Floodplain Restoration Projects Research Articles

Central Valley anadromous salmonid habitat suitability criteria

Habitat suitability criteria (HSC) are a key information source used in designing habitat restoration projects. Many site-specific HSC have been developed in the Central Valley of California for various life stages of anadromous salmonids. Substantial differences between the HSC can be due to watershed characteristics and the methods used to develop the HSC. Spawning HSC generally have optimum depths of 0.3–1 m, optimum velocities of 0.3–1 m/s, and substrate sizes ranging from 25–100 mm. Optimum conditions for fry are generally shallow (less than 0.5 m) and slow (less than 0.1 m/s) with woody cover. Juvenile salmonids use deeper (0.5–1 m) and faster (up to 0.4 m/s) conditions than fry but are similar to fry in their preference for woody cover. HSC developed by the U.S. Fish and Wildlife Service on the Yuba River are recommended for evaluating habitat restoration projects on larger rivers, while HSC developed on Clear Creek are recommended for evaluating habitat restoration projects on smaller Central Valley streams. A key limitation of existing HSC is that they were only developed for in-channel conditions; fishery benefits of floodplain restoration projects are best quantified using total wetted area. Optimal HSC values are most useful in the initial design of habitat restoration projects, while flow-habitat relationships for existing versus proposed conditions can be useful in identifying needed design refinements, such as adding large woody debris.

A place-based risk appraisal model for exploring residents' attitudes toward nature-based solutions to flood risks.

Nature-based solutions (NBS) have gained popularity as a sustainable and effective way of dealing with increasing flood risks. One of the key factors that often hinders the successful implementation of NBS is residents' opposition to their implementation. In this study, we argue that the place where a hazard exists should be considered a critical contextual factor alongside flood risk appraisals and perceptions of NBS themselves. We have developed a theoretical framework-the "Place-based Risk Appraisal Model (PRAM)"-that draws on constructs inspired by theories of place and risk perception. A citizen survey (n=304) was conducted in five municipalities in Saxony-Anhalt, Germany, where dike relocation and floodplain restoration projects have been conducted along the Elbe River. Structural equation modeling was adopted to test the PRAM. Attitudes toward the projects were assessed in terms of "perceived risk-reduction effectiveness" and "supportive attitude." With regard to risk-related constructs, well-communicated information and perceived co-benefits were consistently positive factors for both perceived risk-reduction effectiveness and supportive attitude. Trust in local flood risk management was a positive and threat appraisal a negative predictor of perceived risk-reduction effectiveness affecting "supportive attitude" only through "perceived risk-reduction effectiveness." Regarding place attachment constructs, place identity was a negative predictor of a supportive attitude. The study emphasizes that risk appraisal, pluralities of place contexts to each individual, and their relations are key for determining attitudes toward NBS. Understanding these influencing factors and their interrelationships enables us to provide theory- and evidence-based recommendations for the effective realization of NBS.

Effective restoration measures in river‐floodplain ecosystems: Lessons learned from the ‘Wilde Mulde’ project

AbstractOver the last 40 years, a growing number of restoration projects have been implemented to improve the ecological conditions of highly degraded rivers and their floodplains. Despite considerable investment in these projects, information is still limited about the effectiveness and the success of such river restoration measures, mainly due to a lack of standardised and interdisciplinary assessment approaches. During the project ‘Wilde Mulde—Restoration of a dynamic riverine landscape in Central Germany’, we implemented hydromorphological restoration measures (installation of large wood, removal of rip‐rap, reconnection of a former river side‐arm) along a lowland river in Central Germany. We carried out intensive scientific monitoring of biodiversity, hydromorphology, ecosystem functions and services, as well as socio‐economic aspects. A Before/After‐Control/Impact (BACI) design was used to identify the spatial and temporal effects of the restoration measures and to distinguish them from changes caused by background variation. For this, we used a comprehensive set of indicators, including abiotic (flow velocity, diversity of riverbed topography, and flow resistance), biological (ecosystem respiration, macroinvertebrates, fish, carabids, vegetation, and birds) and socio‐economic (acceptance and public awareness) indicators as well as the ecosystem service indicator aesthetic quality of the landscape. To meet the inherent challenges of such a large‐scale field experiment, like unpredictable environmental conditions, we used an experimental approach that allowed us to demonstrate a measurable success of the implemented restoration measures. The majority of the abiotic and some of the biological and socio‐economic indicators at the restored sites approached values of a natural reference site while already deviating from values of a nonnatural reference site two years after restoration. In addition to the applied interdisciplinary approach, multiple scales of field investigations and data analyses are essential as key components for evaluating successful river and floodplain restoration projects.

