Mitigation of cold‐water thermal pollution downstream of a large dam with the use of a novel thermal curtain

Hypolimnial releases from dams during periods of thermal stratification modify the downstream riverine thermal regime by decreasing water temperature and reducing natural diel thermal variability. This cold‐water thermal pollution in rivers can persist for hundreds of kilometres downstream of dams and impact important ecological processes such as fish spawning. To mitigate this problem, a first‐of‐its‐kind thermal curtain was fitted to the large bottom release Burrendong Dam on the Macquarie River, Australia. The thermal curtain acts by directing warmer, near‐surface epilimnial water to the low‐level hypolimnial offtake. This study aimed to test the efficacy of the thermal curtain by measuring temperatures before and after the curtains installation, quantifying the magnitude and extent of cold‐water thermal pollution along the Macquarie River downstream of Burrendong Dam. Epilimnial releases with use of the curtain increased diel temperature ranges and the mean monthly water temperature below the dam. Epilimnial releases with use of the curtain increased diel temperature ranges from 0.9°C to 2.5°C and reduced the difference between the mean monthly water temperature of an upstream control and a downstream site by up to 3.5°C. A comparison of the monthly temperature means along the river, indicated that thermal recovery, whereby temperatures returned to within the natural range of upstream temperatures occurred 45 km downstream of the dam during summer when the thermal curtain was deployed, compared with approximately 200 km prior to deployment of the curtain. Our study suggests that the use of thermal curtains can reduce cold‐water thermal pollution and improve ecological outcomes for river ecosystems downstream of dams.     

Environmental conditions and timing for the spawning of Murray cod (Maccullochella peelii peelii) and the endangered trout cod (M. macquariensis) in southeastern Australian rivers

The environmental conditions and timing of spawning of Murray cod and trout cod were investigated over three successive years in the regulated Murray River and in the nearby, unregulated Ovens River. Larvae were collected in drift samples from early November. Murray cod larvae were present for up to ten weeks, but trout cod larvae were present for only about two weeks. Cod larvae were collected in both rivers in each year sampled, despite a range of flow conditions. Spawning periods, estimated by back‐calculating larval ages and egg incubation times, were in part, concurrent for the two species, beginning in October when water temperatures had exceeded 15°C, allowing the occasional hybridization that has been noted between these two species. Trout cod larvae (10.0–18.2 mm) were significantly larger than Murray cod larvae (9.5–14.8 mm) in both years and the larvae of both species were significantly larger in 1995/6 than in 1994/5 in the Murray River. There was no relationship between larval size and water temperature, but later spawning times at the upper Murray River site coincided with lower water temperatures. Larval abundance varied significantly between sites, samples and years, with peak larval abundances occurring in November. Murray cod larval abundance was best explained by the explanatory variables of year, day length and change in flow over the previous 7 d. Environmental conditions for the spawning of Murray cod and trout cod are similar, and both species exhibit a similar larval dispersal strategy by emergence into the drift. Spawning occurred regularly under a range of flow conditions and it is likely that recruitment of these species in these rivers is driven by the subsequent survival of larvae and juveniles. Copyright © 2005 John Wiley & Sons, Ltd.     

Modelling the impact and potential mitigation of cold water pollution on Murray cod populations downstream of Hume Dam,Australia

A one‐dimensional hydrodynamic reservoir model is coupled with a stochastic fish population model to examine the impacts of cold water pollution (CWP) on the Australian freshwater fish, Murray cod, downstream of Hume Dam, Australia. Mitigation of CWP through the introduction of selective withdrawal capabilities to access near‐surface water is predicted to increase discharge temperatures during the crucial spring‐early summer post‐spawning period by 4–6°C for normal operating conditions, that is, a full reservoir in early spring. No improvement in discharge temperature was predicted for drought conditions characterized by relatively low storage levels in early spring. The predicted temperature increase using selective withdrawal increased the predicted average minimum female population abundance by 30–300% depending on the assumed spawning behaviour. Increased discharge temperatures appear to be achievable and are expected to reduce the stress currently impacting Murray cod populations due to CWP during crucial post‐spawning periods. This provides evidence that mitigation of this problem may assist in rehabilitating Murray cod populations in the Murray River downstream of Hume Dam. Copyright © 2007 John Wiley & Sons, Ltd.     

