Article

Use and Performance of In-Stream Structures for River Restoration: A Case Study from North Carolina

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Abstract

In-stream structures including cross-vanes, J-hooks, rock vanes, and W-weirs are widely used in river restoration to limit bank erosion, prevent changes in channel gradient, and improve aquatic habitat. During this investigation, a rapid assessment protocol was combined with post-project monitoring data to assess factors influencing the performance of more than 558 in-stream structures and rootwads in North Carolina. Cross-sectional survey data examined for 221 cross sections from 26 sites showed that channel adjustments were highly variable from site to site, but approximately 60 % of the sites underwent at least a 20 % net change in channel capacity. Evaluation of in-stream structures ranging from 1 to 8 years in age showed that about half of the structures were impaired at 10 of the 26 sites. Major structural damage was often associated with floods of low to moderate frequency and magnitude. Failure mechanisms varied between sites and structure types, but included: (1) erosion of the channel bed and banks (outflanking); (2) movement of rock materials during floods; and (3) burial of the structures in the channel bed. Sites with reconstructed channels that exhibited large changes in channel capacity possessed the highest rates of structural impairment, suggesting that channel adjustments between structures led to their degradation of function. The data question whether currently used in-stream structures are capable of stabilizing reconfigured channels for even short periods when applied to dynamic rivers.

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... Chambers et al. [67] found that, in central Nevada, increases in both basin and reach-scale sensitivity were associated with channels characterized by high stream power, large sediment supplies, and channel bed and bank materials that could be easily eroded during moderate floods. A similar combination of factors was identified by Miller and Kochel [68,69] to have controlled the stability of reconstructed channel reaches and the performance of instream structures within the Blue Ridge and Piedmont physiographic provinces of North Carolina. In this case, the potential risk of project failure as defined by significant (threshold crossing) changes in channel form along reconstructed channels were associated with streams possessing high stream powers, large sediment supplies and transport rates, and easily eroded bank materials. ...
... In contrast, between about 35 and 60% of the modern channel banks are now composed of easily eroded legacy sediments (Table S1). Attempting to create a mobile, yet geomorphically stable stream where legacy sediments comprise the channel banks is likely to be difficult at best, given the ease with which loose, sandy sediments can be removed from the banks and from around root wads and other forms of bank treatment [68,69]. It should also be recognized that, during future disturbances in which sediment transport capacity is altered such that it exceeds sediment availability, the primary response will predominately involve bank erosion (e.g., channel widening and/or alterations in planform morphology), rather than rapid or significant incision. ...
... Chambers et al. [67] found that, in central Nevada, increases in both basin and reach-scale sensitivity were associated with channels characterized by high stream power, large sediment supplies, and channel bed and bank materials that could be easily eroded during moderate floods. A similar combination of factors was identified by Miller and Kochel [68,69] to have controlled the stability of reconstructed channel reaches and the performance of instream structures within the Blue Ridge and Piedmont physiographic provinces of North Carolina. In this case, the potential risk of project failure as defined by significant (threshold crossing) changes in channel form along reconstructed channels were associated with streams possessing high stream powers, large sediment supplies and transport rates, and easily eroded bank materials. ...
... In contrast, between about 35 and 60% of the modern channel banks are now composed of easily eroded legacy sediments (Table S1). Attempting to create a mobile, yet geomorphically stable stream where legacy sediments comprise the channel banks is likely to be difficult at best, given the ease with which loose, sandy sediments can be removed from the banks and from around root wads and other forms of bank treatment [68,69]. It should also be recognized that, during future disturbances in which sediment transport capacity is altered such that it exceeds sediment availability, the primary response will predominately involve bank erosion (e.g., channel widening and/or alterations in planform morphology), rather than rapid or significant incision. ...
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Big Harris Creek, North Carolina, possesses a geomorphic history similar to many drainages in the southern Appalachian piedmont, and was used herein as a representative example of the influence of European settlement on contemporary channel form and processes. The integrated use of historical, dendrogeomorphic, stratigraphic, and cartographic data shows that the conversion of land-cover from a mix of natural conditions and small farms to commercial cotton production in the late 1800s and early 1900s led to significant upland soil erosion, gully formation, and the deposition of legacy sediments on the valley floor. Aggradation was followed by catchment-wide channel incision in the mid-1900s in response to reforestation and the implementation of soil conservation measures. Collectively, the responses form an aggradational-degradational episode (ADE) that produced the geomorphic framework for the contemporary processes operating along the drainage network. Defined, characterized, and mapped process zones (stream reaches of similar form and process) show that the type, intensity, and evolutionary sequence of geomorphic responses varied within the catchment as a function of the position along the drainage network, the erosional resistance of the underlying bedrock, and the valley characteristics (particularly width). Understanding the spatially variable influences of the ADE on contemporary, reach-scale geomorphic processes provides valuable insights for restoration as it helps inform practitioners of the sensitivity and ways in which the reach is likely to respond to future disturbances, the potential impacts of processes on proposed manipulations intended to achieve the project’s restoration goals, and the potential risk(s) involved with channel reconstruction. The latter is strongly controlled by geotechnical differences between erosionally resistant precolonial deposits and easily eroded legacy sediments that locally form the channel banks following the ADE.
... Furthermore, Veller and Doyle (2001) noted that the effectiveness of coniferous woody revetments improved with additional anchoring measures and streambank management techniques, such as bank shaping and vegetation planting. In fact, incorporating additional anchoring in woody revetment design was a key finding in numerous monitoring studies (D'Aoust and Miller, 2000;Miller and Kochel, 2013;Shields et al., 2003bShields et al., , 2004Shields et al., , 2006Shields et al., , 2008Veller and Doyle, 2001). D'Aoust and Miller (2000) provided a theoretical approach for determining anchoring requirements for single and multiple log deflectors based on a factor of safety analysis, finding that the gravitational body force, the frictional force on the streambed, and the fluid drag force are the dominant forces acting on a log deflector. ...
... The vast majority of studies reviewed here were conducted at the site scale. While most streambank stabilization projects only occur along a small section of a stream (e.g., a single meander bend), researchers noted the importance of understanding the possible reach-scale and river-scale effects on channel stability (Anstead et al., 2012;Bhuyian et al., 2009;Brooks et al., 2004;Buchanan et al., 2014;Cavaille et al., 2018;Cooperman et al., 2007;Enlow et al., 2018;Florsheim et al., 2008;Gidley et al., 2012;Khosronejad et al., 2013;Larsen and Greco, 2002;Massey et al., 2017;Miller and Kochel, 2013;White et al., 2010;Wu et al., 2005). For example, scour prediction is an important design consideration for instream structures, hardened banks, and streambank toe protection, as excessive scour can cause structures to fail. ...