The Smart Rivers approach: Spatial quality in flood protection and floodplain restoration projects based on river DNA

AbstractMany river rehabilitation projects have been implemented in the past 30 years, strengthening the natural dynamics and ecology of river systems, while reconciling the functions of flood protection, navigation, sediment extraction, and cultural identity. Still, the planning and design of floodplain projects is subject to debate on how to best follow the “natural” characteristics of specific river stretches, the “DNA of the river.” Unlike many other approaches of integrated river management, this approach entails a design strategy for spatial quality in river floodplain development projects at local and regional level, where the current discharge characteristics of the upstream river basin are taken as given. Starting point is the landscape ecological basis of the river, defining the characteristic (hydro‐morphological) processes and geomorphological/geological structures in each stretch of the river and floodplain area. An in‐depth characterization of these structures and processes helps design floodplains that can accommodate the various river management and development objectives. Often economically strong functions, like flood protection, can be partnered with weaker ones, such as ecosystem restoration. To safeguard spatial quality and sustainability in these integrated projects, the governance aspect is essential. Therefore the Smart Rivers approach addresses both substantial aspects (the “DNA of the River”) as well as procedural and governance elements (called the “Quality Relay”). The principles of the approach are applicable to project design along regulated rivers in densely populated areas all over the world.This article is categorized under: Water and Life > Conservation, Management, and Awareness

Sustainable Flood Risk and Stormwater Management in Blue‐Green Cities; an Interdisciplinary Case Study in Portland, Oregon

AbstractBlue‐Green Infrastructure (BGI) is recognized as a viable strategy to manage stormwater and flood risk, and its multifunctionality may further enrich society through the provision of multiple cobenefits that extend far beyond the hydrosphere. Portland, Oregon, is an internationally renowned leader in the implementation of BGI and showcases many best practice examples. Nonetheless, a range of interdisciplinary barriers and uncertainties continue to cloud decision making and impede wider implementation of BGI. In this paper, we synthesize research conducted by the “Clean Water for All” (CWfA) research project and demonstrate that interdisciplinary evaluation of the benefits of Portland’s BGI, focusing on green street bioswales and the East Lents Floodplain Restoration Project, is essential to address biophysical and sociopolitical barriers. Effective interdisciplinary approaches require sustained interaction and collaboration to integrate disciplinary expertise toward a common problem‐solving purpose, and strong leadership from researchers adapt at spanning disciplinary boundaries. While the disciplinary differences in methodologies were embraced in the CWfA project, and pivotal to providing evidence of the disparate benefits of multifunctional BGI, cross‐disciplinary engagement, knowledge coproduction, and data exchanges during the research process were of paramount importance to reduce the potential for fragmentation and ensure research remained integrated.

Monitoring the effectiveness of floodplain habitat restoration: A review of methods and recommendations for future monitoring

