Use of a flow deflector to protect rheophilic fish spawning grounds during hydropeaking

Rheophilic fishes are one of the ecological groups of fishes declining most quickly in number due to various habitat modifications and discharge regulations. Artificial rapid increases and decreases in discharge (hydropeaking) can cause severe damage to the eggs of rheophilic fishes. We investigated whether the effects of a water increase in hydropeaking on a spawning ground may be mitigated by a deflector installed at the top of the weir that diverts flow to other sections. At the research site, rheophilic asp (Leuciscus aspius) spawn annually in early spring, and their success might be affected by hydropeaking, with base discharge ranging from 3 to 7 m³ × s⁻¹ and peak discharge ranging from 16 to 25 m³ × s⁻¹ occurring 4 to 7 times during the asp spawning season and egg development period. To protect the adhesive eggs from detachment during peak discharge, a flow deflector (a wooden wall at the selected part of the weir) was installed to regulate discharge on the protected spawning ground. This measure allowed normal discharge under base flow conditions. During peak flow, a significant portion of the additional water was directed to the part of the river channel where egg abundance was lower and to the mill channel, where asp spawning was not present. While the total discharge increased 4.1 times compared to the base flow, the water discharge in the protected spawning ground increased only 2.7 times. This resulted in more than half of the asp eggs being retained in the protected channel. Although the use of such a measure is limited to specific local conditions where eggs are located just downstream of the weir, it can be a valid solution in highly fragmented rivers with hydropeaking and can lead to higher recruitment of rheophilic fishes.     

Assessing discharge use by spawning Atlantic salmon: A comparison of discharge electivity indices and PHABSIM simulations

The locations used by spawning Atlantic salmon (Salmo salar L.) in a reach of the Girnock Burn, Scotland, were monitored over three successive years. Reach discharge was estimated for each spawning observation using a conversion factor applied to continuous flow data from a gauge located in the catchment. Data on the availability and use of different discharges were used to construct a discharge electivity index for the reach. The index was compared to output from a Physical HABitat SIMulation (PHABSIM) model of the reach. Spawning fish used relatively high discharges, with the highest electivity value being for a discharge approximately three times the reach median flow. The electivity index and the PHABSIM weighted usable area (WUA) versus discharge curve were similar across the low flow range and both suggested similar optimum discharges for spawning (1.1 and 1.4 m³ s^?1 respectively). However, electivity values suggested unsuitable conditions were reached at discharges greater than 1.4 m³ s^?1 whereas PHABSIM predicted relatively high WUA values at discharges up to 2 m³ s^?1. Electivity indices provide an insight into discharge selection that is not dependent on hydraulic simulations or assumptions about microhabitat (depth, velocity, substrate) preferences. Moreover, they can be used to assess discharge suitability in hydraulically complex streams where the one‐dimensional hydraulic models used by PHABSIM may be inappropriate. However, unlike PHABSIM, they cannot be used to predict the suitability of flows outside observed discharge ranges and so are limited in their application. Further work is required to refine the methodology and assess its transferability to other streams. Nonetheless, indices may represent a useful tool that can be used to complement other methods of assessing instream flow needs. Copyright © 2002 John Wiley & Sons, Ltd.     

Flow and spawning habitat relationships for Dolly Varden: Understanding habitat–population dynamics in the Canadian Western Arctic

Northern form Dolly Varden (Salvelinus malma malma) have been designated as a species of Special Concern in Canada due to declines in population abundance and potential threats. Concern over detrimental effects of low flows on population abundance prompted research on how variability in discharge regimes influence habitat availability. Habitat suitability indices for prespawning and spawning adult anadromous Dolly Varden from two streams were integrated into a two‐dimensional hydrodynamic habitat model to assess the effect of flow variability on usable habitat. Regional hydrographs were used to identify an ecologically relevant range of flows that provided optimal spawning habitat for these populations and examine the relationship between abundance and discharge. Adults spawned in the tail end of pools at moderate water depths and water velocities, and used pebble‐ to cobble‐sized substrate for building redds; whereas, prespawning adults occupied deeper pools with moderate velocities and used cobble for cover. Model outputs showed that spawning habitat availability was optimized at flow rates between 1.6 and 3.0 m³/s and between 1.0 and 6.0 m³/s in Fish Hole Creek (FHC) and Little Fish Creek, respectively. A positive relationship between flows during the fall spawning period and abundance of the FHC population suggests that higher flows coinciding with optimal habitat availability may have contributed to positive recruitment. To strengthen and refine this habitat–population relationship for Dolly Varden in this area requires investigation of a broader suite of variables associated with environmental regimes and physical habitat in reaches used for spawning.     

