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Design and Performance of a Channel Reconstruction Project in a Coastal California Gravel-Bed Stream
Abstract
A 0.9 km-reach of Uvas Creek, California, was reconstructed as a sinuous, meandering channel in November 1995. In February 1996, this new channel washed out. We reviewed project documents to determine the basis for the project design and conducted our own historical geomorphological study to understand the processes operating in the catchment and project reach. The project was designed using a popular stream classification system, based on which the designers assumed that a "C4" channel (a meandering gravel-bed channel) would be stable at the site. Our historical geomorphological analysis showed that the reach had been braided historically, typical of streams draining the Franciscan Formation in the California Coast Ranges, with episodic flows and high sand and gravel transport. After the project washed out, Uvas Creek reestablished an irregular, braided sand-and-gravel channel, although the channel here was narrower than it had been historically, probably due to such factors as incision caused by gravel mining. Our study casts doubt on several assumptions common in many stream restoration projects: that channel stability is always an appropriate goal; that channel forms are determined by flows with return periods of about 1.5 years; that a channel classification system is an easy, appropriate basis for channel design; and that a new channel form can be imposed without addressing the processes that determine channel form.
... Friedman et al. (1998) "[A]n active channel (here used to refer to the open, unvegetated sand-and-gravel channel). . ." Kondolf et al. (2001) "Active channel of an alluvial stream is a short-term geomorphic feature subject to change by prevailing discharges; its upper limit is defined by a break in the relatively steep bank slope of the active channel to a more gently sloping surface beyond the channel edge. The break in slope normally coincides with lower limit of perennial vegetation so that the two features, individually or in combination, define the activechannel reference level." ...
... Examples have been documented in the Mediterranean climate of southern California (Kondolf et al. 2001), the semiarid Great Plains (Friedman and Lee 2002), and high desert/semiarid grasslands in southern Arizona (Burkham 1972) and western Colorado (Jaquette et al. 2005). Geomorphologists have distinguished transient and persistent river forms based on the recurrence interval of the flow that creates a form versus the length of time that the river form is present. ...
... The simplifying assumptions underlying concepts such as bankfull and dominant discharge have been carried over into river management in the context of instream flows, channel maintenance flows, environmental flows, and river restoration (Kondolf et al. 2001;Rosgen 2006). The concept of instream flows developed as a tool to preserve some minimum flow within a channel rather than allowing all of the flow to be diverted for consumptive uses outside the channel. ...
For more than 100 years, the ordinary high water mark (OHWM) has been used to define water boundaries in a number of contexts in the United States. This Special Report summarizes the scientific literature pertaining to the indicators used to identify the OHWM in fluvial systems, building on more than a decade of research and publications related to the OHWM in the ongoing process to implement the Clean Water Act and the Rivers and Harbors Act of 1899. This report does not change or redefine the indicators used to identify the OHWM, nor is it a manual for how to delineate the OHWM. This report first reviews established concepts in river science that relate to the OHWM then reviews various sources of information that can be used to delineate the OHWM, discusses geographic variations in OHWM indicators among river segments, reviews human activities that can affect the OHWM, and finally presents examples of the OHWM in diverse channel types and regions.
... Consequently, while bankfull channel designs employing the effective discharge paradigm are a useful starting point, they are a simplification of channel dynamics that, in some cases, may produce spectacular failures. For example, a historically braided gravel-bed river in northern California (Uvas Creek) was re-designed as a single-thread, meandering channel based on bankfull stability analyses, but subsequently reverted to a braided morphology during a low-magnitude, 5-year flood (Kondolf et al., 2001). Subsequent regime analyses demonstrated that Uvas Creek is a transitional stream that can exhibit a stable single-thread morphology during bankfull flows, but will transform to a braided morphology during larger floods (Buffington and Parker, 2005), the transition of Uvas Creek highlights the importance of flood variation in controlling channel morphology, as well as having a clear understanding of historic morphologic conditions prior to restoration (Kondolf et al., 2001). ...
... For example, a historically braided gravel-bed river in northern California (Uvas Creek) was re-designed as a single-thread, meandering channel based on bankfull stability analyses, but subsequently reverted to a braided morphology during a low-magnitude, 5-year flood (Kondolf et al., 2001). Subsequent regime analyses demonstrated that Uvas Creek is a transitional stream that can exhibit a stable single-thread morphology during bankfull flows, but will transform to a braided morphology during larger floods (Buffington and Parker, 2005), the transition of Uvas Creek highlights the importance of flood variation in controlling channel morphology, as well as having a clear understanding of historic morphologic conditions prior to restoration (Kondolf et al., 2001). Because sediment transport and morphologic response are impacted by the history and variability of flow (e.g., Stevens et al., 1975;Redolfi et al., 2018;Davidson and Eaton, 2018;Wang et al., 2019), future restoration designs that use a single-discharge approach for sizing bankfull channel dimensions should additionally account for a sufficient range of flows to capture potential geomorphic responses (e.g., Costa and O'Connor, 1995;Buffington and Parker, 2005;Shields et al., 2008;Davidson and Eaton, 2018). ...
Restoration of an alluvial wet-meadow system was conducted in the late 1990s to reestablish hydraulic interactions between the river, floodplain, and groundwater to support aquatic–riparian ecosystem function. A single-discharge approach sized the bankfull channel dimensions to the effective discharge (Qe) and three degrees of channel widening relative to the Qe design were explored to identify which design attained dynamic equilibrium in the shortest time. The three experimental channel designs were implemented with bankfull widths of 96%, 157%, and 191%, respectively, of the Qe geometry. Response trajectories were documented for channel dimensions, sediment mobility, channel morphology, floodplain connectivity, and riparian vegetation for the three channel designs, and the efficacy of a single-discharge approach for restoration was examined.
Analysis of 20 years of monitoring data and hydraulic modeling revealed that each design responded differently to the imposed initial channel conditions and evolved at substantially different rates. The design with bankfull dimensions most closely approximating Qe reached dynamic equilibrium within four years of restoration, whereas the moderately over-widened channel (57% larger) exhibited slower responses toward dynamic equilibrium for some metrics and did not fully attain the Qe design dimensions within the monitoring period. The extremely-over-widened channel (91% larger) mainly induced slow rates of bed deposition that are projected to take nearly 300 years for the bankfull dimensions to narrow to the Qe width. All reaches had low bed mobility (bankfull Shields stress < 0.03) 14 years after restoration, demonstrating the challenge of reducing the drivers of channel widening, while maintaining sufficient competence for bedload transport and a sustained supply of coarse bed material for salmonid habitat. Restoration that sizes the channel to Qe can provide rapid dynamic equilibrium, but is a first-order simplification of 1) channel dynamics and 2) the range of flows needed for restoring physical and biological processes in wet-meadow systems.
... Other impacts were presented by Kondolf, Smeltzer, & Railsback (2001). According to him, in-stream sand mining degrades the natural equilibrium of a stream, because of a significant distortion of the natural river channel. ...
... Researchers like Byrnes, Hammer, Thibaut, & Synder (2000), Hoering (2008), Myers (1999), Young & Griffith (2009), Viswanathan, (2002, and Kondolf et al. (2001) have remarked on ecological impacts of sand mining. They argued that when mining is done unscientifically it may increase shoreline erosion rates while decreasing the shoreline from sea water especially during ocean disasters and, therefore, exposing human life in danger. ...
... En partant du constat que la prédiction des styles fluviaux est basée sur une connaissance de la géométrie des cours d'eau, Van den Berg (1995) propose d'utiliser la puissance spécifique en se basant sur des valeurs indépendantes. Les auteurs adoptent ainsi le débit correspondant à la crue annuelle moyenne, la pente du fond de vallée et une estimation de la largeur basée sur l'équation de Lacey (1929) Kondolf et al. (2001) rapportent les résultats des travaux de restauration effectués sur un tronçon de 0,9 km du cours d'eau Uvas Creek en Californie. La restauration de ce tronçon défini par un type C4, selon la classification de Rosgen (1994), a été complétement balayée par une crue de période de retour de 6 ans moins d'un an après la réalisation des travaux. ...
... La restauration de ce tronçon défini par un type C4, selon la classification de Rosgen (1994), a été complétement balayée par une crue de période de retour de 6 ans moins d'un an après la réalisation des travaux. L'étude des données historiques permet à Kondolf et al. (2001) d'émettre des doutes sur l'approche employée . Miller et Ritter (1996) et Simon et al. (2007) critiquent également cette approche en soulignant les difficultés à reproduire la méthodologie. ...
