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<br />002385 <br /> <br />From 1972 to 1981, the frequency oflake-wide surveys was increased to a monthly basis. <br /> <br />From 1982 to 1990, sampling activity steadily declined to single lake-wide surveys in 1988 and <br /> <br />1989. Despite the decline in sampling frequency, advances in instrumentation allowed the <br /> <br />collection of higher quality data at finer depth resolution. Continuous monitoring of temperature <br /> <br /> <br />and salinity of the tail water was initiated during this period. <br /> <br /> <br />In 1990, concurrent with the implementation ofGCES Phase II studies, Reclamation?s Lake <br /> <br /> <br />powell monitoring program was restructured. Monitoring frequency was returned to a level of <br /> <br />monthly forebay surveys and quarterly lake-wide surveys. During the Phase II Research Flow <br /> <br />period from 1990 to 1991, the monthly forebay surveys were conducted by the US Geological <br /> <br />Survey (Hart and Sherman, 1995)). This restructuring resulted in a redistribution of resources to <br /> <br />allow the collection of data at a finer spatial resolution while reducing the number of samples <br /> <br />collected for chemical analysis. Sampling for nutrient chemistry and biological conditions was also <br /> <br />initiated. The objective of this phase of monitoring activity was to establish a program of basic data <br /> <br />collection that would balance cost with the ability to track changes in reservoir and release water <br /> <br />quality and evaluate the effects of Glen Canyon Dam operation on these resources <br /> <br />Various agencies and institutions during Lake Powell?s history have conducted other work. <br /> <br />Studies have been conducted by educational consortiums and federal and state agencies on subjects <br /> <br />that include sedimentation, circulation patterns, trace element chemistry, remote sensing, and <br /> <br />public health issues (Potter and Drake, 1989). <br /> <br />C. Details of Current Monitoring Program <br /> <br />The current monitoring program was initiated in 1990 in response to the need to understand how <br /> <br />physical and chemical processes in Lake Powell and the operation of Glen Canyon Dam influence <br /> <br />the quality of water released to Colorado River in Grand Canyon. Based on limited personnel and <br /> <br />06/02/98 <br /> <br />DRAFT <br /> <br />Page 8 of 62 <br />