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CHAPTER II 1 STAGE ONE MONITORING As previously mentioned, the purpose of planning the Grand Valley Unit in stages was to allow Reclamation to begin construction in a por- tion of the valley (the Stage One area) where sufficient data were avail- able to monitor and assess the impacts of the initial development, while investigation and planning could continue on the rest of the unit (the Stage Two area). Stage One construction began in October 1980 by concrete lining a portion of the Government Highline Canal and developing associated cross- drainage facilities. These features were completed in March 1981. Con- struction began in October 1981 to consolidate 13 open channel laterals into 12 pipe laterals. Lateral construction and installation of a moss and debris removal structure were completed in April 1983. • Hydrosalinity monitoring results are being used by Reclamation to assess the effectiveness of Stage One development in reducing salt load- ing into the Colorado River. Wildlife monitoring results were used to determine the effect of Stage One development on the wildlife popula- • tions in the area. The findings form the basis for recommendations to Congress concerning further construction of the Grand Valley Unit. Hydrosalinity Monitoring Preproject hydrosalinity monitoring began in the Stage One area in 1976. Monitoring of Stage One improvements began in 1981 and continued through 1984. A less extensive monitoring program was conducted during 1985. Under the 1981 through 1985 monitoring program, water table measure- ments and water samples were taken bimonthly from observation wells in the Reed Wash study area, a hydrologically isolated basin. Outflow and electrical conductivity were recorded continuously. Data were used for empirically evaluating the effects of all Stage One improvements on ground and surface water flows and quality. Inflow and outflow data in the canals and laterals in the study area were also recorded. Other data, such as additional drain flows and photographic recordings of phre- atophyte growth, provided supplemental information. Reed Wash was selected as a study area within the larger Grand Val- ley because it is an identifiable hydrological basin bounded by topo- graphic ridges of impervious Mancos Shale on the east and west margins. It includes about 10,000 acres--about 4,900 acres of irrigated land and about 5,100 acres of nonirrigated land. These ridges converge in a downstream direction and, along with unweathered shale in the subsurface, 12