Ce travail a pour objectif de proposer des méthodes pour améliorer la compréhension des processus d'évolution de la Loire moyenne sur quelques décennies. L'analyse des évolutions morphologiques est réalisée en découpant le secteur d'étude en tronçons géomorphologiquement homogènes. Une diminution de la pente et une réduction de la largeur de la bande active entre 1955 et 1996 sont observées. Suite à l'arrêt des extractions (1996), les ajustements se poursuivent de façon plus modérés. Des simplifications géométriques et hydrologiques sont ensuite introduites dans un modèle de transport solide unidimensionnel (RubarBE) afin d'être comparées aux résultats obtenus avec la géométrie détaillée et la chronique de débit complète. La géométrie simplifiée permet une modélisation des évolutions du lit pertinente tout en réduisant le temps de calcul; la simplification des chroniques de débit illustre la sensibilité des modèles numériques hydro-sédimentaires à l'hydrologie. Enfin, l'application des simplifications sur l'ensemble de la Loire moyenne sur la période 1996-2006 confirme les tendances observées par l'analyse des données.
... While healthy riverscapes can be generally characterized by a collection of attributes (e.g., Stage 0), the specific location of structural elements and habitat features changes through time while reach-scale metrics remain relatively constant. The desire to reduce uncertainty and precisely predict restoration outcomes has led to practices that tend to emphasize the stability of channels and instream structures (Kondolf et al., 2001). In the context of stream restoration, stability has often meant static. ...
... Generally, restoration has focused more on restoring riverscape form without addressing the underlying processes responsible for that form. In response, the scientific community proposed a process-based restoration philosophy Kondolf et al., 2006;Kondolf et al., 2001). Process-based restoration is defined as protecting, enhancing, and/or restoring "normative rates and magnitudes of physical, chemical, and biological processes that sustain river and floodplain ecosystems" . ...
The purpose of this design manual is to provide restoration practitioners with guidelines for implementing a subset of low-tech tools —namely beaver dam analogues (BDAs) and post-assisted log structures (PALS)—for initiating process-based restoration in structurally-starved riverscapes. While the concept of process-based restoration in riverscapes has been advocated for at least two decades, details and specific examples on how to implement it remain sparse. Here, we describe ‘low-tech process-based restoration’ (LT-PBR) as a practice of using simple, low unit-cost, structural additions (e.g. wood and beaver dams) to riverscapes to mimic functions and initiate specific processes. Hallmarks of this approach include:
- An explicit focus on the processes that a low-tech restoration intervention is meant to promote
- A conscious effort to use cost-effective, low-tech treatments (e.g. hand-built, natural materials, non-engineered, short-term design life-spans) because of the need to efficiently scale-up application.
- ‘Letting the system do the work’ which defers critical decision making to riverscapes and nature’s ecosystem engineers.
Other resources available at: http://lowtechpbr.restoration.usu.edu
... While healthy riverscapes can be generally characterized by a collection of attributes (e.g., Stage 0), the specific location of structural elements and habitat features changes through time while reach-scale metrics remain relatively constant. The desire to reduce uncertainty and precisely predict restoration outcomes has led to practices that tend to emphasize the stability of channels and instream structures (Kondolf et al., 2001). In the context of stream restoration, stability has often meant static. ...
... Generally, restoration has focused more on restoring riverscape form without addressing the underlying processes responsible for that form. In response, the scientific community proposed a process-based restoration philosophy (Beechie and Bolton, 1999;Kondolf et al., 2006;Kondolf et al., 2001). Process-based restoration is defined as protecting, enhancing, and/or restoring "normative rates and magnitudes of physical, chemical, and biological processes that sustain river and floodplain ecosystems" (Beechie et al., 2010). ...
- Riverscapes are composed of connected floodplain and channel habitats that together make up the valley bottom.
- The scope of degradation of riverscapes is massive. Tens of thousands of miles of riverscapes are in poor or fair condition.
- Structural-starvation is both a direct cause of degradation, as well as a consequence of land use changes and direct modification of stream and riparian areas.
- Engineering-based restoration tends to emphasize channel form and stability, rather than promoting the processes that create and maintain healthy riverscapes, which leads to increased costs and a limited ability to restore more miles of riverscapes.
- Process-based restoration focuses on restoring physical processes that lead to healthy riverscapes.
- Low-cost, simple, hand-built structures have been used for over a century. Restoration principles are needed to guide the use of low-tech structures in order to address the scope of degradation, which will require that practitioners "let the system do the work."
- The overarching goal of low-tech restoration is to improve the health of as many miles of riverscapes as possible and to promote and maintain the full range of self-sustaining riverscape processes.
... Reach-scale restoration may involve esthetic or recreational enhancements that do not necessarily improve ecological functions in a river corridor ). Reach-scale restoration sometimes also seeks to create conditions that are not natural or ecologically appropriate for a particular river corridor Fryirs and Brierley 2009), as in the many examples of braided rivers that are viewed as esthetically unattractive and reconfigured to a meandering planform (Kondolf et al. 2001). These scenarios can occur where there is a gap between scientific understanding of a river ecosystem and societal perceptions. ...
... The transition back to meandering occurs over a period of decades as native cottonwood (Populus spp.) trees that germinated immediately after the flood gradually stabilize the floodplain (Friedman and Lee 2002) (Fig. 4.7). Failure to recognize these repeated alterations in process and form within the river corridor can lead to inappropriate restoration targets (Kondolf et al. 2001). ...
This work is designed to broaden the scope with which many people regard a river. Rivers are commonly regarded from a very simplistic perspective as conduits for downstream flows of water. In this context, it may be considered acceptable and necessary to engineer the channel to either facilitate such flows (e.g., channelization, levees) or limit flows and store water (e.g., water supply reservoirs, flood control). The book presents the concept of a river as a spatially and temporally complex ecosystem that is likely to be disrupted in unexpected and damaging ways by direct river engineering and by human activities throughout a drainage basin.
Viewing a river as a complex ecosystem with nonlinear responses to human activities will help to promote a more nuanced and effective approach to managing river ecosystems and to sustaining the water resources that derive from rivers. In this context, water resources refers to ecosystem services including water supply, water quality, flood control, erosion control, and riverine biota (e.g., freshwater fisheries). Chapters in this book draw extensively on existing literature but integrate this literature from a fresh perspective. General principles are expanded upon and illustrated with photographs, line drawings, tables, and brief, site-specific case studies from rivers around the world.
... Reach-scale restoration may involve esthetic or recreational enhancements that do not necessarily improve ecological functions in a river corridor ). Reach-scale restoration sometimes also seeks to create conditions that are not natural or ecologically appropriate for a particular river corridor Fryirs and Brierley 2009), as in the many examples of braided rivers that are viewed as esthetically unattractive and reconfigured to a meandering planform (Kondolf et al. 2001). These scenarios can occur where there is a gap between scientific understanding of a river ecosystem and societal perceptions. ...
... The transition back to meandering occurs over a period of decades as native cottonwood (Populus spp.) trees that germinated immediately after the flood gradually stabilize the floodplain (Friedman and Lee 2002) (Fig. 4.7). Failure to recognize these repeated alterations in process and form within the river corridor can lead to inappropriate restoration targets (Kondolf et al. 2001). ...
People have been altering the environment since prehistory. Archeological records and the stratigraphy of valley bottoms suggest that prehistoric alteration of native upland vegetation for grazing and crops resulted in enhanced sediment yields to river corridors, as well as associated changes in channel dimensions and planform and channel-floodplain connectivity (e.g., Mei-e and Xianmo 1994; Stinchcomb et al. 2011). The magnitude of these changes varied through time and space. Examples of intensive vegetation clearing and valley-bottom aggradation come from diverse regions. In the southeastern United States, nineteenth century row-crop agriculture led to floodplain deposition of more than a meter of sediment (Jackson et al. 2005). In southeastern Australia, nineteenth century land clearance caused channel and floodplain aggradation (Brooks and Brierley 1997). In southern Poland, land clearance for agriculture during the late seventeenth to nineteenth centuries triggered increased sediment yields that changed meandering rivers into braided channels (Latocha and Migoń 2006). Conversely, twentieth century declining resource use, regrowth of upland vegetation, and erosion of channels occurred in mountainous regions of western and central Europe (Latocha and Migoń 2006).
... Reach-scale restoration may involve esthetic or recreational enhancements that do not necessarily improve ecological functions in a river corridor ). Reach-scale restoration sometimes also seeks to create conditions that are not natural or ecologically appropriate for a particular river corridor Fryirs and Brierley 2009), as in the many examples of braided rivers that are viewed as esthetically unattractive and reconfigured to a meandering planform (Kondolf et al. 2001). These scenarios can occur where there is a gap between scientific understanding of a river ecosystem and societal perceptions. ...
... The transition back to meandering occurs over a period of decades as native cottonwood (Populus spp.) trees that germinated immediately after the flood gradually stabilize the floodplain (Friedman and Lee 2002) (Fig. 4.7). Failure to recognize these repeated alterations in process and form within the river corridor can lead to inappropriate restoration targets (Kondolf et al. 2001). ...
