人工阶梯 深潭改善下切河流水生栖息地及生态的作用

本文通过野外试验研究了人工阶梯深潭对下切河流水生栖息地及生态的作用，试验河段位于西南山区的吊嘎河上150m侵蚀下切严重的河段，布置15级人工阶梯，对水流 (水深、流速、水面宽、流量)、河床底质、河床微地貌和水生底栖动物物种及数量变化进行了5个月监测。试     

Sediment storage and shallow groundwater response to beaver dam analogues in the Colorado Front Range,USA

Enthusiasm for using beaver dam analogues (BDAs) to restore incised channels and riparian corridors has been increasing. BDAs are expected to create a similar channel response to natural beaver dams by causing channel bed aggradation and overbank flow, which subsequently raise water tables and support vegetation growth. However, lack of funding for monitoring projects post‐restoration has limited research on whether BDAs actually cause expected channel change in the Front Range and elsewhere. Geomorphic and hydrologic response to BDAs was monitored in two watersheds 1 year post‐restoration. BDAs were studied at Fish Creek, a steep mountainous catchment, and Campbell Creek, a lower gradient piedmont catchment from May to October 2018. At each restoration site, the upstream‐ and downstream‐most BDAs were chosen for intensive study in comparison with unrestored reference reaches. Monitoring focused on quantifying sediment volumes in BDA ponds and recording changes to stream stage and riparian groundwater. Despite differences in physical basin characteristics, BDA pools at both sites stored similar volumes of sediment and stored more sediment than reference pools. Sediment storage is positively correlated to BDA height and pool surface area. However, BDAs did not have a significant influence on shallow groundwater. The lack of groundwater response proximal to BDAs could indicate that local watershed factors have a stronger influence on groundwater response than restoration design 1 year post‐restoration. Systematic, long‐term studies of channel and floodplain response to BDAs are needed to better understand how BDAs will influence geomorphology and hydrology.     

Three‐dimensional flow dynamics around deflectors

Many river rehabilitation projects to enhance the aquatic habitat focus on the creation of pool and riffle habitat by the implementation of flow deflectors, with various degrees of successes and failures. A more comprehensive understanding of the complex three‐dimensional flow dynamics that induces scour around instream structures is required for a more effective design. The objective of this study is to examine the three‐dimensional mean and turbulent flow characteristics around paired flow deflectors for various types of deflector design in a laboratory flume. Three deflector angles (45°, 90° and 135°) and two deflector heights (with flow under and over the deflector height) were tested over a smooth (plexiglas) bed and a sand bed. Three‐dimensional velocity measurements were taken with an acoustic Doppler velocimeter at several planform positions at two heights above the bed. Results show that the 90° deflectors create the most important disturbance in the mean flow field, in turbulence intensity and bed shear stress. There is, however, a marked difference in the spatial distribution of the mean and turbulent parameters over a mobile bed and over a smooth, fixed bed. This stresses the importance of understanding the feedback between bed topography and flow dynamics and limits the applicability of conclusions drawn from plane bed experiments to natural rivers. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparison of methods for analysing salmon habitat rehabilitation designs for regulated rivers

River restoration practices aiming to sustain wild salmonid populations have received considerable attention in the Unites States and abroad, as cumulative anthropogenic impacts have caused fish population declines. An accurate representation of local depth and velocity in designs of spatially complex riffle‐pool units is paramount for evaluating such practices, because these two variables constitute key instream habitat requirements and they can be used to predict channel stability. In this study, three models for predicting channel hydraulics—1D analytical, 1D numerical and 2D numerical—were compared for two theoretical spawning habitat rehabilitation (SHR) designs at two discharges to constrain the utility of these models for use in river restoration design evaluation. Hydraulic predictions from each method were used in the same physical habitat quality and sediment transport regime equations to determine how deviations propagated through those highly nonlinear functions to influence site assessments. The results showed that riffle‐pool hydraulics, sediment transport regime and physical habitat quality were very poorly estimated using the 1D analytical method. The 1D and 2D numerical models did capture characteristic longitudinal profiles in cross‐sectionally averaged variables. The deviation of both 1D approaches from the spatially distributed 2D model was found to be greatest at the low discharge for an oblique riffle crest with converging cross‐stream flow vectors. As decision making for river rehabilitation is dependent on methods used to evaluate designs, this analysis provides managers with an awareness of the limitations used in developing designs and recommendations using the tested methods. Copyright © 2008 John Wiley & Sons, Ltd.     

