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l:'- t'- C\l C., .:-J t...., -' CHAPTER IV STAGE ONE DEVELOPMENT AND MONITORING Under the monitoring program, water table measurements and samples are being taken bimonthly from observation wells to provide data for empirically evaluating the effects of Stage One improvements on ground water flows and quality in tributary drains. Water table levels are recorded cont inuously. Flow data at the boundaries of the basin are also recorded. Results from the monitoring data are being used to quantitatively assess the effectiveness of Stage One development in reducing salt to the Colorado River. Other data such as water tab le depth, drain flows, and photographic recordings of phreatophyte growth provide additional information. Prior to lining, annual seepage from the Government Highline Canal in the Stage One area was estimated to have been 1,700 acre-feet, con- tributing 6,640 tons of salt to the Colorado River and resulting in an increase is salinity concentration at Imperial Dam of 0.67 mg/L. Seepage from laterals in the Stage One area was estimated at 4,930 acre-feet contributing 19,270 tons of salt with an effect of 1.95 mg/L salinity concentration at Imperial Dam. The seepage and salt loading reductions accomplished as a result of Stage One development are presented in Table 3. These reductions were estimated using water and salt inflow/outflow data. The 1982 data have been analyzed and the results indicate that the canal and lateral lining program is reducing seepage and salt loading near ant ic ipated levels. The canal seepage has been reduced from 1,700 acre-feet to 390 acre-feet compared to the anticipated rate of 410 acre-feet resulting in a reduction of about 5,000 tons of salt. The lateral seepage has been reduced from 4,930 acre-feet to 2,970 acre-feet. 24