Search

Summary Infrastructure must become more resilient as the global climate changes and also more affordable in the economic and political context of a post-COVID world. We can solve this dual challenge and drive global infrastructure investment into a more sustainable direction by taking our cues from Nature.

Globally, rising seas, coastal erosion, extended dry periods, and flooding contribute to decreased water security and increased disaster incidence. Nature-Based Solutions (NBS) are increasingly advanced as innovative responses to promote adaptation and build resilience, and they are arguably more sustainable than traditional gray infrastructure. There is a growing body of information regarding the material, social, and technological advances that constitute NBS and the ways in which nature can complement traditional built infrastructure. However, critical gaps remain. Promoting a coupled systems approach, we explore fundamental challenges, including issues of participation and equity, economic valuation, scalar mismatches, the integration of natural and built infrastructure, and governance. NBS do not entail quick solutions, and to reach their full potential NBS require a fundamental rethinking of society’s relationship with nature.

At-a-station hydraulic geometry (AHG), which describes how channel width, depth, and velocity vary with discharge at a river cross section, has long been used to study fluvial processes. For exampl...

River flows exert dominant controls on in-stream biota. Quantifying linkages between hydrology and biology is important for assessing the effects of flow alteration on ecological functions. Hydrologic models are often used to quantify these flow-ecology relationships and guide management actions. Traditional model calibration techniques typically focus on a best overall fit criterion that may not be suitable for environmental flow applications where certain elements of the flow regime exert a dominant influence on biotic composition. We present an approach for hydrologic model calibration that improves the accuracy of calculated flow metrics known to be significant drivers of ecosystem response. First, we developed regional flow-ecology relationships based on streamflow gage and benthic macroinvertebrate data from southern California to determine which streamflow metrics best explain variability in taxonomic and trait-based biotic indices. Next, we developed and calibrated a series of hydrologic models to minimize error in these important flow metrics. For our study sites, flow flashiness and low flow frequency (indicative of drying) were found to best explain biotic condition. Hydrologic models calibrated specifically to minimize errors in these flow metrics predicted macroinvertebrate indices better than models calibrated to maximize fit to the overall flow regime. This ecological-calibration approach requires some a priori knowledge of flow-ecology relationships, but it produces results that can improve assessment of the impacts of changing flow regimes on biota and guide the development of strategies to mitigate ecological degradation.

Water management and infrastructure design depend on quantifying thresholds in minimum flows. Decreasing trends in low flows have been observed at many stream gauges in the Southeast US; ho...

Excessive river erosion and sedimentation threatens critical infrastructure, degrades aquatic habitat, and impairs water quality. Tools for predicting the magnitude of erosion, sedimentation, and channel evolution processes are needed for effective mitigation and management. We present a new numerical model that simulates coupled river bed and bank erosion at the watershed scale. The model uses modified versions of Bagnold’s sediment transport equation to simulate bed erosion and aggradation, as well as a simplified Bank Stability and Toe Erosion Model (BSTEM) to simulate bank erosion processes. The model is mechanistic and intermediate complexity, accounting for the dominant channel evolution processes while limiting data requirements. We apply the model to a generic test case of channel network response following a disturbance and the results match physical understanding of channel evolution. The model was also tested on two field data sets: below Parker Dam on the lower Colorado River and the North Fork Toutle River (NFTR) which responded dramatically to the 1980 eruption of Mount St. Helens. It accurately predicts observed channel incision and bed material coarsening on the Colorado River, as well as observations for the upstream 18 km of the NFTR watershed. The model does not include algorithms for extensive lateral migration and avulsions and therefore did not perform well in the lower NFTR where the channel migrated across a wide valley bottom. REM is parsimonious and useful for simulating network scale channel change in single thread systems responding to disturbance.

An ecohydrological stream type classification was developed to improve decision making for ephemeral and intermittent streams at four military reservations in the southwestern U.S.: Fort Irwin, Yuma Proving Ground (YPG), Fort Huachuca, and Fort Bliss. Agglomerative hierarchical cluster analysis was used to classify stream reaches by ecohydrologic properties (vegetation, hydrologic, and geomorphic attributes derived using geographic information system analyses), and Classification and Regression Trees (CART) were used to determine thresholds for each variable for a predictive model. Final stream types were determined from statistical analyses, cluster validity tests, examination of mapped clusters, and site knowledge. Climate regime and geomorphology were most important for YPG and Fort Irwin where annual precipitation is low. Vegetation variables were important at Fort Bliss and hydrologic variables were important at Fort Huachuca where higher annual precipitation and a bimodal rainfall pattern occur. The classification results and input variables are spatially linked to specific stream reaches, allowing managers to identify locations with similar attributes to support management actions. These methods enable the development of a stream type classification in gauged or ungauged watersheds and for areas where intensive field data collection is not feasible.