Physical modelling of pool and weir fishways with rock weirs

The flow characteristics of pool and weir fishways with rock weirs were studied through physical modelling. Detailed flow measurements were obtained using an acoustic Doppler velocimeter to understand how weir geometry, discharge, and bed slope affect flow patterns, velocity, turbulence kinetic energy, turbulence intensity, and Reynolds shear stresses in the fishway. The weir geometries used in this study are similar to those typically used for river restoration projects. The use of a V‐shaped rock weir was found to reduce the mean streamwise velocity in the pools by about 20% but more than double the maximum velocity magnitude. Two stage–discharge relationships were developed using the standard weir equation and a modified discharge coefficient to account for both flow over the weir and orifice flow through the base of the weir. The use of V‐shaped rock weirs has the potential to offer significant advantages in assisting multispecies fish migration. The results of this study can be applied to the hydrotechnical design of pool and weir fishways with rock weirs and for river restoration projects.     

EFFECTS OF BENTHIC HABITAT RESTORATION ON NUTRIENT UPTAKE AND ECOSYSTEM METABOLISM IN THREE HEADWATER STREAMS

The assemblage of stream habitat types can drive biofilm composition and activity in headwater streams, thereby influencing rates of ecosystem function. However, the influence of human‐induced alterations to the distribution of benthic habitat such as construction, land‐use changes and restoration on biofilm‐mediated processes has not been well studied. We measured nutrient uptake of ammonium, nitrate and phosphate, as well as gross primary production and community respiration in three streams in Michigan, USA, each with an upstream reference and a downstream restored reach. The restoration included a 10‐m sediment trap, paired with 40–60 m of gravel and boulder added downstream and designed to retain sediment, stabilize banks and provide spawning habitat for trout. We sampled four times in the six stream reaches from May 2006 to September 2007. Across streams, restored reaches reflected the structural manipulation with increased predominance of coarse inorganic sediments, higher gas exchange rate and increased transient storage. However, nutrient uptake and community respiration rates were different between reaches at only one site. The ecosystem response by this stream was driven by the large differences in coarse inorganic habitat between reference and restored reaches. We conclude that restorations of benthic habitat which are visually conspicuous, such as creation of settling pools and gravel‐filled reaches, did not universally affect stream ecosystem function. Initial conditions and magnitude of change may be key factors to consider in explaining functional responses, and predicting the influence of habitat restoration on ecosystem function remains a challenge. Copyright © 2011 John Wiley & Sons, Ltd.     

Changes in pool size in response to a reduction in discharge: a flume experiment

Management of river systems can create a reduction in flow with associated potential impacts on channel morphology. A total of 30 flume runs were conducted with two different sediment sizes to determine the effect of a reduction in flow on pool size and depth in confined channels. The experiments were conducted in a 6 m long, 0.5 m wide recirculating flume. Pools were scoured adjacent to a triangular‐shaped obstruction to flow from an initially flat bed. After 3 h of high flow, bed topography was measured and the flow was changed to a level of 50, 67, 80, 85 or 100% of the original flow. Changes in bed topography were then measured after 3 h under the modified flow regime. Results indicate that a reduction in flow creates smaller volume pools. With well sorted, fine‐sand substrate, changes in pool volume, volume of deep habitat and depth were significant for both 50 and 80% reductions in flow level. However, development of an armor level in experiments with poorly sorted, very coarse sand limited sedimentation at lower flows. Consequently, no changes in pool size were statistically significant with this sediment. The results suggest that data on the dimensions of pools are needed prior to any flow modifications in order to detect degradation of the physical pool habitat. Monitoring programs initiated after flow regulation may only identify changes in a limited number of cases where sediments are mobile at low flows and the reduction in flow level is severe. Copyright © 2005 John Wiley & Sons, Ltd.     

