LINKING RIVER MANAGEMENT TO SPECIES CONSERVATION USING DYNAMIC LANDSCAPE‐SCALE MODELS

Efforts to conserve stream and river biota could benefit from tools that allow managers to evaluate landscape‐scale changes in species distributions in response to water management decisions. We present a framework and methods for integrating hydrology, geographic context and metapopulation processes to simulate effects of changes in streamflow on fish occupancy dynamics across a landscape of interconnected stream segments. We illustrate this approach using a 482 km² catchment in the southeastern US supporting 50 or more stream fish species. A spatially distributed, deterministic and physically based hydrologic model is used to simulate daily streamflow for sub‐basins composing the catchment. We use geographic data to characterize stream segments with respect to channel size, confinement, position and connectedness within the stream network. Simulated streamflow dynamics are then applied to model fish metapopulation dynamics in stream segments, using hypothesized effects of streamflow magnitude and variability on population processes, conditioned by channel characteristics. The resulting time series simulate spatially explicit, annual changes in species occurrences or assemblage metrics (e.g. species richness) across the catchment as outcomes of management scenarios. Sensitivity analyses using alternative, plausible links between streamflow components and metapopulation processes, or allowing for alternative modes of fish dispersal, demonstrate large effects of ecological uncertainty on model outcomes and highlight needed research and monitoring. Nonetheless, with uncertainties explicitly acknowledged, dynamic, landscape‐scale simulations may prove useful for quantitatively comparing river management alternatives with respect to species conservation. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.     

The Disconnected Sediment Conveyor Belt: Patterns of Longitudinal and Lateral Erosion and Deposition During a Catastrophic Flood in the Lockyer Valley,South East Queensland,Australia

The sediment (dis)connectivity concept is the water‐mediated transfer of sediment between different compartments of a catchment sediment cascade involving four possible dimensions or linkages (longitudinal, lateral, vertical and temporal). Quantifying the strength of these linkages within and between compartments provides a means to understand the internal sediment flux dynamics of a catchment. The aims of this paper are to examine (1) the dynamics of longitudinal and lateral (dis)connectivity by quantifying patterns of erosion and deposition that occurred during a catastrophic flood, and (2) how the patterns of connectivity can be changed through management actions that better utilise floodplain sediment storages. Multi‐temporal LiDAR and air photos are used to quantify volumetric change with respect to geomorphic settings and units. The results show that over the length of the trunk stream, the high‐magnitude event was net depositional with high longitudinal sediment disconnectivity. At the reach scale, an alternating pattern of high and low longitudinal connectivity associated with contraction and expansion zones was evident. The efficiency of sediment transfer from the uppermost compartment to the most downstream compartment decreased exponentially, while the strength of lateral connectivity increased for each expansion reach. Modelling results show that increasing channel boundary roughness along expansion reaches with riparian revegetation can increase the frequency of lateral connectivity and floodplain sediment storage, thereby decreasing reach‐to‐reach connectivity and reducing end‐of‐catchment sediment delivery. This contrasts with the current trend of building levees along the bank tops of expansion reaches, which decrease lateral connectivity and increase reach‐to‐reach connectivity. Copyright © 2015 John Wiley & Sons, Ltd.     

Physiographic characteristics of bridge‐stream intersections

Bridges that cross streams can be greatly affected by channel instabilities, such as channel widening, lateral migration and channel bed degradation. Attention to channel conditions in the vicinity of bridges is an important aspect of bridge maintenance and safety. Channel stability is also critical to goals of multi‐objective river management. Given that channel stability is important for both river management and the structural stability of bridges, any river management scheme should consider the stability of bridge‐stream intersections. In this paper, the characteristics of bridge‐stream intersections across the United States are described based on existing literature and recent field observations. A set of recommendations for addressing and improving channel stability at bridges is suggested, including: (1) controlling water and sediment discharges at the catchment level; (2) revegetating channel banks with woody vegetation; (3) reshaping the channel cross‐section to a more stable, configuration; (4) removing disturbances from the stream channel, such as cattle and (5) using structures to control flow near channel beds and banks. The physiographic setting is a factor in the solution of at least the first three suggestions in this list. Attention to the physical characteristics of bridge‐stream intersections in the various physiographic regions can lead to sustainable solutions for stabilizing channels at bridge‐stream intersections. Copyright © 2006 John Wiley & Sons, Ltd.     

