DESOLATION and GRAY CANYONS

Harvey and Mussetter (1994) investigated a known Colorado Squawfish spawning bar at the upstream end of Gray Canyon to test a physical process-biological response model for spawning habitat formation developed in the lower Yampa Canyon(Harvey et al. 1993). The model premise is that high discharges construct spawning bars in areas of local backwater effect but bar dissection during recession and low flows flushes fines and prepares spawning habitats on clean cobble substrate in tertiary chute channels. This work illustrates the importance of flow variability and flow timing with respect to fish spawning patterns.

Schmidt and others (1996) investigated the spatial and temporal patterns of habitat availability in Desolation and Gray Canyons. Their work was focused on habitat for endangered humpback chub. They found channel narrowing, vegetation encroachment and channel margin simplification patterns similar to other study reaches. These processes reduce available habitat.

NEAR GREEN RIVER, UTAH

Allred (1997) [and Allred and Schmidt, in review] demonstrates that two episodes of channel narrowing occurred near Green River Utah during the past 100 years. He shows that narrowing is driven primarily by changes in hydrologic regime and only secondarily by the invasion of tamarisk . The channel narrowed between 1930-38 when a shift from wetter than normal conditions to a period of drought led to a reduction in river discharge. This period of time coincided with tamarisk invasion (Graf 1978). Channel width then remained relatively stable until construction of FGD in 1962, despite the presence of tamarisk . Since emplacement of FGD, narrowing has occurred again and continues today, resulting from reduced peak flood magnitudes. They demonstrate that islands attach and nearbank floodplains (inset floodplains) develop thru vertical accretion processes at rates that decrease with time, although the deposits coarsen upward, indicating higher floods are required to emplace sediment at higher elevations. They questioned if the channel could widen if flows increased (opposed to the observations of Lyons et al, and Merritt) and suggest "channel narrowing is a nearly irreversible process" that continues today.

CANYONLANDS NATIONAL PARK

Graf (1978) stated that tamarisk spread throughout CANY between 1925-31, and that the invasive plant has trapped and stabilized sediment, causing an average of 27% reduction in channel width through island enlargement/attachment and bar formation/enlargement. Thus, as Graf and many subsequent authors have pointed out, channel narrowing and tamarisk invasion coincided with a climatic cycle of reduced discharge prior to 1935 that provided bare sand deposits suitable for invasion and lacked floods to periodically scour the sand and arrest vegetation invasion. When high flows occurred in the 1950's, the vegetated landforms were not remobilized because of the anchoring effects of the invading tamarisks. However, native vegetation also quickly colonizes infrequently reworked bare sand deposits and the large thickets of willow and pampas grass on low elevation sandy surfaces in CANY illustrate this. Flow regulation has intensified this process because of further reductions in the magnitude and frequency of floods downstream from FGD.

O'Brien states that peak flow reduction has eliminated out of channel flows and associated fish habitat and aquatic ecosystems in Canyonlands. Post-dam T&E fish habitat is reduced to flooded side canyons of the Green River which have very small areas ranging from 0-5 acres total. Each of the five side canyons have unique morphological characteristics and habitats for given flows with a fairly linear relationship between area and discharge. The side canyon habitats are subject to side canyon debris and sedimentation processes during critical portions of the fish life cycle.

Flow required to initiate inundation of Canyonlands floodplains is about 39000 cfs with current channel shape. This flow has a return period of ~15 yrs post-dam. O'Brien estimated, using USGS topo maps and field observation, that the vegetated low-lying terraces adjacent to the Green River would be inundated by 4-5 foot increase in water surface elevation above bankfull discharge. Extending his area versus discharge relationship he estimated that 53000cfs would inundate 500-acres of out of channel habitat. 53000cfs was a 1 in 15 year event pre-1963 and more than 1 in 100 yrs post-1963.