黄河河口鱼类春季生态需水

黄河河口鱼类春季生态需水主要满足河道淡水鱼类栖息地及产卵场、河道洄游鱼类上溯通道和近海洄游鱼类低盐产卵场需求。综合考虑鱼类生活习性,径流传播以及与近海淡咸水混合时间和小浪底水库运行以来月均流量特征,鱼类需水应重点关注3—5月。依据河道淡水鱼类和洄游鱼类的生活习性,从洄游通道的全程连续性出发,需要的低流量为240 m~3/s。结合自然时期流量脉冲特征,每年需要一次4月中旬持续8 d的峰值为890 m~3/s的流量脉冲;在此条件下,春季入海径流量为21.6亿m~3,已满足近海洄游鱼类低盐产卵环境要求的21亿m~3冲淡水量。小浪底水库运行以来,平均春季径流量已达到21亿m~3。通过优化年内或年际调度模式,满足鱼类春季生态需水具有很大可行性。     

MACROINVERTEBRATE RESPONSE TO FLOW CHANGES IN A SUBALPINE STREAM: PREDICTIONS FROM TWO‐DIMENSIONAL HYDRODYNAMIC MODELS

Two‐dimensional hydrodynamic models are being used increasingly as alternatives to traditional one‐dimensional instream flow methodologies for assessing adequacy of flow and associated faunal habitat. Two‐dimensional modelling of habitat has focused primarily on fishes, but fish‐based assessments may not model benthic macroinvertebrate habitat effectively. We extend two‐dimensional techniques to a macroinvertebrate assemblage in a high‐elevation stream in the Sierra Nevada (Dana Fork of the Tuolumne River, Yosemite National Park, CA, USA). This stream frequently flows at less than 0.03 m³ s^?1 in late summer and is representative of a common water abstraction scenario: maximum water abstraction coinciding with seasonally low flows. We used two‐dimensional modelling to predict invertebrate responses to reduced flows that might result from increased abstraction. We collected site‐specific field data on the macroinvertebrate assemblage, bed topography and flow conditions and then coupled a two‐dimensional hydrodynamic model with macroinvertebrate indices to evaluate habitat across a range of low flows. Macroinvertebrate indices were calculated for the wetted area at each flow. A surrogate flow record based on an adjacent watershed was used to evaluate frequency and duration of low flow events. Using surrogate historical records, we estimated that flow should fall below 0.071 m³ s^?1 at least 1 day in 82 of 95 years and below 0.028 m³ s^?1 in 48 of 95 years. Invertebrate metric means indicated minor losses in response to modelled discharge reductions, but wetted area decreased substantially. Responses of invertebrates to water abstraction will likely be a function of changing habitat quantity rather than quality. Copyright © 2011 John Wiley & Sons, Ltd.     