Ground beetle habitat templets and riverbank integrity

The habitat templet approach was used in a scale‐sensitive bioindicator assessment for the ecological integrity of riverbanks and for specific responses to river management. Ground beetle habitat templets were derived from a catchment‐scale sampling, integrating the overall variety of bank types. This coarse‐filter analysis was integrated in the reach‐scale fine‐filtering approaches of community responses to habitat integrity and river management impacts. Higher species diversity was associated with the higher heterogeneity in bank habitats of the un‐navigable river reaches. The abundant presence of habitat specialists in the riverbank zone allows a habitat integrity assessment based on the habitat templet indicator species. Significant responses were detected for channel morphology in the width‐to‐depth ratio and for hydrological regime in peak frequency and peak velocity, enabling the development of evaluation methods for the impact assessment of river management and flood protection strategies. Copyright © 2005 John Wiley & Sons, Ltd.     

Habitat Restoration in the Context of Watershed Prioritization: The Ecological Performance of Urban Stream Restoration Projects in Portland,Oregon

In Portland (Oregon, USA), restoration actions have been undertaken at the watershed scale (e.g. revegetation and stormwater management) to improve water quality and, where water quality and quantity are adequate at the reach scale, to increase habitat heterogeneity. Habitat enhancement in urban streams can be important for threatened species, but challenging, because of altered catchment hydrology and urban encroachment on floodplains and channel banks. To evaluate reach‐scale restoration projects in the Tryon Creek watershed, we sampled benthic macroinvertebrates and conducted habitat quality surveys pre‐project and over 4 years post‐project. Species sensitive to pollution and diversity of trophic groups increased after restoration. Taxonomic diversity increased after restoration but was still low compared with reference streams. We found no significant changes in trait proportions and functional diversity. Functional diversity, proportion of shredders and semivoltine invertebrates were significantly higher in reference streams than in the restored stream reaches. We hypothesized that inputs of coarse particulate organic matter and land use at watershed scale may explain the differences in biodiversity between restored and reference stream reaches. Habitat variables did not change from pre‐project to post‐project, so they could not explain community changes. This may have been partly attributable to insensitivity of the visual estimate methods used but likely also reflects the importance of watershed variables on aquatic biota—suggesting watershed actions may be more effective for the ecological recovery of streams. For future projects, we recommend multihabitat benthic sampling supported by studies of channel geomorphology to better understand stream response to restoration actions. Copyright © 2014 John Wiley & Sons, Ltd.     

A LIDAR‐DERIVED EVALUATION OF WATERSHED‐SCALE LARGE WOODY DEBRIS SOURCES AND RECRUITMENT MECHANISMS: COASTAL MAINE,USA

In‐channel large woody debris (LWD) promotes quality aquatic habitat through sediment sorting, pool scouring and in‐stream nutrient retention and transport. LWD recruitment occurs by numerous ecological and geomorphic mechanisms including channel migration, mass wasting and natural tree fall, yet LWD sourcing on the watershed scale remains poorly constrained. We developed a rapid and spatially extensive method for using light detection and ranging data to do the following: (i) estimate tree height and recruitable tree abundance throughout a watershed; (ii) determine the likelihood for the stream to recruit channel‐spanning trees at reach scales and assess whether mass wasting or channel migration is a dominant recruitment mechanism; and (iii) understand the contemporary and future distribution of LWD at a watershed scale. We utilized this method on the 78‐km‐long Narraguagus River in coastal Maine and found that potential channel‐spanning LWD composes approximately 6% of the valley area over the course of the river and is concentrated in spatially discrete reaches along the stream, with 5 km of the river valley accounting for 50% of the total potential LWD found in the system. We also determined that 83% of all potential LWD is located on valley sides, as opposed to 17% on floodplain and terrace surfaces. Approximately 3% of channel‐spanning vegetation along the river is located within one channel width of the stream. By examining topographic and morphologic variables (valley width, channel sinuosity, valley‐side slope) over the length of the stream, we evaluated the dominant recruitment processes along the river and often found a spatial disconnect between the location of potential channel‐spanning LWD and recruitment mechanisms, which likely explains the low levels of LWD currently found in the system. This rapid method for identification of LWD sources is extendable to other basins and may prove valuable in locating future restoration projects aimed at increasing habitat quality through wood additions. Copyright © 2011 John Wiley & Sons, Ltd.     