The previous chapter reviewed a long list of human activities that have directly and indirectly altered process and form in river ecosystems, with an associated loss of ecosystem services. Management in many river basins now focuses on trying to restore some balance between existing, typically consumptive or homogenizing uses of river resources versus restoration of diversity, sustainability, and river ecosystem health. None of the latter three terms is easy to define. Diversity refers to variety but, as discussed in Chap. 2, there are multiple ways to define physical or biotic diversity and no particular metric is consistently better in all situations or for all purposes. Sustainability in an ecological context typically refers to the ability of ecosystems to remain diverse and productive. In a physical context, sustainability may refer to the ability of a system to continue functioning or providing natural resources. River health also has multiple potential definitions. Even using the relatively simple definition in Chap. 1, that river health is the degree to which a river ecosystem matches natural conditions, requires understanding natural conditions. On the one hand, use and understanding of words matters and people may use similar words but have different objectives or desired outcomes. On the other hand, diversity, sustainability, and river health are now widely used and there is at least broad consensus on the meaning of these words. So, what is being done to protect and restore river corridors? This chapter reviews the development of river restoration during the latter twentieth century and early twenty-first century; discusses particular concepts used in restoration; and presents specific examples of watershed-scale restoration.
... Reach-scale restoration may involve esthetic or recreational enhancements that do not necessarily improve ecological functions in a river corridor ). Reach-scale restoration sometimes also seeks to create conditions that are not natural or ecologically appropriate for a particular river corridor Fryirs and Brierley 2009), as in the many examples of braided rivers that are viewed as esthetically unattractive and reconfigured to a meandering planform (Kondolf et al. 2001). These scenarios can occur where there is a gap between scientific understanding of a river ecosystem and societal perceptions. ...
... The transition back to meandering occurs over a period of decades as native cottonwood (Populus spp.) trees that germinated immediately after the flood gradually stabilize the floodplain (Friedman and Lee 2002) (Fig. 4.7). Failure to recognize these repeated alterations in process and form within the river corridor can lead to inappropriate restoration targets (Kondolf et al. 2001). ...
This chapter reviews the different physical components of the river corridor, the physical processes that create and maintain those components, and the interactions between physical processes and living organisms. Among the critical aspects of physical processes and physical-biotic interactions are transfers of matter and energy and the occasional disturbances that reconfigure the river ecosystem and the processes occurring within the ecosystem. Individual rivers and segments of rivers respond differently to these disturbances and the nature of the response is characterized by how much the river ecosystem changes and how quickly the ecosystem recovers from change.
... Indeed, some meander restorations have increased habitat heterogeneity in river reaches (Moerke et al. 2004;Pedersen et al. 2007b;Nakano and Nakamura 2008) and enhanced the diversity and abundance of aquatic organisms such as fish and macroinvertebrates (Lorenz et al. 2009;Nakamura et al. 2014), and similar positive biological responses are expected at other sites in the future (Trexler 1995;Pedersen et al. 2007b;Hauer et al. 2014). Conversely, a number of meander restoration projects have failed to facilitate a significant recovery of target species and assemblages due to a lack of understanding of key habitats, including floodplain waterbodies, and large-scale factors that control features of river reach and segment such as sediment load (Holubova and Lisicky 2001;Kondolf et al. 2001;Kawaguchi et al. 2005;Kondolf 2006). Numerous studies have described the structure and function of natural habitats of fish in various river systems (e.g., Murphy et al. 1989;Fausch and Northcote 1992;Inoue and Nakano 1999;Peterson and Rabeni 2001;Beechie et al. 2005;Schwartz and Herricks 2008;Zeug and Winemiller 2008;Nagayama et al. 2012;Wolter et al. 2016). ...
... Our findings indicate that what is important is not simply the reconstruction of a meandering channel but the recovery of habitat diversity and the dynamic processes that occur through channel meandering. There have been a number of meander restorations that were designed with the objective of creating a stable, single-thread, meandering channel with bank protection at the outer bends (Kondolf et al. 2001;Kondolf 2006). However, in meander restorations of this type, populations of lentic fishes (such as the sticklebacks in our study) may not recover due to the lack of wood and lateral habitats (which include inter-levee oxbow lakes). ...
This study examined the structure and function of habitats for fish, the contribution to fish populations, and the effects of channel modification on habitats and fish populations in the lowland meandering Shibetsu River, northern Japan. Electrofishing and environmental measurements were conducted in bank areas of habitats constituting natural meandering and modified reaches. All types of habitats in a meandering reach highly contributed to the fish population(s). In particular, the contributions of lateral and wood habitats to fish populations were generally high, despite the low spatial extent of these habitats. The modified reach was simplified and had fewer types of habitats with uniform currents, and there was a low abundance of most fish within these habitats. Abundance of each fish group (taxa) was negatively affected by the changes in the habitats and/or channel shortening (i.e., decrease in the absolute abundance of habitat) due to river modification, which was implemented during 1950–1978. This study suggests that the recovery of all the habitat types is important in meander restoration and that the changes in habitat types and abundance should be examined in monitoring meander restoration and channel shortening.
... Based on the findings of this study, the projects Miller and Kochel (2010) studied that experienced larger adjustments (>20%) likely were subjected to changing boundary conditions (e.g., Q w , Q s ), which stream restoration projects typically do not address. Kondolf et al. (2001) and Nagle (2007) have also equated large post-restoration adjustments to instability. ...
... Historical ecology is not simply concerned with describing the landscape as it was at one point in the past, but rather with providing insight into system dynamics and their drivers to either understand those past conditions or understand how those same dynamics might still influence the landscape (Safford et al. 2012, Safran et al. 2017. Identifying and understanding the history and biophysical functions of sites can help to avoid restoration failures resulting from a lack of such knowledge (Kondolf et al. 2001, Jacobs et al. 2011. The goal of historical ecology is not simply to describe how a landscape was, but how it functioned. ...
... An integrated-systems view that gives attention to both stakeholder values and scientific information concerning the potential consequences of alternative restoration actions on key ecosystem indicators is required van Zyll de Jong 2004, King et al. 2022). An explicit, value-laden, decision-driven approach based on the best available information is required that links values to facts (Kondolf et al. 2001, Downs and Kondolf 2002, Gregory et al. 2012. If the practice of river restoration is to improve, project designs must be able to demonstrate evidence of ecological success to qualify as sound restoration . ...
... Natural or anthropological causes greatly influence the shape of the river network and the hyrdology [41]. Some of the crucial aspects influencing river network are ecoregiondependent susceptibility [77], land use and land cover [33,54], demographic distribution, sprawling [24,64,84], carry-over effects [36], convolution of loadings from upstream to downstream [22], flow splitting [6], bank capacity and flow capacity [9,16]. ...
A river network is a beautiful natural geomorphological arrangement of stream segments extending from the headstream to the medium streams eventually moving further to join the main streams. Through morphological assessment, it has been observed that the structure of the river network is greatly influenced and dictated by the geographical landscaping of the terrain. Research initiatives conceived towards the morphological analysis of the river network necessarily mandate a sound knowledge of network types as well as the generation of attributes associated with various streams. Some of the important stream attributes associated with a stream segment belonging to a river network are stream order, stream number, bifurcation ratio, weighted mean bifurcation ratio, stream length, mean stream length, length ratio, weighted mean length ratio, area coverage, carriage capacity, coordinate trails and length of the mainstream. Traditionally, river network digitization and estimation of attributes were performed through the deployment of labor-intensive manual techniques. These techniques are intensive, extremely time-consuming and expensive, moreover, the results obtained are often found biased towards the digitizer’s experience. Inaccurate digitization will not only influence the structure of the river network but also generate erroneous attributes. It will also have an adverse impact on the confidence of the inferences drawn from the analysis process. This problem can be tactfully handled by conceiving and realizing effective and efficient knowledge-based automated computational programs aided by the selection of appropriate data structures. Further, such programs can be easily advanced to generate desired stream attributes. With due regard to the above, this research initiative proposes an effective and efficient generic knowledge-based automated computational program equipped with a proficient spiral traversal technique capable of accurately digitizing river networks of different types with advanced abilities for generating various stream attributes with the desired level of confidence. Further, this work also highlights some of the prominent application domain of the proposed initiative.
... Morphological measures are also critical when considering the sustainability of rehabilitation because they act on river energy, resistance, and responsiveness, which have direct implications on river adjustments and future channel states. Many examples of unsuccessful rehabilitation actions have been reported by scientists (e.g., [11][12][13]). Most of the time, such failures are related to a lack of a priori knowledge of the morphodynamics and geomorphological context, and the actions are therefore not adapted to the situation, and the expected recovered habitats are rapidly lost or never appear. ...
River rehabilitation and ecological engineering are becoming critical issues for improving river status when ecological habitats and connectivity have been altered by human pressures. Amongst the range of existing rehabilitation options, some specifically focus on rebuilding fluvial forms and improving physical processes. The aim of this contribution is to illustrate how geomorphological expertise and process-based thinking contribute to river rehabilitation success. This semantic contribution is intended to feed the rehabilitation debate, particularly concerning the design of actions and the proposed references for monitoring target reaches and evaluating rehabilitation effects empirically. This article is also based on lessons learned from practical cases, mainly in gravel-bed rivers. Geomorphic understanding is needed at a local level to achieve an adequate diagnosis of river functioning, estimate human impacts and potential remnant river responsiveness, and to assess the gains and risks from rehabilitation, as well as to appraise success or failure through several pre- and post-project assessment strategies. Geomorphological studies can also be upscaled in a top-down manner (from high-order controls to small-scale processes, understanding detailed processes in their regional or basin-wide context), providing large-scale information at the regional, national, or even global level, information that can be used to diagnose the health of riverscapes in relation to local site-specific contexts. As such, geomorphological studies support strategic planning and prioritization of rehabilitation works according to specific contexts and river responsiveness, so as to move from opportunistic to objective-driven strategies.