AbstractFloodplains are some of the most ecologically important and human‐impacted habitats throughout the world. Large efforts are underway in North America, Europe, Australia, and elsewhere to restore floodplain habitats, not only to increase fish and aquatic biota but to restore ecological diversity. As the scale, number, and complexity of floodplain restoration projects has increased, so has the need for rigorous monitoring and evaluation to demonstrate effectiveness and guide future floodplain restoration efforts. Moreover, technological advances in remote sensing, genetics, and fish marking have been evolving rapidly and there is need to update guidance on the best methods for monitoring physical and biological response to floodplain restoration. A comprehensive review of the restoration literature located 180 papers that specifically examined the effectiveness of various floodplain restoration techniques. The various methods that were historically and currently used to evaluate the physical (channel and floodplain morphology, sediment, flow, water quality [temperature and nutrients]) and biological (fish, invertebrates, and aquatic and riparian plants) effectiveness of floodplain restoration were reviewed and used to provide recommendations for future monitoring. For each major physical and biological monitoring method, we discuss their importance, how they have historically been used to evaluate floodplain restoration, newer methodologies, and limitations or advantages of different methodologies and approaches. We then discuss monitoring the effectiveness of small (<2 km in main channel length) and large (>2 km of main channel length) floodplain projects, with recommendations for various study designs, parameters, and monitoring methodologies.This article is categorized under: Water and Life > Conservation, Management, and Awareness Water and Life > Methods

Effects of environmental flows in a restored floodplain system on the community composition of fish, macroinvertebrates and macrophytes

Floodplains were extensively altered by anthropogenic activities, resulting in modified flow dynamics essential for maintaining diverse riverine communities. There is growing interest in restoring environmental flows by artificially modulating discharge as a potential management option in regulated rivers. In the context of a large floodplain restoration project along the upper Danube, the effects of different magnitudes of discharge on fish, macroinvertebrates and macrophytes in different habitat types of the floodplain system were studied. Community composition of fishes and macroinvertebrates changed after peak-flows of up to a 20-fold increase of mean discharge, whereas species richness and coverage of macrophytes were hardly affected. Over all habitat types, similar community response patterns were evident for macroinvertebrates, whereas in fishes, the most pronounced changes occurred in floodplain ponds that only become connected to the main channel at high flows. Community changes for fish and macroinvertebrates were mostly attributed to higher numbers of individuals (3-fold increase for fishes) rather than to changes of species richness (maximum fish species richness change <10%), however, rheophilic specialists such as Barbus barbus were much more abundant after e-flows. These findings suggest that environmental flows can have meaningful and desired conservation effects on the aquatic community composition of fishes and macroinvertebrates, depending on the magnitude of the flow and on the specific habitat type. They also stress the importance of managing dynamic flow regimes that must comprise both minimum low flows as well as flood extremes to sustain freshwater biodiversity of high conservation value.

Restoration of floodplain meadows: Effects on the re-establishment of mosses.

Vascular plants serve as target species for the evaluation of restoration success as they account for most of the plant species diversity and vegetation cover. Although bryophytes contribute considerably to the species diversity of meadows, they are rarely addressed in restoration projects. This project is a first step toward making recommendations for including mosses in alluvial floodplain restoration projects. The opportunity to assess the diversity and ecological requirements of mosses on floodplain meadows presented itself within the framework of a vegetation monitoring that took place in 2014 on meadows located along the northern Upper Rhine. In this area, large-scale meadow restoration projects have taken place since 1997 in both the functional and fossil floodplains. Other studies have shown that bryophytes are generally present in green hay used in restoration, providing inadvertent bryophyte introduction. We compared bryophyte communities in donor and restored communities and correlated these communities with environmental variables—taking into account that the mosses on the restoration sites possibly developed from green hay. This analysis provided insights as to which species of bryophytes should be included in future restoration projects, what diaspores should be used, and how they should be transferred. Data on bryophyte occurrence were gathered from old meadows, and from restoration sites. We found distinct differences in bryophyte composition (based on frequency) in restored communities in functional flood plains compared to donor communities. Generally, restoration sites are still characterized by a lower species-richness, with a significantly lower occurrence of rare and red listed species and a lower species-heterogeneity. In conclusion, our research establishes what mosses predominate in donor and restored alluvial meadows along the northern Upper River, and what microsite conditions favour particular species. This points the way to deliberate introduction of moss diaspores for more complete alluvial meadow restoration.

