SPDSS_Task58_Review Previous Estimates of Potential CU

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SPDSS Task 58 Memo August 5, 2004 Page 12 of 22 Colorado River Basin Denver Water commissioned lysimeter studies of consumptive use of mountain meadows at high altitudes in Grand County in the mid 1980's. Results from these studies are reported by Carlson (1991) and often used by engineers in Water Division 5 to support PCU estimates. Gunnison River Basin In addition to the lysimeter studies conducted near Gunnison (Kruse and Haise, 1974), the Upper Gunnison Water Conservancy District has sponsored lysimeter based investigations of irrigated meadow grass consumptive use from 1999 through 2003 by Colorado State University (Smith, 2004). As indicated earlier, an initial conclusion of the program operators is that the Hargreaves method calculated ETr (grass based reference base) provides reasonable estimates of PCU of irrigated grasses at high elevations. Bucket "Turf' Lysimeters While not really a "crop", various lysimeter based investigations have been conducted of the PCU and return flow characteristics of lawn grass using small bucket type lysimeters. Lawn grass lysimeter studies were conducted in 1977 and 1978 in Colorado (Danielson, et al., 1980), in 1984 and 1985 by Spronk (1986), in 1986 and 1987 by Fosha and Thompson (1986, 1987) (known as the Cottonwood studies), and in 1992-1996 by Oad and DiSpigno (1996). Though it is known that a large weighing lysimeter at the Agricultural Engineering Research Campus in Fort Collins was used to compare to the bucket lysimeter data, no additional information on other results from this large lysimeter were found. 5. Climate Station Networks Three networks of automated climate stations exist in the SPDSS study area that provide current daily estimates of ET. Climate data from these networks supplement data available from NOAA stations. Historical ET data is available for these networks as indicated below. Northern Colorado Water Conservation District Network The District operates a network of remote, solar powered, automated weather stations throughout its service area. The weather station network is currently composed of twenty-one stations, ten sited in alfalfa fields and eleven (three of which are owned by cooperators) sited over urban turf grass. Stations are approximately 25 to 30 miles apart to provide the best practical coverage for the District's 1.5 million-acre service area. Each station collects air temperature, relative humidity, wind speed and solar radiation data, which are used to calculate ETR (alfalfa based reference evapotranspiration) on a daily basis using the ASCE standardized Penman-Montieth combination equation for both alfalfa and turf grass. Some of the climate stations and associated ET calculations date back to 1996. The Internet site for the NCWCD ET calculations is http://www.ncwcd.or~/ims/ims Weather form.asP.