AUTOMATIC DELINEATION OF FUNCTIONAL RIVER REACH BOUNDARIES FOR RIVER RESEARCH AND APPLICATIONS

The river reach is a pervasive term within contemporary river research and applications. Yet, despite its prevalence, there is a notable lack of consistency in its definition. This paper identifies the presence of two broad types of reach definition within the academic literature, operational and functional, and argues that a functional definition is more suitable for applications within river research and management. A range of sequence zonation algorithms that were originally derived for geological well‐log analysis were compared for their ability to automatically identify functional reach boundaries. An analysis of variance‐based global boundary hunting algorithm was identified as the most suitable. To demonstrate the potential practical applications of automatic reach delineation methods, two case studies where functional reach boundaries have been identified were described: first, in a sequence of predicted sediment transport capacities for use in a reach‐based sediment transport model; and second, in a sequence of RHS Habitat Quality Assessment scores for identification of lengths of channel in need of habitat restoration efforts. Finally, the paper discusses how this type of functional reach identification procedure might be applied in other areas of river research and applications and how a multivariate version of a statistical zonation algorithm might prove useful in facilitating integrated catchment management by identifying reach boundaries common across all variables of interest in the system. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

THE SOLAR‐TO‐STREAM POWER RATIO: A DIMENSIONLESS NUMBER EXPLAINING DIEL FLUCTUATIONS OF TEMPERATURE IN MESOSCALE RIVERS

The diel variation of temperature in mesoscale river reaches (catchment area > 1000 km²) is analysed using concurrent measurements of water temperature and of those meteorological (incident short‐wave radiation, air temperature, relative humidity and wind speed variables) and hydraulic variables (streamflow, top width, channel slope and flow depth) controlling the thermal regime. Measurements were taken along two river reaches located in central Chile, on the Itata (11 290 km², Strahler's order 6, reach length 30 km, Q_bankfull = 400 m³ s^?1) and Vergara (4340 km², Strahler's order 5, reach length 20 km, Q_bankfull = 85 m³ s^?1) rivers. The measuring frequency was 15 min. The relevant energy fluxes at the air–water interface, that is, atmospheric long‐wave radiation, net short‐wave radiation, radiation emitted by the water body, evaporation (latent heat) and conduction heat are computed and analysed for four scenarios of 12 days duration each, representing typical conditions for the austral winter, spring, summer and autumn. We find large differences in the diel river temperature range between the two sites and across seasons (and thus, flows and meteorological conditions), as reported in previous studies, but no clear relationship with the controlling variables is overtly observed. Following a dimensional analysis, we obtain a dimensionless parameter corresponding to the ratio of solar‐to‐stream power, which adequately explains the diel variation of water temperature in mesoscale rivers. A number of our own measurements as well as literature data are used for preliminary testing of the proposed parameter. This easy‐to‐compute number is shown to predict quite well all of the cases, constituting a simple and useful criterion to estimate a priori the magnitude of temperature diel variations in a river reach, given prevailing meteorological (daily maximum solar radiation) and hydrologic–hydraulic (streamflow, mean top width) conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

CATCHMENT CHARACTERISTICS AND PLANT RECRUITMENT FROM SEDIMENT IN STREAM AND MEADOW HABITATS

Streams and rivers constitute a dense network with a large interface to the surrounding landscape and are thus highly susceptible to anthropogenic pressures related to land‐use activities in adjacent riparian and upland areas. In the present study, we investigated the influence of catchment characteristics on potential propagule and species recruitment from sediment in lowland stream ecosystems. We tested the following hypotheses: (1) catchment characteristics affect species recruitment from stream sediment in both stream and riparian habitats and (2) recruitment of species associated with undisturbed fen‐meadow habitats is higher in places with natural vegetation in the riparian zones. A large number of wetland species emerged from the stream sediment and sediment recruitment and therefore can act as an important dispersal corridor for common species in stream ecosystems. The recruited propagules were dominated by terrestrial species, but amphibious and aquatic species also appeared, particularly in the artificial stream channels. These included among others species within the genera Ranunculus sp., Callitriche sp. and Potamogeton sp. The large between‐site differences in land‐use characteristics in the riparian zones of the studied stream reaches, both locally and along upstream reaches, were not reflected in species recruitment from the stream sediments. Thus, most recruited species were common and widely distributed, and they were dominated by species with ruderal and competitive life history strategies, whereas only few species associated with fen‐meadow vegetation were recruited. From these findings, we infer not only that hydrochorous dispersal of species can be a potential efficient dispersal vector in agricultural landscapes but also that limitations can exist as to which species can be recruited. We suggest that further studies are performed to elucidate this issue further. Copyright © 2012 John Wiley & Sons, Ltd.     