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Highlights Eleven general streambank stabilization (SBS) techniques have been used worldwide. Rules-of-thumb and practitioner experience are still heavily applied in SBS design. Research needs include assessing the spatiotemporal variability of SBS and improving numerical simulation. Future SBS experiments need to include design details with results that can be easily communicated to designers. Abstract. Streambank stabilization techniques, designed to maximize localized streambank shear strength and/or minimize the forces acting on a streambank, have been in existence for centuries and are still a popular river management technique used by practitioners worldwide. The purpose of this literature review is to identify common streambank stabilization techniques, compile and summarize the recent peer-reviewed journal articles on these techniques, and determine research needs. Eleven general streambank stabilization practices, consisting of both instream structures and streambank management techniques, are identified in this literature review. Over 140 peer-reviewed journal articles on these techniques have been published over the last 20 years. To improve design and implementation of streambank stabilization techniques, two major research needs were identified: (1) further assess and quantify the spatiotemporal effects that streambank stabilization practices have on bank erosion, hydraulics, sediment transport, and habitat and (2) continue to improve numerical models for streambank stabilization design in order to holistically evaluate and address these effects. In addition, a list of specific research needs for each stabilization technique is provided. To help address these research needs, it is recommended that future streambank stabilization publications should (1) use consistent technique nomenclature, (2) provide characteristic details about the techniques and channels studied, (3) justify the experimental setup, and (4) explain how the research will improve streambank stabilization design. Keywords: Bankfull bench, Barb, Bioengineering, Deflector, Dike, Dyke, Groin, Groyne, Jetty, Large woody debris, LPSTP, Retarder, Revetment, Riprap bank, River training, Shaping, Spur, Stream restoration, Streambank erosion, Streambank stabilization, Toe rock, Toe
... Stream restoration often entails stream channel modifications that reduce surface velocities and promote exchange with the subsurface (hyporheic exchange). Common structures used for this purpose include cross-vanes, J-hooks, channel spanning logs, boulder weirs, and root wads (Doll et al., 1999;Roni et al., 2006;Daniluk et al., 2013;Miller and Kochel, 2013;Palmer et al., 2014). These structures can also potentially improve water quality by regulating temperature (Arrigoni et al., 2008;Hester et al., 2009;Menichino and Hester, 2014), removing toxins (Bencala and Walters, 1983;Harvey and Fuller, 1998;Fuller and Harvey, 2000), and retaining excess dissolved and suspended nutrients (Craig et al., 2008;Hester et al., 2016). ...
... We performed six experiments (E1 through E6) that differed in terms of number of in-stream structures and/or flow rate in the channel (Table 1). We installed a series of structures (weirs) in the treatment reach to simulate natural debris dams as well as stream restoration structures such as log dams, boulder weirs, w-weirs, and upstream v's (Bilby and Likens, 1980;Brooks et al., 2004;Roni et al., 2006;Bhuiyan et al., 2007;NRCS, 2007;Miller and Kochel, 2013). We varied the number of structures from 0 to 10 and installed them in stages between E1, E2, E3, and E4 to test the effect of weir number/density on transient storage parameters. ...
Article
In-stream structures can potentially enhance surface and subsurface solute retention. They form naturally in small streams and their installation has gained popularity in stream restoration for multiple purposes, including improved water quality. Yet few studies have quantified the cumulative effect of multiple structures on solute transport at the reach scale, nor how this varies with changing stream flow. We built a series of weirs in a small stream to simulate channel spanning structures such as natural debris dams and stream restoration log dams and boulder weirs. We conducted constant rate conservative (NaCl) tracer injections to quantify the effect of the weirs on solute transport at the reach scale. We used a one dimensional solute transport model with transient storage to quantify the change of solute transport parameters with increasing number of weirs. Results indicate that adding weirs significantly increased the cross-sectional area of the surface stream (A) and transient storage zones (As) while exchange with transient storage (α) decreased. The increase in A and As is due to backwater behind weirs and increased hydrostatically driven hyporheic exchange induced by the weirs, while we surmise that the reduction in α is due at least in part to reduced hydrodynamically driven hyporheic exchange in bed ripples drowned by the weir backwater. In order for weir installation to achieve net improvement in solute retention and thus water quality, cumulative reactions in weir backwater and enhanced hydrostatically driven hyporheic exchange would have to overcome the reduced hydrodynamically driven exchange. Analysis of channel flow variation over the course of the experiments indicated that weirs change the relationship between transient storage parameters and flow, for example the trend of increasing α with flow without weirs was reversed in the presence of weirs. Effects of flow variation were substantial, indicating that transient storage measurements at a single point in time typically cannot be extrapolated to estimate net annual effects. Thus, rigorous evaluation of water quality effects of stream restoration structures requires measurements at multiple channel flow rates.
... For example, bridge damage states describe visible damage to bridge components, such as the abutment, shear keys, deck, and columns (ODOT, 2009). Regarding stream modification, stages of damage to installed structures have been recognized in multiple studies (Brown, 2000;Unger and Hager, 2006;Holburn et al., 2009;Miller and Kochel, 2013). Regarding stream channels, there are protocols in use that define states of quality, rather than damage, for natural channels (Barbour et al., 1999;Johnson, 2005). ...
... Damage to structures is evaluated based on descriptions for structural integrity and erosion developed by Miller and Kochel (2013). Two failure modes for installed structures are addressed in this category of damage, movement of structure components, and local erosion leading to detachment from the bank. ...
Article
Complex relationships between stream functions and processes make evaluation of stream modification projects difficult. Informed by vague objectives and minimal monitoring data, post-construction project evaluations can often be a subjective attribution of success or failure. This article provides a simple framework to rapidly describe the degree of damage in stream modification projects performed in constrained settings. Based on widely accepted evaluations of physical habitat quality and stream stability, the damage states framework describes a continuum of damage in multiple categories that relate natural stream functions to the often desired state of static equilibrium. Given that channel form is closely related to stream function, it follows that changes to the channel form result in changes in function. The damage states focus on damage to flow hydraulics, sediment transport and channel equilibrium, hydraulic, and geomorphic parameters that describe basic stream functioning and support higher level functions in the modified channel. The damage states can be used in decision making as a systematic method to determine the need for repair and design adjustments.
