The development of hydraulic and geomorphic complexity in recently formed streams in Glacier Bay National Park,Alaska

Geomorphic and hydraulic complexity within five streams representing 200 years of stream development were examined in Glacier Bay National Park, Alaska. Channel geomorphic units (CGUs) were mapped using a hierarchical approach, which defined stream habitat according to morphological and hydraulic characteristics. Detailed hydraulic assessment within the geomorphic units allowed differences in hydraulic characteristics across the 200‐year chronosequence to be documented. Channel geomorphology and hydrology changed as stream age increased. Younger streams were dominated by fast flowing geomorphic units such as rapids and riffles with little hydraulic or landscape diversity. As stream age increased, slower flowing habitat units such as glides and pools became more dominant, resulting in increased geomorphic, hydraulic and landscape diversity. These results suggest that geomorphic and hydraulic complexity develop over time, creating habitat features likely to be favoured by instream biota, enhancing biodiversity and abundance. Copyright © 2009 John Wiley & Sons, Ltd.     

Two‐dimensional modelling of habitat suitability as a function of discharge on two Colorado rivers

The quantity of water that should be retained in streams and rivers for the benefit of fish during periods of water scarcity is a question of considerable interest to river managers and biologists. Although instream flow methodologies have existed since the 1970s, no single method has been widely accepted for use on large warm‐water rivers because of their high species richness and generalized fish habitat use patterns. In this paper, we present an approach similar to instream flow incremental methodology, but which uses two‐dimensional flow models and biomass estimates derived from multiple sites on two Colorado rivers for predicting the effect of discharge on adult standing stocks of two native fish species. Suitability criteria are developed for bluehead and flannelmouth sucker (Catostomus discobolus and C. latipinnis) by comparing adult biomass in individual meso‐habitat units with modelled depths and velocities. We find that roundtail chub (Gila robusta) biomass is not correlated with depth and velocity, but appears to be positively associated with indices of habitat heterogeneity. Species biomass and total usable habitat area are predicted as a function of discharge for each site and data show good correlation between predicted and measured biomass. Results suggest that the Colorado and Yampa Rivers have similar potential for native fish biomass, but low summer discharges limit native fish biomass on the Yampa River. Copyright © 2005 John Wiley & Sons, Ltd.     

Climate change impacts on native cutthroat trout habitat in Colorado streams

Headwater streams support vital aquatic habitat yet are vulnerable to changing climate due to their high elevation and small size. Coldwater fish are especially sensitive to the altered streamflow and water temperature regimes during summer low flow periods. Though previous studies have provided insights on how changes in climate and alterations in stream discharge may affect habitat availability for various native cutthroat trout species, suitable physical habitats have not been evaluated under future climate projections for the threatened Greenback Cutthroat Trout (GBCT) native to headwater regions of Colorado, USA. Thus, this study used field data collected from selected headwater streams across the current distribution of GBCT to construct one-dimensional hydraulic models to evaluate streamflow and physical habitat under four future climate projections. Results illustrate reductions in both predicted streamflow and physical habitat for all future climate projections across study sites. The projected mean summer streamflow shows greater decline (−52% on average) compared to the projected decline in mean August flow (−21% on average). Moreover, sites located at a relative higher elevation with larger substrate and steeper slope were projected to experience more reductions in physical habitat due to streamflow reductions. Specifically, streams with step-pool morphologies may experience grater changes in available habitat compared to pool-riffle streams. Future climate change studies related to coldwater fish that examine spatial variation in flow alteration could provide novel data to complement the existing literature on the thermal characteristics. Tailoring reintroduction and management efforts for GBCT to the individual headwater stream with adequate on-site monitoring could provide a more holistic conservation approach.     

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.     