The broad scope and definition of sustainability has perplexed assessment of water infrastructure systems, especially for the purpose of directing engineering practices when quantified criteria are desired. An input-oriented data envelopment analysis (DEA) was improved to benchmark the relative sustainability of the water infrastructure of 157 cities in China. The DEA calculates a single sustainability score using seven inputs and five outputs that represent the economic, resource and environmental dimensions of sustainability. Overall, 69 out of the 157 sampled systems obtained high sustainability scores. Eight specific efficiency indicators based on individual DEA input to output ratio were evaluated to identify the causes of performance differences. Compared to water supply systems, the performance of wastewater treatment plants has greater influence on the sustainability score of the overall system. For all systems, the sustainability scores are more sensitive to sludge production and electricity consumption than capital investment and removal efficiency of treatment processes. The DEA provides guidelines to cities for setting priorities in order to meet specific sustainability criteria. Statistical analysis indicates that the overall sustainability score primarily depends on the system scale, meteorological conditions such as air temperature and rainfall, and source water quality.

It is increasingly recognized that effective river management requires a catchment scale approach. Sediment transport processes are relevant to a number of river functions but quantifying sediment fluxes at network scales is hampered by the difficulty of measuring the variables required for most sediment transport equations (e.g. shear stress, velocity, and flow depth). We develop new bedload and total load sediment transport equations based on specific stream power. These equations use data that are relatively easy to collect or estimate throughout stream networks using remote sensing and other available data: slope, discharge, channel width, and grain size. The new equations are parsimonious yet have similar accuracy to other, more established, alternatives. We further confirm previous findings that the dimensionless critical specific stream power for incipient particle motion is generally consistent across datasets, and that the uncertainty in this parameter has only a minor impact on calculated sediment transport rates. Finally, we test the new bedload transport equation by applying it in a simple channel incision model. Our model results are in close agreement to flume observations and can predict incision rates better than a more complicated morphodynamic model. These new sediment transport equations are well suited for use at stream network scales, allowing quantification of this important process for river management applications.

The Colorado Front Range flood of September 2013 induced a diverse range of geomorphic changes along numerous stream corridors, providing an opportunity to assess responses to a large flood in a semiarid landscape. We defined six classes of geomorphic change related to peak unit stream power and valley confinement for 531 stream reaches over 226 km, spanning a gradient of channel scales and slope. Geomorphic change was generally driven by erosion of channel margins in confined reaches and by a combination of deposition and erosion in unconfined reaches. The magnitude of geomorphic change typically increased with unit stream power ( ω ), with greater responses observed in unconfined channels. Cumulative logit modeling indicated that total stream power or unit stream power, unit stream power gradient, and valley confinement are significant predictors of geomorphic response for this flood event. Based on this dataset, thresholds for geomorphic adjustment were defined. For channel slopes ω > 230 W/m 2 (16 lb/ft-s; at least 10% of the investigated sites experienced substantial channel widening) and a credible potential for avulsions, braiding, and loss of adjacent road embankments associated with ω > 480 W/m 2 (33 lb/ft-s; at least 10% of the investigated sites experienced such geomorphic change). Infrequent to numerous eroded banks were very likely with ω > 700 W/m 2 (48 lb/ft-s), with substantial channel widening or major geomorphic change shifting from credible to likely. Importantly, in reaches where there were large reductions in ω as the valley form shifted from confined to relatively unconfined, large amounts of deposition-induced, reach-scale geomorphic change occurred in some locations at relatively low ω . Additionally, alluvial channels with slopes > 3% had greater resistance to geomorphic change, likely caused by armoring by larger bed material and increased flow resistance from enhanced bedforms. Finally, we describe how these results can potentially be used by practitioners for assessing the risk of geomorphic change when evaluating current or planned conditions.

Rising sea levels and growing coastal populations are intensifying interactions at the land-sea interface. To stabilize upland and protect human developments from coastal hazards, landowners commonly emplace hard armoring structures, such as bulkheads and revetments, along estuarine shorelines. The ecological and economic consequences of shoreline armoring have garnered significant attention; however, few studies have examined the extent of hard armoring or identified drivers of hard armoring patterns at the individual landowner level across large geographical areas. This study addresses this knowledge gap by using a fine-scale census of hard armoring along the entire Georgia U.S. estuarine coastline. We develop a parsimonious statistical model that accurately predicts the probability of armoring emplacement at the parcel level based on a set of environmental and socioeconomic variables. Several interacting influences contribute to patterns of shoreline armoring; in particular, shoreline slope and the presence of armoring on a neighboring parcel are strong predictors of armoring. The model also suggests that continued sea level rise and coastal population growth could trigger future increases in armoring, emphasizing the importance of considering dynamic patterns of armoring when evaluating the potential effects of sea level rise. For example, evolving distributions of armoring should be considered in predictions of future salt marsh migration. The modeling approach developed in this study is adaptable to assessing patterns of hard armoring in other regions. With improved understanding of hard armoring distributions, sea level rise response plans can be fully informed to design more efficient scenarios for both urban development and coastal ecosystems.