The effect of Keepit Dam on the temperature regime of the Namoi River,Australia

Modifications to water temperature caused by the release of hypolimnetic water from thermally stratified reservoirs pose a major threat to the aquatic biota of lowland rivers in Australia's Murray–Darling basin. Keepit Dam is earmarked as one of several deep‐release structures in the basin causing ecologically significant temperature modification over a large length of river. This study utilized discrete and continuously monitored historical water temperature data from stream gauging stations, together with reservoir thermal profile data, to assess the impacts of Keepit Dam on the thermal regime of the Namoi River. Modifications to selected components of the river's annual temperature cycle were quantified in relation to a pre‐dam temperature regime estimated from statistical models incorporating catchment, hydrological and sample attributes. Keepit Dam has modified the thermal regime of the Namoi River. The effect was greatest immediately downstream from the dam where the annual maximum daily temperature was approximately 5.0 °C lower and occurred three weeks later than the pre‐dam condition. This change was sufficient to disrupt thermal spawning cues for selected Australian native fish species. The magnitude of disturbance progressively diminished with distance from the dam. Key aspects of the river's annual temperature cycle were largely restored to the pre‐dam condition within 100 river km downstream from the dam, which is closer than previous estimates. However, there was marked inter‐annual variation in the magnitude of thermal modification and ecological impact as a result of year to year changes in tributary flow and reservoir behaviour. Copyright © 2002 John Wiley & Sons, Ltd.     

Effects of river impoundment on body condition and reproductive performance of the Australian native fish, Macquarie perch (Macquaria australasica)

This study attempts to evaluate the influence of the impounding of Lake Dartmouth (36°35′S, 147°31′E; on Mitta Mitta River in Victoria) on the Macquarie perch (Macquaria australasica, Cuvier 1830), an Australian percichthyid fish of riverine origin. In this study the yearly changes in body condition and spawning performance of adult populations in the impoundment were evaluated in relation to lake features, in particular the water level. Body condition of the spawning population of Macquarie perch in Lake Dartmouth, in year n was related to mean annual storage volume of the lake, with a time lag of one year during the post‐filling phase of the lake (1991–1997). The influence of condition on the reproductive performance of captive female Macquarie perch from Lake Dartmouth using artificial propagation techniques was evaluated over the period 1991–1997. The mean relative fecundity (mrf), expressed as the number of eggs produced per kilogram of body weight of hypophysed fish, showed a decrease over the period, but the mean weight of hypophysed fish did not decrease over the same time period. The mrf (Y_mrf) was positively correlated to yearly mean relative condition factor (X_Rc), the relationship being: The spawning variables, mean percentage fertilization (Y_fn) (1991–1997) and mean larval production (Y_ln) (1992–1996) in each year (n) were also related to the mean relative condition factor (X_Rc) of female fish that spawned after hypophysation in each year. It is suggested that the declining success in the artificial propagation of this species is caused by a declining maternal condition of female fish collected from the impoundment, resulting from poor nutrition.     

Influence of dam operation on mayfly assemblage structure and life histories in two south-eastern Australian streams

The mayfly fauna, and in particular the life histories of two mayflies, Coloburiscoides sp. and Baetis sp. 3, was studied in two nearby streams located in the headwaters of the River Murray, SE Australia. The Mitta Mitta River is regulated by the Dartmouth Dam which releases cold water in summer for irrigation. Snowy Creek is a tributary of the Mitta Mitta River with natural flow and temperature regimes. The structure of the mayfly assemblage differs in the two streams. In the regulated Mitta Mitta there are 11 species, of which, caenids (Tasmanocaenis tonnoiri and River Murray sp. C), Coloburiscoides sp. and Baetis sp. 3 dominate. Snowy Creek, with a richer assemblage of 17 species, was dominated by Coloburiscoides sp., Baetis sp. 3 and two Austrophlebioides species. Monthly collections of mayfly nymphs and adults between September 1987 and August 1988, in both streams, allowed evaluation of possible life history changes in relation to dam operation. Coloburiscoides sp. and Baetis sp. 3 had synchronous life histories at both regulated and unregulated sites. Coloburiscoides appeared to be univoltine, and Baetis polyvoltine. At the regulated site, nymphal abundance in both Coloburiscoides and Baetis declined during the summer release, which coincided with the beginning of nymphal recruitment and appeared to delay nymphal hatching in Coloburiscoides. © 1998 John Wiley & Sons, Ltd.     