O'Brien summarized channel changes in the Canyonlands reach: extensive vegetation encroachment, natural levee building along the banks in dense vegetation, reduced sediment load, conversion of floodplains to terraces. These changes are the result of reduced flows, not increased channel capacity (which would result from channel incision). Low flow stage comparisons in Canyonlands suggest the channel has narrowed and aggraded, resulting in higher stage for a given discharge. This situation is favorable for inundating floodplains with lower discharges. A lack of island and bank reworking, by high flows, is leading to stabilization by vegetation and ultimate removal of these features from the active channel. Tamarisks and other invaders need to be scoured from river banks ~2-3 years to prevent their stabilization of the substrate.

Guensch and Schmidt (1996) compared 15 channel cross sections at Mineral Bottom in response to the 1996 flood. The study area was considered critical habitat for Colorado Pikeminnow, particularly as nursery habitat, by the Utah Division of Wildlife Resources. No important conclusions came from this abbreviated study.

Knowledge Gaps:

· There appears to be potential for inundating the lowest elevation floodplains in CANY by frequently occurring flow events if the flow peaks were increased by a small amount. If there is indeed a connection between floodplains and TE fish habitats, NPS needs to know where these low elevation floodplains occur, their size and more accurately what discharges are required for inundation as well as area/inundation relationships.

· site specific sediment and hydraulic/hydrologic conditions required for successful cottonwood establishment

Suggested Actions:

· obtain additional detailed channel and flow field measurements during a normal peak flow period

· identify most likely floodplains for restoration

· develop detailed 2-d hydraulics models of candidate floodplains to predict results and relative benefits of various discharges

· couple above investigations with flow routing model to develop flow recommendations

· obtain site specific recommendations for successful cottonwood establishment

GENERAL - SEDIMENT SUPPLY and CHANNEL GEOMORPHOLOGY

Andrews (1986) showed that while the drainage areas of the Little Snake and Yampa Rivers are about equal above the Little Snake, only 27 of the water at Deerlodge Park is provided from the Little Snake, but 69 percent of the total sediment, with most of the sediment being derived from the lower portion of the Little Snake basin (below Baggs, WY). Pre-FGD, the drainage area upstream of the dam site supplied 27 percent of the total basin discharge but only 2.2 percent of the mean annual sediment loading. [However, Andrews paper states that the drainage area immediately downstream of the dam site supplied 36% of the total basin discharge and 21% of the mean annual sediment loading. This is overlooked (?) by RCI.] RCI and Andrews agree that the large water-contributing portions of the basin lie around the rim, particularly in the northeast divide, while the sediment contributing areas are located in the central and southern parts of the basin. Therefore, FGD has primarily reduced transport capacity in the Green River, and to a lesser extent sediment supply.

After completion of the reservoir, Andrews concluded that the reach downstream to the Yampa River (68 miles) degraded, limited somewhat by armoring. From the Yampa to the Duchesne River the channel was in equilibrium, and downstream of the Duchesne the channel was aggradational. He also concluded that the greatest impact of FGD is not immediately downstream, but instead several hundred miles downstream. He also found that the magnitude of effective discharge had decreased significantly in all reaches and that channel width had narrowed, however, he concluded that a new equilibrium had not been achieved and significantly more narrowing could occur. Andrews and Nelson (1988) found that the most significant process narrowing the channel was aggradation of channel bars resulting in attachment to the bank and incorporation into the floodplain. Pucherelli (1988) and Lyons (1989) generally concurred with this assessment, indicating 40 percent of the observed channel narrowing was attributed to island attachment. Lyons, however, concluded that the Green River channel below FGD had reached a new equilibrium (at various times at greater distances downstream) and no more significant changes in channel geometry should occur. Widening of the channel in response to the high runoff during the 1980's indicates the potential for future channel changes in response to changes in water and sediment discharge conditions.

Williams and Wolman (1983) stated that regulation of flows is the only dam-related factor certain to encourage vegetation growth. Reduced high flows decrease seedling scour from sand bars and increased low flows support young plant growth. FGD operations have increased the frequency of flows >2000cfs from 72% to 89%.

Decreased computed sediment loads (i.e. Andrews 1986 paper), although alarming, are attributed to two factors; decreased sediment supply because of reservoir storage and decreased transport capacity because of reduced peak flows.