A method for improving predictions of bed-load discharges to reservoirs

Effective management options for mitigating the loss of reservoir water storage capacity to sedimentation depend on improved predictions of bed‐load discharges into the reservoirs. Most predictions of bed‐load discharges, however, are based on the assumption that the rates of bed‐load sediment availability equal the transport capacity of the flow, ignoring the spatio‐temporal variability of the sediment supply. This paper develops a semiquantitative method to characterize bed‐load sediment transport in alluvial channels, assuming a channel reach is non‐supply limited when the bed‐load discharge of a given sediment particle‐size class is functionally related to the energy that is available to transport that fraction of the total bed‐load. The method was applied to 22 alluvial stream channels in the USA to determine whether a channel reach had a supply‐limited or non‐supply‐limited bed‐load transport regime. The non‐supply‐limited transport regime was further subdivided into two groups on the basis of statistical tests. The results indicated the pattern of bed‐load sediment transport in alluvial channels depends on the complete spectrum of sediment particle sizes available for transport rather than individual particle‐size fractions represented by one characteristic particle size. The application of the method developed in this paper should assist reservoir managers in selecting bed‐load sediment transport equations to improve predictions of bed‐load discharge in alluvial streams, thereby significantly increasing the efficiency of management options for maintaining the storage capacity of waterbodies.     

A numerical study of pumping effects on flow velocity distributions in Mosul Dam reservoir using the HEC‐RAS model

Water flow direction and velocity affect and controls erosion, transport and deposition of sediment in rivers, reservoirs and different hydraulic structures. One of the main structures affected is pumping stations within the dams wherein the velocity distribution near the station intake is disturbed. The two‐dimensional (2‐D) HEC‐RAS 5.01 model was utilized to study, analyse and evaluate the effects of pumping rates and flow depth on the flow velocity distribution, flow stream power and their effects in the Mosul Dam reservoir. The pumping station was considered as a case study. The station is suffering from sediment accumulation around, and in, its intake and suction pipes. The main inflow sources to the reservoir are the Tigris River and run‐off from the valleys within its basin. The reservoir was divided into two parts for the present study, including the upper part near the pumping station (analysed as a two‐dimensional zone), while the lower part was analysed as a one‐dimensional flow to reduce the simulation period computation time (1986–2011). Different operation plans (i.e. pumping rate and water depth) were considered. The results of the depth‐averaged velocity model indicated that when the pumping station was working at a range from the designed full capacity (100% to 25% of its full capacity), the maximum flow velocity increased from 75 to 4 times the normal velocity when there is no pumping dependent on pumping rate and flow depth. For the same operation plans, the flow stream power varied from around zero values to 400 times at full pumping capacity and low flow depth. For sediment routing along the reservoir, the considered statistical criteria indicated the model performance in estimating the total sediment load deposition and invert bed level is much better than in the case of erosion and deposition areas for different considered bed sections of the reservoir.     

Process‐based assessment of success and failure in a constructed riffle‐pool river restoration project

Although there is increasing consensus that river restoration should focus on restoring processes rather than form, proven techniques to design and monitor projects for sediment transport processes are lacking. This study monitors bedload transport and channel morphology in a rural, an urban unrestored, and an urban restored reach. Objectives are to compare bedload transport regimes, assess the stability and self‐maintenance of constructed riffle‐pool sequences, and evaluate the impact of the project on coarse sediment continuity in the creek. Sediment tracking is done using radio frequency identification tracers and morphologic change is assessed from repeated cross‐section surveys. Mean annual velocity is used to quantify the average downstream velocity of tracers, defined as the mean overall tracer travel length divided by the total study duration. The channel reconstruction slows down the downstream velocity of particles in the D₇₅ and D₉₀ size classes, but does not significantly change the velocity of particles in the D₅₀ size class or smaller. Surveys show that riffle features remain stable and that pool depths are maintained or deepened, while tracer paths match with what has been observed in natural riffle‐pools. However, the slowdown of coarse sediment and increase in channel slope may lead to future failures related to over‐steepening of the banks and a disruption in the continuity of sediment transport in the creek. This study demonstrates how bedload tracking and morphological surveys can be used to assess river restoration projects, and highlights the importance of incorporating coarse sediment connectivity into restoration design and monitoring.     