... One of the river restoration methodologies is based on the use of natural materials (Renaturalization), such as tree trunks and branches from dead trees (Lüderitz et al., 2011;Miller & Kochel, 2013). The addition of these natural materials to the river can result in an increase in the accumulation of sediments, a decrease in water flow, the creation of habitats (habitat diversity), an increase in the channel complexity, and meanders formation, which enhances the diversity and abundance of macroinvertebrates (Beaune & Sellier, 2021). ...
Article
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Gualaxo do Norte River (GNR), in southeastern Brazil, was impacted by iron ore tailings from the Fundão Dam rupture (November 2015). The deposition of tailings on the riverbed has changed the hydrogeomorphological characteristics of the GNR, resulting in a decrease in the diversity of physical habitats and the ecological biodiversity. As part of the process of restoration and management of this damaged ecosystem, the river restoration project ReNaturalize was implemented to restructure the geomorphological characteristics and the physical habitat, and to enhance the reestablishment of biota, mainly for macroinvertebrates and fishes. For this goal, 203 wooden structures, such as tree trunks, branches and grass were installed in two sections of GNR (T6R and T7R), totaling 1.8 km long. The effectiveness of the project was evaluated by an assessment that followed a before/after and control/impacted (BACI) design. Upstream of each Restored reach there is a Control and a Reference reach. Four campaigns were carried out, 2 before and 2 after the restoration process. After 14 months of the woody installation, an increase in hydraulic retention in the restored reaches was observed (T6R‐20.2%; T7R‐63.5%), when compared to the control reaches, which favored the accumulation of sediments (T6R‐388 metric tons; T7R‐396 metric tons). This enhanced the formation of natural tailings barriers and promoted enrichment of substrate types (T6R‐39.2%; T7R‐43%). The benthic macroinvertebrate community showed an increase in the total abundance (T6 ‐ 110%), including the most sensitive groups (T6R‐124%; T7R‐124%). For fish, the increase was up to 81.38% with hand nets capture, indicating recruitment of juveniles; and the abundance and the biomass of some species were also higher (up to 100%) than the Control reaches. The results indicated that the Restored reach is already qualitatively and quantitatively better than Control reach and similar to the Reference reach, indicating the success of the study. This article is protected by copyright. All rights reserved. Integr Environ Assess Manag 2022;00:0–0.
... Bending stress can be reduced significantly by adding a third anchor between the typical two anchors at the location of maximum moment ( Figure 14). This echoes other authors' suggestions that additional anchoring could reduce failures in woody debris structures (D'Aoust & Millar, 2000;Miller & Craig Kochel, 2013;Shields Jr., Knight, Morin, & Blank, 2003). The results in Table 6 indicate that with only two anchors, bending stress may induce failure even in the asbuilt condition should a sufficiently large hydrologic event occur. ...
Article
A cedar tree revetment is a bioengineering technique intended to stabilize eroding stream banks using longitudinally placed cedar trees. This technique, which has been implemented on many rivers and streams across the United States, has been proposed as a less expensive, ecologically compatible bank stabilization method. The limited documentation of these types of bioengineering techniques indicates high failure rates. River engineers need to understand the potential failure modes of cedar tree revetments, so they can take appropriate countermeasures when applying this technique. This article documents four common failure modes observed during post‐project site assessments on 12 streams in eastern Kansas, USA that took place in 2019 and 2020. These modes are (1) bed degradation with structure perching, (2) failure in flexion, (3) loose cables, and (4) lack of sediment infilling. Computed factors of safety for top of bank discharge range from 0.3 to 6.0 in flexion (bending stress vs. strength) and range from 1.7 to 40.1 for anchor forces vs. anchor strength. These factors of safety suggest that failure in flexion is an important failure mechanism that should be considered and mitigated during design of cedar tree revetments. Moreover, failure rate varies directly with project age. The authors hypothesize that progressive processes such as breaking of bankside branches may cause loose cables and cyclical loading and wetting/drying may lower the bending strength of the trees over time. Avoiding degrading streams, additional anchoring, and trimming the bank‐side branches of the cedar trees are suggested as means to reduce these types of failures.
... Hydrologic analysis and reference reach information may be sufficient for the design of small projects with relatively low risk, but additional lines of evidence, including information on both process and form, are warranted as risk, scale, and uncertainty increase (NASEM 2017). Monitoring efforts for stream restoration projects are often limited and underfunded (Bash and Ryan 2002;Bernhardt et al. 2007;Rubin et al. 2017), and disparate success rates have been reported for those projects that have been evaluated (Roni et al. , 2018Miller and Kochel 2012). The effectiveness of stream restoration remains uncertain, partially due to inconsistent definitions (Dufour and Piégay 2009;Cockerill and Anderson 2014;Wohl et al. 2015) and insufficient monitoring (Bash and Ryan 2002;Rubin et al. 2017;Roni 2019). ...
Article
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Over a century of metals pollution and channel disturbance associated with historical mining, land use, and water development contributed to degradation of aquatic and riparian habitat within the upper Arkansas River watershed near Leadville, Colorado. Following water quality remediation, habitat restoration was conducted for a 17.7‐km reach characterized as an over‐wide channel that lacked velocity refuge and overwinter habitat for trout. The primary goals of restoration were to improve Brown Trout Salmo trutta populations and individual fish health, with a target to increase fish metrics by 10% within five years after restoration. Fish metrics included Brown Trout density, biomass, quality, and relative weight, where quality was defined as the density of trout over 356 mm in length. Changes in all fish metrics were evaluated with a before‐after‐control‐impact (BACI) study design that utilized five control sites and five impact sites. Biomass was the only metric that exhibited a significant interaction between site type and period (before and after), with increases of 12% and 21% at control and impact sites, respectively. Increased density (10%) and relative weight (2.4%) were observed across all sites regardless of type. Changes at individual sites were less evident, with only one impact site showing significant increases in biomass (99%) and quality trout (306%). These results suggest that Brown Trout populations within the upper Arkansas River have continued to improve following large‐scale water quality remediation and stream restoration efforts. Additional monitoring is recommended to evaluate long‐term trends and inform adaptive management.
... report disparate and variable success rates for common restoration treatments (Miller & Kochel, 2012Roni et al., 2002). To address uncertainty in restoration outcomes, a comprehensive, long-term monitoring programme was implemented for a stream restoration project on the Upper Arkansas River (UAR). ...