Reducing Carryover Effects on the Migration and Spawning Success of Sockeye Salmon through a Management Experiment of Dam Flows

Effective dam management requires an understanding of the ecological impact of a facility and its operations on individual fish and fish populations. Traversing high flows downstream of dams is an energetically challenging activity that could influence survival and spawning success following passage. Carryover effects, however, are an underappreciated consequence of dam passage that have been overlooked by researchers and natural resource managers. We conducted a large‐scale management experiment to determine if the operation of dam attraction flows could be changed to reduce high sockeye salmon Oncorhynchus nerka mortality following passage and increase spawning success. We tested two flow conditions: (i) a baseline condition—currently used by managers—that released high attraction flows directly adjacent to the entrance to a vertical‐slot fishway and (ii) an alternative condition that released attraction flows 10 m away from the fishway entrance to reduce the flows fish swim through while approaching the passage structure. We tagged 637 sockeye salmon with telemetry tags to monitor dam passage, post‐passage survival to spawning grounds and spawning success under the two flow conditions. Validated fish counters at the exit of the fishway and on spawning grounds were used to generate population level estimates of survival to spawning grounds. Individuals exposed to baseline flow conditions spent two times longer recovering from dam passage and exhibited 10% higher mortality following passage than those exposed to alternative flows. Release of alternative flows for 10 days assisted approximately 550 fish (or 3% of total spawners) in reaching spawning grounds. Once on spawning grounds, female spawning success was strongly influenced by individual spawning characteristics (longevity and date of arrival on spawning grounds) and not dam flow condition. Our findings highlight a cost‐effective solution that decreases mortality following passage simply by altering the location of dam flow releases and not reductions in discharge. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.     

THE RELATIONSHIP BETWEEN THERMAL REGIME ALTERATION AND SPAWNING DELAY OF THE FOUR MAJOR CHINESE CARPS IN THE YANGTZE RIVER BELOW THE THREE GORGES DAM

Large dams often alter flow and thermal regimes downstream, resulting in fish spawning delays and larval abundance declines. Accurate prediction of the delayed spawning period under changed thermal regime is critical for selecting a correct timing to modify dam operation and to release the environmental flow needed to enhance fish spawning. We used correlation analysis to investigate the relationship between thermal regime alteration and spawning delay of the four major Chinese carps (FMCC) below the Three Gorges Dam in the Yangtze River, China, using a 13‐year ecological data series (1997–2009). Eighteen variables were defined to quantify thermal regime and related to two variables representing spawning timing. Our results demonstrate that the start of FMCC spawning has been delayed from early May to middle June since the Three Gorges Dam initiated operation in 2003. Water temperature declines of 2 °C–4 °C in March, April and May (a critical period for gonad development) were the principal reason for the observed spawning delay. The variable most associated with spawning timing was the arrival date of the cumulative temperature needed for gonad development from stages IV to V (D_DegDayIV–V), which describes the long‐term impacts of the timing, magnitude and duration of thermal regime upon gonad development. Only the cumulative temperature for gonad development and the minimum temperature for FMCC spawning (18 °C) are both satisfied, the occurrence of suitable flow conditions, that is, flow increase or flash flood, would produce a successful spawning event. Consequently, we suggest that the experimental flow increase process of the Three Gorges Reservoir aimed at enhancing FMCC spawning should initiate after 15 June when the requisite thermal regime can be met. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermal regime suitability: Assessment of upstream range restoration potential for Colorado pikeminnow,a warmwater endangered fish

Dams have reduced distribution of the endangered Colorado pikeminnow Ptychocheilus lucius in the upper Colorado River basin: low‐head diversion dams blocked upstream passage and large dams inundated free‐flowing segments and cooled downstream reaches with deep‐water releases. To date, range restoration efforts in the Colorado and Gunnison Rivers have focused on building fish ladders around diversion dams to allow recolonization of upstream reaches. Upstream thermal suitability for this warmwater cyprinid was assessed using temperature data and existing distributional information from river reaches where Colorado pikeminnow movements were unrestricted. Among‐site thermal regime comparisons were made using mean annual thermal units (ATU), derived from mean daily temperatures during 1986–2005 and the relation between temperature and Colorado pikeminnow growth. Upstream distributional limits in the Yampa and Gunnison Rivers occurred where in‐channel thermal regimes fell below a long‐term mean of 47–50 ATU, suggesting that two Colorado River fish ladders will make available an estimated 17 km of thermally suitable habitat. A Gunnison River fish ladder successfully re‐established access to 54 km of suitable habitat, but 32 km of critical habitat upstream remains unsuitable. Suitability there could be achieved by raising temperatures only 1–2°C from late May to mid‐October with installation of a temperature control device on an upstream dam. Maximum, main‐channel, summer temperatures did not limit Colorado pikeminnow distribution in downstream reaches of the upper Colorado River. Published in 2010 by John Wiley & Sons, Ltd.     

