WSP11035

• File Number: 8541
• Description: San Luis Valley Project
• State: CO
• Basin: Rio Grande
• Water Division: 3
• Date: 9/30/1982
• Title: Final Supplement to Final Environmental Statement
• Water Supply Pro - Doc Type: EIS

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2. Effects.
8,460 of the existing
ect boundaries.

Construction and operation of the p~oject will affect
43,122 acres of wetlands (wetland habitats) within proj-

An overall reduction of total plant (biomass) production will occur in wetlands
which are located over shallow water tables of 5 feet or less below the natural
ground surface. Also, the retention time of spring surface snowmelt runoff in
some wetlands that normally receive annual runoff will be decreased. Lowering
the shallow water table beneath these wetlands will result in an increased soil
infiltration rate and, thereby a shortened time period during the summer when
surface water was present. Evaporation is the primary cause of water loss from
wetland areas.

Drawdown pumping will in specific areas increase wind erosion of soils. This
effect will most likely occur in specific areas where the existing shallow
aquifer is close to the ground surface and where very sandy soils are present.
Plant vigor and density will be reduced because of drawdown pumping in some
areas. Existing livestock grazing capabilities and production will also be
affected in these same areas.

Construction of the 42-mile conveyance channel will affect natural existing
overland flow of surface waters which encounter the channel. Since annual
precipitation within project boundaries amounts to only 6 to 8 inches, most
of the annual surface water runoff is derived from snowmelt from adjacent
mountain ranges. Almost all of the surface runoff water is located in the
northern part of the project area in Stages 3, 4, and 5. Only minimal surface
flows are received in the southern part, or Stage 1-2 of the project. Channel
construction will not affect any natural overlaRd flows in Stage 1-2.

In Stages 3, 4, and 5, conveyance channel construction will affect the natural
overland flow of surface runoff waters through about 4,920 acres of existing
wetlands and wetland habitat. At identifiable drainage points of the conveyance
channel, structures will pass runoff waters under or over the channel. The
locations of the structures have not been specifically determined at this time
but will be positioned to minimize interruptions of overland flows.

Construction of roads (about 10 feet wide) for access to pump well sites along
the lateral delivery system will directly displace about 80 acres of wetlands or
wetland habitats. When possible, pump wells will be located outside wetland
depressions and will, therefore, have minimum effect on wetlands or wetland
habitat because of construction.

A total of 4,946 acres of wetlands will be affected by construction of the
42-mile conveyance channel (26 acres on the Blanca WHA) and 80 acres by con-
struction of roads associated with the pump well field system. The total
amount of wetlands and wetland habitats affected by construction activities
within project boundaries will, therefore, be 5,026 acres.

The total amount of wetlands adversely affected by drawdown pumping within
project boundaries is 3,434 acres, of which 173 acres are on the Blanca WHA.
A large portion of the 5,026 acres of wetlands identified above as being

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