Article
Full-text available
Stream restoration was implemented on the Upper Arkansas River near Leadville, Colorado, to improve brown trout (Salmo trutta) populations. Metals pollution and channel disturbance associated with historic mining, land use, and water development degraded aquatic and riparian habitat. Changes in instream habitat quality following restoration were investigated with a before–after–control–impact study design. Baseline, as‐built, and effectiveness surveys were conducted in 2013, 2014, and 2016, respectively. Two‐dimensional hydrodynamic modelling with River2D was used to estimate weighted usable area (WUA) for adult, juvenile, fry, and spawning brown trout across a range of flows. WUA was calculated from habitat suitability curves for velocity, depth, and channel substrate. Foraging positions (FP) and habitat heterogeneity were also evaluated as indices of habitat quality. All results were analysed with analysis of variance. At impact sites, WUA increased by 12.2% from 2013 to 2014 but decreased by 10.2% from 2014 to 2016, whereas FP increased by 24.8% from 2013 to 2014 but decreased by 26.1% from 2014 to 2016. Spawning habitat increased 53.3% from 2014 to 2016 at impact sites. The 15.4% increase in depth variability from 2013 to 2016 indicates that habitat heterogeneity was enhanced at impact sites. No changes in WUA, FP, or habitat heterogeneity were observed at control sites. Although changes in WUA and FP suggest that initial habitat improvements were not sustained, increased spawning habitat and depth heterogeneity suggest otherwise. Our results highlight the value of monitoring strategies that utilize multiple lines of evidence to evaluate restoration effectiveness, inform adaptive management, and improve restoration practices.
... In particular, structures that produce a hydraulic gradient by creating a backwater behind a channel obstruction or a drop in the channel surface include cross vanes, constructed riffles, and weirs (Hester and Gooseff, 2011;Gordon et al., 2013;Zimmer and Lautz, 2015). Partially channel-spanning structures like rock vanes or J-hooks function similarly but have been shown to better retain channel structural integrity than fully channel-spanning structures like cross vanes (Miller and Kochel, 2013). Buried structures are blocks of streambed sediment with altered hydraulic conductivity (K) that promote hyporheic exchange and reactions in modeling studies (Vaux, 1968;Ward et al., 2011;Herzog et al., 2016). ...
Article
Excess nutrients commonly lead to eutrophication and harmful algal blooms. Stream restoration is increasingly popular for nutrient removal enhancing exchange with the reactive hyporheic zone. Hyporheic reactions such as denitrification are often transport-limited and instream restoration structures have been proposed to enhance hyporheic exchange and nutrient removal. However, the comparative effects of instream structure types and watershed setting (i.e. environmental characteristics such as sediment hydraulic conductivity, stream slope) are still poorly understood. Here we used MIKE SHE to model groundwater and surface water interaction and nitrate removal (denitrification) in a 200 m second order stream reach. We simulated various in-stream structures (channel-spanning weirs, partially spanning structures such as cross veins, buried structures) and investigated the effect of controlling environmental characteristics that vary with watershed setting. We found that the environmental characteristics had the greatest effect on surface water-groundwater exchange and therefore denitrification, including streambed hydraulic conductivity, natural or background stream topography and slope, and groundwater levels. Type and number of instream structures also influenced surface water-groundwater exchange and denitrification, but to a lesser degree. Human effects at the watershed scale from agriculture and urbanization likely play a role in whether reach-scale restoration practices succeed in achieving water quality goals both through effect on exchange itself (e.g., altering bed sediment texture) and on nitrate sources. More broadly, restoration efforts at the watershed scale itself, such as reducing fertilizer use or improving stormwater management, may be necessary to achieve ambitious water quality goals. Nevertheless, reach-scale restoration efforts such as in-stream structures may play a useful role in certain watershed settings, for example where groundwater conditions induce neither strong gaining nor strong losing conditions. The interaction of reach-scale modifications and watershed setting must be understood to optimize nutrient removal from stream restoration through enhanced hyporheic exchange.
... Modern approaches to river restoration increasingly focus on reestablishing natural geomorphic processes, including erosion and deposition, to create aquatic and floodplain habitat Kondolf et al., 2006;Beechie et al., 2010). An older, contrasting approach emphasizes channel form and imposes a predetermined channel morphology fixed in place with static instream structures designed to limit bank and bed erosion (Rosgen and Fittante, 1986;Rosgen, 2001;Thompson and Stull, 2002;Roni et al., 2008;Small and Doyle, 2012;Miller and Kochel, 2013). These different approaches reveal opposing views of bedload movement as either an essential habitat-forming processes or simply a flux of material that must be funneled through the design reach. ...
Article
Zealand River, NH contains the second oldest major stream-stabilization project in the U.S. that extensively used gabions, which are stone-filled, wire-mesh baskets used to construct revetment walls, grade-control sills, or groin deflectors. In 2014, a study was conducted on a 4.5-km stretch of river to determine the status of gabion structures installed from 1960 to 1963, and the impact of those gabions on geomorphic channel stability. Longitudinal profiles, cross-sectional surveys and field observations provide evidence of channel incision, narrowing and avulsions at collapsed walls. Gabion sills failed first, which allowed 1–2 m of localized incision that undercut gabion walls, which then toppled into the eroded channel. Corrosion and abrasion by bedload movement, floating large wood and winter ice enhanced failure of gabion structures by breaking wire at the base of walls. Gabions with broken wires often spilled their rock fill and lost their structural integrity. Although gabions were intended to stabilize the river, they enhanced vertical channel incision, failed to prevent bank instability, and created localized channel widening and avulsions associated with depositional reaches.
... Projects that restore physical form (geomorphology) of short reaches yet fail to produce ecological improvements are common (Bernhardt and Palmer, 2011;Meisenbachh et al., 2012;Violin et al., 2011). The use of instream structures in warmwater streams (Thompson, 2005), particularly in an effort to stabilize channel reconfiguration projects (Miller and Kochel, 2013), has often been followed by structural failure or channel instability. Stream restoration outcomes for nonsalmonid fishes (Roni et al., 2008) and macroinvertebrates (Haase et al., 2012;Miller et al., 2010;Palmer et al., 2009;Sundermann et al., 2011;Tullos et al., 2006Tullos et al., , 2009 are often weak or undetectable. ...
Chapter
Rivers and streams worldwide have degraded ecosystems due to a wide range of anthropomorphic drivers and pressures. Recent decades have seen the rise of an interdisciplinary science of stream restoration, which seeks to rehabilitate damaged systems to yield degraded or destroyed ecosystem services. About $1 billion is expended annually on such projects in the United States alone, exclusive of several extraordinary projects that target whole regions or long reaches of larger rivers. The best approaches for restoring rivers are far from settled, as few projects have been sufficiently monitored to positively document effects. Future efforts should feature monitoring and sharing of information, working at larger spatial scales, and restoration of key processes rather than forms.