Movement and summer habitat of brown trout (Salmo trutta) below a pulsed discharge hydroelectric generating station

Radiotelemetry was used to investigate detailed movement and summer habitat of brown trout Salmo trutta (size range 157–488 mm TL, n=18) in the Kananaskis River, Alberta. Flows in the Kananaskis River respond to pulsed daily discharge from an upstream hydroelectric generating facility (range 0.15–25 m³ s⁻¹). Wetted area available for brown trout doubled during periods of high flow. Fluctuating river levels did not appear to influence the degree to which brown trout moved within the study site. However, there was evidence that brown trout used cover and pools more as discharge increased. During high flow conditions, brown trout used similar depths (63 cm), and significantly lower surface water velocities than during low flow conditions. Brown trout also moved closer to shore into interstitial spaces among woody debris and root complexes during high flow. Pool habitats were used most often compared with all other habitat types combined. Pools with large woody debris accounted for 75% of all habitat observations. Woody debris was used more often than all other cover types. Results of the study indicate that the effects of river regulation on brown trout appear to have been moderated by woody debris in pools and along river banks, which provided refuge from high water velocities during periods of high flow. Copyright © 1999 John Wiley & Sons, Ltd.     

Application of a 2D hydrodynamic model to design of reach‐scale spawning gravel replenishment on the Mokelumne River,California

In‐stream chinook salmon (Oncorhynchus tschawytscha) spawning habitat in California's Central Valley has been degraded by minimal gravel recruitment due to river impoundment and historic gravel extraction. In a recent project marking a new direction for spawning habitat rehabilitation, 2450 m³ of gravel and several boulders were used to craft bars and chutes. To improve the design of future projects, a test was carried out in which a commercial modelling package was used to design and evaluate alternative gravel configurations in relation to the actual pre‐ and post‐project configurations. Tested scenarios included alternate bars, central braid, a combination of alternate bars and a braid, and a flat riffle with uniformly spaced boulders. All runs were compared for their spawning habitat value and for susceptibility to erosion. The flat riffle scenario produced the most total, high, and medium quality habitat, but would yield little habitat under flows deviating from the design discharge. Bar and braid scenarios were highly gravel efficient, with nearly 1 m² of habitat per 1 m³ of gravel added, and yielded large contiguous high quality habitat patches that were superior to the actual design. At near bankfull flow, negligible sediment entrainment was predicted for any scenario. Copyright © 2004 John Wiley & Sons, Ltd.     

Migratory behaviour of adult fast-growing brown trout (Salmo trutta,L.) In relation to water flow in a regulated Norwegian river

The migration pattern of spawners of brown trout (Salmo trutta) in relation to water flow was analysed by radio-tracking in the regulated River Gudbrandsdalslågen, Norway. During the upstream spawning migration in the high flow period, trout (2–12 kg) were caught, tagged and released 15 km downstream of a fish ladder at the Hunderfossen waterfall. The released fish displayed a systematic and directional upstream movement to the outlet of the tunnel from the hydroelectricity plant. In autumn and winter there is a minimum water discharge of 20–2 m³/s on p.s. in the river between the dam and the outlet of the tunnel, which has a discharge of 200–300 m³/s. When the water flowing over the Hunderfossen dam decreased to 20 m³/s, the ascent of brown trout up the river stopped and fish periodically entered the power plant tunnel. To determine the flow necessary to attract fish into the spawning reach above the tunnel outlet, two experiments were undertaken using 12 and 17 radio-tagged trout. In the first experiment, 60 m³/s of water released for 24 h resulted in the migration of 50% of the trout up the river. The second experiment, releasing 60 m³/s for 24 h, followed by 30 m³/s for 24 h two days later, resulted in the migration of 60% of the trout. Only one fish ascended the river at a flow of 30 m³/s. It is recommended that a repeated release of water at 60 m³/s is made in periods of minimum water discharge to save the spawning migration. The results demonstrate the advantage of using radio-tracking in experiments dealing with fish migration in relation to water-flow management.     