High resolution spatiotemporal patterns of flow at the landscape scale in montane non-perennial streams

Intermittent and ephemeral streams in dryland environments support diverse assemblages of aquatic and terrestrial life. Understanding when and where water flows provide insights into the availability of water, its response to external controlling factors, and potential sensitivity to climate change and a host of human activities. Knowledge regarding the timing of drying/wetting cycles can also be useful to map critical habitats for species and ecosystems that rely on these temporary water sources. However, identifying the locations and monitoring the timing of streamflow and channel sediment moisture remains a challenging endeavor. In this paper, we analyzed daily conductivity from 37 sensors distributed along 10 streams across an arid mountain front in Arizona (United States) to assess spatiotemporal patterns in flow permanence, defined as the timing and extent of water in streams. Conductivity sensors provide information on surface flow and sediment moisture, supporting a stream classification based on seasonal flow dynamics. Our results provide insight into flow responses to seasonal rainfall, highlighting stream reaches very reactive to rainfall versus those demonstrating more stable streamflow. The strength of stream responses to precipitation are explored in the context of surficial geology. In summary, conductivity data can be used to map potential stream habitat for water-dependent species in both space and time, while also providing the basis upon which sensitivity to ongoing climate change can be evaluated.     

The relationship between geomorphic river adjustment and management actions over the last 50 years in the Upper Hunter Catchment,NSW, Australia

The installation of 517 river works in the upper Hunter catchment, New South Wales over the last 50 years is linked to geomorphic river adjustment and flood history at catchment and reach scales. Nineteen types of works are classified into three categories consisting of engineering, heavy machinery and vegetation works. Since 1952, a transition in techniques has been detected from engineering‐based approaches, to river training/maintenance, to more ecosystem‐based approaches. From the 1950s to the mid‐1980s extensive river engineering was undertaken. Projects were concentrated along laterally unconfined rivers and were generally implemented after major phases of geomorphic river adjustment. Neither the type of river nor the type of river adjustment guided the implementation of differing management techniques or their distribution in the catchment. A blanket approach was adopted, applying the same types of works across all types of river. Emphasis was placed upon concerns for bank instability rather than bed instability. Hence in many cases, river works addressed the symptoms (i.e. bank erosion) rather than the underlying causes of river change (i.e. bed incision). Since the mid 1980s, techniques have evolved towards vegetation‐based procedures. The development of more effective river rehabilitation programmes requires that greater consideration is given to proactive strategies which build upon an understanding of geomorphic river adjustments at the catchment scale. Copyright © 2008 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.     

Hydraulic and Physical Structure of Runs and Glides Following Stream Restoration

Hydraulic units are often linked to ecological habitat through geomorphic structure, and a better understanding of the turbulent characteristics of the units is needed. Our work examined the near‐bed turbulent structure of runs and glides in a restored river and investigated the physical characteristics that influenced the near‐bed hydraulics in these units. The research was completed in three restored reaches and one reference reach at the Virginia Tech Stream Research, Education, and Management Laboratory. The laboratory is unique because three different restoration treatments were applied contiguously along a stream, and the restoration practices ranged from passive to active. The passive reach included cattle exclusion, while the active reaches included cattle exclusion as well as vegetation plantings, bank sloping and the construction of inset floodplains. Three‐dimensional velocities were measured near the channel bed in run and glide biotopes within the three restored reaches, as well as an upstream reference reach. The velocities were utilized to analyse and compare near‐bed turbulent structure across the reaches. While the restoration activities did not address the channel bed directly, differences in physical structure of the two physical biotopes were observed among restoration treatments, likely because of changes in bank shape and roughness due to vegetation differences. Differences between reference and restored reaches were still evident approximately 3 years after cattle exclusion and construction activities. Few differences were observed in the hydraulic structure between runs and glides, and the near‐bed flow structure in both runs and glides was related to local roughness. Copyright © 2016 John Wiley & Sons, Ltd.     