Habitat diversity and connectivity govern the conservation value of restored aquatic floodplain habitats

Floodplains have been strongly altered by human activities such as channelization and other river regulations. Globally, there is a growing interest in their restoration because of an increasing understanding of the ecological importance of these habitats for feeding, spawning, nursery or overwintering of aquatic species. In this study, a large floodplain restoration project of the upper Danube River was used to investigate colonization and succession patterns of fish, macroinvertebrates, macrophytes and periphyton in relation to abiotic habitat variables that can be restored through ecosystem management. Highest species diversity was detected near the contact zones of the floodplain channel to the main stem of the Danube, and in the transition zones of river sections (RS) and oxbow lakes (OS). The highest proportions of all taxa (82%) and of distinctive species (22%) were detected in RS, followed by OS (66% of all taxa, 8% distinctive species) and floodplain ponds (FP, 47% of all taxa, 5% distinctive species). The habitat types RS, OS and FP significantly differed in overall community composition and their colonization processes comprising fast colonization of current-adapted specialists in RS, and mostly generalist species in OS and FP. Our results indicate that restoration of floodplain habitats should not only consider the re-establishment of maximum connectivity, but also provide a mosaic of distinct habitat types with different degrees of connectivity and disturbance. Each habitat type in the floodplain supported a unique assemblage of species, which suggests that such habitat mosaics can facilitate exceptionally diverse ecosystems.

Lateral and longitudinal patterns of water physico-chemistry and trace metal distribution and partitioning in a large river floodplain

Floodplain water bodies provide habitat to diversified ecological communities. Floodplains are also among the most impacted aquatic ecosystems. While the link between the lateral connectivity of floodplain sites to the main channel and their plant, fish and invertebrate communities has been well established, detailed information on chemical characteristics and particularly on trace metal spatial distribution and partitioning is scarce. The aim of this study was to examine the link between the lateral connectivity and physico-chemical variables, their trace metal concentrations and partitioning as well as the upstream-downstream gradient of these parameters. In connected and disconnected water bodies of the Rhône River upstream and downstream of the city of Lyon, we measured major ions, dissolved organic carbon, trace metal concentrations (Al, Cr, Ni, Cu, Zn, Cd, Pb and U) in water, suspended particulate matter (SPM) and sediment. The results revealed a clear difference between connected and disconnected water bodies. pH, SPM, Na+, and NO3− concentrations were lower in disconnected sites while conductivity, DOC, Ca2+ and Mg2+ were higher. Conductivity and a part of the major ion concentrations increased in the downstream sections. Trace metal concentrations and partitioning varied between connected and disconnected sites. In the dissolved fraction, trace metal concentrations were higher in connected sites. In the surface sediment, concentrations were higher in disconnected sites for the majority of metals. The upstream-downstream gradient was less important than the connected-disconnected gradient. Only three metals in the dissolved fraction (Cu, Cd and Pb) showed a clear increase in downstream sections. Overall, the study shows that the functioning of floodplains produces strong spatial patterns concerning the concentrations and partitioning of trace metals. These findings improve our understanding of trace metal biogeochemistry in floodplains and have important applications for floodplain restoration projects.

A conceptual approach for evaluating the multiple benefits of urban flood management practices

This paper focuses on the spatial distribution of the dominant and relevant benefits of urban flood management based on context‐ and location‐specific evaluations. We explore the conceptual rationale and describe a detailed methodology for assessing the benefit profile, benefit intensity, and comment on benefit dependencies arising from urban flood management practices that utilise green infrastructure. A case study is described which demonstrates the application of the concepts in Portland, Oregon, USA. A Geographic Information System approach is developed to evaluate some of the multiple benefits of the East Lents Floodplain Restoration Project. Results are presented in the form of a comparative benefit profile, and a spatially distributed benefit intensity. The paper concludes with the implications of the methodology for future multiple benefit evaluation of urban drainage and flood management systems.