Larval fish catches in the lower Milk River,Montana in relation to timing and magnitude of spring discharge

Larval fishes were sampled in the Milk River, Missouri River drainage, Montana from May to August 2002, 2003 and 2004 to describe temporal spawning distribution in relation to spring discharge. Total larval catch‐per‐unit‐effort (CPUE) in 2002 (28.9 fish/100 m³) was an estimated 29 times greater than in 2003 (0.99 fish/100 m³) and 16 times greater than in 2004 (1.78 fish/100 m³). In 2003 and 2004 more than one third of the total catch occurred before 12 June whereas in 2002, only 5% of the total catch occurred before 12 June. Marked differences in larval species composition were also observed between years, suggesting that a later peak in discharge may benefit some species and an earlier peak others. In 2002, when flows peaked later (at 77 m³ s^?1), common carp Cyprinus carpio represented 37% of the total larval catch. Common carp were proportionally less abundant in 2003 (7.2%) and 2004 (1.4%) than in 2002. In 2004, when flows peaked (at 163 m³ s^?1) 32 days earlier than in 2002 but only 15 days earlier than in 2003 (at 73 m³ s^?1), shorthead redhorse Moxostoma macrolepidotum and suckers Catostomus sp. were the numerically dominant taxa. These results indicate that the timing, not necessarily the magnitude, of peak spring discharge may influence spawning success in the lower Milk River, as indicated by larval fish catches. Copyright © 2008 John Wiley & Sons, Ltd.     

A review of the effects of water transfers in the La Grande Hydroelectric Complex (Québec,Canada)

Construction of the La Grande Complex in Eastern Canada called for complete or partial diversion of six rivers, the mean annual discharge of which varied from 60 to 1600 m³ s^?1, and the transfer of water from two adjoining watersheds (1586m³ s^?1) into La Grande Rivière. Three of these rivers with reduced flow, Eastmain (from 700 to 95m³ s^?1), Opinaca (from 260 to 35m³ s^?1), and Caniapiscau (from 1708 to 960m³ s^?1) and the waterways with increased flows, Boyd-Sakami (from 1 to 811m³ s^?1) and La Grande Rivière (from 1760 to 3400m³ s^?1) were intensively monitored from 1978 to 1988, while the others were surveyed sporadically. Very few modifications were observed, compared to previous conditions, in banks stability, water quality, and aquatic fauna of the affected rivers: those which appeared can be explained by the water level fluctuations, the water quality of the tributaries of the residual drainage basin, and/or by the direct influence of the reservoirs. In James Bay, the areal extent of the Eastmain River and La Grand Rivière plumes varied with discharge in an exponential relation, mostly under ice cover; resources from the coastal environment had not yet undergone any major changes. Because of the very small population dwelling in the area, less than 3000 inhabitants, modifications in the hydrological regime of these rivers did cause relatively few impacts, the main being greater banks instability in specific locations, reduction of the thickness and ice cover on La Grande Rivière, enhancement of navigation constraints on Eastmain River, and higher mercury levels in fish related to operation of the reservoirs.     

淮河流域环境流变化及其对洪泽湖鱼类栖息地的生态影响

为分析淮河流域环境流要素的变化趋势及其对洪泽湖鱼类栖息地的生态影响,以淮河中下游河段为研究区,采用IHA法,将蚌埠水文站1950—2015年径流序列划分为2002年蚌埠闸扩建前后两个时期,采用5种流量事件筛选出32种环境流评价指标,分析了水文变异条件下5种环境事件的生态效应;以鳜鱼为洪泽湖指示鱼类,综合考虑栖息地限制因子,运用PHABSIM模型得到栖息地加权可利用面积-流量曲线,计算了鳜鱼产卵期的生态流量。结果表明:淮河中下游环境流组成趋于单一化,大洪水事件减少,枯水流量增大,高脉冲流量持续时间缩短,出现次数增加,对下游生态环境不利;洪泽湖鳜鱼4—6月产卵期的最小生态流量为300 m~3/s,适宜生态流量为550 m~3/s;需合理调控环境流,增加鱼类补充和物质循环,并采取湖泊生态修复等措施,维持洪泽湖的生态平衡。     