... Doyle et al., 2015 Uvas Creek(Kondolf et al., 2001) Ruisseau Taché, Saguenay Projet d'aménagement du canal Saint-Georges (Port-Menier)Partenaire externe en HGM Cours d'eau d'origine anthropique Exclusion des recommandations de l'HGMConception incohérente au contexte ...
Le concept d’Anthropocène est couramment mobilisé afin de caractériser l’époque durant laquelle les activités humaines deviennent le principal moteur de l’évolution du système Terre. L‘approche de la sociogéomorphologie invite toutefois à dépasser cette définition en ajoutant qu’il implique une gamme d'interactions complexes entre des processus biophysiques et sociaux. Elle reconnait notamment leur coproduction des paysages terrestres, qui est cristallisée dans une trajectoire ni réellement naturelle, ni totalement anthropique. Cette communication montrera comment la sociogéomorphologie permet d’approfondir et de documenter ces interactions dans le contexte de la construction et de l’évolution des cours d’eau. Au Québec, cette trajectoire peut être dépeinte en trois temps : (1) un aménagement des cours d’eau en fonction de besoins économiques et de représentations comme des milieux dangereux ; (2) l’établissement de cadres réglementaires entourant la gestion des cours d’eau qui considèrent ces derniers comme des entités statiques, dû notamment aux pratiques historiques orientées vers une maîtrise de leur dynamique naturelle ; et (3) une expression plus marquée de la mobilité des cours d’eau causée par un ralentissement des activités de stabilisation, et une plus grande reconnaissance des bénéfices humains des cours d’eau de qualité. Celle-ci se manifeste par une multiplication des initiatives visant leur restauration et leur naturalisation. Cependant, les cadres réglementaires en vigueur orientent ces activités en limitant les possibilités de diminuer les dégradations anthropiques historiques et de laisser davantage de liberté aux processus fluviaux. De nouvelles législations tentent de surmonter ces freins et, bien qu’elles visent une plus grande considération de la dynamique naturelle des systèmes fluviaux, elles contribuent toujours au fléchissement de leur trajectoire, notamment en fonction d’éclairages apportés par l’hydrogéomorphologie. Dans leur état actuel, la majorité des cours d’eau québécois peuvent ainsi être considérés comme des hybrides, manifestations de la coévolution des processus biophysiques et sociaux et de leur coproduction des systèmes fluviaux. Dans l’Anthropocène, l’étude de ces objets hybrides, de leur construction et de leur évolution nécessite enfin un dialogue critique soutenu entre sciences naturelles et sociales.
... Depending on project objectives, managers may base the assessment of restored streams on the economic, aesthetic, or enhanced social values the streams provide (Kondolf, Smeltzer & Railsback, 2001;Johansson & Nilsson, 2002) but in ecological terms, scientists believe that no restoration can be adjudged successful without ecological success (Dufour & Piégay, 2009). ...
The widespread anthropogenic degradation of the lotic system has necessitated the restoration of many rivers worldwide. In Europe, the EU WFD mandates all member states to restore rivers to good ecological status and proposes an assessment based on the structural elements of the ecosystem for monitoring the ecological status of restored streams. However, the components of the ecological status of streams comprise both structural and functional elements. Therefore, consequent on the inconsistent outcomes from the assessments of biodiversity as indicators of the ecological status of restored streams, there has been a growing call for better and more inclusive assessment protocols. We proposed streambed oxygenation and litter decomposition rate as functional indicators in addition to the classical macroinvertebrate community indices for monitoring restoration success in headwater streams. We found that these functional indicators complemented biological diversity in tracking the trajectory of ecological recovery in headwater streams. We also found that in combination with biodiversity indices, these functional indicators are useful in disentangling the effects of other confounding factors from the impacts of restoration activities on the health of the streams. This thesis also highlights the imperativeness of a long enough monitoring program to determine the short and long-term effects of restoration activities in streams.
... This concept is further reinforced by designing stream banks fortified with rip rap and large woody debris, and increasing capacity for water rather than letting beyond bank-full events move onto the flood plain (Kondolf, 1996;Palmer et al., 2005). These single-thread projects often fail within 2-5 years because the waterway was not meant to be forced into a single-thread meandering stream, resulting in additional expense and damages (Kondolf et al. 2001;Kondolf, 2006). Due to lack of knowledge, understanding and training to particular sites, lack of proactive monitoring communities, scientists and engineers fail to create long-term fixes to our environmental problems and indeed may be making them worse. ...
... Prediction helps determine what is/ is not possible, and the likelihood and associated confidence of a given scenario occurring over a particular timeframe. Management applications that build on an incomplete information base, or an inaccurate approach to geomorphic analysis and interpretation, are destined to fail (e.g., Brierley and Fryirs, 2009;Kondolf et al., 2001;Simon et al., 2007). ...
The process of interpretation, and the ways in which knowledge builds upon interpretations, has profound implications in scientific and managerial terms. Despite the significance of these issues, geomorphologists typically give scant regard to such deliberations. Geomorphology is not a linear, cause-and-effect science. Inherent complexities and uncertainties prompt perceptions of the process of interpretation in geomorphology as a frustrating form of witchcraft or wizardry – a dark art. Alternatively, acknowledging such challenges recognises the fun to be had in puzzle-solving encounters that apply abductive reasoning to make sense of physical landscapes, seeking to generate knowledge with a reliable evidence base. Carefully crafted approaches to interpretation relate generalised understandings derived from analysis of raw data with field observations/measurements and local knowledge to support appropriately contextualised place-based applications. In this paper we develop a cognitive approach (Describe-Explain-Predict) to interpret landscapes. Explanation builds upon meaningful description, thereby supporting reliable predictions, in a multiple lines of evidence approach. Interpretation transforms data into knowledge to provide evidence that supports a particular argument. Examples from fluvial geomorphology demonstrate the data-interpretation-knowledge sequence used to analyse river character, behaviour and evolution. Although Big Data and machine learning applications present enormous potential to transform geomorphology into a data-rich, increasingly predictive science, we outline inherent dangers in allowing prescriptive and synthetic tools to do the thinking, as interpreting local differences is an important element of geomorphic enquiry.
... Taking some of the most critical papers on Rosgen (1994) (Kondolf, 1995(Kondolf, , 1998Miller and Ritter, 1996;Doyle and Harbor, 2000; Juracek and Fitzpatrick, J o u r n a l P r e -p r o o f Journal Pre-proof 2003;Smith and Prestegaard, 2005;Simon et al., 2007;Roper et al., 2008), 492 works have cited these articles, namely, ~50% of his citations come from criticisms of Rosgen (1994) (since before the tool was normalised in practice (e.g., Sear, 1994) until today, therefore, it seems that these are not criticisms derived from the commercial success of NCD). All this without taking into consideration Rosgen (1996) (for example, Kondolf et al. (2001) only cites that reference) or the cross relationships between Rosgen (1994) and Rosgen (1996), which could be considered as a citation of the same work. Is Rosgen"s contribution controversial or are all those researchers wrong? ...
In his comment on our recent article “Promoting fluvial geomorphology to ‘live with rivers’ in the Anthropocene Era” (García et al., 2021), Dave Rosgen (2021) suggests that we make three erroneous claims about him and his technical protocol Natural Channel Design (NCD). In this reply, we contextualize and address his comments, analysing the repeated critiques in recent decades of NCD. In doing so, we touch on issues such as scientific and technical knowledge, the need to adapt to advances in science and techniques, the need to understand inherent gaps present in technical protocols and what is and is not a classification tool, as well as the narrow line between science and ethics.
... Bien que son approche ubiquiste permette de classer la majorité des lits fluviaux de la zone tempérée, son travail a été essentiellement réalisé aux Etats-Unis et n'est applicable qu'à petite échelle. L'intérêt opérationnel a été remis en question par divers auteurs (Miller & Ritter, 1996 ;Kondolf et al., 2001 ;Juracek & Fitzpatrick, 2003 ;Kondolf et al., 2003). En effet, les schémas ubiquistes sont d'un faible intérêt pratique et plutôt conceptuels. ...
A hydro-geomorphological typology proves to be a basic tool for these new management methods, responding to the terms of an "integrated management of the water resource of management, responding to the terms of an "integrated management of water resources, its maintenance and maintenance and recovery by 2015 of the "good ecological status" of water bodies" defined by the by the European Water Framework Directive (European Council and European Parliament, 2000). The typologies must therefore be sufficiently precise to allow access to the hydro-geomorphological and ecological functioning of watercourses. It is this fine level of perception that we retain in this work which tends to define a methodology of classification based on quantitative and objective observations.