... In response, they have mounted a series of powerful anti-Rosgen polemics in journal articles and at professional conferences. [53][54][55][56][57][58][59][60][61][62][63][64][65][66] Some of these critique have more intellectual legitimacy than others, but regardless of whether one agrees with critics' claims, it is clear that they have failed to delegitimize Rosgen. 67 The current dominance of Rosgen and his NCD approach in US stream restoration has a variety of social and physical impacts. ...
Article
Stream restoration is deeply shaped by social influences. A substantial body of literature has demonstrated the ways in which social dynamics shape myriad aspects of restoration practice. After illustrating these findings via brief reviews of existing research on public participation and environmental justice, I turn to the less commonly addressed influence of social dynamics on the practice and content of river science. I first review the approach and some of the key findings of Science and Technology Studies, a body of research that takes the practice of science as its empirical object of study. I then use the Rosgen Wars, a conflict that has strongly influenced the development of stream restoration science and practice in the United States, as a case study for examining the impacts of social dynamics on the practice of river scientists, the redistribution of scientific authority, and on fluvial landscapes more broadly. Given that is impossible to avoid social influences, I argue that it is crucial that we examine them, and that we choose research and implementation practices that reflect our ecological, scientific, and political commitments rather than passively accepting the existing commitments embedded in our work.For further resources related to this article, please visit the WIREs website.
... However, these results do not necessarily represent the full spectrum of restoration measures implemented all over the world, as only a small proportion of restoration projects is being published in international literature. Nevertheless, it is interesting to see that Chinese literature mainly reported bioengineering as their favoured river restoration measure (Wang et al. 2014;Wu et al. 2013;Zhang et al. 2013a, b), while in the Americas and Europe channel bed remodelling and habitat provision were reported most often (Amoros 2001;Buijse et al. 2002;Doll 2003;Filoso and Palmer 2011;Gilvear et al. 2012;Haase et al. 2013;Habersack and Piégay 2008;Henry et al. 2002;KCI Associates 2003;Kondolf et al. 2013;Lorenz and Feld 2013;Louhi et al. 2011;Mendiondo 2008;Miller and Kochel 2013;Muhar et al. 2008;North Carolina Department of Transportation 1999;Richardson and Pahl 2005). Furthermore, all investigated European countries except one reported floodplain rehabilitation as implemented restoration measure (Amoros 2001;Buijse et al. 2002;Gilvear et al. 2012;Haase et al. 2013;Habersack and Piégay 2008;Henry et al. 2002;Lorenz and Feld 2013;Muhar et al. 2008;Pataki et al. 2013), while only one and two projects reported these restoration measures for China (Wang et al. 2014) and the Americas (Filoso and Palmer 2011;Richardson and Pahl 2005), respectively. ...
Article
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In the age of climate change and ecosystem degradation, governments realise more and more that it is crucial to protect ecosystem health, to preserve water resources and to maintain flood protection. Therefore, several countries, among those Switzerland, have implemented laws to make the restoration of riverine ecosystems a legal obligation. In Switzerland, restoration projects were implemented as early as 1979, prior to these laws coming into force. For this article, 848 Swiss restoration projects, implemented between 1979 and 2012, were investigated, spanning a total of 307 river kilometres. No correlation was found between the geographical distribution of total restored lengths in a way that larger cantons performed more restorations. Neither was there a correlation between the total restored length and the canton's population density or financial status. Restoration activities increased steadily after 1992, with most restorations being reported for the years 2004, 2005 and 2009. The average restoration rate was 9.8 km per year, ranging between 0.5 km in 1979 and 23.9 km in 2004. Restoration measures were very diverse, ranging from measures that directly affected the wildlife, e.g. by providing habitats, to measures which indirectly enhanced conditions for the ecosystem, such as water quality ameliorations. Data regarding success evaluation was only available for 232 of the 848 projects, making it difficult to state whether the implemented restoration projects reached the intended objectives. Over the next 80 years, a further 4,000 km of Swiss rivers will be restored, requiring a restoration rate of 50 km per year, which, according to the data, is an achievable goal.
... Palmer et al., 2005;Lake, Bond & Reich, 2007), knowledge is mainly gained empirically, relying on documenting the successes and failures of projects (e.g. Kondolf, 1998;Roni et al., 2002;Miller & Kochel, 2013). However, monitoring and reporting on the outcomes of stream restoration projects have typically been poorly executed or completely ignored (Bernhardt et al., 2007). ...
Article
Extreme hydrological events (floods, droughts) in flowing waters can alter habitat availability and structure and produce significant shifts in biodiversity, species assemblages and ecosystem processes.Extreme floods and droughts occur over large spatial extents and can greatly alter links between streams and their catchments. The nature and strengths of these links differ between degraded and intact streams and their catchments, strongly influencing the responses to and recovery from extreme events. It is essential that these catchment–stream linkages be identified and considered when planning stream restoration.Despite the scarcity of comprehensive, long-term monitoring of most stream restoration projects, our understanding of the influence of extreme events on running waters suggests both positive and negative impacts on restoration efforts. Extreme hydrological events can impair stream restoration efforts giving rise to delays or complete failures in achieving restoration objectives. Alternatively, extreme floods may facilitate progress towards restoration goals by engendering key ecological processes.Understanding the impacts and the temporal–spatial scales over which extreme events alter the ecological structure and function of streams (in both natural and damaged systems), as well as their underlying mechanisms, is a challenge for stream restorers that will only progress with the accumulation of long-term data. Restorers should recognise and plan for hydrological extreme events and their interactions with other disturbances (e.g. fire, urban development). Increasing connectivity of restoration efforts along with their spatial extent can lessen the negative effects of extreme hydrological events on stream restoration.Successful ecological stream restoration requires long time spans and thus with a changing climate the prediction of more frequent and intense extreme events only strengthens the need to incorporate their likelihood into restoration planning and implementation.