SHOVELNOSE STURGEON SPAWNING IN RELATION TO VARYING DISCHARGE TREATMENTS IN A MISSOURI RIVER TRIBUTARY

Many lotic fish species use natural patterns of variation in discharge and temperature as spawning cues, and these natural patterns are often altered by river regulation. The effects of spring discharge and water temperature variation on the spawning of shovelnose sturgeon Scaphirhynchus platorynchus have not been well documented. From 2006 through 2009, we had the opportunity to study the effects of experimental discharge levels on shovelnose sturgeon spawning in the lower Marias River, a regulated tributary to the Missouri River in Montana. In 2006, shovelnose sturgeon spawned in the Marias River in conjunction with the ascending, peak (134 m³/s) and descending portions of the spring hydrograph and water temperatures from 16 °C to 19 °C. In 2008, shovelnose sturgeon spawned in conjunction with the peak (118 m³/s) and descending portions of the spring hydrograph and during a prolonged period of increased discharge (28–39 m³/s), coupled with water temperatures from 11 °C to 23 °C in the lower Marias River. No evidence of shovelnose sturgeon spawning was documented in the lower Marias River in 2007 or 2009 when discharge remained low (14 and 20 m³/s) despite water temperatures suitable and optimal (12 °C?24 °C) for shovelnose sturgeon embryo development. A similar relationship between shovelnose sturgeon spawning and discharge was observed in the Teton River. These data suggest that discharge must reach a threshold level (28 m³/s) and should be coupled with water temperatures suitable (12 °C?24 °C) or optimal (16 °C?20 °C) for shovelnose sturgeon embryo development to provide a spawning cue for shovelnose sturgeon in the lower Marias River. Copyright © 2012 John Wiley & Sons, Ltd.     

Evidence of lake trout (Salvelinus namaycush) spawning and spawning habitat use in the Dog River,Lake Superior

Lake trout spawn primarily in lakes, and the few river-spawning populations that were known in Lake Superior were believed to be extirpated. We confirmed spawning by lake trout in the Dog River, Ontario, during 2013–2016 by the collection of and genetic identification of eggs, and we describe spawning meso- and microhabitat use by spawning fish. Between 2013 and 2016, a total of 277 lake trout eggs were collected from 39 of 137 sampling locations in the river. The majority of eggs (220) were collected at the transition between the estuary and the river channel crossing the beach. Lake trout eggs were most often located near the downstream end of pools in areas characterized by rapid changes in depth or slope, coarse substrates, and increased water velocities, where interstitial flows may occur. Depths in wadeable areas where eggs were found averaged 0.9?m (range: 0.4 to 1.3?m) and substrate sizes consisted of large gravel, cobble, and boulder; comparable to spawning characteristics noted in lakes. Water velocities averaged 0.66?m·s^?1 (range: 0.33 to 1.7?m³·s^?1) at mid-depth. This information on spawning habitat could be used to help locate other remnant river-spawning populations and to restore river-spawning lake trout and their habitat in rivers that previously supported lake trout in Lake Superior. The Dog River population offers a unique opportunity to understand the ecology of a river spawning lake trout population.     

A model to predict outbreak periods of the pest blackfly Simulium chutteri Lewis (simuliidae,Diptera) in the Great Fish River,Eastern Cape province,South Africa

Elevated, more constant flows characterize the current flow regime of the Great Fish River (Eastern Cape province, South Africa) following the completion of an interbasin transfer scheme (IBT) in 1977, where prior to this the winter months were often characterized by zero flows. Changes in aquatic macroinvertebrate communities, and in particular outbreaks of the pest blackfly Simulium chutteri Lewis (Diptera: Simuliidae) have been documented in response to these altered flows. Integrated control measures of pest blackfly have been advocated based on flow reductions during the winter months. In this study, a site‐specific discharge threshold of 2 m³ s^?1 was identified as a flow reduction target based on the amount of hydraulic habitat available to S. chutteri larvae within a particular rapid. Hydrological analyses showed that flow conditions have created ideal blackfly larval habitat in this rapid, with prolonged uninterupted periods (>3 months) exceeding this threshold. A model was developed to predict probabilities and severities of blackfly outbreaks, based on flow periods and water temperatures, both of which determine the success and duration respectively of the aquatic phase of S. chutteri. July was identified as the critical month for flow restriction to 2 m³ s^?1 for a period of 38 days, in order to reduce the winter populations of S. chutteri in the Great Fish River at the study site and avoid the typical spring outbreaks of blackfly. Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of variation in streamflow and channel structure on smallmouth bass habitat in an alluvial stream

