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I I I I I I I I I I I I I I I I I I I 1.0 INTRODUCTION This document is the 1994 Annual Summary Report for Study #FG-I0 entitled Effects of Flow Regulation and Ice Formation on Overwinter Nurserv Habitat of Al!e-O Colorado Squawfish in the Green River below Flaminl! Gorl!e Dam. This Winter Ice Study is part of the Five Year Flaming Gorge Research Program - FY94 of the Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin. Included in this report are findings and preliminary data analysis from the first year of this three year study. This investigation was conducted under Contract No. 90-2558 with the Utah Division of Wildlife Resources (UDWR). Study design and progress reports are reviewed by the Flaming Gorge Work Group of the Recovery Program. The purpose of this investigation is to measure backwaters on the Green River between Echo Park and Ouray, UT in fall (September) and winter (January and February) to determine the effect of flow regulation and ice formation on habitat availability. The principal hypothesis is Ho: Ice development in backwaters reduces habitat availability and therefore. winter survival of al!e-O Colorado squawfish in the Green River below Flaminl! Gorl!e Dam. The objectives of this study are to: 1. Determine availability of nursery backwater habitat for age-O Colorado squawfish during winter months (December through February). 2. Determine longevity of backwaters exposed to winter flow regulation and ice formation. 3. Recommend winter flows and spring habitat maintenance flows to protect nursery habitat of age-O Colorado squawfish. Daily fluctuating powerplant releases from Flaming Gorge Dam, combined with relatively warm hypolimnetic water, may be producing ice conditions that reduce availability of overwinter nursery habitat for age-O Colorado squawfish in the Green River. Historically, surface ice formed on the Green River about 4 of 5 years, and together with low steady flows, produced a relatively stable winter environment for fish. Today, warm ( =4O"C) fluctuating releases from Flaming Gorge Dam, and the steep gradient in Lodore Canyon, create ice-free winter conditions for about 65 miles downstream to the Yampa River. Below this confluence, fluctuating releases continually break and jam the ice, altering flow and potentially affecting fish habitat for as much as 100 miles downstream. The effects of ice formation and flow regulation on age-O Colorado squawfish and their habitat are important in understanding winter flow releases from Flaming Gorge Dam. 2.0 STUDY AREA This investigation was conducted on the Green River in Utah. The study area extended from Island Park (RM 333), within Dinosaur National Monument, to the Ouray Bridge (RM 248) at Ouray, UT (Figure 1). All river miles (RM) cited denote miles upstream from the confluence of the Green and Colorado rivers. Table 1 provides a list of sites referenced in this report with corresponding river miles and distance downstream from Flaming Gorge Dam. The study area was divided into three reaches based on channel morphology and projected influence of fluctuating flows (Valdez and Masslich 1989). Reach 1 extehded from Island Park (RM 333) to SplitsMountain Canyon (RM 327). This area had a relatively steep gradient with gravel-boulder substrate. Reach 2 extended from the Split Mountain Campground (RM 319) to the Bonanza Bridge (RM 290). This reach had a moderate gradient with gravel-cobble substrate in. the upper regions and sand substrate in the lower regions. Reach 3 extended from the Bonanza Bridge (RM 290) to Ouray, UT (RM 248). This lower reach had a low-gradient with primarily sand substrate. The influence of fluctuating flows was projected to be most pronounced in Reach 1, with reduced influence in Reaches 2 and 3. 1