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.     

The impact of cold water releases on the critical period of post‐spawning survival and its implications for Murray cod (Maccullochella peelii peelii): a case study of the Mitta Mitta River,southeastern Australia

The effects of cold water releases, as a by‐product of storing irrigation water in large dams, has been a source of great concern for its impact on native freshwater fish for some time. The Mitta Mitta River, northeast Victoria, is impacted by altered thermal regimes downstream of the fourth largest dam in Australia, Dartmouth dam, with some daily temperatures 10–12°C below normal. Murray cod (Maccullochella peelii peelii) were endemic to the Mitta Mitta River; however, resident Murray cod have not been found in this river since 1992. The response of eggs and hatched larvae from Murray cod to different temperature gradients of water were measured and the post‐spawning survival recorded. As a case study, post‐spawning survival was then inferred from flow data for each year of operation of Dartmouth Dam, recorded since first operation in 1978, and included in a stochastic population model to explore the impact of the altered (historical) thermal regime on population viability. Experimental results revealed no egg and larval survival below 13°C and predicted historical temperature regimes point to more than 15 years of low temperatures in the Mitta Mitta River. Population modelling indicates that the impact of cold water releases on post‐spawning survival is a significant threatening process to the viability of a Murray cod population. Additionally, we consider changes to the thermal regime to explore how the thermal impact of large dams may be minimized on downstream fish populations through incrementally increasing the temperature of the releases. The modelled Murray cod population responds to minor increases in the thermal regime; however, threats are not completely removed until an increase of at least 5–6°C. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of elevated water temperature on fish and macroinvertebrate communities below small dams

Many studies have investigated the ecological changes that occur below dams that release cold, hypolimnetic water, but very few studies have looked at the effects of the release of warm, surface waters. The effect of small, surface release dams on downstream thermal regimes is a major habitat concern for many cold‐water systems, however. The objective of this study was to examine the effects of summer temperature increases due to impoundment on downstream fish and macroinvertebrate communities in cold‐water streams. We sampled fish, macroinvertebrates and habitat upstream and downstream of dams on ten rivers during the summers of 1998 and 1999. Changes in mean summer temperature downstream varied from a cooling of 1 °C to an increase of more than 5 °C. Increasing temperatures downstream coincided with lower densities of several cold‐water fish species, specifically brown trout (Salmo trutta), brook trout (Salvelinus fontinalis) and slimy sculpin (Cottus cognatus) while overall fish species richness increased downstream. Density of mottled sculpin (Cottus bairdi), another cold‐water species, was not related to temperature changes below the dams. Macroinvertebrates showed shifts in community composition below dams that increased temperature. This study provides information useful for determining the extent of impact of these small, surface release dams, which are abundant across the country. Copyright © 2003 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.     

Physical and Biological Responses to an Alternative Removal Strategy of a Moderate‐sized Dam in Washington,USA

Dam removal is an increasingly practised river restoration technique, and ecological responses vary with watershed, dam and reservoir properties, and removal strategies. Moderate‐sized dams, like Hemlock Dam (7.9 m tall and 56 m wide), are large enough that removal effects could be significant, but small enough that mitigation may be possible through a modified dam removal strategy. The removal of Hemlock Dam in Washington State, USA, was designed to limit channel erosion and improve fish passage and habitat by excavating stored fine sediment and reconstructing a channel in the former 6‐ha reservoir. Prior to dam removal, summer daily water temperatures downstream from the dam increased and remained warm long into the night. Afterwards, a more natural diel temperature regime was restored, although daily maximum temperatures remained high. A short‐lived turbidity pulse occurred soon after re‐watering of the channel, but was otherwise similar to background levels. Substrate shifted from sand to gravel–cobble in the former reservoir and from boulder to gravel–cobble downstream of the dam. Initially, macroinvertebrate assemblage richness and abundance was low in the project area, but within 2 years, post‐removal reaches upstream and downstream of the dam had diverse and abundant communities. The excavation of stored sediment and channel restoration as part of the dam removal strategy restored river continuity and improved benthic habitat while minimizing downstream sedimentation. This study provides a comparison of ecological effects with other dam removal strategies and can inform expectations of response time and magnitude. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

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.     