One‐dimensional sediment transport modeling of pool recovery along a mountain channel after a reservoir sediment release

A reservoir sediment release along the North Fork Cache la Poudre River (North Fork) in northern Colorado resulted in a massive fish kill and channel sedimentation that filled pools critical to fish as overwinter habitat. Recognition of the hazards associated with a large influx of sediment into a riverine ecosystem is critical for a greater understanding of the effects of sediment releases, and hence, future management of sediment within reservoirs. Two one‐dimensional sediment transport models, HEC‐6 and GSTARS 2.0, were evaluated for applicability to predict sediment removal along the steep gradient, bedrock‐controlled pool‐riffle North Fork. The ability of both models to identify flushing discharges that assist channel recovery was also evaluated. Two modeling scenarios representing a low and high flushing discharge were modeled. Within each scenario, two levels of simulations were conducted to represent conditions of data availability, a default simulation for limited data input, and a robust simulation that utilized the entire set of field data, collected over a 1‐year period. The models were calibrated against quantitative measurements of pool bed elevation obtained during field resurveys. Preliminary analyses were conducted to identify the appropriate sediment transport equations. HEC‐6 results indicate that long‐term, robust simulations yield the closest agreement between predicted and measured pool bed elevation change. More than 50% of the actual scour and deposition within three pools was modeled using HEC‐6. Modeling accuracy using GSTARS 2.0 was considerably lower, and it appears that the present construct of the model does not reflect the physical processes operating along the North Fork. Computer models are useful tools in the sediment management decision process, provided adequate data collection and calibration are conducted. In situations where restrictions exist on available flushing discharges, sediment transport modeling can assist management decisions, and modeling is always preferable to uncalibrated estimates. Copyright © 2001 John Wiley & Sons, Ltd.     

Experimental study on the bed topography evolution in alluvial meandering rivers with various sinuousnesses

The bed morphology in alluvial meandering rivers is composed of both alternatively distributed free bars and curvature related point bars. To study the influence of channel sinuousness on the flow and sediment transport, and consequently the bed morphology in meandering rivers, experiments were carried out in a series of curved channels with erodible bed fixed side walls. Measurements on the surface flow field, bed topography evolution and sediment transport rate were performed. Experimental results show a high velocity area near convex bank at a streamwise position a little bit upstream of the apex and the increasing in sinuousness of channel tends to increase the cross-sectional variation of flow velocity at the apex of bends. Point bars and pools appear in the channel bends in all experimental runs the bedform has an obvious tendency of downstream migration as a whole. The quasi-equilibrium bedform in the channel bends are dominated by two independent factors: the influence of curvature and the influence of flow-bed instability inside the channel. The increasing of flow rate leads to a faster development of bars and pools, as well as faster downstream migration of the entire bedform. The increase of sinuousness in channel bends leads to the increase of both the spatial and the temporal fluctuation of bedforms. Bedload is dominant in the sediment transport and the sediment transport rate tends to increase with the increasing of the inlet flow rate but decrease with the increasing of the channel sinuousness. Computational results on the bed topography in river bends was also presented based on empirical models, showing that the highly sinuous channels have more uncertainty in bed morphology and more difficult to be predicted with mathematical models when compared with slightly sinuous channel bends. The coupled interaction of point bars, mid-channel bars, alternative bars and even sand ripples are thought to complicate the mechanism and make the bed morphology difficult to predict. The experiment results can be useful for further theoretical study on the dynamics of river meanders with water depth-width ratio as small as 1/10 to 1/20 and bedload dominated sediment transport.     