We evaluated the effects of streamflow‐related changes in channel shape and morphology on the quality, quantity, availability and spatial distribution of young‐of‐year and adult smallmouth bass Micropterus dolomieu habitat in an alluvial stream, the Baron Fork of the Illinois River, Oklahoma. We developed Habitat Suitability Criteria (HSC) for young‐of‐year and adult smallmouth bass to assess changes in available smallmouth bass habitat between years, and compare predicted smallmouth bass Weighted Usable Area (WUA) with observed WUA measured the following year. Following flood events between 1999 and 2000, including a record flood, changes in transect cross‐sectional area ranged from 62.5% to 93.5% and channel mesohabitat overlap ranged from 29.5% to 67.0% in study three study reaches. Using Physical HABitat SIMulation (PHABSIM) system analysis, we found that both young‐of‐year and adult smallmouth bass habitat were differentially affected by intra‐ and inter‐annual streamflow fluctuations. Maximum WUA for young‐of‐year and adults occurred at streamflows of 1.8 and 2.3 m³ s^?1, respectively, and WUA declined sharply for both groups at lower streamflows. For most microhabitat variables, habitat availability was similar between years. Habitat suitability criteria developed in 1999 corresponded well with observed fish locations in 2000 for adult smallmouth bass but not for young‐of‐year fish. Our findings suggest that annual variation in habitat availability affects the predictive ability of habitat models for young‐of‐year smallmouth bass more than for adult smallmouth bass. Furthermore, our results showed that despite the dynamic nature of the gravel‐dominated, alluvial Baron Fork, HSC for smallmouth bass were consistent and transferable between years. Published in 2008 by John Wiley & Sons, Ltd.     

Evaluation of the Missouri River shallow water habitat using a 2D‐hydrodynamic model

Many of the Upper Missouri River dikes have been notched to create additional shallow water habitat (SWH, operationally defined as areas in the stream with depth < 1.5 m, and velocity < 0.75 m s^?1) for fish populations. The goal of this study was to quantify the additional SWH gained from notching these dikes and to evaluate their performance under different flow conditions. A coupled field and numerical study was performed on a reach of the Missouri River, near Nebraska City, NE, which contains a number of dikes notched in 2004. The numerical simulations showed that the SWH criterion for depth was more difficult to satisfy in the study reach than the SWH criterion for velocity. Notching the dikes resulted in a slight shift of the bankline due to local erosion in the vicinity of the dikes and the formation of scour holes downstream of the notches. Results from the study suggested that notching the dikes had limited impact on the SWH because the area gained from the bankline shift was offset by the area lost from the scour holes formation. The performance of the notched dikes in sustaining the minimum habitat suitability conditions for the Missouri River ecosystem was also investigated. These conditions corresponded to discharges < 709 m³ s^?1 for the period from mid‐July to mid‐August, or equivalently SWH areas > 5225 m² dike^?1 during the same period. Analysis of the Missouri River annual discharge records at the study site showed that the dikes can provide the minimum required SWH for mean annual discharges < 667 m³ s^?1. For mean annual discharges > 667 m³ s^?1, new alternative structures or restoration facilities were needed, in addition to the existing dikes, to sustain the minimum required SWH. The dikes were not effective in providing any SWH for mean annual discharges > 2000 m³ s^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

基于鱼类栖息地需求的雅鲁藏布江中游环境流量计算

针对水利工程影响下,河道下游天然水文情势改变造成鱼类产卵场面积减小和质量降低等潜在生态问题,通过数值模拟与统计建立拉萨裸裂尻鱼产卵期栖息地适宜度模型,采用栖息地模拟法计算了雅鲁藏布江中游藏木水电站坝下米林—尼洋河汇口处38.9 km河段的环境流量。结果表明:拉萨裸裂尻鱼产卵期适宜水深为0.7～1.0 m,适宜流速为0.4～0.6 m/s;研究河段内拉萨裸裂尻鱼产卵期环境流量为432 m~3/s。     