Why experiment with success? Opportunities and risks in applying assessment and adaptive management to the Emiquon floodplain restoration project

The Nature Conservancy’s wetland restoration at the Emiquon Preserve has been a success to date, but there are warning signs of undesirable change if left unmanaged. A water control structure built in 2016 will increase management capabilities, but periodic connection to the river, which has experienced human alterations typical of rivers in eastern North America and Europe, also introduces risks. The Conservancy’s planning process has identified (1) management targets (e.g., diverse native fish populations); (2) Key Ecological Attributes (KEAs) that maintain the targets (e.g., relatively deep over-wintering habitats for fishes); (3) measurable indicators for the KEAs (e.g., depth in winter); and (4) desirable ranges for the indicators (e.g., 10% of the aquatic area has depths of 2–3 m and dissolved oxygen levels of 4–6 mg/l). Assessments and experiments completed to date have focused on documenting the restoration, evaluating effects of the record flood of 2013, and predicting outcomes of management actions. Simulation models of hydrology, hydraulics, and vegetation response developed during the planning process allayed some concerns of stakeholders, but not all outcomes are predictable from either current theory or management experience. Therefore, each action can be considered not only as an adaptive management experiment focused on sustaining targets, but also contributing to ecological theory and restoration practice on a broader scale.

Hydromorphological conditions in eighteen restored floodplain channels of a large river: linking patterns to processes

Summary Over the past few decades, numerous floodplain restoration projects have attempted to re‐establish complex and diverse river floodplains. They often aim to restore lateral connectivity (i.e. interactions between the main river channel and floodplain channels) and rejuvenate floodplain habitats which are no longer maintained or created by fluvial processes. Nonetheless, results of these experiences in terms of hydromorphological conditions and adjustments are rarely shared. The Rhône River is a large, highly regulated system where lateral connectivity has been greatly reduced. We investigated habitat dynamics (using sedimentological indicators as proxies) in 18 floodplain channels that were restored between 1999 and 2006. Environmental data (bathymetry and grain size of surficial fine sediments) were acquired on 3–5 surveys for each channel covering 6–12 years after restoration. In addition, a pre‐restoration survey was made in 12 of the 18 channels. Using pressure sensors in the floodplain channels and rating curves in the main channel, we quantified the upstream overflow frequency and magnitude (i.e. maximum shear stress) in the channels and tested how these variables explain observed sedimentological patterns. Between‐channel diversity accounted for 81% of the sedimentological variability observed after restoration. Time‐averaged sedimentological conditions were robust and well predicted from overflow frequency and magnitude. Similarly, an indirect index of lateral connectivity used by hydrobiologists was also predictable from overflow frequency and magnitude. The remaining 19% of the sedimentological variability was attributed to temporal variation within channels and was mainly related to changes in longitudinal grain size gradient. This emphasises that grain size patterns are periodically reworked as a result of the flooding regime (backflow versus overflow) without significantly affecting average grain sizes. However, trajectories of grain size changes were stochastic and not always related to the hydrological regime. Accordingly, the partial pre‐restoration data suggest that post‐restoration sedimentological conditions were often similar to those observed before restoration, except in a few channels where major restoration works were performed. Our results quantify how changes in upstream overflow frequency and magnitude can modify physical conditions in the floodplain channels. They can be used to design habitats that are infrequent or missing at the floodplain scale. These results also suggest that changes in upstream plug morphology are a primary habitat driver. Such changes could be more frequently implemented in the Rhône and elsewhere to maximise the diversity of physical conditions in floodplains.

“Functional fit” versus “politics of scale” in the governance of floodplain retention capacity

After major floods occurred in 2003 on the Rhone River (France), the State and local authorities created a new institution at river level, in order to tackle flood issues at a supposedly more functional scale. Called Plan Rhone, this new partnership combined several policy sectors and several administrative levels, with the aim of developing the river territory and preserving floodplain retention capacity. The plan included a floodplain restoration project. However, after five years of negotiation, the project was finally abandoned. In this article, we analyze the drivers behind the failure to preserve floodplain retention capacity by focusing on scale issues, using two theoretical frameworks: the concept of “functional fit” between the scale of ecological issues and that of the institutions in charge of those issues, and the concept of “politics of scale” in which scale results from historical processes. We conclude that the scaling of an issue results from history. It legitimates a specific point of view and hampers alternative ways of seeing reality at other scales.