Not all breaks are equal: Variable hydrologic and geomorphic responses to intentional levee breaches along the lower Cosumnes River,California

The transport of water and sediment from rivers to adjacent floodplains helps generate complex floodplain, wetland, and riparian ecosystems. However, riverside levees restrict lateral connectivity of water and sediment during flood pulses, making the re‐introduction of floodplain hydrogeomorphic processes through intentional levee breaching and removal an emerging floodplain restoration practice. Repeated topographic observations from levee breach sites along the lower Cosumnes River (USA) indicated that breach architecture influences floodplain and channel hydrogeomorphic processes. Where narrow breaches (<75 m) open onto graded floodplains, archetypal crevasse splays developed along a single dominant flowpath, with floodplain erosion in near‐bank areas and lobate splay deposition in distal floodplain regions. Narrow breaches opening into excavated floodplain channels promoted both transverse advection and turbulent diffusion of sediment into the floodplain channel, facilitating near‐bank deposition and potential breach closure. Wide breaches (>250 m) enabled multiple modes of water and sediment transport onto graded floodplains. Advective sediment transport along multiple flow paths generated overlapping crevasse splays, while turbulent diffusion promoted the formation of lateral levees through large wood and sediment accumulation in near‐bank areas. Channel incision (>2 m) upstream from a wide levee breach suggests that large flow diversions through such breaches can generate water surface drawdown during flooding, resulting in localized flow acceleration and upstream channel incision. Understanding variable hydrogeomorphic responses to levee breach architecture will help restoration managers design breaches that maximize desired floodplain topographic change while also minimizing potential undesirable consequences such as levee breach closure or channel incision.     

A Synthesis of Stream Restoration Efforts in Florida (USA)

Studies summarizing stream restoration projects in the US are outdated and omit the majority of restoration projects in Florida. To address this gap, we compiled stream restoration data from diverse sources to create a Florida Stream Restoration Database (FSRD, available at http://www.watershedecology.org/databases.html ) containing information on project type, location, completion date, and costs. The FSRD contains 178 projects categorized by restoration type, including riparian management (23%), stream reclamation (19%), flow modification (13%), bank stabilization (12%), channel reconfiguration (11%), in‐stream habitat improvements (11%), floodplain reconnection (6%), invasive species removal (4%), and dam removal (1%). Projects were spatially clustered into three geographic regions, providing insight on the diversity of initiatives, needs, and funding sources of land management agencies and private landowners that motivated restoration efforts. Projects in the Florida panhandle emphasized in‐stream habitat restoration, while peninsular projects were dominated by flow modification, and projects in the west central region focused on stream reclamation to mitigate surface mining practices and water quality and habitat improvements in tidal streams. Results suggest that Florida is spending much more on stream restoration than previously documented. Between 1979 and 2015, the mean and median stream restoration project costs in Florida were $15.4 million and $180 000, respectively, indicating a strongly skewed distribution because of the large Kissimmee River restoration project in central Florida. This work highlights the need for, and utility of, statewide and national restoration databases to improve restoration tracking. This need will become increasingly critical as more stringent water quality and habitat mitigation rules are implemented across the country. Copyright © 2016 John Wiley & Sons, Ltd.     

Integrating remotely acquired and field data to assess effects of setback levees on riparian and aquatic habitats in glacial‐melt water rivers

