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~ (,j f'- ..-4 (_J c; ....,.! " .j ">~ low velocity habitats were generally confined to backwaters formed by tributary stream channel encroachment. At flows below 1,200 cfs, area and size of backwater and secondary channel habitats from RM 67 to RM 52 was substantially less than from RM 158 to RM 68. Airborne videography habitat mapping was also conducted in 1992 (Goettlicher and Pucherelli 1993). During 1992, the San Juan River was mapped on four occasions at flows ranging from 585 to 9,290 cfs. These flows were substantially higher than during 1991 and represented test flows from Navajo Dam timed to coincide with runoff in the Animas River. Results of habitat mapping in 1992 showed similar patterns to those seen during 1991. Sidechannel area showed a positive response with flow, while backwater areas responded negatively. The effects of the "high flow habitat zone" were apparent from RM 158 to RM 68 as in 1991. Bliesner and Lamarra (1994, 1995) presented a more detailed analysis of habitat composition relative to flow in the San Juan River. Their analysis used six different periods representing 1992 base flow (December), 1993 peak flow (June), suspected spawning period for Colorado squawfish (July), 1993 fall base flow (October), 1994 peak flow (June), and 1994 summer low flow (August). Data were obtained using four separate sets of aerial videography provided by the Bureau from flyovers during flows ranging from 812 to 9,960 cfs for the 1992 to 1993 period and three sets of aerial videography for flows ranging from 469 to 10,000 cfs for the 1994 period. Three additional mappings of habitat composition using airborne videography were conducted on the San Juan River during November 1994 and April and September 1995, representing spring intermediate flow and two fall base flow conditions. Crews were also sent into the field to map aerial distribution of habitat types as close to the same flow encountered during the initial filming as possible. Habitat mapping data were then rectified to geo-referenced base maps and digitized into ArcCAD software for analysis. Habitat types were grouped into seven categories for analysis including: 1. 2. 3. 4. 5. 6. 7. Runs Riffles Shoals Low Velocity Habitats Vegetative Associated Habitats Slackwaters Others Each category consisted of two to nine specific habitat types (e.g., the riIne category included riffle, shore riffle, riffle chute, and shoal/riffle). These categories were summarized based on total cumulative area and percent of wetted area for selected reaches of the San Juan River during each period (Table 3). A Shannon-Wiener diversity index was also calculated for habitat at each flow level. San Juan River Recovery Implementation ProgranT Summary Report 15 17 January 1997 PR-576-2