WSP03031

• File Number: 8543
• Description: Closed Basin Division
• State: CO
• Basin: Rio Grande
• Water Division: 3
• Date: 6/1/1981
• Title: Fish and Wildlife Plan - Closed Basin Division - San Luis Valley Project
• Water Supply Pro - Doc Type: Report/Study

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V'J be all wetlands within 1,000 feet of the channel and which were located to the
.~~ south-southwest of the channel. Direction of flow is important since overland
,',:) flows in Stages 3-5 generally come from the north-northeast direction. The
(~) wetlands adversely affected by conveyance channel construction were determined
to be 4,946 acres.

The road construction adjacent to the wetlands was estimated to affect about
80 acres, based on a 20-foot road width. Only direct displacement of wetland
acreage was considered here.

The total acreage of wetlands adversely affected by conveyance channel and road
construction is therefore 5,026 acres. Approximately 25 acres of the 5,026
acres of wetlands affected by conveyance channel construction occur on the
Blanca WHA. '

The acreage of wetlands in the project area that could be potentially impacted
by project pumping was also determined. These wetlands were determined using
the 1978-1980 water table maps as having ground ,water within 2-1/2 feet of the
ground surface. Wetlands with ground water within 2-1/2 feet of the ground
surface but outside of the projected USGS drawdown areas were deleted. Wetlands
impacted by the construction of the conveyance channel were not included again
under wetlands affected by project pumping impacts. A final delineation was
made to include only the percentage of wetlands that was shown to have high
infiltration rates (0.25 foot/day) from BR infiltration tests in the project
area.

Using the above criteria, it was determined that 3,434 acres of wetlands would
be adversely impacted by water drawdowns. Approximately 173 acres of the 3,434 '
acres of drawdown affected wetlands occur on Blanca WHA, while about 670 acres
of wetlands in the San Luis/Head Lake area are affected.

Thus, total wetlands adversely impacted by the project would be 8,460 acres.

In addition to the quantifiable impacts to wetlands identified above, a whole
series of indirect impacts could be expected, mainly as a result of decreased
plant vigor when ground water tables are drawn down. The following items
illustrate this thought:

(a) Increased wind erosion of soils, which could lead to more sediment
deposition in wetland depressions;

(b) Reduced biomass in the wetlands as vegetation species lose their vigor
and experience decreased density;

(c) Reduced retention time of overland (surface) runoff coming into
existing wetlands. As the project area in the vicinity of these wetlands becomes
"drier" due to drawdown pumping, more of the surface runoff will tend to
infiltrate into the ground quicker. Retention of surface runoff in the existing

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