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5000 \ \ .-. .........------,." I I I I I I I I I I I , I I I I I I I complete. RESULTS Hydrology and Reservoir Elevation Though, the past decade has been the wettest on record, runoff from the Colorado River was just below average (89%) in 1999 (4,807,000 acre/ft) and well below (72%) average (3,856,000 acre/ft) in 2000. Flows from the San Juan Rive- were similar but of a lesser magnitude (Figure 3). Runoff (1,671,000 acre/ft) in 1999 was slig tly higher (110%) than normal and was substantially lower than normal in 2000. Colorado River - - - San Juan River 20000 15000 10000 o Oct 98 Apr99 Oct 99 AprOO Jan 99 Jul 99 Jan 00 Jul 00 Figure 3. Hydrographs showing Colorado and San Juan river flows (cfs) into Lake Powell for October 1998 to September 2000. Lake Powell's elevation attained its annual low (1,120.8 m) in late April 1999 and rose 5.3 m (1,126.1 m) during spring runoff (Figure 4). Detectible river currents extended downstream to RM 51 in April 1999, just upstream of the Piute Farms boat landing. By July, the reservoir extended upstream beyond Clay Hills (RM 56). Lake Powell's rate of filling (8 cm/d) in June and July 1999 allowed us to sample areas that were dry the previous trip. The inflow ofthe Colorado River was confined to Narrow Canyon. At full pool, Lake Powell inundates areas as far upstream as Imperial Rapids (RM-200). Narrow Canyon starts about 4 km downstream of Imperial Rapids and extends downstream to RM-171 where the river broadens at the confluence of the Dirty Devil River (RM-170). The reservoir was at nearly full (90%) pool during the course of the study and backed up beyond RM-195 both years. Backwater or slack water habitat was virtually nonexistent in the Colorado River inflow. 8