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001735 12 passing the Grand Canyon gage, located 102 miles downstream of Glen Canyon Dam, exceeded total estimated tributary inputs; except during the period of June through August 2000 (Low Summer Steady Flow test), when dam operations were held constant at 8,000 cfs. Sand mass-balance data for October 2000 through November 2001, do show evidence of some accumulation of sand upstream of Phantom Ranch (river mile 87), in response to an approximate 1,000,000 metric ton input of sand from the Paria River in October 2000, in combination with relatively low-flow releases from Glen Canyon Dam throughout Water Year 2001. Additional sand inputs from the tributaries that occurred during September of Water Year 2002, also accumulated in the channel bed under the low-flow operations of September through December 2002. However, preliminary observations during January through March 2003, suggest that experimental fluctuating flows exported 2002 sand inputs from critical reaches above Phantom Ranch. Indeed, mass-balance calculations for Marble Canyon and Upper Grand Canyon (Lees Ferry to Phantom Ranch) indicate that sediment export has exceeded input since August 1999 (Figure 1.2). Further, Figure 1.2 indicates that significant export during the winter experimental fluctuating flows is contributing to the negative mass-balance. Significant tributary inputs during fall 2004, led to an experimental high-flow release from Glen Canyon Dam, as discussed in a subsequent section updating experimental flows. MASS-BALANCE SAND BUDGET BElWEEN LEES FERRY AND THE GRAND CANYON GAGE 4.0 3.0 0;- c: 00 2.0 f-o WE >" t=E ~g 1.0 <>:= IS Uo> 0.0 l1j81 <>:~ !f'!! -1.0 (f)C) (f)~ ..:..: ::Oz -2.0 00 zf- ;:j..: I f- -3.0 -4.0 35,000 - MASS-BALANCE UNCERTAINTY ENVELOPE - WATER DISCHARGE 30,000 25,000 20,000 15,000 10,000 5,000 o 2000 2001 2002 2003 2004 o en () I )> ;;0 G) m )> -l -l I m r m m (f) "T1 m ;;0 ;;0 -< G) ~ m S _w .!!!- Figure 1.2. Mass-balance of fine sediment between Lees Ferry and Grand Canyon since August 1999 (data are provisional and subject to review and revision). GCMRC FY2006 Annual Work Plan (Draft February 15,2005)