7618 - Laserfiche WebLink

Home Browse Search

;' ft/sec, and generally represents pool habitat. It is apparent from field observations at the study site that optimal pool and eddy habitats occur at much higher flows than 200 cfs. Thus, it appears that this set of SI curves may not be applicable at the Spawning Bar Site. It also appears that depth, velocity and substrate, by themselves, may not be adequate to describe optimum habitat conditions for Colorado squawfish. Moreover, species criteria (HSI Curves) developed from focal point data collected from off-channel or shoreline habitats may not always be compatible with hydraulic data collected along main channel transects. The deposition SI curves suggested that available spawning habitat maximized at 2000 cfs. This number corresponds to a reasonable estimate within the range of observed flows for spawning Colorado squawfish (H. Tyus, U.S. Fish and Wildlife Service, personal communication). The velocity curve peaks at 2.27 ft/sec, with an optimum depth of 2.04 feet, over rubble substrate. Water temperatures, which may initiate spawning activity have not been incorporated into this analysis. 2. REPLICATE SITE The Replicate study site, located at RM 18.5, was first surveyed and modeled with the IFG4 program in 1983. Once again, Wahle made four modifications to the original data decks, (Table 6) recalibrated the decks, and reran the modified data decks through the HABTAT program. Similar to the Spawning Bar site, the data deck used in this analysis retained the corrected stage-of-zero flow (SIF) values, as well as modified substrate code, and a corrected CAL card. The geomorphic site stability was evaluated in conjunction with the Spawning Bar study site through aerial photographs. Only a minor increase in mid- channel bars from 1961 to 1982 appeared on the photographs. Thus, the Replicate study site was assumed to be stable (Wahle and Johnson 1984). Calibration The Replicate study site was modeled in five data decks to accommodate an emergent island at transect 3 and 4, and to model changes in both scoured and filled bed profiles at transect 5 (Figure 2). The lowered profile represents a scoured bed in which the channel is degraded. The raised profile represents a filled bed in which deposited sediments raise the bed elevation. 1 Transects 1 and 2 are modeled as a single data deck. Transect 3 and 4 are divided into right and left channels, with 82 percent of the flow running through the left channel (looking downstream) and 18 percent flowing through the right. Transects 5 and 6, as mentioned above, are modeled in two data decks, one for the scoured channel condition, and one for the filled channel. The five data decks were calibrated and run through the IFG4 program with three sets of velocity and WSL measurements from each transect. Results of the calibration are presented in Table 7. All of the decks were assigned a "good" rating with 83 to 100 percent calibration. 8