Measuring the reach‐scale geomorphic diversity of streams: application to a stream disturbed by a sediment slug

There is increasing evidence that greater physical diversity in a stream leads to a greater diversity of habitats, and hence species. Human impact has reduced the physical diversity within many stream systems. This paper reviews a range of techniques used to measure the physical diversity of a stream reach and specifically examines variability measures of a stream's thalweg, cross‐section and sediment size at the scale of millimetres to metres. Each measure was evaluated against synthetic data with different levels of diversity. From the original thirteen, eight measures were considered appropriate for application to data measured in the field. Creightons Creek (Victoria, Australia) was selected as a test site as it contains areas that are in their original geomorphic condition, as well as sections that have been disturbed by increased bed‐load in the form of a sediment slug. All eight measures showed that the area impacted by the sediment slug was less diverse in terms of its geomorphic variability than the unimpacted reaches. This suggests that massive increases in sediment load to streams will reduce the geomorphic complexity of a stream, and in turn, the diversity of habitat for biological communities. Copyright © 2005 John Wiley & Sons, Ltd.     

Linking a spatially explicit watershed model (SWAT) with an in‐stream fish habitat model (PHABSIM): A case study of setting minimum flows and levels in a low gradient,sub‐tropical river

As changes in landuse and the demand for water accelerate, regulators and resource managers are increasingly asked to evaluate water allocation against the need for protection of in‐stream habitat. In the United States, only a small number of river basins have the long‐term hydrograph data needed to make these assessments. This paper presents an example of how to bridge the conceptual and physical divide between GIS‐based watershed modelling of basin‐discharge and in‐stream hydraulic habitat models. Specifically, we used a Soil and Water Assessment Tool (SWAT) model for the Hillsborough River to produce data for use in a Physical HABitat SIMulation (PHABSIM) model of the same river. This coupling of models allowed us to develop long‐term discharge data in ungauged river systems based on watershed characteristics and precipitation records. However this approach is not without important limitations. Results confirm that accuracy of the SWAT‐predicted hydrograph declines significantly when either the DEM resolution becomes too coarse or if DEM data are resampled to a coarser or finer resolution. This is due to both changes in the size and shape of the river basin with the varying DEMs and subsequent shifts in the proportions of land use, soils and elevation. Results show the use of 30 m DEMs produced hydrographic patterns amenable for using in‐stream habitat protocols like PHABSIM model, especially where little or no hydrographic and land use information exists. Copyright © 2010 John Wiley & Sons, Ltd.     

Evaluation of pool‐riffle naturalization structures on habitat complexity and the fish community in an urban Illinois stream

Urbanization and its associated stressors such as flow alteration, channel modification and poor water quality is a leading cause of ecological degradation to rivers and streams. Driven by public concern to address this issue, there has been a dramatic increase in urban restoration projects since 1990 using in‐stream structures. Attempts at restoring the ecological condition of urban streams using structures have produced varied results, but projects do not often meet planned ecological goals. A major challenge to improving the ecological health of urban streams is to better understand how to incorporate ecological assessments into a ‘restoration’ design framework with reasonable expectations for ecological recovery. A naturalization design framework was used in a project on a 0.62‐km reach of the North Branch of the Chicago River in Northbrook, Illinois. Initial surveys of channel morphology, habitat and biota identified poor pool‐riffle bed structure and fish biodiversity, which became the basis for research and development of a pool‐riffle structure specifically designed for constrained, low‐gradient channels. Habitat and fish surveys were conducted pre‐ and post‐construction. The project improved mesohabitat structure, and fish abundance, and biomass and diversity were greater for 2 years following construction (2002–2003) compared to 3 years prior to construction (1999–2001). However, the improved fish metrics were in the low range when compared to rural streams in the same ecoregion, and the fish community consisted primarily of tolerant, slow‐water species. Absent were intolerant and riffle dwelling species, such as insectivorous cyprinids and darters. Assessment of pre‐ and post‐project ecological condition and the use of species information provided a basis for ecologically informed design and expanded our understanding of the limitations to restoring urban streams. Copyright © 2007 John Wiley & Sons, Ltd.     