Salmonid observations at a Klamath River thermal refuge under various hydrological and meteorological conditions

The Beaver Creek confluence with the main‐stem Klamath River was studied to assess salmonid use in a thermal mixing zone under various summer hydrological and meteorological conditions. Main‐stem flow releases from Iron Gate Dam ranged from 17 cms (615 cfs) to 37 cms (1320 cfs) during the study period and main‐stem water temperatures ranged from 19.5 to 26°C. A grid was constructed to define the thermal refuge as a system of cells. Temperatures were monitored using remote temperature loggers and fish counts were conducted using daytime snorkelling. Most juvenile salmonids were observed moving into the refuge when main‐stem temperatures exceeded 22–23°C. Salmonids in the thermal refuge did not necessarily seek the coolest water, but were generally located in habitats commensurate with species‐specific behavioural needs within their thermal tolerance range. Such ranges largely occurred within refuge areas. Variable meteorological conditions confounded observable biological thermal benefit to fish resulting from higher or lower main‐stem flows. Thermal regime dynamics indicated that under the hydrological and meteorological conditions observed, higher flows from Iron Gate Dam showed some ability to change the structure of the refuge area. It appeared that without the thermal refuge, main‐stem flows alone could not sustain the salmonid population because high water temperatures usually exceeded their published thermal tolerance limits. Copyright © 2007 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.     

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.     

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.     

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.     

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.     

Tributary confluences are dynamic thermal refuges for a juvenile salmonid in a warming river network

As rivers warm, cold‐water fish species may alleviate thermal stress by moving into localized thermal refuges such as cold‐water plumes created by cool tributary inflows. We quantified use of two tributary confluence plumes by juvenile steelhead, Oncorhynchus mykiss, throughout the summer, including how trout positioned themselves in relation to temperature within confluence plumes. At two confluences, Cedar and Elder creeks, along the South Fork Eel River, California, USA, we monitored temperatures using in situ logger grids throughout summer 2016. Fish were counted within confluences via snorkel surveys five times a day on 5 days at each site. We found diel and seasonal dependence on confluence use by steelhead, especially at the Cedar Creek confluence, where mainstem temperatures exceeded 28°C. At this site, fish moved into the confluence on the warmest days and warmest times of the day. Fish observed within the Cedar Creek confluence plume were most common in locations between 20–22°C, rather than the coldest locations (14.5°C). At Elder Creek, where mainstem temperatures remained below 24°C, there was little relationship between mainstem temperature and steelhead presence in the confluence plume. At both sites, steelhead distribution within plumes was influenced by spatial variation of temperature and mean temperature in surveyed grid cells. Our results show that cool tributaries flowing into warmer mainstem reaches (over 24°C) likely create important thermal refuges for juvenile steelhead. As mainstem rivers warm with climate change, cool‐water tributary inputs may become more important for sustaining cold‐water salmonids near the southern end of their range.     

三门峡大坝温度观测资料分析

三门峡水利枢纽大坝为混凝土重力坝,原设计选择其溢流坝和安装场坝为重点观测坝段,因此,在施工中埋设了各种观测仪器1000多支。经对1958～1988年气温、坝体混凝土温度、基岩温度及水库水温观测资料分析表明:三门峡大坝温度变化规律虽与一般重力坝不同,但它却比较全面地反映了防洪与径流发电具体运用的特性。     

控制幕作用下水库温流场特征初步研究

大型水库建成后由于库区水动力学特性、光混特性、热量特性等发生了改变,水库垂向水温将呈现出明显的分层现象,对库区及其下游河道的生态环境造成显著影响,常通过采用分层取水措施加以改善。针对控制幕分层取水方法,通过温分层水槽试验,研究了分层水体中设置水温控制幕后,控制幕前水温、流速分布特征以及下泄水温的变化情况。试验考虑了不同热冷水流量比、控制幕距取水口距离、取水口位置和控制幕遮挡率等因素的影响。试验结果表明:控制幕设置后,控制幕上游近幕布区域温跃层厚度减小,温跃层强度增大,水体掺混受到抑制;控制幕下游温跃层厚度增大明显,控制幕促进了控制幕下游水体的垂向扩散,破坏了原水体分层现象;控制幕上游近幕布区域,热冷水流量比越小取水口位置越低,控制幕遮挡率越小温跃层厚度越厚,温跃层强度越小。热冷水流量比增大,取水口位置提高以及控制幕遮挡率增加均会使下泄水温升高。     

Effects of the Cernadilla–Valparaiso reservoir system on the River Tera

Water chemistry and macroinvertebrates were studied in the River Tera (north-western Spain) to assess the effects on the river of two chained reservoirs with hypolimnetic release during the stratification period in 1991. The river-water variables most affected by the dam in this study are temperature, pH, conductivity, silicate, ammonia, nitrate and phosphate. Of these, temperature, with more constant values in the river after the dams, in contrast with diel and seasonal cycles, generates a special environment (short thermal amplitude) several kilometres downstream. On the other hand, ammonia, owing to the magnitude of its changes, seems to be the main factor affected by the dams, and a modifier of river water quality, although its values do not seem to be critical. Although dissolved oxygen is greatly affected by the dams, particularly during stratification conditions, bottom release by hollow-cone solves the problem of reoxygenation downstream from the dam. Unregulated stations presented the most diverse macroinvertebrate communities and also the highest values of the biotic index BMWP', typical of very clean waters. The stations influenced by the dams showed lower values, but with a gradual trend towards recovery downstream from the dam. At 10 km below the reservoir system, benthic communities showed an important recovery. Some management tools related to the ecological problems caused by this type of reservoir are discussed. © 1997 John Wiley & Sons, Ltd.     