Andrews analysis of the morphologic changes along the Green River that he attributed to the emplacement of FGD (i.e., degradation and channel narrowing) was based on the assumption that the river was in a state of quasi-equilibrium before dam construction. RCI 1990 reviewed literature in the Green and Yampa River basins under contract to the Colorado Water Conservancy District and the Wyoming Water Development Commission. RCI cites more recent literature (Schumm et al., 1987; Schumm and Gellis, 1989) that suggests that the sediment load of the Colorado River has been decreasing since the mid-1920's and that an abrupt decrease occurred in the period 1940-45. The declining sediment load is attributed to (1) drought in the sediment producing areas of the drainage basin (Thomas et al., 1963), (2) changes in sediment sampling procedures by the USGS (Schumm et al., 1987), (3) major reductions in livestock numbers and implementation of erosion control efforts on grazing lands (Hadley, 1974), and (4) the cycle of sediment storage in entrenched channels and arroyos following the widespread occurrence of channel trenching in the latter part of the 19^th century (Hereford, 1984, 1985; Graf et al., 1987; Schumm and Gellis, 1989).

Regardless of the actual causes of decline in sediment loads in the river draining the Colorado Plateau, the fact that a period of decline was taking place during the time frame when FGD was emplaced casts doubt on the equilibrium status of the Green River prior to dam emplacement.

GENERAL - FISHES

Channel narrowing and margin simplification has reduced in-channel fish habitat. This primarily affects the endangered Colorado River Squawfish. The loss of overbank flood flows has virtually eliminated floodplain habitats for the endangered razorback sucker, a species that requires out-of-channel nursery habitat. At the present time the floodplain habitat requirements of the razorback are less well known than the in-channel habitat needs of the Squawfish. This is primarily because floodplains and flooding are very controversial issues and few studies have been commissioned to improve our understanding of this problem.

Valdez (1994) synthesized winter investigations of endangered fish in the Green River basin. Apparently two winter studies were conducted by Wick and Hawkins (1989) on the Yampa River, and Valdez and Masslich (1989) downstream from FGD. Both studies tracked movements of radiotagged adult Colorado Pikeminnow and razorback suckers. Both studies revealed preference for overwintering sites in moderately deep, low-velocity habitats. Both species were locally active, but rarely left a habitat, except during flow changes or to avoid ice jams and frazil ice masses.

Both studies recommended low, relatively stable winter flows to stabilize low velocity habitats, allow formation of a persistent ice cover to insulate from supercooling, dampen moderate fluctuations, and minimize incidence of ice jams and frazil ice. Several studies were recommended to evaluate other life stages of the native fishes.

Wick (1997) documented a sediment transport problem related to timing for spawning razorback suckers near the DINO quarry. Razorbacks spawn in a side channel which becomes a low velocity zone as discharge increases, because of a downstream constriction and backwater effect. When a critical discharge of approximately 10000-12000 cfs is reached on the rising limb of a hydrograph, sedimentation occurs on the spawning gravels, sometimes burying eggs before they hatch. This sequence is dependent on the timing of Yampa River flows and the corresponding operation of FGD. To ensure the spawning and larval production of razorbacks Wick recommended that releases from FGD be closely coordinated to forecasts of flow and runoff potential for the Yampa River and monitoring at this site. It is common that FGD releases precede Yampa flooding by several weeks as dam operators evacuate the reservoir to make storage available for the runoff. There is also an issue of temperature required for razorback spawning that can be affected by cold releases from FGD.

GENERAL - RIVER/ECOSYSTEM MANAGEMENT

Stanford (1994) convened a panel of experts to review and synthesize ecological information, issues, methods and rationale used to prescribe instream flow needs to assist the recovery of endangered fishes in the Upper Colorado River basin. Purpose of the study was to identify critical uncertainties and to provide recommendations for determining the instream flow needs of the endangered fishes. Stanford concluded that studies to date strongly indicated that truncation of peak flows and higher, fluctuating baseflows have altered complex biophysical processes that form and maintain suitable habitats required for survival of the fishes. He further states that an apparent ecological tradeoff exists where very high flows are needed occasionally to produce habitats that he fish need to survive, but at the expense of reproductive success. This quandary is the basis of uncertainty and indecision in biological resource management.