Two visions oppose each other concerning the implementation of an evaluation process or a methodology. An inductive approach, based on the objective observation of facts and on basic data (field measurements) basic data (field measurements) from which one tries to define theories. It opposed to a deductive approach, which tries to simplify the problems in order to make them easier to easier to read and which relies on scientific justifications to provide quality information verified by verified by specific observations. Each in their own way, these two approaches answer the questions posed, but both have their advantages and limitations.
... The methods used for designing bank stabilization programs at times lead to overdesigned structures and deteriorates the natural river aesthetics, and are inadequately adapted in the natural environment (Kondolf et al. 2001). Thus, it becomes a challenge in identifying the fundamental problems in controlling riverbank erosion. ...
Sundarban area of the lower Gangetic plain experiences embankment failure almost every year due to the formation of toe undercuts. Waves generated due to the continuous action of wind and tidal currents are paramount in the growth and development of these undercuts. Existing literature suggests that grids are effective in modulating the scales of turbulence. The present investigation is carried out with the objective of looking into whether grids can be effective in controlling the undercutting process and thereby restraining the failure of these embankments. To explore this artefact, laboratory flume experiments were carried out using cylindrical grid placed near the toe of a cohesive bank. Turbulent 3-D velocity was measured using micro-Acoustic Doppler velocimeter (ADV) at the junction of the grid and at the near bank region to get insight into the governing mechanism of grid-influenced flow on the bank. The present investigation revealed that the installation of the cylindrical grids at the toe region of the bank is effective in modulating the scales of turbulence. The scales of Reynolds shear stress fluctuations showed a reduced magnitude due to the presence of near bank grid. The results show that the grid breaks the large scales (larger eddies) of turbulence into smaller eddies through eddy cascading process and thereby modulate the turbulent shear stresses. This probably slowed down the erosion rate preventing the formation of the undercuts and thus restraining bank/embankment failure. Thus, it is envisaged that the proposed methodology on implementation at the riverbanks would serve as an effective measure in the protection of these embankments.
... The fundamental idea behind process-based restoration in rivers and streams is that channels have degraded because processes thought critical to sustaining these freshwater ecosystems have either been eliminated, or their rates or magnitudes have changed (Kondolf et al. 2001, 2006, Palmer et al. 2005, Beechie et al. 2010. In principle, if these processes are restored at some historically relevant rates and magnitudes, stream ecosystems should recover accordingly. ...
Beaver-related restoration is a process-based strategy that seeks to address wide-ranging ecological objectives by reestablishing dam building in degraded stream systems. Although the beaver-related restoration has broad appeal, especially in water-limited systems, its effectiveness is not yet well documented. In this article, we present a process-expectation framework that links beaver-related restoration tactics to commonly expected outcomes by identifying the set of process pathways that must occur to achieve those expected outcomes. We explore the contingency implicit within this framework using social and biophysical data from project and research sites. This analysis reveals that outcomes are often predicated on complex process pathways over which humans have limited control. Consequently, expectations often shift through the course of projects, suggesting that a more useful paradigm for evaluating process-based restoration would be to identify relevant processes and to rigorously document how projects do or do not proceed along expected process pathways using both quantitative and qualitative data.
... Monitoring results indicated that restoration projects often fail to achieve the intended ecological objectives ( Palmer et al., 2010 ) or the long-term persistence of geomorphic (e.g. Kondolf et al., 2001 ) or hydraulic effects (e.g. Geerling et al., 2008 ). ...
Relatively short time that passed since the onset of river restoration activities worldwide and a scarcity of monitored restoration projects cause that scientific evidence of changes in restored rivers is still meagre, particularly with respect to innovative restoration techniques and long-term effects of restoration activities. Restoration projects realized in the first half of the 2010s in three Polish Carpathian watercourses resulted in establishing of an erodi- ble corridor in reaches of the Biała and the Raba rivers and installation of block ramps in the deeply incised channel of Krzczonówka Stream downstream of a lowered check dam. Environmental monitoring was conducted in the initial and final phases of the restoration projects and is to be repeated 5 years after their completion. This paper (i) introduces the area of the restoration projects, (ii) informs on their objectives and implementation, (iii) outlines the methodology of the environmental monitoring and of the analysis of imme- diate and long-term effectiveness of the projects in improving the ecological state of the watercourses and reducing flood hazard, and (iv) overviews papers presenting outcomes from the initial phase of the monitoring. The analysis of the monitoring data will increase knowledge on effects of the innovative, cost-effective restoration measures that could be widely used in the Carpathian context, and thus will be useful for changes in the manage- ment of degraded mountain rivers.
... Stability -The desire to reduce uncertainty and precisely predict restoration outcomes has inadvertently caused stream restoration to emphasize the stability of channels and instream structures (Kondolf et al. 2001). ...
The following document outlines a low-tech process-based (LTPBR) restoration design for a 0.7 - mile section of Whychus Creek, a tributary to the upper Deschutes river in Jefferson and Deschutes Counties.
The following restoration design for the Willow Springs Preserve was developed following low-tech process-based restoration (LTPBR) principles (see Wheaton et al. 2019). LTPBR utilizes simple, cost-effective, hand-built structures that mimic beaver dams (i.e., beaver dam analogs, BDAs) and wood accumulations (i.e., post-assisted log structures, PALS), structural elements that occur in abundance within functioning stream systems. These structural elements are strategically introduced to the river system using a design intended to amplify natural hydrologic, geomorphic, and biological processes that accelerate the recovery trajectory of degraded streams. Unlike more traditional practices that rely on engineering plans and heavy construction equipment (e.g., excavators) to impose channel and floodplain restoration designs, LTPBR ultimately defers design decisions to the characteristics and limitations set by individual riverscapes. Reducing design and implementation costs and allowing natural stream processes to do much of the restoration “work” minimizes economic and ecological risks associated with stream restoration implementation. Ultimately, the restoration design is intended to invoke a more resilient riverscape capable of maintaining a diverse and self-sustaining set of fluvial and riparian processes that benefit an abundance of aquatic and terrestrial fish and wildlife species.
... However, not all stream/riparian restoration projects withstood the test of time. Sometimes, in-stream channel improvements and bank stabilization measures did not withstand high flows long enough for riparian vegetation to become established as was the case with the Uvas Creek Park Preserve Restoration Project (Kondolf et al. 2001;Rosgen 2006;Rosgen 2008). ...
In the Preface to volume 1, we discuss the development of riparian ecology as one of the newest of ecological fields that gained significant momentum in the 1950s and 1960s as part of the general “riparian movement” in the United States. The field expanded rapidly throughout the latter half of the 1900s. Volume 2 involves more than two dozen authors—most with decades of experience—who expand upon riparian and other topics introduced in volume 1. Two important recent developments are global climate change and impacts of introduced tamarisk leaf beetles (Diorhabda spp.) in the American West. Other chapters in volume 2 that provide current information evaluate the losses of riparian habitat, including “extirpation” of a large number of mesquite bosques (woodlands) in the Southwest; the restoration of riparian ecosystems damaged by anthropogenic activities; the importance of a watershed; and the importance of riparian ecosystems to recreation. The combination of volumes 1 and 2 examines the evolving understanding of scientific implications and anthropogenic threats to those ecosystems from Euro-American settlement of the region to present.
... Only protecting riparian corridors alongside a stream (indispensable patterns described in Forman 2002) as a solution to landscape ecological planning does not address the stream processes that might scour the riparian vegetation with large flows and shift the channel position over time creating dynamic habitats that change over time. A more sustainable multifunctional approach to river restoration would be to restore the physical river processes wherever possible (Beechie 2010, Kondolf et al. 2001). An issue with waiting for the river to do the work of shaping its own channel form is the long amount of time that may be required, in contrast with shorter human project timelines and the expectation that the river should look more "natural" after restoration work. ...
... Determining what is 'expected' in any given system is a key issue in managing sediment (dis)connectivity at the catchment scale. Some systems such as the Waiapu in New Zealand are overloaded with sediment, while others such as the Bega in southeastern Australia are sediment starved (cf., Brooks and Brierley, 2004;Florsheim et al., 2006;Fryirs and Brierley, 2016;Kondolf, 1998;Kondolf et al., 2001;Smith et al., 2011). Agricultural streams, such as the Fugnitz in Austria (Poeppl et al., 2019b) often have a high fine-grained sediment (and nutrient/ contaminant) load derived from soil erosion and sediment transport processes (Owens et al., 2005;Vanmaercke et al., 2011). ...
Globally, rivers systems are under considerable and increasing threat from multiple anthropogenic stresses, including different types of direct (e.g. channel engineering) and indirect human impacts (e.g. land cover and land use changes) that alter water and sediment dynamics. (Dis)connectivity relationships determine the source, timing and rates of water and sediment flux in catchments and thus their geomorphic sensitivity to disturbance. However, most river and catchment management plans overlook the role of sediment (dis)connectivity. Here we use examples from different environmental settings with different sediment-related problems to show how understandings of sediment (dis)connectivity can inform catchment-based management plans. We focus on concerns for river conservation and recovery, using examples from Austria, New Zealand and Australia. Finally, we present questions for practitioners to consider to appropriately contextualise management applications when using (dis)connectivity concepts in practice. Our findings revealed that differences in sediment (dis)connectivity relationships exert profound catchment-specific variability in (eco)-geomorphic response to disturbance. Understanding (dis)connectivity and system history is therefore essential to forecast the effects of on-ground management actions.