Response of sandhill crane (Grus canadensis) riverine roosting habitat to changes in stage and sandbar morphology

Over the past century, flow regulation and vegetation encroachment have reduced active channel widths along the central Platte River, Nebraska. During the last two decades, an annual program of in‐channel vegetation management has been implemented to stabilize or expand active channel widths. Vegetation management practices are intended to enhance riverine habitats which include nocturnal roosting habitat for sandhill cranes. Evaluating the success of other management treatments such as streamflow modification requires an understanding of how flow shapes the sandbars in the river and how sandbar morphology interacts with flow to create crane habitat. These linkages were investigated along a 1‐km managed river reach by comparing the spatial pattern of riverine roosts and emergent sandbars identified with aerial infrared imagery to variables computed with a two‐dimensional hydraulic model. Nocturnal observations made multiple years showed that the area and patterns of riverine roosts and emergent sandbars and the densities of cranes within roosts changed with stage. Despite sandbar vegetation management, low flows were concentrated into incised channels rather than spread out over broad sandbars. The flow model was used to compute hydraulic variables for identical streamflows through two sandbar morphologies; one following a period of relatively high flow and the other following the low‐flow period. Compared with the simulation using the morphology from the antecedent high flow, the simulation using the morphology from the antecedent low flow produced a smaller quantity of available wetted area. These remote‐sensing observations and hydraulic simulations illustrate the importance of considering flow history when designing streamflows to manage in‐channel habitat for cranes. Published in 2008 by John Wiley & Sons, Ltd.     

Fluid speed variability and the importance to managing fish habitat in rivers

To properly manage streams for fish habitat it is necessary to move beyond standard evaluations and the acceptance of relationships between variables that are derived either from rivers of much greater scale or those which are based on time-averaged conditions. Clearly, the relationship between moving fluid and channel boundary is the most important in smaller streams that are used as habitat by fish, as variations in speed patterns causing erosion or sedimentation of the bed will determine the success of spawning activity. To this end, an evaluation of fluid speed profiles is presented using field data collected from spawning streams in Ontario, Canada. The data have been subjected to an interpolation algorithm, minimum curvature, to deliver a more accurate view of fluid speed patterns. The results show that fluid speed patterns vary completely within the same cross-section under different flow regimes, even when the mean depth and mean speed of the flow are virtually unchanged, and that mean speed depiction of flow is inaccurate when considering particle transport/deposition. A comparison of data collection practices is presented which shows that flow measurement from the common 60% of the depth at mid-channel produces large errors in speed prediction on moving towards the bed and surface of the channel. Errors in the prediction of near-bed fluid speeds can result in the entrainment of particles within the preferred spawning range of salmonids, which was not predicted through the use of mean fluid speed for the cross-section or through the less intense data collection technique. The minimum curvature technique of data interpolation is shown to be an accurate method for visualizing fluid speed patterns.     

Behaviour of two small pelagic and demersal fish species in diverse hydraulic environments

Increased hydraulic diversity could be a means to promote fish diversity in rivers, but little is known of the behaviour of fish in hydraulic environments. This study concerns the behaviour of two species of small native Australian freshwater fish in variable hydraulic environments and ecological habit, with regard for (a) whether the apparent differences in swimming ability are reflected in the behaviour of the species and (b) the influence of changing hydraulic conditions on their patterns of use. An artificial channel was constructed with three levels of discharge, and fish were allowed to swim freely for 3 h without human interference. Their movements and habitat choices reflected their swimming ability and ecological habit, in that the stronger swimming, pelagic common galaxias (Galaxias maculatus) spent most time cruising in the open channel, preferring the turbulent inflow, and the demersal flat‐headed gudgeon (Philypnodon grandiceps) remained in the shelter of boulders. In effect, the galaxias changed their behaviour with changes in hydraulic conditions, while the gudgeons continued to use their preferred habitat. This study, therefore, provides support for the use of hydraulic diversity as a tool to foster fish diversity. Copyright © 2010 John Wiley & Sons, Ltd.     

基于液压系统的离心模拟试验大荷载施加方法研究

离心模拟试验是通过离心机的转动创造超重力场,使小比尺模型处于原型应力状态,从而模拟土工构筑物力学特性的一种研究手段。随着工程技术的不断发展和技术难度的逐渐提高,在超重力场中开展模拟实际工况中的特定动作,逐渐成为离心模拟试验中的一个热点问题,而如何在超重力场中实现大荷载力的施加是离心模型试验研究中的一个难点。为解决这一问题,中国水利水电科学研究院基于液压技术,开发了可在超重力场中模拟各种施工动作的试验系统,本文介绍了该系统的工作原理和主要特点,并结合试验案例,证明该系统的实用与可靠性。     