Flushing flow recommendations for maintenance of salmonid spawning gravels in a steep,regulated stream

A study was conducted to develop flushing flow recommendations for maintaining the quantity of salmonid spawning gravels in the North Fork of the Feather River, a regulated stream in California, U.S.A. This required the development of a technique which would prescribe flows to remove sediments from the gravels without removing the gravels themselves, which are in finite supply in the river. Field studies involved the use of a ‘two-point-are’ procedure which allowed depth, velocity, and substrate measurements to be concentrated over spawning gravels at each site. Measurements were repeated at each site at three different flows ranging from 1.7 to 11.3 m³ s^?1. The local velocity and depth measurements were used to evaluate hydraulic conditions within areas containing spawning gravels. Four flow levels were derived which would provide varying degrees of sediment transport and flushing; (1) surficial flushing of gravels; (2) mobilization of gravels; (3) surficial flushing of cobbles; and (4) mobilization of cobbles. Results of the study indicated a flushing flow of 56.6 m³ s^?1 occurring as a planned release or natural flow for from 1–3 days would be sufficient to transport sediment from spawning gravels. This flow was intermediate to levels which maximize surficial gravel flushing and levels which maximize surficial cobble flushing.     

River regulation: A regional perspective—Northumbrian water authority

In the past three decades, river regulation has become a key component of integrated water management in the U.K. water industry. This paper reviews the concept and operation of river regulation with reference to the Northumbrian Water Authority region. The role of regulating the Rivers Tyne and Tees is considered within a regional perspective. Regulation began on the River Tees in 1965 and the regulation potential of the region was completed with the Kielder Scheme on the River Tyne in 1981. During the year, regulation in Teesdale is largely determined by abstraction demands. Hydropower releases from Kielder have an important effect on the River Tyne. The control patterns and priorities are discussed in general and specifically with regard to statutory and other requirements. These include minimum maintained flows, drought orders, riparian and amenity interests, water-quality, and ecology. Flexibility and cooperation are key concepts; the management of water-quality remains arguably the major problem.     

Hydraulic geometry of New Zealand rivers and its use as a preliminary method of habitat assessment

‘Downstream’ hydraulic geometry relationships describe the variation of water depth, velocity, and water surface width between rivers of different size at a characteristic discharge, whereas ‘at-a-station’ geometry describes the variation of hydraulic geometry with discharge within a reach. The instream flow incremental methodology (IFIM) also predicts the variation in water depth and velocity with discharge at a reach scale, so that hydraulic geometry relationships can potentially be used as a preliminary method of habitat assessment. Hydraulic geometry relationships were calculated from instream habitat surveys of 73 New Zealand river reaches with mean flows varying from 0.6 to 204 m³ s⁻¹ and an average gradient of 0.0047. The exponents of both at-a-station and downstream hydraulic geometry relationships were within the range of values reported in other international studies, although the exponents indicated that New Zealand rivers tended to experience greater changes in velocity and less in depth than the international average, probably because of high average gradient. The frequency distributions of water depth and velocity were positively skewed in most rivers, and on average the modal velocity was 90% of the mean velocity and the modal depth was 80% of mean depth. The use of at-a-station hydraulic geometry relationships for instream habitat assessment was compared to depth and velocity predictions using habitat simulation techniques (IFIM) in two streams. Measurements of stream width and depth at five cross-sections at two calibration discharges were used to establish at-a-station hydraulic geometry relationships. These predicted mean depth and velocity within 8% of the reach average values of the IFIM surveys within the range of calibration discharges and within 10–15% of the IFIM reach average when extrapolated beyond the calibration discharges. Hydraulic geometry can be used to indicate whether hydraulic conditions approach a ‘threshold’ such as a minimum acceptable depth or velocity, thus predicating the need for more extensive habitat survey and analysis. © 1998 John Wiley & Sons, Ltd.