Stanford recommends a holistic instream flow methodology with additional study to resolve uncertainties (adaptive management?). Specifically, he recommends re-establishing seasonality with Spring peaks that approach the amplitude and frequency of preregulation events, and Summer and Winter baseflows with daily changes limited to near preregulation conditions (~<5%/day). Success would be determined by long-term trends in endangered fish populations.

GENERAL - VEGETATION

Fischer et al. (1983) studied vegetation along the unregulated Yampa River in comparison to vegetation along the regulated Green River upstream and downstream from the Yampa River confluence. The authors goal was to describe the potential effects on streamside vegetation communities of flow regulation (threatened impoundment) on the Yampa River. The effect of reduced maximum discharges was observed in Lodore Canyon where a there is clear evidence of a downward movement of riparian and upland species (boxelder, juniper, rabbitbrush, and Chrysopsis) into the pre-dam floodzone. Coupled with reduced peak flows is increased minimum flows, which Fischer et al. Predicted would kill the plants presently established along the low water line but would probably easily reestablish higher on the floodzone. More importantly, the authors felt that the floodzone was reduced to a very narrow band, from 30 to 5 meters wide on the Green River, and that the species composition had changed as a result of flow regulation. The authors also discussed the visual impact and impact on campsite size and numbers that vegetation encroachment would cause.

A commonly reported outcome of regulated flow is reduced reproduction by seed of large woody perennials, including boxelder, cottonwood, and tamarisk. Upstream from the Yampa confluence, boxelder seedlings were found on the Green River. Downstream, seedlings of cottonwood and tamarisk were found limited to the floodzone area resulting from the variable seasonal input of the Yampa. Reduced seedling reproduction and a decline in riparian tree populations on the upper terraces of the floodplain have been attributed to reduced peak flows. This response to flow regulation on the Green River near the Yampa River confluence is similar to responses observed on other river systems of the world (various literature cited by the authors).

GENERAL - HYDROLOGY AND DAM OPERATIONS

Muth et al 2000

Draft report 2000 Flow and Temperature Recommendations for Endangered Fish in the Green River Down Stream of Flaming Gorge Dam. The report documents the development of integrated flow and temperature recomendations for release fro FGD to support dendangerd fish species recovery. Information on each endangered fish species was used to develop integrated flow and temperature recommendations for the Green River downstream of Flaming Gorge Dam. The goal of the recommendations is to provide the annual and seasonal patterns of flow and temperature in the Green River that would enhance populations of the endangered fishes. Six objectives were developed to achieve this goal: (1) provide appropriate conditions that allow gonadal maturation and environmental cues for spawning movements and reproduction; (2) form low-velocity habitats for pre-spawning staging and post-spawning feeding and resting areas; (3) inundate floodplains and other off-channel habitats at the appropriate time and for an adequate duration to provide warm, food-rich environments for fish growth and conditioning, and to provide river-floodplain connections for the restoration of natural ecosystem processes; (4) restore and maintain the channel complexity and dynamics needed for formation and maintenance of high-quality spawning, nursery, and adult habitats; (5) provide base flows that promote favorable conditions in low-velocity habitats during summer, autumn, and winter; and (6) minimize differences in water temperature between the Green River and Yampa River in Echo Park to prevent temperature shock and possible mortality to larval Colorado pikeminnow transported from the Yampa River and into the Green River during summer.

Specific peak- and base-flow target levels are recommended for each reach for five hydrologic conditions as defined by exceedance probability: wet (0-10% exceedance), moderately wet (10-30% exceedance), average (30-70% exceedance), moderately dry (70-90% exceedance), and dry (90-100% exceedance). At the time of this update the flow recommendations were still in draft and may change therefore the details of the recomendations are no included in this literature review.

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