基于渗透系数序贯高斯模拟的水库渗漏量不确定性分析

水库库底地层渗透系数是影响水库渗漏量的主要因素之一,研究渗透系数的空间变异特征可为水库渗漏量计算结果的可靠性分析提供科学依据。以天津市北塘水库库底地层渗透系数为研究对象,先利用克里金插值对该参数系列进行了插补,再对插补后的渗透系数系列进行了500次序贯高斯模拟,最后分析了其空间变异性对库区渗漏量计算值不确定性的影响。结果表明:库底地层垂向渗透系数空间结构可用球状模型描述,在变程1210 m范围内具有高度空间相关性。以2005年7月16日渗漏量计算值总体为例,最小值与最大值分别为1 389.49 m3/d、1 897.30 m3/d,且落在区间1 600~1 850 m3/d的频率高达77.6%。     

考虑水力学和矿化参数空间变异下土壤水氮运移的数值分析

以北京东郊永乐店一块农田为背景,将田问取样点所在的土壤剖面假设为一系列不发生相互作用的一维土柱,根据实测的土壤有机质含量,假定不同取样点的土壤有机氮的矿化速率常数（零级动力学）与有机质含量成正比,运用HYDRUS-1D软件,分别就考虑和不考虑有机氮矿化速率的空间变异性两种方案,对2001年夏玉米生育期农田尺度下土壤水分运动和硝态氮淋失动态进行了数值分析。模拟结果表明：有机氮矿化速率的空间变异性对剖面250cm埋深处累积硝态氮淋失量的影响很小,其差异主要在于前者影响了土壤氮素的转化量;剖面250cm埋深处平均的土壤水渗透量和累积硝态氮淋失量分别为1．35mm、0．0065mg／cm^2,变异系数大于1．8,表现出很强的空间变异性。模拟结果的地统计学分析表明：蒸发量和蒸腾量,收获时剖面250、150cm埋深处的土壤水通量的半方差函数均可用球状模型描述,其变程相近,约为8．7m;土壤水渗透量与累积硝态氮淋失量表现为相互独立的空间结构。考虑有机氮矿化速率空间变异性的土壤氮素净转化量可用球状模型描述,其变程与有机质含量的变程接近,约为4．7m。     

A comparison of avian communities and habitat characteristics in floodplain forests associated with valley plugs and unchannelized streams

Channelization of streams associated with floodplain forested wetlands has occurred extensively throughout the world and specifically in the southeastern United States. Channelization of fluvial systems alters the hydrologic and sedimentation processes that sustain these systems. In western Tennessee, channelization and past land‐use practices have caused drastic geomorphic and hydrologic changes, resulting in altered habitat conditions that may affect avian communities. The objective of this study was to determine if there were differences in avian communities utilizing floodplain forests along unchannelized streams compared to channelized streams with valley plugs, areas where sediment has completely filled the channel. During point count surveys, 58 bird species were observed at unchannelized sites and 60 species were observed at valley plug sites. Species associated with baldcypress‐tupelo (Taxodium‐Nyssa) swamps (e.g. Great Egret (Ardea albus) and Black‐crowned Night Heron (Nycticorax nycticorax)) and mature hardwood forests with open midstories (e.g. Eastern Wood‐Pewee (Contopus virens), Yellow‐throated Vireo (Vireo flavifrons), Cerulean Warbler (Dendroica cerulea) and Scarlet Tanager (Piranga olivacea)) were either only found at unchannelized sites or were more abundant at unchannelized sites. Conversely, species associated with open and early successional habitats (e.g. Tree Swallow (Tachycineta bicolor), Northern Mockingbird (Mimus polyglottos) and Blue Grosbeak (Passerina caerulea)) were either only found at valley plug sites or were more abundant at valley plug sites. Results of habitat modelling suggest that the habitat characteristics of floodplain forests at unchannelized sites are more suitable for Neotropical migrant bird species of conservation concern in the region than at valley plug sites. This study, in combination with previous research, demonstrates the ecological impacts of valley plugs span across abiotic and biotic processes and tropic levels. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessment of the water surface profile model: Accuracy of predicted instream fish habitat conditions in low-gradient,warmwater streams