... Morphological objectives were the most frequently referred ones during all studied periods in both Dutch restoration projects and scientific publications (Fig. 2, second panel, Table S1). The measures involved were re-profiling of the stream bed and banks and remeandering of the stream channel, in the Netherlands as well as abroad (e.g., Rinaldi and Johnson, 1997;Kondolf et al., 2001;Kasahara and Hill, 2006;Krapesch et al., 2009;Schiff et al., 2011;Kristensen et al., 2014). ...
Stream restoration efforts have increased, but the success rate is still rather low. The underlying reasons for these unsuccessful restoration efforts remain inconclusive and need urgent clarification. Therefore, the aim of the present study was to evaluate over 40 years of stream restoration to fuel future perspectives. To this purpose we evaluated the influence of policy goals on stream restoration efforts, biophysical restoration objectives, restoration measures applied including the scale of application and monitoring efforts. Information was obtained from five stream restoration surveys that were held among the regional water authorities in the Netherlands over the last 40 years and from an analysis of the international scientific publications on stream restoration spanning the same time period. Our study showed that there was a considerable increase in stream restoration efforts, especially motivated by environmental legislation. However, proper monitoring of the effectiveness of the measures was often lacking. Furthermore, a mismatch between restoration goals and restoration measures was observed. Measures are still mainly focused on hydromorphological techniques, while biological goals remain underexposed and therefore need to be better targeted. Moreover, restoration practices occur mainly on small scales, despite the widely recognized relevance of tackling multiple stressors acting over large scales for stream ecosystem recovery. In order to increase the success rate of restoration projects, it is recommended to improve the design of the accompanying monitoring programmes, allowing to evaluate, over longer time periods, if the measures taken led to the desired results. Secondly, we advise to diagnose the dominant stressors and plan restoration measures at the appropriate scale of these stressors, generally the catchment scale.
... For example, knowledge of reference conditions and trajectories of change through time can be used to constrain effective management options (Brierley & Fryirs, 2016). A well-documented example of failure to use such knowledge comes from a river restoration project at Uvas Creek in California (Kondolf et al., 2001). A meandering channel form fixed in place with bank stabilization was completed at the site in November 1995. ...
Logging, urbanization, and dam building are a few ways people have significantly altered natural river ecosystems. Understanding that influence is a grand challenge of our time.
... For example, knowledge of reference conditions and trajectories of change through time can be used to constrain effective management options (Brierley & Fryirs, 2016). A well-documented example of failure to use such knowledge comes from a river restoration project at Uvas Creek in California (Kondolf et al., 2001). A meandering channel form fixed in place with bank stabilization was completed at the site in November 1995. ...
Legacies are persistent changes in natural systems resulting from human activities. Legacies that affect river ecosystems can result from human alterations outside of the river corridor, such as timber harvest or urbanization, or from alterations within the river corridor, including flow regulation, river engineering, and removal of large wood and beaver dams. Human alterations of river ecosystems have been occurring for thousands of years in some parts of the world and are now ubiquitous, yet both river scientists and the public may be unaware of the persistent effects of historical activities. Failure to recognize the legacy of historical activities that no longer occur can skew perceptions of river process and form and the natural range of variability in river ecosystems. Examples come from rivers of the Mid‐Atlantic Piedmont and the Pacific Northwest regions of the United States. Mid‐Atlantic Piedmont streams in which legacy sediment accumulated behind now‐abandoned mill dams experienced a complete transformation from wide, shallow, marshy valleys to sinuous rivers lined with tall cutbanks, but the existence and the cause of this river metamorphosis was not widely recognized until the first decade of the 21st century. Rivers of the Pacific Northwest from which large wood was removed have changed during the past century from spatially heterogeneous, multichannel systems closely connected to their floodplains via frequent channel avulsion and lateral migration to single‐thread channels with more homogeneous floodplains and less lateral connectivity. Again, this river metamorphosis has only been recognized within the past two decades. In each of these regional examples, river process and form have changed so substantially that the river ecosystems can be described as having assumed an alternative state. In these and many other examples, the alternative state provides lower levels of ecosystem services such as habitat, biodiversity, and attenuation of downstream fluxes of water, sediment, organic carbon, and nutrients. River management designed to enhance and restore these ecosystem services can be more effective if the continuing effects of these historical legacies are recognized. The grand scientific challenges resulting from historical human alterations of river ecosystems include the following: (1) to recognize the existence of a legacy that continues to affect river ecosystem process and form; (2) to understand the source of the legacy with respect to chronology, type, spatial extent, and intensity of human activities; (3) to understand the implications of the legacy regarding how river process and form and river ecosystem services have changed; and (4) to design management or restoration strategies that can mitigate the loss of river ecosystem services. In summary, the existence of forgotten legacies challenges river scientists to recognize the continuing effects of human activities that have long since ceased and also poses challenges for the application of scientific understanding to resource management. Societal expectations for attractive, simple, stable rivers are commonly at odds with scientific understanding of rivers as dynamic, spatially heterogeneous, nonlinear ecosystems. Knowledge of how human actions, including historical actions that have long since ceased, continue to alter river ecosystems can help to bridge the gap between societal and scientific perceptions of rivers.
... River restoration as currently practiced in many US projects that emphasize deliberately designed channel forms and flow regimes can be regarded as simply the latest iteration of river engineering and the domination of river restoration by engineers is to be expected. Fluvial geomorphologists largely became involved in river restoration by explaining how lack of geomorphic understanding led to the failure of specific restoration projects (e.g., Kondolf et al., 2001) or to limitations in river restoration in general (e.g., Wohl et al., 2005). ...
During the past 50 yr, the number and variety of papers written by U.S. fluvial geomorphologists that examine human alterations of rivers has accelerated substantially. From an initial focus primarily on how human-induced changes in land cover influence sediment yield and river dynamics, the literature has expanded to emphasize the effects of flow regulation, channel engineering, removal of large wood and beavers, and changing climate. These multiple human influences are now widely recognized to have resulted in global-scale cumulative effects including significantly altered fluxes of water, sediment, nitrogen, and carbon, and complete transformation of river networks across much of the planet. One outgrowth of this recognition is the increasing involvement of geomorphologists in diverse forms of river restoration, a form of river management that thus far has largely been dominated by engineers. Acknowledging the ubiquity of human alteration of rivers implies that (i) investigators cannot assume that even the most remote and seemingly pristine river segment has not been affected at least indirectly by people, (ii) the use of reference conditions requires careful consideration with respect to what reference sites indicate about past conditions, as well as their relevance for the future, (iii) detailed geomorphic understanding of the nature and timing of past human alterations of rivers is likely to be critical to effective restoration, and (iv) each scientist must decide how to engage within the context of research and advocacy with the issues of ecosystem degradation and loss of river form and function.
... Biedenharn, Copeland, Thorne, Soar, & Hey, 2000;Kondolf, Podolak, & Grantham, 2013), even if field measurements have shown that this discharge might not represent the formative condition (e.g. Kondolf, Smeltzer, & Railsback, 2001). The bankfull discharge is traditionally derived from channel geometry and bed characteristics (e.g. ...
Alluvial rivers are shaped by sequences of water flows excavating their channels. Observations show that besides the magnitude, the frequency and duration of streamflow oscillations might also be important for the river channel formation. In addition, the river morphology appears influenced by both size and degree of uniformity of the sediment. Nevertheless, many morphodynamic studies still represent the flow regime with a single value of the discharge, often corresponding to the bankfull condition, and the sediment with its median grain size. This work investigates the effects of streamflow variability and sediment characteristics on channel width formation, analysing the evolution of experimental streams with different sediments and discharge hydrographs. Results show that the formative condition of the channel width is not the geometric bankfull flow but a rather frequent peak flow. Remarkably different channel configurations arise from different sediment characteristics in the laboratory, where sediment non-uniformity produces more stable banks.
... Despite knowledge based on extensive practical experience, restora- tion activities frequently fail to achieve their ecological goals (Palmer et al., 2010) or the long-term persistence of their hydraulic and geomor- phic effects (e.g. Geerling et al., 2008;Kondolf et al., 2001). This proba- bly reflects an emphasis on designing and creating channel forms that look more natural rather than re-establishing or working with hydro- logical and geomorphic processes that can induce and sustain changes in channel form and habitat structure. ...
... Hauer et al., 2008) and U.S.A. (e.g. 115 Kondolf et al. 2001) report rapid initial morphological responses of these systems in relation 116 to bedform and sediment deposits formation, with subsequent vegetation development. 117 ...
