WSP09248

• File Number: 8040.960
• Description: Section D General Studies - Dams
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/2004
• Author: Denver Water
• Title: Williams Fork Hydroelectric Project - FERC Number 2204 - Noxious Weed Survey Report
• Water Supply Pro - Doc Type: Report/Study

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up to 33 percent (USFWS 1988). Yarrow (Achillea millefolium), another FACU species,
is faithfully associated with Canada thistle in these apparently moisture-related instances
of its distribution.

Most of these populations of Canada thistle are less than one-half acre in size with typical
cover estimated at 10 percent. In one area adjacent to the west campgroundlboat launch
(NOX3-610), percent cover was estimated at 90 percent in the main area and to average
50 percent throughout. In the largest area surveyed (NOX3-604), which was delineated at
6,61 acres, patches of Canada thistle were estimated to cover perhaps one-third of the
total area, with percent cover within the patches of 30 to 50 percent. In a 2.61-acre moist
meadow located between the west dam road causeway and the reservoir, cover of Canada
thistle ranged up to 100 percent in small areas (NOX3-612). Photographs NOX3-610,
NOX3-604, and NOX3-612 in Appendix C illustrate typical conditions at these sites,
respectively,

3.2 Yellow Toadllax

Yellow toadflax is the second most widely distributed noxious weed species at the
Williams Fork Project, occurring at 14 of the 48 sites identified during the noxious weed
survey. It occurs as scattered individuals or small clumps distributed throughout the
campgroundlboat launch area on the east side of the Williams Fork Reservoir (NOX 1-
513, NOXI-516, NOXI-517, NOXI-519, NOXI-521, NOXI-523), It also occurs at an
isolated disturbed site north of the west campground/launch area (NOX 1-507), which,
being accessible by vehicle, appears to receive heavy use by fishermen. Like Canada
thistle, yellow toadflax occupies these areas in response to removal of native vegetation
and disturbance of soils associated with intense pedestrian and vehicular use of these
public access sites,

Yellow toad flax also occurs as small to medium-sized patches in grassy upland roadside
communities along the access road to the east campgroundlboat launch area (NOX 1-524
through NOX 1-526) and at the intersection of the east dam access road a'1d Grand
County Road 3 (NOX3-611 and NOX 1-509). Interestingly, it also occurs as small to
medium-sized patches in grassy wet meadows near the Williams Fork River inlet to the
reservoir with willows. Canada thistle, and oxeye daisy (NOXI-527, NOX3-613),
Photograph NOX3-613a in Appendix C illustrates habitat conditions at the latter site.
With one exception, these sites are not noticeably disturbed, and the reason for the
invasion of such sites by yellow toadflax is not apparent. At NOX3-611, yellow toad flax
and houndstongue occur together surrounding a utility pole, suggesting that their
presence there may be in response to site disturbance (see Photograph NOX3-611 in
Appendix C).

3.3 Houndstongue

Houndstongue was found at six of the noxious weed sites, Two locations are disturbed
sites within the east campgroundlboat launch area (NOX 1-508, NOX 1-509), another is a

William!. Furk Reservoir
Hydroelectric Project
January 2004

Steiger.; Corporation
NO'(IOUS Weed Survey Report

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