Understanding the Thermal Regime of Rivers Influenced by Small and Medium Size Dams in Eastern Canada

Although small and medium‐size dams are prevalent in North America, few studies have described their year‐round impacts on the thermal regime of rivers. The objective of this study was to quantify the impacts of two types of dams (run‐of‐river, storage with shallow reservoirs) on the thermal regime of rivers in eastern Canada. Thermal impacts of dams were assessed (i) for the open water period by evaluating their influence on the annual cycle in daily mean water temperature and residual variability and (ii) for the ice‐covered winter period by evaluating their influence on water temperature duration curves. Overall, results showed that the run‐of‐river dam (with limited storage capacity) did not have a significant effect on the thermal regime of the regulated river. At the two rivers regulated by storage dams with shallow reservoirs (mean depth < 6 m), the annual cycle in daily mean water temperature was significantly modified which led to warmer water temperatures in summer and autumn. From August to October, the monthly mean water temperature at rivers regulated by storage dams was 1.4 to 3.9°C warmer than at their respective reference sites. During the open water period, the two storage dams also reduced water temperature variability at a daily timescale while increased variability was observed in regulated rivers during the winter. Storage dams also had a warming effect during the winter and the winter median water temperature ranged between 1.0 and 2.1°C downstream of the two storage dams whereas water temperature remained stable and close to 0°C in unregulated rivers. The biological implications of the altered thermal regimes at rivers regulated by storage dams are discussed, in particular for salmonids. Copyright © 2016 John Wiley & Sons, Ltd.     

Simulating effects of hydro‐dam alteration on thermal regime and wild steelhead recruitment in a stable‐flow Lake Michigan tributary

Hydroelectric dams may affect anadromous fish survival and recruitment by limiting access to upstream habitats and adversely affecting quality of downstream habitats. In the Manistee River, a tributary to Lake Michigan, two hydroelectric dams potentially limit recruitment of anadromous rainbow trout (steelhead) by increasing tailrace water temperatures to levels that significantly reduce survival of young‐of‐year (YOY) fish. The objectives of this study were to determine whether proposed restoration scenarios (dam removals or a bottom withdrawal retrofit) would alter the Manistee River thermal regime and, consequently, improve wild steelhead survival and recruitment. Physical process models were used to predict Manistee River thermal regimes following each dam alteration scenario. Empirical relationships were derived from historical field surveys to quantify the effect of temperature on YOY production and potential recruitment of Manistee River steelhead. Both dam alteration scenarios lowered summer temperatures and increased steelhead recruitment by between 59% and 129%, but total recruitments were still low compared to other Great Lakes tributaries. Considering only temperature effects, bottom withdrawal provides the greatest promise for increasing natural steelhead recruitment by decreasing the likelihood of year‐class failures in the warmest summers. Results of this study may allow managers to evaluate mitigation alternatives for Manistee River dams during future relicensing negotiations, and illustrate the utility of physical process temperature models in groundwater‐fed rivers. Copyright © 2004 John Wiley & Sons, Ltd.     

Environmental flow enhances native fish spawning and recruitment in the Murray River,Australia