Setback levees, in which levees are reconstructed at a greater distance from a river channel, are a promising restoration technique particularly for alluvial rivers with broad floodplains where river‐floodplain connectivity is essential to ecological processes. Documenting the ecological outcomes of restoration activities is essential for assessing the comparative benefits of different restoration approaches and for justifying new restoration projects. Remote sensing of aquatic habitats offers one approach for comprehensive, objective documentation of river and floodplain habitats, but is difficult in glacial rivers because of high suspended‐sediment concentrations, braiding and a lack of large, well‐differentiated channel forms such as riffles and pools. Remote imagery and field surveys were used to assess the effects of recent and planned setback levees along the Puyallup River and, more generally, the application of multispectral imagery for classifying aquatic and riparian habitats in glacial‐melt water rivers. Airborne images were acquired with a horizontal ground resolution of 0.5 m in three spectral bands (0.545–0.555, 0.665–0.675 and 0.790–0.810 µm) spanning from green to near infrared (NIR) wavelengths. Field surveys identified river and floodplain habitat features and provided the basis for a comparative hydraulic analysis. Broad categories of aquatic habitat (smooth and rough water surface), exposed sediment (sand and boulder) and vegetated surfaces (herbaceous and deciduous shrub/forest) were classified accurately using the airborne images. Other categories [e.g. conifers, boulder, large woody debris (LWD)] and subdivisions of broad categories (e.g. riffles and runs) were not successfully classified either because these features did not form large patches that could be identified on the imagery or their spectral reflectances were not distinct from those of other habitat types. Airborne imagery was critical for assessing fine‐scale aquatic habitat heterogeneity including shallow, low‐velocity regions that were not feasible or practical to map in the field in many cases due to their widespread distribution, small size and poorly defined boundaries with other habitat types. At the reach‐scale, the setback levee affected the amount and distribution of riparian and aquatic habitats: (1) the area of all habitats was greater where levees had been set back and with relatively more vegetated floodplain habitat and relatively less exposed sediment and aquatic habitat, (2) where levees confine the river, less low‐velocity aquatic habitat is present over a range of flows with a higher degree of bed instability during high flows. As river restoration proceeds in the Pacific Northwest and elsewhere, remotely acquired imagery will be important for documenting its effects on the amount and distribution of aquatic and floodplain habitats, complimenting field data as a quantitative basis for evaluating project efficacy. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of urbanization on stream hydraulics

Urbanization results in major changes to stream morphology and hydrology with the latter often cited as a primary stressor of urban stream ecosystems. These modifications unequivocally alter stream hydraulics, but little is known about such impacts. Hydraulic changes due to urbanization were demonstrated using two‐dimensional hydrodynamic model simulations, comparing urban and non‐urban stream reaches. We investigated three ecologically relevant hydraulic characteristics: bed mobilization, retentive habitat, and floodplain inundation, using hydraulic metrics bed shear stress, shallow slow‐water habitat (SSWH) area, and floodplain inundation area. We hypothesized that urbanization would substantially increase bed mobilization, decrease retentive habitat, and due to increased channel size would decrease floodplain inundation. Relative percent area of bed disturbance was 4 times higher, compared with that of the non‐urban stream at bankfull discharge. SSWH availability rapidly diminished in the urban stream as discharge increased, with SSWH area and patch size 2 times smaller than the non‐urban stream for a frequently occurring flow 0.7 times bankfull discharge. Floodplain inundation decreased in frequency and duration. These results demonstrate changes in hydraulics due to urbanization that may impact on physical habitat in streams. New “water sensitive” approaches to stormwater management could be enhanced by specification of hydraulic regimes capable of supporting healthy stream habitats. We propose that a complete management approach should include the goals of restoration and protection of natural hydraulic processes, particularly those that support ecological and geomorphic functioning of streams.     

Physical constraints on the distribution of macrophytes linked with flow and sediment dynamics in British rivers

