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Findings <br />Results of resurveys of cross - sections originally surveyed in 1962 indicated that only minor changes <br />in channel bottom elevations have occurred since Navajo Dam was completed (Bliesner and Lamarra <br />1994). Five of the cross - sections showed slight narrowing and deepening. Two of the transects <br />showed only slight narrowing, one possibly resulting from construction of a levee to protect an oil <br />well. The remaining cross - sections showed that most changes in position of the channel were due <br />to the river changing course in a meander area, although channel bed elevations showed little change. <br />Another finding of the resurvey was the change in riparian vegetation. Bliesner and Lamarra (1994) <br />speculated that the lack of natural flooding events and introduction of exotic vegetation, particularly <br />Russian olive, promoted channel stabilization, with the net result being a narrowing of the channel <br />resulting in a reduced flood capacity. They also noted that during high flow events, Russian olives <br />were eroded from the bank and deposited in the channel, thereby contributing to channel complexity. <br />Preliminary results of comparisons of yearly survey data of pre- and post - runoff bed elevations along <br />26 representative transects established during 1992 and 1993 indicated that changes in channel <br />geometry are highly variable in response to annual hydrographs. However, a general trend of net <br />scour was observed from 1992 to 1995, with an average elevation loss in the cross - sections of 0.3 <br />meter (m) through 1995. In 1996, a low flow year, the cross - sections demonstrated a net increase <br />in bed elevation due to deposition. A moderately high flow year, 1997 saw net scour, but elevations <br />did not return to the low level seen in 1995. This suggests that the channel scoured in response to <br />the changed flow regime, but is stabilizing at a new, slightly lower elevation within the study area <br />(Bliesner and Lamarra 1996, Bliesner 1997). <br />Summary <br />The channel of the San Juan River changed at about the time Navajo Dam was closed (i.e., 1962). <br />The channel is more stable, likely due to invasion of nonnative riparian vegetation and a reduction <br />in natural flooding due to Navajo Dam. Data on recent changes in channel morphology indicate that <br />the channel has become deeper in association with current flow regimes and conditions in the system <br />but may be approaching a new equilibrium condition. Further analysis of channel morphology <br />changes from earlier time periods using historical aerial photography should provide additional <br />information on changes that have occurred since closure of Navajo Dam. This information, in <br />addition to results of surveys already completed and final analysis of ongoing channel geometry <br />studies, should provide the information to adequately meet this objective. <br />5.2.3. Quantify and Compare / Contrast Available Aquatic Habitats as a <br />Response(s) to Natural and Manipulated Flows. <br />5.2.3.1. Monitor the Fate of Habitat Availability as a Result of Different Flows. <br />Contributing Investigations <br />The effect of flow on habitat availability in the San Juan River has been addressed by several studies, <br />including Pucherelli and Goettlicher (1992), Goettlicher and Pucherelli (1994), Bliesner and Lamarra <br />(1994, 1995, 1996), and Buntjer et al. (1994). <br />San Juan River Recovery Implementation Program December 1997 <br />Summary Report 13 PR -602 -1 <br />