Environmental flows aim to mimic components of a river's natural flow variability, including the magnitude, frequency, timing, duration, rate of change and the predictability of flow events. Aspects of the natural flow regime are thought to be linked to critical components of the life history strategies of many riverine fishes, including spawning and recruitment. In the Murray River, Australia, environmental flows are increasingly being used as a restoration tool; however, there is little information about the response of fish to these managed flow events. This study reports on the results from a 3‐year study on the effects of water management on the spawning and recruitment of four native fish species in the mid‐Murray River system. Two of these years were hydrologically similar, while the third year encompassed an extensive period of floodplain inundation, including the use of the largest environmental flow allocation to date in Australia. Drift nets were used to collect the drifting eggs and larvae of four iconic native species throughout their spawning season each year. Young‐of‐year were collected in the following autumn. Although golden perch and silver perch eggs were collected in all 3 years, both species increased their spawning activity during the major flood period compared to the previous two seasons. Murray cod and trout cod appeared not to increase their spawning activity in the flood year, but their recruitment may be increased when floodplain inundation occurs at times when their larvae and juveniles are present, most likely through the generation of abundant food resources. Whilst further study is required to confirm the role and mechanism of flooding in the spawning and recruitment of these species; this study provides important evidence of a link between the provision of an environmental flood and fish spawning and recruitment, and has significant implications for managing flows in regulated rivers. Copyright © 2008 John Wiley & Sons, Ltd.     

A simplified water temperature model for the Colorado River below Glen Canyon Dam

Glen Canyon Dam, located on the Colorado River in northern Arizona, has affected the physical, biological and cultural resources of the river downstream in Grand Canyon. One of the impacts to the downstream physical environment that has important implications for the aquatic ecosystem is the transformation of the thermal regime from highly variable seasonally to relatively constant year‐round, owing to hypolimnetic releases from the upstream reservoir, Lake Powell. Because of the perceived impacts on the downstream aquatic ecosystem and native fish communities, the Glen Canyon Dam Adaptive Management Program has considered modifications to flow releases and release temperatures designed to increase downstream temperatures. Here, we present a new model of monthly average water temperatures below Glen Canyon Dam designed for first‐order, relatively simple evaluation of various alternative dam operations. The model is based on a simplified heat‐exchange equation, and model parameters are estimated empirically. The model predicts monthly average temperatures at locations up to 421 km downstream from the dam with average absolute errors less than 0.5°C for the dataset considered. The modelling approach used here may also prove useful for other systems, particularly below large dams where release temperatures are substantially out of equilibrium with meteorological conditions. We also present some examples of how the model can be used to evaluate scenarios for the operation of Glen Canyon Dam. Published in 2008 by John Wiley & Sons, Ltd.     

Thermal habitat assessment of alternative flow scenarios in a tailwater fishery

Tailwaters below hydropower dams can create desirable coldwater trout fisheries; however, a flow regime ideal for hydropower often presents challenges for management of the fishery. The Smith River tailwater (Henry County, VA) offers a self‐sustaining brown trout fishery managed for trophy trout (≥ 406 mm), yet trophy‐sized fish are rare. Slow growth and small size are likely caused by any one or a combination of thermal habitat, limited food resources, and/or physical habitat. To evaluate the potential for thermal habitat improvement, temperature changes resulting from alternative flows were assessed with a one‐dimensional hydrodynamic model coupled with a water temperature model. Simulated temperatures from each flow scenario were assessed every 2 river kilometres over a 24 kilometre river section below the dam for occurrence of optimal growth temperatures, as well as compliance with Virginia Department of Environmental Quality hourly temperature change and daily maximum temperature standards. The occurrence of optimal growth temperatures increased up to 11.8% over existing conditions by releasing water in the morning, decreasing the duration of release, and not increasing baseflow. Incidences of hourly temperature changes greater than 2°C were reduced from 4% to 0–1.2% by non‐peaking releases, increasing baseflow, morning releases, and decreasing the duration of release. Maximum temperature occurrence (> 21°C) decreased from 1.3% to 0–0.1% by releasing flows daily to prevent elevated temperatures on non‐generation days, increasing baseflow, increasing duration of release, and releasing in the morning rather than evening. Despite conflicting adjustments to best improve all thermal criteria concurrently, a 7‐day/week, morning, one hour release regime was determined to improve all criteria throughout the tailwater compared to existing conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Modelling the effects of dam removal on migratory walleye (Sander vitreus) early life‐history stages