RIVERBED DIGITAL ELEVATION MODELS AS A TOOL FOR HOLISTIC RIVER MANAGEMENT: MOTUEKA RIVER,NELSON, NEW ZEALAND

River management in New Zealand's laterally active gravelly rivers has permitted floodplain development and protection of agricultural resources and infrastructure. Management of these dynamic systems has been hailed as a success for the approaches adopted, namely straightening and confining the river using bank protection and managing riverbed levels by gravel extraction. However, this activity also impacts river morphological/habitat diversity and potential gravel resource, by replacing broad riparian corridors with narrower channels and reducing lateral connectivity with the floodplain. This paper quantifies river behaviour in three laterally confined reaches in the upper Motueka River over a 7‐year period, using annual high‐resolution ground surveys to address the nature of morphological change and associated sediment flux in these reaches with a view to informing management of the gravel resource. Surveys between 2004 and 2010 acquired data to construct digital elevation models (DEMs) of the active riverbed in three ~1‐km‐long reaches. Morphological budgeting based on differencing between successive DEM surfaces reveals complex spatial and temporal patterns of erosion and deposition, demonstrating complex reach dynamics. Overall, volumetric changes suggest these narrowed reaches have been net exporters of sediment, associated with continued channel degradation. This has left bar features, traditionally the focus of gravel extraction in the reaches, relatively isolated from all but extreme flows, limiting replenishment of the gravel resource. The paper demonstrates the utility of riverbed DEMs as a potential tool to frame river character and behaviour at the reach scale in gravel‐bed rivers, thereby providing an important contribution to holistic river management in these systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Flood energy dissipation in anabranching channels

This study examines the character of developing anabranched channel networks on the River Wear, north England, using metre‐scale aerial LiDAR. DSM‐DTM interpretation reveals a well‐developed vegetation structure and a locally diverse terrain, dominated by an interlinked channel network split by low‐elevation depositional areas with the gross morphology of the reach resembling that of a strongly active meandering/wandering channel suggesting that an anabranching network may develop within systems that were initially active meandering and wandering, evolving in line with floodplain vegetative succession. Utilization of the LiDAR DEM in the hydrological component of the CAESAR‐Lisflood (version 1.4) morphodynamic model has generated local hydraulic variable estimates through the anabranched reaches for a range of flows. These data clearly demonstrate how elevated flows are transferred out of the primary channel and distributed along the interconnected secondary channel network, creating a diverse set of hydraulic environments. Areas between the channels rapidly become inundated as flows increase, dissipating flow energy. Shear stress estimates throughout the study site reveal a generally reduced ability to mobilize sediments and erode channel margins, in comparison with a single‐thread reach immediately downstream. Anabranched secondary channels appear to operate in disequilibrium and act predominantly as aggradational zones, although with some evidence of scour at channel bifurcation and confluence points. It would appear that the topographic character of anabranching sites efficiently manages flood flow energy, activating secondary channels and low‐elevation areas to distribute flood flows. These findings contrast with the hydraulic data from an adjacent single‐thread reach, characterized by flood flows concentrated in‐channel creating a high erosive potential. We propose that anabranching rivers could play an important role in natural flood and sediment management in many U.K. river systems.     

Quantifying the effect of riparian forest versus agricultural vegetation on river meander migration rates,central Sacramento River,California, USA

Riparian forest vegetation is widely believed to protect riverbanks from erosion, but few studies have quantified the effect of riparian vegetation removal on rates of river channel migration. Measured historical changes in a river channel centreline, combined with mapped changes in floodplain vegetation, provide an opportunity to test how riparian vegetation cover affects the erodibility of riverbanks. We analysed meander migration patterns from 1896 to 1997 for the central reach of the Sacramento River between Red Bluff and Colusa, using channel planform and vegetation cover data compiled from maps and aerial photography. We used a numerical model of meander migration to back‐calculate local values for bank erodibility (i.e. the susceptibility of bank materials to erosion via lateral channel migration, normalized for variations in near‐bank flow velocities due to channel curvature). A comparison of migration rates for approximately 50 years before and after the construction of Shasta dam suggests that bank migration rates and erodibility increased roughly 50%, despite significant flow regulation, as riparian floodplains were progressively converted to agriculture. A comparison of migration rates and bank erodibilities between 1949 and 1997, for reaches bordered by riparian forest versus agriculture, shows that agricultural floodplains are 80 to 150% more erodible than riparian forest floodplains. An improved understanding of the effect of floodplain vegetation on river channel migration will aid efforts to predict future patterns of meander migration for different river management and restoration scenarios. Copyright © 2004 John Wiley & Sons, Ltd.     