A floodplain restoration project on the River Rhône (France): analyzing challenges to its implementation

Floodplain restoration projects are part of sustainable flood management model. However, in practice, they are rarely implemented. We analyze the failure of a floodplain restoration project that was supposed to be implemented on the River Rhône (France). Based on the analysis of floodplain restoration projects implementation literature, we identified several constraints on the implementation of the project. In accordance with the literature, institutional factors were found to have played a critical role in the failure of the project. Other factors such as opposing representations between inhabitants and river managers were also important. Moreover, the strong involvement of the State alongside river managers proved to be a major constraint on implementation.

Carbon storage and soil organic matter stabilisation in near-natural, restored and embanked Swiss floodplains

Over recent decades, the number of floodplain restoration projects has increased worldwide. In Switzerland, several projects have been implemented to maintain or recreate ecological functions of floodplains. Despite this, little is known about the potential of floodplain soils to release and/or accumulate carbon. In alluvial soils, carbon storage is strongly influenced by fluvial dynamics, and therefore a better understanding of carbon fluxes and stocks in such settings is clearly needed.To evaluate the impact of river restoration on carbon storage in alluvial soils, we aimed to quantify and explain carbon storage and soil organic matter (SOM) stabilisation in the uppermost soil humic layer. Three floodplains were investigated showing each of them different levels of human disturbance: a near-natural section along the Rhine River, and both restored and embanked sections along the Thur River and Emme River. Carbon storage was determined by total organic carbon (TOC) stocks. SOM stabilisation was evaluated by considering the TOC content in different granulometric fractions (1000–2000μm, 500–1000μm, and 250–500μm) and the macro-aggregate formation, i.e. the abundance of water-stable aggregates (WSA) and the mean weight diameter of macro-aggregates (MWD).Our results show that the carbon storage and SOM stabilisation parameters were all related to soil properties such as clay, silt and total iron contents of the upper humic layer. Within each floodplain, carbon storage and SOM stabilisation parameters differed according to soil profile groups, thus reflecting a soil gradient evolution from bare alluvium soils to more stabilised soils and a hydric functioning (soils with hydromorphic features). In addition, river restoration showed various impacts on carbon storage and SOM stabilisation parameters depending on the floodplains, with a significant difference between embanked and restored sections for the Emme floodplain and no difference for the Thur floodplain.

Water Quality Monitoring Station Design for Remote Sites Experiencing Extreme Water Level Fluctuation

AbstractThe Nature Conservancy and the US Fish and Wildlife Service initiated a multiyear floodplain restoration project on the Mollicy Farms tract of the Upper Ouachita National Wildlife Refuge (UONWR) located in north‐east Louisiana. Large magnitude flood pulses, remote setting and other factors presented major challenges to the monitoring effort. A planning and design process resulted in the creation of a water quality monitoring station that could deploy Yellow Springs Instruments water sampling equipment in areas with large ranges in water level throughout the UONWR floodplain. Details of the station design, fabrication and diagrams are provided. Monitoring data will help measure the impact that large‐scale floodplains have on water quality once they are reconnected to river systems. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Economic value of the nutrient retention function of restored floodplain wetlands in the Elbe River basin

This paper presents an application of an indirect method, the alternative or replacement cost method to value a regulatory ecosystem service: the retention of river nutrient loads by floodplain wetlands. The paper presents a cost-minimisation model for nutrient abatement measures for the River Elbe. The model is applied to estimate the shadow price of phosphate and nitrogen nutrient retention services by restored floodplains. It is shown that the shadow price of restored floodplain area is a function of the nutrient load reduction target for the river basin. The scope of the floodplain restoration projects is shown to have a lesser impact on the estimated shadow price.In addition, this paper presents an empirical cost function for the costs of floodplain restoration measures in the Elbe Basin. In conjunction with the shadow prices, this allows for a rapid strategic assessment of the costs and benefits of 45 potential restoration sites along the Elbe trajectory. In spite of the large investment costs for dike realignments, the nutrient retention effects alone may in many cases generate sufficient benefits to generate an economic efficiency gain. Floodplain restoration may therefore, under advantageous circumstances, constitute a cost effective nutrient abatement measure. However the key thrust of the argument is that floodplain restoration projects have to be assessed as multifunctional projects, with the positive impacts on water quality being one of several benefit dimensions.