Many dams in the USA have outlived their intended purpose and an increasing number are being considered for removal. Yet, quantitative studies of the potential physical, biological and ecological responses are needed to assess dam removal decisions. In this paper, the responses of migratory walleye (Sander vitreus) to increased spawning habitat availability as a result of dam removal was studied by comparing scenarios with and without a high‐head dam in the Sandusky River (Ohio), a major tributary to Lake Erie. A conceptual, ecological model was proposed to define the relationship between hydrodynamics and walleye spawning, egg hatching, larval drift and survival. A mathematical, ecological model of the early life‐history stages was then developed and coupled with time series of depth and velocity predictions over the spawning grounds from a 1‐D hydrodynamic model. Model simulations were run for 1984–1993 for both the with‐ and without‐dam scenarios to assess the potential benefit of dam removal. The simulation results demonstrated that velocity, depth and water temperature are major factors influencing adult walleye spawning success. Without the dam, 10 times the amount of spawning habitat would be available for walleye to spawn. This increase in spawning habitat area resulted in up to five times the total egg deposition and seven times the larval output to the nursing grounds, based on the assumption that 5% of the walleye population of Lake Erie migrated up the Sandusky River to spawn. We concluded that the spawning habitat in the current condition (with the dam) is limiting and additional spawning habitat upstream could significantly increase the number of larval walleye drifting to Lake Erie. The model sensitivity analysis showed that the number of walleye migrating up the river in spring is the dominant factor for larval recruitment to the lake. Copyright © 2006 John Wiley & Sons, Ltd.     

Toledo Bend reservoir and geomorphic response in the lower Sabine River

Downstream geomorphic responses of stream channels to dams are complex, variable, and difficult to predict, apparently because the effects of local geological, hydrological, and operational details confound and complicate efforts to apply models and generalizations to individual streams. This sort of complex geomorphic response characterizes the Sabine River, along the Texas and Louisiana border, downstream of the Toledo Bend dam and reservoir. Toledo Bend controls the flow of water and essentially prevents the flux of sediment from three‐quarters of the drainage basin to the lower Sabine River. Although the channel is scoured immediately downstream of the dam, further downstream there is little evidence of major changes in sediment transport or deposition, sand supply, or channel morphology attributable to the impoundment. Channels are actively shifting, banks are eroding, and sandbars are migrating, but not in any discernibly different way than before the dam was constructed. The Sabine River continues to transport sand downstream, and alluvial floodplains continue to accrete. The relatively small geomorphic response can be attributed to several factors. While dam releases are unnaturally flashy and abrupt on a day‐to‐day basis, the long‐term pattern of releases combined with some downstream smoothing creates a flow regime in the lower basin which mimics the pre‐dam regime, at least at monthly and annual time scales. Sediment production within the lower Sabine basin is sufficient to satisfy the river's sediment transport capacity and maintain pre‐dam alluvial sedimentation regimes. Toledo Bend reservoir has a capacity: annual inflow ratio of 1.2 and impounds 74% of the Sabine drainage basin, yet there has been minimal geomorphic response in the lower river, which may seem counterintuitive. However, the complex linked geomorphic processes of discharge, sediment transport and loads, tributary inputs, and channel erosion include interactions which might increase as well as decrease sediment loads. Furthermore, if a stream is transport‐limited before impoundment, the reduced sediment supply after damming may have limited impact. Copyright © 2003 John Wiley & Sons, Ltd.     

Modification of temperature behaviour through regulation of a British river system

The effects of flow regulation on temperature behaviour in the River Exe, Devon, U.K. have been studied, and attention is given to the local impact of impoundment and its downstream persistence. Temperature levels and seasonal thermal regime are considered as well as diel temperature fluctuations and temperatures during extreme weather conditions. Variations in temperature during individual reservoir releases have also been monitored. The impact of impoundment has been to make the stream environment immediately below the dam more homothermous so that temperatures rearely rise above 17·5°C or fall below 2·0°C, and monthyl average diel ranges are < 3 and < 1°C in summer and winter months respectively. In contrast to other reservoirs in Britain and abroad, this effect has been largely caused by increased groundwater flow downstream from the reservoir following impoundment. Regulation has also affected downstream temperature behaviour and has moderated the thermal regime of the Exe mainstream. This influence is generally restricted to a distance of up to 20 km from the dam, but in conditions of hot weather and low flows it may extend to almost 40 km from the impoundment.     