The prediction of the morphological evolution of renaturalized streams is important for the success of restoration projects. Riparian vegetation is a key component of the riverine landscape and is therefore essential for the natural rehabilitation of rivers. This complicates the design of morphological interventions, since riparian vegetation is influenced by and influences the river dynamics. Morphodynamic models, useful tools for project planning, should therefore include the interaction between vegetation, water flow and sediment processes. Most restoration projects are carried out in U.S.A. and Europe, where rivers are highly intervened and where the climate is temperate and vegetation shows a clear seasonal cycle. Taking into account seasonal variations might therefore be relevant for the prediction of the river morphological adaptation. This study investigates the morphodynamic effects of riparian vegetation on a re-meandered lowland stream in the Netherlands, the Lunterse Beek. The work includes the analysis of field data covering 5 years and numerical modelling. The results allow assessing the performance of a modelling tool in predicting the morphological evolution of the stream and the relevance of including the seasonal variations of vegetation in the computations. After the establishment of herbaceous plants on its banks, the Lunterse Beek did not show any further changes in channel alignment. This is here attributed to the stabilizing effects of plant roots together with the small size of the stream. It is expected that the morphological restoration of similarly small streams may result in important initial morphological adaptation followed by negligible changes after full vegetation establishment.
Process‐based river restoration seeks to restore processes such as channel‐floodplain connectivity that create and maintain river corridor functions. Process‐based restoration can fail to produce the desired results if geomorphic context is not effectively incorporated into restoration design. Geomorphic context of a river reach refers to the controls on contemporary river form and process. Controls at the catchment‐ to reach‐scale include geologic history, biophysical characteristics, legacies of past human alterations, position within the river network, river corridor geometry, base level stability, disturbance regime, and contemporary human alterations of the river corridor. We conceptualize a river corridor as reflecting the interactions among fluxes of material and the geomorphic context. We discuss how an understanding of geomorphic context can be used to select a restoration approach and provide examples of how restoration can fail to achieve desired outcomes when geomorphic context is not considered. Within the toolbox of methods used to implement process‐based restoration, we differentiate the alteration of inputs to the river corridor and fluxes of material through the corridor from alteration of form and/or connectivity within the river corridor. Historical, biotic, geologic/geomorphic, and reference sites can be used to inform process‐based restoration targets. Restoration is strongly influenced by human perceptions of what is appropriate and achievable at a site and diverse communities influencing restoration at a site may differ in their perceptions. Geomorphically based conceptual guidelines, such as the River Styles Framework, provide an effective platform for incorporating an understanding of geomorphic context into process‐based river restoration.
River corridors integrate the active channels, geomorphic floodplain and riparian areas, and hyporheic zone while receiving inputs from the uplands and groundwater and exchanging mass and energy with the atmosphere. Here, we trace the development of the contemporary understanding of river corridors from the perspectives of geomorphology, hydrology, ecology, and biogeochemistry. We then summarize contemporary models of the river corridor along multiple axes including dimensions of space and time, disturbance regimes, connectivity, hydrochemical exchange flows, and legacy effects of humans. We explore how river corridor science can be advanced with a critical zone framework by moving beyond a primary focus on discharge-based controls toward multi-factor models that identify dominant processes and thresholds that make predictions that serve society. We then identify opportunities to investigate relationships between large-scale spatial gradients and local-scale processes, embrace that riverine processes are temporally variable and interacting, acknowledge that river corridor processes and services do not respect disciplinary boundaries and increasingly need integrated multidisciplinary investigations, and explicitly integrate humans and their management actions as part of the river corridor. We intend our review to stimulate cross-disciplinary research while recognizing that river corridors occupy a unique position on the Earth's surface.
Assuming that the equilibrium geometry of river channels does not depend on their initial state but solely on boundary conditions, several formulas have been derived that relate the channel depth and width to the river bankfull discharge and bed material. However, due to the existence of a threshold for sediment motion and the strong non-linearity between sediment transport and flow rate, this assumption might not be generally valid for gravel-bed rivers. This research clarifies the role of the initial conditions, more specifically the initial channel width, on the geometry of gravel-bed rivers considering a variety of boundary conditions. The approach includes laboratory experiments and two-dimensional modelling, reproducing the evolution of alluvial channels with different starting widths, discharge regimes and sediment input rates. The experiments represent the Arc River (France). Thus, the characteristics of this river were used in the numerical model to obtain a realistic virtual case complementing the experiments. Different boundary and starting conditions resulted in either braided or single-thread channels. We found that the initial width strongly influences the evolution process and leaves a footprint on the river braid-belt extension. The active width of braided systems and the width of single-thread channels do not depend on the starting condition. They depend on sediment input rather than on discharge variability. Different initial widths result in different final bed levels. This indicates that the initial channel width may affect the degree of channel incision or aggradation. The results of this study justify the use of equilibrium formulas for single-thread rivers.
Truths of the Riverscape refer to the use of geomorphological principles to inform sustainable approaches to nature-based river management. Across much of the world a command-and-control philosophy continues to assert human authority over rivers. Tasked to treat rivers as stable and predictable entities, engineers have ‘fixed rivers in place’ and ‘locked them in time’. Unsustainable outcomes ensue. Legacy effects and path dependencies of silenced and strangled (zombified) rivers are difficult and increasingly expensive to address. Nature fights back, and eventually it wins, with disastrous consequences for the environment, society, culture and the economy. The failure to meet the transformative potential of nature-based applications is expressed here as a disregard for ‘Truths of the Riverscape’. The first truth emphasises the imperative to respect diversity , protecting and/or enhancing the distinctive values and attributes of each and every river. A cross-scalar (nested hierarchical) lens underpins practices that ‘know your catchment’. The second truth envisages management practices that work with processes , interpreting the behaviour of each river. This recognises that erosion and deposition are intrinsic functions of a healthy living river—in appropriate places, at appropriate rates. This premise underpins the third truth, assess river condition , highlighting the importance of what to measure and what to measure against in approaches that address the causes rather than the symptoms of unexpected river adjustment. The fourth truth interprets evolutionary trajectory to determine what is realistically achievable in the management of a given river system. Analysis of whether the river sits on a degradation or recovery pathway (i.e., condition is deteriorating or improving), alongside assessment of catchment-specific recovery potential, is used to foresight river futures. Viewed collectively, Truths of the Riverscape provide a coherent platform to develop and apply proactive and precautionary catchment management plans that address concerns for biodiversity loss and climate change adaptation.
Process-based classification of rivers is widely used for assessing the effects of past landscape disturbance, current biophysical conditions, and likely responses to future disturbance, including land management and restoration activities. This article reviews the purposes of geomorphic channel classification, the different types of classifications that have been developed, their use, compatibility, and popularity (i.e., why some classifications are used more than others), and concludes with a look at future needs and directions for channel classification.
Human settlement in Sundarbans deltaic region of India adopted a method of erecting embankments along the riverside to prevent the river water from spilling over to the colonised areas. These embankments develop undercut at toe region that lead to failure by the swirling currents coupled with tidal surges and strong winds. To protect the embankments from erosion, embankment face is covered with bamboo logs as bamboos are easily available locally and are economically viable. However, from the field investigations it is pertinent that the use of bamboo logs for the prevention of embankment erosion is found to be ineffective in Sundarbans region. The present investigation was carried out to develop insight into why the use of bamboo logs for embankment protection does not provide quintessential solution for bank stabilization. The current work underlines on appraisal of the turbulent flow characteristics in proximity of the bamboo logs and sediment bank interface.
Cambridge Core - Geomorphology and Physical Geography - River Dynamics - by Bruce L. Rhoads
The influence of surrounding land use on stream ecosystems is scale‐dependent, whereby instream habitat structure and organic matter inputs are determined primarily by local conditions such as vegetation cover, whereas nutrient supply, sediment input, hydrology and channel characteristics are influenced by regional conditions, including landscape features and land use types at some distance upstream and lateral to each specific site. Yet, the underlying mechanisms linking adverse in stream ecological effects to stream valley land use are still not fully understood. The aim of this thesis was therefore to unravel the mechanisms by which land use affects structure and functioning of lowland stream ecosystems. To this end, 1- 40 years of stream restoration practices by assessing the influence of policy goals on stream restoration efforts, the biophysical restoration objectives, the restoration measures, the scale on which these measures were applied, and the accompanying monitoring efforts was evaluated; 2- the mechanisms by which terrestrial runoff affects sediment composition and macroinvertebrate community composition in deposition zones of lowland stream ecosystems was unraveled; 3- lowland stream sediment characteristics in terms of food resources and habitat structure are land use specific and if they shape macroinvertebrate communities was determined; 3- the impact of catchment land use on the structure and functioning of lowland stream ecosystems was assessed; 4- the success of stream restoration projects, consisting of the addition of sand to the stream channel in combination with the introduction of coarse woody debris, to restore sandy‐bottom lowland streams degraded by channelization was evaluated.
