcomes. The first is the completion of the
revisions on the WRENS S hydrologic m.odel for Hydrologic Region 4, the cold snow zone of the
central and northern Rocky Mountains. :Previously, it had been anticipated that the model would
be incorporated into the current version of WRNSHED, the Canadian version of the WRENSS
hydrologic model supported by Robert Swanson. That is still an expectation, but in the interim, a
stand-alone SAS version has been developed. Although the simulation of water yield differs
from the WRENSS mode;l used in the earlier North Platte analysis Troendle and Nankervis 2000)
and the historical analysis reported o:n in this report, the predictions of change are quite
comparable. Secondary :>imulations of c;hange in flow following timber harvest at Fool Creek,
Deadhorse Creek, and Coon Creek were; more accurate and consistent using the cunent version
of the model. This was r.iot totally unexpected, however, since the current model was developed
using the data from all ithree watershed.s rather than only Fool Creek, as was the case for the
earlier WRENSS hydrolc?gic model.
Based on the projectiori of current stand conditions into the future, hydrologic simulations
indicate tha.t current streaun flow levels vn the North Platte River Basin will be further reduced by
20,000 acre-feet of annuLal water yield, or more, during the period from 1997 to 2017. Forest
removal, if continued at t:he rate at which it has occurred from 1997 to 2001, will recapture about
5000 acre-feet (0.05 area inches of watE;r yield) of tha.t reduction. Although not included in the
totals, it can be expected that tree mortallity, from both pest and fire, will increase stream flow to
some degree.
Seven to 9 stream gauges ha.ve been ide;ntified in both the North and South Platte River Basins
that may be useful in documenting future changes in water yield resulting from Forest Service
management activities. Comparative aria.lysis is achieved using long-term snow courses and
precipitation gauges. Troendle and Nank:ervis (2000) noted earlier that detection of flow changes
that result from vegetal;ion changes vvill be difficult using the USGS gauging stations as
reference sites. The longer the post-199'l record, the greater the probability of change detection,
should change occur. :[t is critical that monitoring at all reference sites (stream flow,
precipitation, and snow pack) be continued in the same manner as done presently. We found in
our analysis that proceduxal changes, such as moving gauge sites or conversion of manual snow