Responses of macroinvertebrate communities to river restoration in a channelized segment of the Shibetsu River,Northern Japan

The effects of restoration of channel meandering and of groyne structures on physical variables and river‐dwelling macroinvertebrates were examined in a lowland river, the Shibetsu River in Northern Japan. The lowland segment of the Shibetsu River, which previously meandered, was straightened by channelization and groynes installed on some portions of the channelized reach. In 2002, the channelization works were partly reversed to improve the degraded river ecosystem. Physical environment variables and macroinvertebrate community structure and composition were compared among reconstructed meanders and channelized reaches with and without groynes. The shear stress of the river edge in reconstructed meanders and groyne reaches was lower than that in a channelized reach. In addition, the edge habitat near the stream bank created by the reconstructed meander and groyne reaches had higher total density and taxon richness of macroinvertebrates than those of the channelized reach. Restoration provided a relatively stable edge habitat, contributing to the recovery of macroinvertebrate communities in such channelized lowland rivers. The placement of groynes can be an effective method of in‐stream habitat restoration for macroinvertebrates. Copyright © 2006 John Wiley & Sons, Ltd.     

Modelling reach‐scale variability in sediment mobility: An approach for within‐reach prioritization of river rehabilitation works

Many Australian river ecosystems have been, and continue to be, adversely affected by increased channel dimensions and sediment supplies occurring in the period since European settlement. One of the key aims of river rehabilitation in these rivers is to help reduce sediment yield by preventing ongoing bank erosion and remobilization of instream bed material stores. While various tools have been developed to help identify sediment sources at the catchment scale, this is often at a resolution that is too coarse to be translated directly to on‐ground rehabilitation works, as most riverworks programs are designed and implemented at the reach or within‐reach scale. This paper provides a method of prioritizing rehabilitation at the within‐reach scale by using a high‐resolution reach‐scale modelling approach to examine the relative entrainment potential of sediment stores. The method has been developed for a 10 km reach of the upper Hunter River, NSW, Australia. Shear stress distribution is examined using the widely available model HEC‐RAS, and incorporating a detailed, LiDAR‐derived, representation of the in‐channel vegetation into a spatially distributed Manning's roughness layer. At the geomorphic unit scale, the results highlight that the elevated ‘bench’ units, which represent significant stores of sand and silt, are much more vulnerable to remobilization than the lower elevation gravel bar units. At the sub‐reach scale (500–2000 m) shear stresses are greatest in the most confined sections. While instream geomorphic heterogeneity has been significantly reduced in these locations, ongoing erosion is limited by bedrock and buried coarse gravel terrace material in the bed and banks. These results highlight the need for targeted rehabilitation strategies that account for within‐reach variability in entrainment potential as well as on‐the‐ground knowledge of sediment supply and geological controls. Copyright © 2010 John Wiley & Sons, Ltd.     

River widening: an approach to restoring riparian habitats and plant species

‘River widenings’ are commonly used in river restoration to allow channel movement within a spatially limited area. Restoration seeks to restore fluvial processes and to re‐establish a more natural riparian community. This study investigates the performance of five river widenings in Switzerland, focusing on the re‐establishment of riparian (semi‐)terrestrial habitats and species, and highlights some factors that seem to influence their performance. The restoration projects are compared with pre‐restoration conditions and near‐natural conditions, which are assumed to represent the worst‐ and best‐case conditions along a gradient of naturalness. Fuzzy ordination of vegetation data and calculation of landscape metrics based on habitat maps revealed marked differences between the degree of naturalness achieved by each individual restoration project. However, in general river widenings were found to increase the in‐stream habitat heterogeneity and enhanced the establishment of pioneer habitats and riparian plants. Analyses of species pools based on a hierarchic list of indicator species and correspondence analysis showed that the ability of river widenings to host typical riparian species and to increase local plant diversity strongly depends on the distance to near‐natural stretches. Species dispersal and establishment might be hampered by decisions taken outside the scope of the restoration project. Therefore we conclude that action on the catchment scale is needed to maximize the benefits of local management. Copyright © 2005 John Wiley & Sons, Ltd.