Article
Urbanization alters the delivery of water and sediment to receiving streams, often leading to channel erosion and enlargement, which increases loading of sediment and nutrients, degrades habitat, and harms sensitive biota. Stormwater control measures (SCMs) are constructed in an attempt to mitigate some of these effects. In addition, stream restoration practices such as bank stabilization are increasingly promoted as a means of improving water quality by reducing downstream sediment and pollutant loading. Each unique combination of SCMs and stream restoration practices results in a novel hydrologic regime and set of geomorphic characteristics that interact to determine stream condition, but in practice, implementation is rarely coordinated due to funding and other constraints. In this study, we examine links between watershed‐scale implementation of SCMs and stream restoration in Big Dry Creek, a suburban watershed in the Front Range of northern Colorado. We combine continuous hydrologic model simulations of watershed‐scale response to SCM design scenarios with channel evolution modeling to examine interactions between stormwater management and stream restoration strategies for reducing loading of sediment and adsorbed phosphorus from channel erosion. Modeling results indicate that integrated design of SCMs and stream restoration interventions can result in synergistic reductions in pollutant loading. Not only do piecemeal and disunited approaches to stormwater management and stream restoration miss these synergistic benefits, they make restoration projects more prone to failure, wasting valuable resources for pollutant reduction. We conclude with a set of recommendations for integrated planning of SCMs and stream restoration to simultaneously achieve water quality and channel protection goals.
Article
Water quality monitoring records were combined with geomorphic and stratigraphic data to determine the controls on suspended sediment transport dynamics within the headwaters of Big Harris Creek, the site of one of the largest stream restoration projects in North Carolina, USA. Land-use change associated with European settlement resulted in spatially variable geomorphic responses that produced reaches possessing semi-homogeneous landforms and processes, referred to as process zones. Downstream, process zones were dominated by entrenched channels possessing banks characterized by sandy post-settlement deposits that overlie finer-grained pre-settlement deposits. Spatial variations in the resulting process zones strongly influenced modern suspended sediment concentrations (SSC) and loads in the catchment, which are among the highest reported for the southeastern United States. The source and transport dynamics of suspended sediment differed between low magnitude floods (characterized by minimal changes in water level elevations) and moderate to high magnitude floods. Low magnitude floods were characterized by SSCs that varied over several orders of magnitude, and that were unrelated to flow conditions. Precipitation, during these events, rapidly mobilization fine-grained pre-settlement deposits associated with bank failures and cattle crossings along entrenched alluvial channels. Moderate to high magnitude floods within larger tributary basins exhibited more systematic discharge-SSC relationships. Suspended sediment transport was dominated by sand-sized particles derived from post-settlement legacy sediments eroded from the channel banks and headwater gullies. The observed temporal and spatial differences in SSC between low and moderate to high magnitude floods complicates the quantification of water quality, and shows that comparisons of water quality before and following the implementation of restoration projects need to differentiate between distinct populations of suspended sediment transport.
Article
Full-text available
River restoration projects are carried out actively in several countries as an alternative flood protection measure, and also to improve/restore water quality and habitat diversity. The implication of various river restoration measures on water quality is seldom studied. In this review, case studies of restoration projects that aimed at water quality improvement were selected from four industrialized countries in three continents. The water quality concerns and the systematic development of legislative policies towards better water quality management in the different countries considered were assessed. The best management practices for river restoration with respect to water quality amelioration were evaluated with the perspective of the case studies selected. In the various case studies discussed, a combination of different restoration measures were implemented in tandem. The restoration measures were adapted to suit the local conditions and problems. A pre- and post-restoration investigation of the main success indicators was found to be an important criterion for the evaluation of the outcome of restoration projects. Successful restoration projects were found to focus on reduction of pollutant/nutrient input to the rivers, in addition to the implementation of suitable restoration measures. This has been achieved by public infrastructure development (like installation of storm water controls and sewage treatment plants). This review is aimed to act as an inventory for future restoration projects with water quality amelioration as their main target.
Conference Paper
Civil engineers provide services aimed at meeting society's primary infrastructure needs in a safe and cost-effective manner. In most cases, work in one discipline does not adversely affect the value or sustainability of the resources and services in other disciplines. However, in the field of stormwater management, a case can be made that the opposite is true. Conventional stormwater management is widely documented as a primary driver of stream channel instability, which, in turn, causes adverse impacts to adjacent infrastructure such as roads, bridges, and utility lines. The fact that design decisions in one field result in a shortened design life of public/private assets from other disciplines is by definition unsustainable. Moreover, what's bad for our nation's infrastructure is also detrimental to the quality and biotic integrity of our water resources. By compiling available cost data of infrastructure damages attributable to channel instability in a Northern Kentucky case study, this paper underscores the business case for a recalibration of stormwater management for stream channel stability and infrastructure sustainability.
Article
Full-text available
The durability of 3,946 instream structures in 94 streams that had floods with return intervals exceeding 5 years were assessed. Overall structure durability (defined as the degree to which a structure remained at its original location) was high; less than 20% of the sampled structures had been removed from the site of original placement. The magnitude of flood events had a significant effect on structure durability with higher magnitude floods reducing durability. Stream order also affected structure durability; structures in large streams were 20 times more likely to have been removed from the site of original placement than structures in small streams. Other conditions that affected structure durability included location of the structure within the stream channel, whether the structure was anchored or not, structure material, and upslope landslide frequency. Instream structures are most appropriate when used as short-term tools to improve degraded stream conditions while activities that caused the habitat degradation are simultaneously modified. When instream structures are part of a properly sequenced watershed restoration strategy, they can improve habitat conditions through a range of flow conditions including large floods.
Article
Full-text available
Among the most visually striking river restoration projects are those that involve the creation of a new channel, often in a new alignment and generally with a form and dimensions that are different from those of the preproject channel. These channel reconstruction projects often have the objective of creating a stable, single-thread, meandering channel, even on rivers that were not historically meandering, on rivers whose sediment load and flow regime would not be consistent with such stable channels, or on already sinuous channels whose bends are not symmetrical. Such meandering channels are often specified by the Rosgen classification system, a popular restoration design approach. Although most projects of this type have not been subject to objective evaluation, completed postproject appraisals show that many of these projects failed within months or years of construction. Despite its, at best, mixed results, this classification and form-based approach continues to be popular because it is easy to apply, because it is accessible to those without formal training in fluvial geomorphology, and probably because it satisfies a deep-seated, although unrecognized, cultural preference for single-thread meandering channels. This preference is consistent with 18th-century English landscape theories, which held the serpentine form to be ideal and led to widespread construction of meandering channels on the country estates of the era. The preference for stability in restored channels seems to be widely accepted by practitioners and funders despite the fact that it is antithetical to research showing that dynamically migrating channels have the greatest ecological richness. Copyright © 2006 by the author(s). Published here under license by the Resilience Alliance.