Response of epiphytic diatom communities from the tailwaters of glen Canyon Dam,Arizona, to elevated water temperature

The composition of epiphytic diatom communities from the cold tailwaters (12°C) of Glen Canyon Dam, Arizona, was analysed after a 2 wk incubation period at 12°C, 18°C and 21°C. There was a significant change in diatom composition between 12°C and 18°C, while no significant changes occurred between 18°C and 21°C. This suggests that a temperature threshold exists between 12°C and 18°C for the diatom flora in the tailwaters of Glen Canyon Dam. At the two higher water temperatures, smaller and closely adnate taxa became more important numerically than larger, upright, cold water stenotherms. The potential importance of this compositional shift in epiphytic diatoms on macroinvertebrate grazers has management implications regarding different release programs from reservoirs.     

小湾拱坝温度场及温度应力全过程仿真研究

小湾拱坝作为高拱坝,其温控防裂是保证坝体正常施工和安全运行的重要措施。采用三维有限元法对小湾拱坝22号坝段施工期温度场及温度应力进行全过程仿真分析,得到了其温度场及温度应力变化的一般规律。仿真中考虑了坝体材料的热力学性能、浇筑过程、环境温度变化、封拱和蓄水过程,仿真结果对小湾高拱坝的温控设计有参考价值。     

Influence of dams on river water‐quality signatures at event and seasonal scales: The Sélune River (France) case study

Dams and reservoirs are known to disturb river‐water composition, among other impacts, with potential implications for downstream river ecosystems and water uses. Existing studies have emphasized the variable influence of dams on water composition according to the element, its speciation (dissolved vs. particulate), reservoir properties (residence times), reservoir functions (e.g., hydropower, irrigation), and management (water releases). A now common approach to analyzing hydrological, geochemical, and biological controls on element export from unregulated rivers is to study hydrochemical signatures such as concentration‐flow relationships. We investigated a case study to analyze hydrochemical signatures of a regulated river (Sélune River, western France) upstream and downstream of a chain of two hydropower dams, assuming that the dams disturbed the river's signatures, and that those disturbances would provide information about processes occurring in the reservoirs. Both seasonal and event‐scale signatures were analyzed over two contrasting hydrological years and a range of storm events. The dams induced a chemostatic downstream response to storm events whenever elements were diluted or concentrated upstream. Dams did not disturb the seasonality of major anions but did modify silica and phosphorus concentration‐flow relationships, especially during low flow. Such changes in dynamics of river‐water composition may affect downstream biological communities. This study presents an initial state of the hydrochemical signature of the downstream river, before the removal of the two dams.     

Influence of the Abaeté River on the reproductive success of the neotropical migratory teleost Prochilodus argenteus in the São Francisco River,downstream from the Três Marias Dam,southeastern Brazil

The curimatã‐pacu Prochilodus argenteus is an important characiform from the São Francisco River basin that performs long‐distance migrations for spawning upstream during the rainy season, when the temperature and photoperiod are elevated. Despite the interruption of the migratory routes by the Três Marias Dam and accentuated decline in fishing, the curimatã‐pacu still sustains the fisheries at the Três Marias region in recent decades. The objective of this study was to evaluate the reproductive activity of P. argenteus in two sections of the São Francisco River, downstream from the Três Marias Dam, during the rainy season. In the first 34 km of the river, immediately below the dam, most of the females were in gonadal resting. At 34–54 km downstream from the dam, following the confluence with a medium‐sized tributary, the Abaeté River, there was a high frequency of males and females in reproductive activity. Follicular atresia was more frequent in the upper section of the river while postovulatory follicles occurred predominantly in the lower section. Fulton's condition factor and gonadosomatic index indicated that the females were in a better physiological and reproductive condition below the confluence with the Abaeté River. In contrast to the females, the males were less affected by damming, and testicular maturation was largely achieved in two river sections. Thus, although the section of the São Francisco River immediately below the Três Marias Dam was found to be unfavourable for the reproduction of the migratory fishes due principally to the hypolimnetic water from the reservoir, reproductive success of P. argenteus was achieved below the Abaeté River. In this section, the species encountered appropriate conditions for maturation and spawning, i.e. warm temperatures above 24°C, high water flow and dissolved oxygen, and low water transparency. These results indicate the importance of a non‐regulated tributary to minimize the ecological impact of a dam on the downstream native fish communities. Copyright © 2005 John Wiley & Sons, Ltd.