The Instream Flow Group's (U.S. Fish and Wildlife Service) Physical Habitat Simulation (PHABSIM) model, the major component of the incremental methodology (IFIM) is presently the most widely employed instream flow assessment procedure. PHABSIM consists of both biological and hydrological components. The Water Surface Profile (WSP) hydrologic model is commonly recommended and employed in many PHABSIM applications. While several recent studies have critically addressed and questioned the validity of PHABSIM as a management tool from a biological perspective, there has been surprisingly limited attention given to problems of use, accuracy, bias, and the effect of errors in the WSP hydraulic simulation on the final PHABSIM output (i.e. weighted usable area (WUA) estimates). Therefore, the purpose of this study was to examine the effectiveness of the WSP hydraulic model for predicting hydraulic conditions in low-gradient, warmwater streams in east-central Illinois. Attempts were made to calibrate the WSP model at four locations on the Salt Fork and Middle Fork rivers and compare simulated results to actual measured conditions at different discharges. We conclude that in low-gradient warmwater streams, the WSP model: (1) does not adequately simulate low-flow habitat conditions, due to an inability to calibrate the model; (2) is, at best, difficult to calibrate, even within hydraulically uniform channels; (3) requires several field measurements and calibrations to simulate a sufficiently wide range of naturally occurring flows: (4) provides poor estimates of cell depth and velocity; and, results in highly erratic and often poor estimates of WUA for adults and fry of smallmouth bass. Finally, our results indicate that similar or better estimates of actual WUA can be attained by monitoring the distributions of depth, velocity, and substrate at a series of representative transects at different discharges and interpolating WUA from observed field data using less expensive and time consuming regression models.     

Hybrid modelling of low velocity zones in an asymmetrical channel with sidewall longitudinal rib to assist fish passage

Channels with longitudinal beams have been studied for decades in chemical engineering, environmental and sanitary engineering, aeronautics, astronautics, biology and geology. In the current study, a combination of physical and numerical Computational Fluid Dynamics (CFD) modelling was undertaken to test whether an asymmetrical channel equipped with a sidewall longitudinal rib could provide flow conditions conducive to upstream fish passage. The study focused on small‐bodied fish and juveniles of larger fish, typically less than 100 mm in total length. A detailed hydrodynamic study was conducted in an asymmetrical rectangular channel equipped with a sidewall square rib in a culvert barrel channel. Both free‐surface velocity and boundary shear stress measurements showed strong secondary currents of Prandtl's second kind. The channel asymmetry contributed to intense secondary motion, associated with turbulent dissipation. The channel design provided a small well‐defined highly turbulent low‐velocity zone beneath the rib. In the context of hydraulic structure designs, uttermost care must be considered because of manufacturing, installation and operational practices. In many instances, alternative engineering designs with small baffles and asymmetrical appurtenance should be preferred to assist with fish passage in hydraulic structures.     

Downstream effects of diversion dams on sediment and hydraulic conditions of Rocky Mountain streams

Reduced streamflow via flow diversion has the potential to limit the sediment‐transport capacity of downstream channels and lead to accumulation of fine sediments and habitat degradation. To investigate, we examined the effects of variable levels of flow diversion on fine‐sediment deposition, hydraulic conditions and geomorphic alteration. Our study consisted of a detailed field analysis pairing reaches above and below diversion dams on 13 mountain streams in north‐central Colorado and southern Wyoming USA. Diversions are ubiquitous across the American West, yet previous comparative studies on the effects of flow diversion have yielded mixed results. Through application of strict site‐selection criteria, multiple fine‐sediment measures, and an intensive sampling scheme, this study found that channels downstream of diversions contained significantly more fine sediment and slow‐flowing habitat as compared to upstream control reaches. Susceptibility to fine‐sediment accumulation was associated with decreasing basin size, decreasing bankfull depth and smaller d₈₄, and it appears to be magnified in streams of less than 3% slope. Copyright © 2010 John Wiley & Sons, Ltd.     