Article
Full-text available
Millions of dollars are spent annually on watershed restoration and stream habitat improvement in the U.S. Pacific Northwest in an effort to increase fish populations. It is generally accepted that watershed restoration should focus on restoring natural processes that create and maintain habitat rather than manipulating instream habitats. However, most process-based restoration is site-specific, that is, conducted on a short stream reach. To synthesize site-specific techniques into a process-based watershed restoration strategy, we reviewed the effectiveness of various restoration techniques at improving fish habitat and developed a hierarchical strategy for prioritizing them. The hierarchical strategy we present is based on three elements: (1) principles of watershed processes, (2) protecting existing high-quality habitats, and (3) current knowledge of the effectiveness of specific techniques. Initially, efforts should focus on protecting areas with intact processes and high-quality habitat. Following a watershed assessment, we recommend that restoration focus on reconnecting isolated high-quality fish habitats, such as instream or off-channel habitats made inaccessible by culverts or other artificial obstructions. Once the connectivity of habitats within a basin has been restored, efforts should focus on restoring hydrologic, geologic (sediment delivery and routing), and riparian processes through road decommissioning and maintenance, exclusion of livestock, and restoration of riparian areas. Instream habitat enhancement (e.g., additions of wood, boulders, or nutrients) should be employed after restoring natural processes or where short-term improvements in habitat are needed (e.g., habitat for endangered species). Finally, existing research and monitoring is inadequate for all the techniques we reviewed, and additional, comprehensive physical and biological evaluations of most watershed restoration methods are needed.
Article
Full-text available
The durability of 3,946 instream structures in 94 streams that had floods with return intervals exceeding 5 years were assessed. Overall structure durability (defined as the degree to which a structure remained at its original location) was high; less than 20% of the sampled structures had been removed from the site of original placement. The magnitude of flood events had a significant effect on structure durability with higher magnitude floods reducing durability. Stream order also affected structure durability; structures in large streams were 20 times more likely to have been removed from the site of original placement than structures in small streams. Other conditions that affected structure durability included location of the structure within the stream channel, whether the structure was anchored or not, structure material, and upslope landslide frequency. Instream structures are most appropriate when used as short-term tools to improve degraded stream conditions while activities that caused the habitat degradation are simultaneously modified. When instream structures are part of a properly sequenced watershed restoration strategy, they can improve habitat conditions through a range of flow conditions including large floods.
Article
Full-text available
The degradation of inland aquatic habitats caused by decades of human activities has led to worldwide efforts to rehabilitate freshwater habitats for fisheries and aquatic resources. We reviewed published evaluations of stream rehabilitation techniques from throughout the world, including studies on road improvement, riparian rehabilitation, floodplain connectivity and rehabilitation, instream habitat improvement, nutrient addition, and other, less-common techniques. We summarize current knowledge about the effectiveness of these techniques for improving physical habitat and water quality and increasing fish and biotic production. Despite locating 345 studies on effectiveness of stream rehabilitation, firm conclusions about many specific techniques were difficult to make because of the limited information provided on physical habitat, water quality, and biota and because of the short duration and limited scope of most published evaluations. Reconnection of isolated habitats, floodplain rehabilitation, and instream habitat improvement have, however, proven effective for improving habitat and increasing local fish abundance under many circumstances. Techniques such as riparian rehabilitation, road improvements (sediment reduction), dam removal, and restoration of natural flood regimes have shown promise for restoring natural processes that create and maintain habitats, but no long-term studies documenting their success have yet been published. Our review demonstrates that the failure of many rehabilitation projects to achieve objectives is attributable to inadequate assessment of historic conditions and factors limiting biotic production; poor understanding of watershed-scale processes that influence localized projects; and monitoring at inappropriate spatial and temporal scales. We suggest an interim approach to sequencing rehabilitation projects that partially addresses these needs through protecting high-quality habitats and restoring connectivity and watershed processes before implementing instream habitat improvement projects.
Article
Full-text available
In recent years an increasing share of fishery management resources has been committed to alteration offish habitat with artificial stream structures. We evaluated rates and causes of physical impairment or failure for 161 fish habitat structures in 15 streams in southwest Oregon and southwest Washington, following a flood of a magnitude that recurs every 2–10 years. The incidence of functional impairment and outright failure varied widely among streams; the median failure rate was 18.5% and the median damage rate (impairment plus failure) was 60%. Modes of failure were diverse and bore no simple relationship to structure design. Damage was frequent in low-gradient stream segments and widespread in streams with signs of recent watershed disturbance, high sediment loads, and unstable channels. Comparison of estimated 5–10-year damage rates from 46 projects throughout western Oregon and southwest Washington showed high but variable rates (median, 14%; range, 0–100%) in regions where peak discharge at 10-year recurrence intervals has exceeded 1.0 m·s·km. Results suggest that commonly prescribed structural modifications often are inappropriate and counterproductive in streams with high or elevated sediment loads, high peak flows, or highly erodible bank materials. Restoration of fourth-order and larger alluvial valley streams, which have the greatest potential for fish production in the Pacific Northwest, will require reestablishment of natural watershed and riparian processes over the long term.
Article
Full-text available
Summary 1. Increasingly, river managers are turning from hard engineering solutions to ecologi- cally based restoration activities in order to improve degraded waterways. River resto- ration projects aim to maintain or increase ecosystem goods and services while protecting downstream and coastal ecosystems. There is growing interest in applying river restoration techniques to solve environmental problems, yet little agreement exists on what constitutes a successful river restoration effort. 2. We propose five criteria for measuring success, with emphasis on an ecological perspective. First, the design of an ecological river restoration project should be based on a specified guiding image of a more dynamic, healthy river that could exist at the site. Secondly, the river's ecological condition must be measurably improved. Thirdly, the river system must be more self-sustaining and resilient to external perturbations so that only minimal follow-up maintenance is needed. Fourthly, during the construction phase, no lasting harm should be inflicted on the ecosystem. Fifthly, both pre- and post- assessment must be completed and data made publicly available. 3. Determining if these five criteria have been met for a particular project requires development of an assessment protocol. We suggest standards of evaluation for each of the five criteria and provide examples of suitable indicators. 4. Synthesis and applications. Billions of dollars are currently spent restoring streams and rivers, yet to date there are no agreed upon standards for what constitutes ecolog- ically beneficial stream and river restoration. We propose five criteria that must be met for a river restoration project to be considered ecologically successful. It is critical that the broad restoration community, including funding agencies, practitioners and citizen restoration groups, adopt criteria for defining and assessing ecological success in restoration. Standards are needed because progress in the science and practice of river restoration has been hampered by the lack of agreed upon criteria for judging ecological success. Without well-accepted criteria that are ultimately supported by funding and implementing agencies, there is little incentive for practitioners to assess and report restoration outcomes. Improving methods and weighing the ecological benefits of various restoration approaches require organized national-level reporting systems.