Aquatic vegetation plays a role in engineering river channels by altering patterns of flow velocity, sediment dynamics and, consequently, development and turnover of habitats. This could potentially aid in the rehabilitation of over‐widened, straightened channels, and, less desirably, reduce channel conveyance and contribute to flooding problems. Therefore, it is important to understand the environmental conditions in which in‐stream and marginal vegetation can reach sufficient abundance for these engineering roles to have a significant impact on the physical environment. Macrophyte and environmental data from 1653 river reaches across Great Britain were collated. Specific stream power (SSP) was calculated to represent hydrological disturbance and a median bed calibre index and percentage sand and finer sediment were used to characterize substrate size, since stream energy and sediment properties are two major physical controls on aquatic vegetation. Correlation and Principal Component Analysis (PCA) revealed subtly different physical habitat ‘preferences’ between species of contrasting morphology. Correlations of additional environmental data with SSP indicated that this physical disturbance variable also reflects gradients in stress variables describing nutrient availability and latitude and so is a useful integrator of a number of important pressures on plant survival. A conceptual model was produced which indicates ranges of SSP which may determine the significance of aquatic macrophytes in channel engineering processes. This model could contribute to predicting the potential for macrophyte growth within a given reach thus indicating its capacity for self‐restoration or the likelihood of weed problems. Copyright © 2010 John Wiley & Sons, Ltd.     

高坝下游水垫塘内典型流态演变问题探讨

为揭示高坝泄洪消能机理及水垫塘防护措施，系统地研究了水垫塘内的流态特征。根据高坝下游水垫深度的不同，塘内水流呈现自由冲击射流、淹没冲击射流和面流三种流型。结合二滩、小湾等工程试验资料，本文给出了不同流态之间转变的实用判别条件。     

Controls on the size and occurrence of pools in coarse‐grained forest rivers

Controls on pool formation are examined in gravel‐ and cobble‐bed rivers in forest mountain drainage basins of northern California, southern Oregon, and southeastern Alaska. We demonstrate that the majority of pools at our study sites are formed by flow obstructions and that pool geometry and frequency largely depend on obstruction characteristics (size, type, and frequency). However, the effectiveness of obstructions to induce scour also depends on channel characteristics, such as channel gradient, width:depth ratio, relative submergence (ratio of flow depth to grain size), and the calibre and rate of bed material supply. Moreover, different reach‐scale channel types impose different characteristic physical processes and boundary conditions that further control the occurrence of pools within a catchment. Our findings indicate that effective management of pools and associated aquatic habitat requires consideration of a variety of factors, each of which may be more or less important depending on channel type and location within a catchment. Consequently, strategies for managing pools that are based solely on single‐factor, regional target values (e.g. a certain number of wood pieces or pools per stream length) are likely to be ineffective because they do not account for the variety of local and catchment controls on pool scour and, therefore, may be of limited value for proactive management of complex ecosystems. Copyright © 2002 John Wiley & Sons, Ltd.     

A hydrogeomorphic dynamics approach to assess in‐stream ecological functionality using the functional flows model,part 1—model characteristics

The functional flows model integrates hydrogeomorphic processes and ecological functions for stream physical habitat evaluations. Functional flows are discharge values that serve ecological uses. Assessments of functional flows are based on evaluation of shear stress dynamics. The analysis is based on the occurrence of sediment transport regimes defined by threshold values of Shields stress estimated from discharge (Q), a parameter (f) governing depth response to incremental discharge changes, water surface slope (S) and media grain size (D₅₀). As an example, the model was tuned for fall‐run Chinook salmon spawning. Ecological functions studied were bed occupation (spawning, incubation and emergence) and bed preparation (river bed reworking periods)—both reliant on shear stress dynamics. A numerical experiment and sensitivity analysis using a wide range of realistic values of input variables indicated the effect of each variable on flow functionality. Combinations of S = 0.001, 0.005 and 0.01, D₅₀ = 0.02, 0.05, 0.1 m, f = 0.2, 0.3, 0.4, 0.5 and four sediment transport stages produced 144 scenarios. Ranges of functional flows were greater for scenarios for low f (0.2) with low slope (0.001,0.05), for high f (0.5) with small grain size (0.02 m) and for intermediate low f (0.3) with coarse grain size (0.1 m). The functional flows model incorporates in‐stream habitat processes by including metrics of hydrologic, hydraulic, geomorphic and ecologic dynamics. Model uncertainties related to input data, calculation algorithms, and model structure are analysed. Functional flows analysis can be useful in studying water management alternatives to improve habitat conditions for target species and lifestages. Copyright © 2009 John Wiley & Sons, Ltd.