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<br />will reduce salt loading to the Colorado
<br />River.
<br />Wetlands have been created by seepage
<br />from inefficient water delivery systems,
<br />drainage ditches and irrigated fields. These
<br />areas support a variety of native and exotic
<br />plants and animals, filling to some extent the
<br />void created when historic natural wetlands
<br />' were drained or drastically altered in their
<br />conversion to other uses. Proposed water
<br />management improvements for salinity control
<br />will alter, reduce or destroy these irriga-
<br />tion-induced wetlands, displacing wildlife and
<br />plants.
<br />The inventory and evaluation of wetlands
<br />in the Lower Gunnison River Basin, conducted
<br />under the direction of BOR, SCS and the
<br />University of Colorado was designed to assess
<br />the existing resource, and recommend ways to
<br />mitigate the adverse impacts of salinity
<br />reduction improvements on wetland habitat.
<br />STUDY AREA DESCRIPTION
<br />The 72,800-ha study area is in the Lower
<br />Gunnison River Basin of western Colorado and
<br />includes parts of Montrose and Delta counties.
<br />Boundaries of the study area are the Gunnison
<br />River on the north, the West Canal diversion
<br />on the south, the Selig and Loutzenhizer
<br />canals on the east, and the West and Montrose-
<br />Delta canals on the west (fig. 1).
<br /> This area is along the western flank of
<br /> the Rocky Mountains with elevations ranging
<br /> from 1,500 to 2,400 m. It is divided by the
<br /> Uncompahgre River which flows from southeast
<br />t .- to northwest with a gradient.of 6.4 m/km. The
<br /> Uncompahgre Valley, 50 km in length, ranges in
<br /> width from several hundred meters at the West
<br />; - Canal to 3.3 km at its confluence with the
<br /> Gunnison River. To the west is a series of
<br /> mesas rising 120 m above the valley floor.
<br /> Clayey hills, outcrops of saline Mancos Shale
<br /> locally called "adobe", parallel the valley to
<br /> the east, while the Grand Mesa overlooks the
<br /> {- area from the north. Soils in the area vary
<br /> from sandy loam riverbottoms to gravelly loam
<br />r a mesas to clayey adobe hills and are underlain
<br />« with Mancos Shale.
<br />The climate is typical of lower inter-
<br />mountain valleys of the West, with low annual
<br />precipitation (19.7 tp 24.2 cm), low humidity,
<br />abundant sunshine and a wide range in annual
<br />and daily temperatures. Long-term tempera-
<br />tures have ranged from -32.7° to 41.1°C with a
<br />mean annual temperature of 9.9°C.
<br />In 1881, following the resettlement of
<br />the Ute Indians in Utah, land in the lower
<br />Gunnison River Basin became available for
<br />agricultural development. Low rainfall
<br />precluded dryland farming. Therefore,
<br />earthen irrigation canals were constructed
<br />from the Uncompahgre River to supply water to
<br />4,250 ha of land. In 1909 additional land
<br />was brought under irrigation using 30 m3/s
<br />of Gunnison River water diverted through the
<br />Gunnison Tunnel.
<br />Currently, river flows, combined with
<br />storage reservoirs, provide a steady, high
<br />quality water supply through the 150-day
<br />growing season. Crops grown on the 40,000 ha
<br />under irrigation include corn, alfalfa, small
<br />grains, pinto beans, potatoes, onions, sun-
<br />flowers and fruits.
<br />STUDY METHODS
<br />A complete description of study methods
<br />is found in Rector et al. (1979). The study
<br />was conducted in two phases. Phase I was an
<br />extensive inventory of wetlands that included
<br />100 percent coverage of the eight major deli-
<br />very canals and the Gunnison and Uncompahgre
<br />riverbottoms; a partial (45%) wetland inven-
<br />tory was made in the remaining area. Data
<br />were recorded by: location, U.S. Fish and
<br />Wildlife Service (FWS) wetland classification
<br />modified from Cowardin et al. (1976), canal
<br />or river name, vegetative cover and inter-
<br />spersion types adapted from Golet (1973,
<br />1973a), soil series (Cline et al. 1967) and
<br />water pH or conductivity or soil pH.
<br />The apparent source or sources of water
<br />supporting each wetland were identified:
<br />natural (river, stream, drainage), on-farm
<br />irrigation management, canal, or combinations
<br />of these three primary sources.
<br />Inventoried wetlands were rated for
<br />their value as wildlife habitat using a
<br />system developed by Golet (1973, 1973a).
<br />Evaluation was based on water permanence,
<br />wetland class, size, class diversity, sub-
<br />class diversity, location (bottomland,
<br />upland, lakeside, deltaic, streamside,
<br />isolated), surrounding habitat type, water
<br />and vegetation interspersion, vegetative
<br />interspersion, juxtaposition with other
<br />wetlands and water quality.
<br />Wetlands were mapped and measured on
<br />aerial photographs. Wildlife, as well as
<br />dominant vegetation, were noted for each
<br />inventoried wetland.
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