Article
Full-text available
Site assessment and monitoring data were analyzed for 26 stream restoration projects in North Carolina where the channel was reconfigured. Post-project changes in channel capacity were highly variable from site to site, but more than 60% of the projects underwent, on average at a given site, at least a 20% change in channel capacity. An analysis of site and basin geomorphology revealed that large post-construction adjustments were associated with highly dynamic stream channels characterized by a combination of high sediment transport capacity, large sediment supply, and/or easily eroded bank materials. In-stream structures along dynamic, reconfigured channels also exhibited high incidences of damage. Thus, the design and construction of channels in a state of equilibrium, which do not exhibit excessive erosion or deposition along highly dynamic rivers is currently problematic. In light of these findings, a conceptual framework based on geomorphic parameters is put forth to assess the likelihood of project success early in the design process to (1) eliminate high risk sites from consideration of channel reconfiguration and (2) improve upon the implemented management strategies that are ultimately used. It is also argued that where space permits an enhanced natural channel, adjustment approach is likely to be more effective than projects based on natural channel design.
Article
Prohibiting grazing dramatically improved riparian vegetation, streambanks, and stream channel conditions, but this improvement was countered by off-site, upstream influences and on-site, instream improvement structures that functioned as fine sediment traps. Fish populations did not respond to improving habitat conditions because the relatively small size of the livestock exclosure did not reduce incoming, limiting influences created by upstream conditions.-from Authors
Article
In recent years an increasing share of fishery management resources has been committed to alteration offish habitat with artificial stream structures. We evaluated rates and causes of physical impairment or failure for 161 fish habitat structures in 15 streams in southwest Oregon and southwest Washington, following a flood of a magnitude that recurs every 2–10 years. The incidence of functional impairment and outright failure varied widely among streams; the median failure rate was 18.5% and the median damage rate (impairment plus failure) was 60%. Modes of failure were diverse and bore no simple relationship to structure design. Damage was frequent in low-gradient stream segments and widespread in streams with signs of recent watershed disturbance, high sediment loads, and unstable channels. Comparison of estimated 5–10-year damage rates from 46 projects throughout western Oregon and southwest Washington showed high but variable rates (median, 14%; range, 0–100%) in regions where peak discharge at 10-year recurrence intervals has exceeded 1.0 m3·s–1·km–2. Results suggest that commonly prescribed structural modifications often are inappropriate and counterproductive in streams with high or elevated sediment loads, high peak flows, or highly erodible bank materials. Restoration of fourth-order and larger alluvial valley streams, which have the greatest potential for fish production in the Pacific Northwest, will require reestablishment of natural watershed and riparian processes over the long term.
Article
The descriptions, design specifications, placement locations, spacing and various applications of Cross-Vane, W-Weir and J-Hook Vane structures are presented. These structures were developed and subsequently applied to: 1) establish grade control, 2) reduce streambank erosion, 3) facilitate sediment transport, 4) provide for irrigation diversion structures, 5) enhance fish habitat, 6) maintain width/depth ratio, 7) improve recreational boating, 8) maintain river stability, 9) dissipate excess energy, 10) withstand large floods, 11) maintain channel capacity, 12) be compatible with natural channel design, and 13) be visually acceptable to the public. Relations to determine the minimum size of rock for these structures are presented based on bankfull shear stress. Drawings for each structure are provided that display appropriate use of footers, cross-section shape, profile shape, appropriate channel locations, angles, slopes, spacing and elevations. Velocity isovels are presented to describe changes in the distribution of energy produced by the structures. The structures all reduce near-bank shear stress and stream power, while increasing center channel shear stress and stream power to retain both flood-flow and sediment transport capacity. These structures have been installed on 14 rivers with bankfull widths varying from 9m (Lower Blanco River in Southwestern Colorado) to 150m (Bitterroot River in Northwestern Montana) and slopes varying from 0.05 to .0003 and in bed material ranging from cobble and gravel to sand bed streams. Since 1986, the author has restored and monitored a wide variety of stream types involving over 48 km of rivers and evaluated various structure performance following major floods. This monitoring has resulted in the development, implementation and assessment of the Cross-Vane, W-Weir and J-Hook vane structures.
Article
Described is a method for channel erosion control and habitat rehabilitation featuring intermittent placement of structures made of large woody debris. This method is expressly tailored to address severe problems typical of incised channels with little sediment coarser than sand. In these types of environments, buoyancy forces are typically more important factors in woody debris stability than fluid drag. Buoyant forces are counteracted by the weight of the structure, earth anchors, and sediment deposits. Design concepts were tested in a demonstration project constructed along 2 km of channel draining a 37-km2 watershed. Large woody debris structures reduced velocities in the region adjacent to the bank toe and induced sediment deposition and retention. Construction costs per unit channel length were 23-58% of costs for recent stone bank stabilization projects within the same region. During the second year following construction, 31% of the structures failed during high flows, probably due to inadequate anchoring.
Article
Among the most visually striking river restoration projects are those that involve the creation of a new channel, often in a new alignment and generally with a form and dimensions that are different from those of the preproject channel. These channel reconstruction projects often have the objective of creating a stable, single-thread, meandering channel, even on rivers that were not historically meandering, on rivers whose sediment load and flow regime would not be consistent with such stable channels, or on already sinuous channels whose bends are not symmetrical. Such meandering channels are often specified by the Rosgen classification system, a popular restoration design approach. Although most projects of this type have not been subject to objective evaluation, completed postproject appraisals show that many of these projects failed within months or years of construction. Despite its, at best, mixed results, this classification and form-based approach continues to be popular because it is easy to apply, because it is accessible to those without formal training in fluvial geomorphology, and probably because it satisfies a deep-seated, although unrecognized, cultural preference for single-thread meandering channels. This preference is consistent with 18th-century English landscape theories, which held the serpentine form to be ideal and led to widespread construction of meandering channels on the country estates of the era. The preference for stability in restored channels seems to be widely accepted by practitioners and funders despite the fact that it is antithetical to research showing that dynamically migrating channels have the greatest ecological richness.
Evaluation of North Carolina stream restoration projects, biological responses to habitat change
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