Salmonid habitat modelling studies and their contribution to the development of an ecologically acceptable release policy for Kielder Reservoir,North‐east England

1. Kielder Reservoir regulates the Rivers North Tyne and Tyne. It provides a regular supply of water for downstream users, supports abstractions for a major water transfer scheme and provides hydroelectric power (HEP). Kielder's release regime typically alternates between a 1.3 m³ s⁻¹ compensation flow and 10–15 m³ s⁻¹ HEP releases of between 3 and 7 days in duration. Occasionally releases of up to 30 m³ s⁻¹ are made for the purpose of encouraging fish runs, for recreational events or to help in water quality management. The impacts of this release regime on Atlantic salmon (Salmo salar) and brown trout (S. trutta) habitat at four sites on the North Tyne are assessed and alternative regimes, designed to minimize impacts, are presented. 2. There is no evidence that the compensation flow results in extreme loss of instream habitat. A discharge of 1.3 m³ s⁻¹ ensures that water is maintained over most of the channel area at sites representative of upper, middle and lower sections of the North Tyne. This discharge lies above breaks in slope of respective site discharge versus wetted area curves; thus, disproportionate increases in discharge would be needed to increase wetted area. Simulations using the Physical Habitat Simulation System (PHABSIM) suggest that the compensation flow provides between 50% and 90% of the maximum possible weighted usable area (WUA) for juvenile (0+) salmonids. 3. During HEP releases, juvenile salmonid habitat (WUA) apparently falls to between 20 and 40% of site maxima. Newly emerged juvenile fish (March and April) are most affected by HEP releases because they are relatively small (25 mm in length) and water temperatures are relatively low at this time of year. During March and April, critical near‐bed displacement velocities for newly emerged fish may be exceeded across large parts (80%) of sites up to 8 km downstream from Kielder Reservoir; fish would either be displaced downstream or forced to relocate to flow refuge areas. 4. The availability of Atlantic salmon spawning habitat (WUA) at a key site is limited by the compensation flow; 1.3 m³ s⁻¹ provides approximately one third of the habitat available at the optimum discharge (4 m³ s⁻¹). At this site, a discharge of approximately 2 m³ s⁻¹ is needed to ensure most of the bed is inundated by water. Regulation has reduced the duration of flows exceeding 2 m³ s⁻¹ from 90 to 60% of the spawning season. 5. Simulations suggest that when discharge drops from 30 m³ s⁻¹ to the compensation flow, up to 60% of the optimum spawning habitat available at the former discharge may be left stranded (dry). This could potentially lead to egg or alevin mortality. 6. PHABSIM simulations suggest that increasing the compensation flow to 4 m³ s⁻¹ during the spawning period (November and December) is likely to increase the availability of suitable spawning habitat. Also, increasing the compensation flow to 2 m³ s⁻¹ during the incubation period (January through March) would minimize redd stranding. Reductions in the number of HEP releases in March and April would limit the extent to which newly emerged fish are exposed to velocities that potentially displace them. Such changes to the Kielder release regime may have implications for water resource management. While it is important that the biological instream flow requirements of the North Tyne are incorporated into the Kielder operating policy, these should be integrated along with the need for channel maintenance flows, downstream water supply abstractions and HEP generation, as well as for transfers of water to other catchments. Copyright © 2000 John Wiley & Sons, Ltd.     

Explaining Spatial Patterns of Mussel Beds in a Northern California River: The Role of Flood Disturbance and Spawning Salmon

Despite considerable effort, predicting habitat preferences for freshwater mussels has remained elusive. This study identified four parameters that correlate with bed stability to decipher fine‐scale spatial patterning of habitat use by the western pearl shell mussel (Margaritifera falcata) in the Trinity River of Northern California. Logistic regression analysis correctly predicted the occurrence of 83% of mussel bed areas based on water depth, velocity, substrate size, and distance to the stream bank as estimated from hydrodynamic modelling of low‐flow conditions. These parameters coincide with bed stability at high flow and provide support for the ‘refugia hypothesis’. Our data clearly demonstrate that mussel beds occupied the most stable portions of the riverbed; however, habitat was partitioned with one of their primary host fish, Chinook salmon (Oncorhynchus tshawytscha), a species that also requires stable bed areas for spawning. Mussels occupied significantly deeper and lower velocity areas that were closer to the streambank compared with spawning salmon, but where habitats directly overlapped (30% of potential mussel habitat) mussels were excluded because the act of spawning disturbs the riverbed. By necessity, mussels and salmon must co‐exist, but results of this study indicate that they compete for stable bed areas that may be limiting in dynamic river systems. Copyright © 2015 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.