The impact of different sediment concentrations and sediment transport formulas on the simulated floodplain processes

Summary Overbank sedimentation is an important process in river floodplain ecosystems and is a component of the floodplain geomorphologic evolution. The impact of suspended sediment supply on floodplain processes is still unclear because sediment deposition can be influenced by many factors. We quantified the effect of sediment supply (suspended sediment) and transport formulas on simulated floodplain processes using a coupled two-dimensional hydrodynamic and sediment transport model (MIKE21C). Erosion and deposition depths, net sedimentation depth and total volume were quantified based on the last time step of the simulation period. The MIKE21C model was validated by comparing simulated water surface elevations to those from a one-dimensional hydrodynamic model. We compared the sediment transport model simulated suspended sediment concentrations (SSCs) to measured concentrations at a gage station. Erosion and deposition processes were simulated using five hydrograph scenarios as a function of high and low SSC and two sediment transport equations, Van Rijn (1984) and Engelund and Hansen (1967) . A specific location could be an erosional or depositional zone at different time steps of the simulation. Thus, floodplain deposition is a discontinuous function of river discharge and varies spatially and temporally over the floodplain. Large flows with high SSC were more effective for floodplain deposition than lower discharges, which dominantly caused sediment scour. Coupled hydrodynamic and sediment transport models that account for feedback processes between topography and hydraulics should be given first preference for future floodplain restoration projects. From a restoration perspective, larger flows are required for greater floodplain deposition rates and maintenance of dynamic processes. The Engelund and Hansen (1967) equation simulated higher transport rates than the Van Rijn equation (1984) . For future studies, transport equations should be selected based on the study objectives and field characteristics. The current model might be used to analyze the impact on floodplain processes from altered SSC due to Libby Dam operation.

Mercury bioaccumulation in estuarine food webs

We tested for unintended mercury contamination problems associated with estuarine floodplain restoration projects of the Louisiana coastal zone, USA. Barataria Bay and Breton Sound are two neighboring deltaic estuaries that were isolated by levees from the Mississippi River about 100 years ago. These estuaries recently have been reconnected to the nutrient-rich Mississippi River, starting major river diversion (input) flows in 1991 for Breton Sound and in 2004 for Barataria Bay. We collected > 2100 fish over five years from 20 stations in these estuaries to test two hypotheses about Hg bioaccumulation: (H1) Background Hg bioaccumulation in fish would be highest in low-salinity upper reaches of estuaries, and (H2) recent river inputs to these upper estuarine areas would increase Hg bioaccumulation in fish food webs. For H1, we surveyed fish Hg concentrations at several stations along a salinity gradient in Barataria Bay in 2003-2004, a time when this estuary lacked strong river inputs. Results showed that average Hg concentrations in fish communities were lowest (150 ng/g dry mass) in higher salinity areas and -2.4x higher (350 ng/g) in low-salinity oligohaline and freshwater upper reaches of the estuary. For H2, we tested for enhanced Hg bioaccumulation following diversion onset in both estuaries. Fish communities from Breton Sound that had long-term (> 10 years) diversion inputs had -1.7x higher average Hg contents of 610 ng/g Hg vs. 350 ng/g background values. Shorter-term diversion inputs over 2-3 years in upper Barataria Bay did not result in strong Hg enrichments or stable C isotope increases seen in Breton Sound, even though N and S stable-isotope values indicated strong river inputs in both estuaries. It may be that epiphyte communities on abundant submerged aquatic vegetation (SAV) are important hotspots for Hg cycling in these estuaries, and observed lesser development of these epiphyte communities in upper Barataria Bay during the first years of diversion inputs may account for the lessened Hg bioaccumulation in fish. A management consideration from this study is that river restoration projects may unintentionally fertilize SAV and epiphyte-based food webs, leading to higher Hg bioaccumulation in river-impacted floodplains and their food webs.