Effects of Dam Removal on Tule Fall Chinook salmon Spawning Habitat in the White Salmon River,Washington

Condit Dam is one of the largest hydroelectric dams ever removed in the USA. Breached in a single explosive event in October 2011, hundreds‐of‐thousands of cubic metres of sediment washed down the White Salmon River onto spawning grounds of a threatened species, Columbia River tule fall Chinook salmon Oncorhynchus tshawytscha. We investigated over a 3‐year period (2010–2012) how dam breaching affected channel morphology, river hydraulics, sediment composition and tule fall Chinook salmon (hereafter ‘tule salmon’) spawning habitat in the lower 1.7 km of the White Salmon River (project area). As expected, dam breaching dramatically affected channel morphology and spawning habitat due to a large load of sediment released from Northwestern Lake. Forty‐two per cent of the project area that was previously covered in water was converted into islands or new shoreline, while a large pool near the mouth filled with sediments and a delta formed at the mouth. A two‐dimensional hydrodynamic model revealed that pool area decreased 68.7% in the project area, while glides and riffles increased 659% and 530%, respectively. A spatially explicit habitat model found the mean probability of spawning habitat increased 46.2% after dam breaching due to an increase in glides and riffles. Shifting channels and bank instability continue to negatively affect some spawning habitat as sediments continue to wash downstream from former Northwestern Lake, but 300 m of new spawning habitat (river kilometre 0.6 to 0.9) that formed immediately post‐breach has persisted into 2015. Less than 10% of tule salmon have spawned upstream of the former dam site to date, but the run sizes appear healthy and stable. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

EFFECTS OF FLOW RELEASES ON MACROINVERTEBRATE ASSEMBLAGES IN THE INDIAN AND HUDSON RIVERS IN THE ADIRONDACK MOUNTAINS OF NORTHERN NEW YORK

The effects of flow releases (daily during spring and four times weekly during summer) from a small impoundment on macroinvertebrate assemblages in the lower Indian River and upper Hudson River of northern New York were assessed during the summers of 2005 and 2006. Community indices, feeding guilds, dominant species and Bray–Curtis similarities at three sites on the Indian River, below a regulated impoundment, were compared with those at four control sites on the Cedar River, below a run‐of‐the‐river impoundment of comparable size. The same indices at four less‐likely affected sites on the Hudson River, below the mouth of the Indian River, were compared with those at an upstream control site on the Hudson River. Results show that the function and apparent health of macroinvertebrate communities were generally unaffected by atypical flow regimes and/or altered water quality at study reaches downstream from both dams in the Indian, Cedar and Hudson Rivers. The lentic nature of releases from both impoundments, however, produced significant changes in the structure of assemblages at Indian and Cedar River sites immediately downstream from both dams, moderate effects at two Indian River sites 2.4 and 4.0 km downstream from its dam, little or no effect at three Cedar River sites 7.2–34.2 km downstream from its dam, and no effect at any Hudson River site. Bray–Curtis similarities indicate that assemblages did not differ significantly among sites within similar impact categories. The paucity of scrapers at all Indian River sites, and the predominance of filter‐feeding Simulium gouldingi and Pisidium compressum immediately below Abanakee dam, show that only minor differences in dominant species and trophic structure of macroinvertebrate communities occurred at affected sites in the Indian River compared to the Cedar River. Thus, flow releases had only a small, localized effect on macroinvertebrate communities in the Indian River. Copyright © 2011 John Wiley & Sons, Ltd.     

Post‐Spawning Survival and Downstream Passage of Landlocked Atlantic Salmon (Salmo salar) in a Regulated River: Is There Potential for Repeat Spawning?

Repeat salmonid spawners may make large contributions to total recruitment and long term population stability. Despite their potential importance, relatively little is known about this phase of the life history for anadromous populations, and nothing has been reported for landlocked populations. Here, we studied post‐spawning behaviour and survival of landlocked Atlantic salmon in relation to downstream dam passage in the River Klarälven, Sweden. Eight hydropower stations separate the feeding grounds in Lake Vänern from the spawning grounds in the River Klarälven, and no measures to facilitate downstream migration are present in the river. Forty‐nine percent of the salmon survived spawning and initiated downstream migration. Females and small fish had higher post‐spawning survival than males and large fish. The post‐spawners migrated downstream in autumn and spring and remained relatively inactive in the river during winter. Downstream migration speed in the free flowing part of the river was highly variable with a median of 9.30 km/day. Most fish passed the first hydropower station via upward‐opening spill gates after a median residence time in the forebay of 25 min. However, no tagged fish survived passage of all eight hydropower stations to reach Lake Vänern. This result underscores the need for remedial measures to increase the survival of downstream migrating kelts. Copyright © 2015 John Wiley & Sons, Ltd.