Large wood (re)introduction can deliver multiple benefits in river restoration, but there is a dearth of the detailed and longer‐term post‐project monitoring and evaluation required for improving best practice. We present findings from an academic partnership approach to post‐project evaluation, based on successive MSc research projects on restored large wood in the Loddon catchment, UK. Field and modelling data reveal: (i) key differences in large wood features between restored and natural reaches; (ii) increased hydraulic retention and changes to mesohabitats associated with large wood; (iii) differences in macroinvertebrate community composition around large wood but a lack of site‐level effects; (iv) interactions between macrophytes and large wood that may be specific to restored reaches; (v) a need for further field and modelling studies to inform the accurate representation of large wood in hydraulic models. Some key challenges in partnership working are identified to aid planning and effectiveness of future collaborations.
It is easy to talk of improving river condition. It is more difficult to pin down exactly what this means. Emerging from ecology, the concept of river health presented an attempt to provide a broad framework for freshwater management incorporating both natural and human values. Initially criticised as subjective and unscientific, river health was nevertheless mainstreamed through being rendered quantifiable. Tracing the (re)definition of river health from a holistic but hazy ethic of environmental care to prescriptive indicators for intervention, I examine how common-sense understandings of river condition were first challenged by, and then incorporated within, the scholarly and political project of river health. Arguing that the search for objectivity entrenched assumptions that naturalness was both desirable and attainable, I explore the potential value of a reimagined, revitalised river health as a constructive platform for renegotiating and broadening what matters for freshwater.
In the design of stream restorations, boundary shear stress (shear stress) during high flow events is one of the key parameters in the assessment of the risk of morphological failure associated with channel bed and bank erosion and sediment transport. The use of two-dimensional hydrodynamic models (2D models) is becoming more common to estimate shear stress for stream restorations. These models can provide detailed distribution of shear stress over channels and floodplain surfaces. Obtaining accurate and reliable estimates of stress requires an accurate digital terrain model, estimates of input flows, and surface roughness coefficients. Impediments to the use of these models include the cost associated with extensively detailed terrain surveys, distributed information about the roughness coefficients, and the determination of appropriate flow conditions that must be modeled to identify erosion susceptible components. In the present research, the two-dimensional hydrodynamic model TUFLOW is employed to assess the sensitivity of shear stress to flow magnitude, upstream extent of the model, and roughness coefficients. Topography and hydraulic data obtained from monitoring efforts of the restored channel and floodplain of Slabcamp Creek located in Rowan County, Kentucky, was used to develop and calibrate the 2D model. Flow magnitude, the location of the upstream inflow boundary condition, and the roughness coefficients were varied to determine the sensitivity of the shear stress at a critical location in the restoration. The shear stress analysis was conducted along cross sections located in areas identified as being potentially at risk for high shear stress. The shear stress distribution was found to be relatively insensitive to the location of the upstream boundary condition and most sensitive to the flow and roughness coefficients of the floodplain. An interesting observation was that the shear stress in the channel decreased with the increased roughness of the floodplain.
In view of considerable work done of late, it has become possible to have a new look at the prevalent theories about river channel patterns. In order to gain insight into the subject, this attempt is preceded by a classification of rivers. Theories about braided and meandering channels are next dealt with. Correlations concerning channel patterns achieve importance in field applications. Various available correlations are presented and correspondence or contradictions in them discussed.
Eleven possible definitions of ?bank-full? have been used by various investigators. The active floodplain is the most meaningful bank-full level to the fluvial geomorphologist, whereas the banks of the valley flat are the most important to engineers. Comparison of 16 ways of determining bank-full discharge suggests that bank-full discharge at gaged sites should be obtained from the station's rating curve, where bank-full gage height is determined from a longitudinal profile of the floodplain along the entire reach. At ungaged sites, bank-full discharge can be estimated from the empirical equation of this study or from the Gauckler-Manning equation. In the latter case the resistance coefficient n should be estimated at the field site for bank-full flow; a measured low-flow n should not be used. Bank-full discharge does not have a common recurrence frequency among the rivers studied, and the discharge corresponding to the 1.5-year recurrence interval in most cases does not represent the bank-full discharge.
Ecological integrity in floodplain rivers is based in part on a diversity of water bodies with differing degrees of connectivity with the main river channel. Collectively, these water bodies occupy a wide range of successional stages, thereby forming a mosaic of habitat patches across the floodplain. This diversity is maintained by a balance between the trend towards terrestrialization and flow disturbances that renew connectivity and reset successional sequences. To counter the influence of river regulation, restoration efforts should focus on re-establishing dynamic connectivity between the channel and floodplain water bodies. -from Authors
This paper describes the fundamental design features. and construction methods and sequence, of a rehabilitation project on a small suburban creek in Moscow, Idaho, USA. A meandering channel pattern was reestablished for approximately 280 m of straightened, dredged channel, a new floodplain was excavated, and the new riparlan zone was replanted. The new stream channel was sized to accommodate an estimated natural bankfull discharge (similar to 5.6 ems), and floodplain design attempted to match the conveyance of the old enlarged channel (14-20 ems). The project was coordinated by a local nonprofit environmental organization, and the design and construction were tailored to donated materials and a largely volunteer labor force. A high-magnitude flood event (ca. 50-year recurrence interval) six months after construction had no significant impact on the newly constructed channel and revetments, but underscored the need for important detailing of the structures. The use of volunteer labor, while entailing certain benefits, complicates project planning and construction. The most general lesson learned from this project is that sponsoring agencies and clients need to be informed of the many steps and sequencing of properly constructed, complex stream rehabilitation projects as well as the high time and cost requirements for these tasks.
Bank storage contributions to base flow may be important on alluvial rivers with highly permeable bank materials, such as the lower Carmel River, Monterey County, California. The recharge phase of bank storage occurs during flood stage in the river when a hydraulic gradient exists from the river into the banks. In general, discharge from bank storage is most important on the recession limb of individual floods, with most stored water typically being discharged within 2–3 flood periods. As the river stage continues to fall, a hydraulic gradient from the banks to the river will be maintained and stored water will drain from the banks. On the Carmel River, the seasonal recession limb provides conditions of a gradually declining stage over several months. In 1982, a moderately wet year, bank storage contributions were detected two months after the last peak flow of the winter rainy season, during a period of critical importance to steelhead trout and probably to riparian vegetation. However, in 1983, an extremely wet year, bank storage was undetectable two months after the season's last peak flow, probably because the sustained base flow from the upper basin overwhelmed the more transient bank storage contribution.Groundwater withdrawal from the alluvial aquifer locally lowered the water table so that streamflow was influent to the banks in the reach of major pumping wells. This effect was striking in its persistence, whether the Carmel River was gaining or losing overall in its alluvial reach. Pumping rates were roughly comparable to flow losses across the well field.
/ This paper describes the fundamental design features, and construction methods and sequence, of a rehabilitation project on a small suburban creek in Moscow, Idaho, USA. A meandering channel pattern was reestablished for approximately 280 m of straightened, dredged channel, a new floodplain was excavated, and the new riparian zone was replanted. The new stream channel was sized to accommodate an estimated natural bankfull discharge ( approximately 5.6 cms), and floodplain design attempted to match the conveyance of the old enlarged channel (14-20 cms). The project was coordinated by a local nonprofit environmental organization, and the design and construction were tailored to donated materials and a largely volunteer labor force. A high-magnitude flood event (ca. 50-year recurrence interval) six months after construction had no significant impact on the newly constructed channel and revetments, but underscored the need for important detailing of the structures. The use of volunteer labor, while entailing certain benefits, complicates project planning and construction. The most general lesson learned from this project is that sponsoring agencies and clients need to be informed of the many steps and sequencing of properly constructed, complex stream rehabilitation projects as well as the high time and cost requirements for these tasks. KEY WORDS: Stream corridor restoration; Channel design; Streambank revetments
Applied River Morphology. Privately pub-lished by Wildland Hydrology Consultants, Pagosa Springs, Colorado. Sear, D. A. 1994. River restoration and geomorphology
- D L Rosgen
Rosgen, D. L. 1996. Applied River Morphology. Privately pub-lished by Wildland Hydrology Consultants, Pagosa Springs, Colorado. Sear, D. A. 1994. River restoration and geomorphology. Aquatic Conservation: Marine and Freshwater Ecosystems 4:169 – 177.
Changes in the hydraulic and morpholog-ical characteristics of a relocated stream channel
- S M Smith
Smith, S. M. 1997. Changes in the hydraulic and morpholog-ical characteristics of a relocated stream channel. MS thesis, University of Maryland, College Park.
Santa Clara County Atlas (1: 32,400-scale) Available in the Earth Sciences Library, Mc-Cone Hall, University of California, Berkeley. US ACE (US Army Corps of Engineers). 1984. Uvas Creek Levee at Gilroy, General Design Memorandum
- Thompson
- Crest
- Co
Thompson & Crest Co. 1876. Santa Clara County Atlas (1: 32,400-scale). Available in the Earth Sciences Library, Mc-Cone Hall, University of California, Berkeley. US ACE (US Army Corps of Engineers). 1984. Uvas Creek Levee at Gilroy, General Design Memorandum. US ACE Sacramento District, Sacramento, California, Report No. PA-18-04.