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<br />CC16vl <br /> <br />the canals at the five canal sites; therefore the difference in hydraulic head between the canal and <br />the water table was not a factor in determining the seepage rates, Gould and Hansen (1994, p, <br />19) considered about 0.2 foot per dilY to be an appropriate estimate for canal operating <br />conditions over an irrigation season. The Bureau of Reclamation (1994c) used channel <br />permeameters in an effort to estimate seepage rates from the Rio Grande in the Albuquerque <br />area. Although the results were inconclusive, they recommended that the procedures be <br />modified and additional work of this type be done (Bureau of Reclamation, 1994c, p. 11-12). <br />Seepage rates between the aquifer and drains is variable throughout the Albuquerque area <br />because of the dependency on the water-table elevation and the use of some drains for the <br />conveyance of irrigation and storm water. Bjorklund and Maxwell (1961, p. 55) noted that flow <br />in some drains varies significantly seasonally and annually. <br /> <br />As noted in the previous "Canpls" sections, the essential information needed to better <br />quantify canal seepage is canal dimensions, bottom elevations, operating stage, proportion of <br />time they contain water, and location of lined and unlined segments. The essential information <br />needed to better quantify drain seepage is drain dimensions, bottom elevations, location of <br />nonfunctional interior drains, and the reaches of drains that convey irrigation water (see <br />previous "Drains" section). Estimates of seepage rates between the river channel and the aquifer <br />are essential for model adjustments. <br /> <br />Seepage of water between a river system and an aquifer can be estimated by determining <br />the difference in flow along particular reaches, if the river gain or loss is significantly greater <br />than the measurement error of the flow in the river system. Flow records of the Rio Grande <br />through Albuquerque are generally considered good, which means that 95 percent of the daily <br />flow values are considered to be accurate within plus or minus 10 percent (Borland and Ong, <br />1995, p. 10, 189). Total loss of flow from the Rio Grande surface-water system between Bernalillo <br />and Isleta Pueblo was estimated by Hansen (in press) to be about 113,500 acre-feet per year, <br />which is almost 11 percent of the Rio Grande average annual flow of 1,053,000 acre-feet (Borland <br />and Ong, 1995, p. 189). Because this estimate is very close to the measurement error of flow in <br />the river, detecting loss of water in the surface-water system between two points of <br />measurement would be difficult using single sets of measurements. However, by calculating the <br />difference between long-term averages of flow measurements upstream and downstream from a <br />reach during periods of low flow and accounting for inflows and outflows within the reach, <br />statistically significant estimates can be made. This calculation becomes more complicated for <br />the growing season because of riparian evapotranspiration and the diversion of water for crop <br />irrigation. For the winter, however, when crop irrigation is not a factor and evapotranspiration is <br />minimal, these calculations may produce realistic results. . <br /> <br />The USGS monitors five streamflow-gaging stations on the Rio Grande in the Albuquerque <br />area (fig. 4). Two of the gages, Rio Grande near Bernalillo (08329500) and Rio Grande near Isleta <br />(08331000; continuous recording gage installed upstream of site where periodic water-discharge <br />measurements were previously made), were installed in 1995 to provide measurements of Rio <br />Grande flow into and out of the Albuquerque area. The five gages provide measurements of <br />flow through four reaches of the river in the Albuquerque area. <br /> <br />River, canal, and drain flow at sections across the inner valley at the Rio Grande near <br />Alameda (08329928) and Rio Grande at Rio Bravo Bridge (08330150) gages has been measured <br />(Thorn, 1995) to calculate total surface-water inflow and outflow of the reach between the gages. <br />To calculate total flow of the Rio Grande surface-water system into and out of the Albuquerque <br />area it is essential to measure river, canal, and drain flow at sections across the inner valley at the <br />two new gages (08329500 and 08331000; fig. 4). <br /> <br />25 <br />