Threats to public health and environmental quality from septic systems are more prevalent in areas with poorly draining soils, high water tables, or frequent flooding. Significant research gaps exist in assessing these systems’ vulnerability and evaluating factors associated with higher rates of septic systems replacement and repair. We developed a novel GIS-based framework for assessing septic system vulnerability using a database of known septic system specifications and a modified Soil Topographic Index (STI) that incorporates seasonal high groundwater elevation to assess risks posed to septic systems in coastal Georgia. We tested the hypothesis that both the modified STI and septic system specifications such as tank capacity per bedroom and drainfield type would explain most of the variance in septic system repair and replacement using classification inference tree and generalized logistic regression models. Our modeling results indicate that drainfield type (level vs. mounded) is the most significant variable (p-value < 0.001) in predicting septic systems functionality followed by septic tank capacity per bedroom (p-value < 0.01). These show the importance of septic system design regulations such as a minimum requirement for horizontal separation distance between the bottom of trenches and seasonal water table, and adequate tank capacity design. However, for septic systems with a mounded drainfield and a larger tank capacity per bedroom, the modified STI representing hydrological characteristics of septic system location is a significant predictor of a high septic system repair and replacement rate. The methodology developed in this study can have important implications for managing existing septic systems and planning for future development in coastal areas, especially in an environment of rapid climatic change.

Eutrophication of aquatic ecosystems is one of the most pressing water quality concerns in the United States and around the world. Bank erosion has been largely overlooked as a source of nutrient loading, despite field studies demonstrating that this source can account for the majority of the total phosphorus load in a watershed. Substantial effort has been made to develop mechanistic models to predict bank erosion and instability in stream systems; however, these models do not account for inherent natural variability in input values. To quantify the impacts of this omission, uncertainty and sensitivity analyses were performed on the Bank Stability and Toe Erosion Model (BSTEM), a mechanistic model developed by the US Department of Agriculture – Agricultural Research Service (USDA-ARS) that simulates both mass wasting and fluvial erosion of streambanks. Generally, bank height, soil cohesion, and plant species were found to be most influential in determining stability of clay (cohesive) banks. In addition to these three inputs, groundwater elevation, stream stage, and bank angle were also identified as important in sand (non-cohesive) banks. Slope and bank height are the dominant variables in fluvial erosion modeling, while erodibility and critical shear stress had low sensitivity indices; however, these indices do not reflect the importance of critical shear stress in determining the timing of erosion events. These results identify important variables that should be the focus of data collection efforts while also indicating which less influential variables may be set to assumed values. In addition, a probabilistic Monte-Carlo modeling approach was applied to data from a watershed-scale sediment and phosphorus loading study on the Missisquoi River, Vermont to quantify uncertainty associated with these published results. While our estimates aligned well with previous deterministic modeling results, the uncertainty associated with these predictions suggests that they should be considered order of magnitude estimates only. Copyright © 2016 John Wiley & Sons, Ltd.

Measuring precipitation in semi-arid landscapes is important for understanding the processes related to rainfall and run-off; however, measuring precipitation accurately can often be challenging especially within remote regions where precipitation instruments are scarce. Typically, rain-gauges are sparsely distributed and research comparing rain-gauge and RADAR precipitation estimates reveal that RADAR data are often misleading, especially for monsoon season convective storms. This study investigates an alternative way to map the spatial and temporal variation of precipitation inputs along ephemeral stream channels using Normalized Difference Vegetation Index (NDVI) derived from Landsat Thematic Mapper imagery. NDVI values from 26 years of pre- and post-monsoon season Landsat imagery were derived across Yuma Proving Ground (YPG), a region covering 3,367 km2 of semiarid landscapes in southwestern Arizona, USA. The change in NDVI from a pre-to post-monsoon season image along ephemeral stream channels explained 73% of the variance in annual monsoonal precipitation totals from a nearby rain-gauge. In addition, large seasonal changes in NDVI along channels were useful in determining when and where flow events have occurred.

Summary The decision to use either daily-averaged or sub-daily streamflow records has the potential to impact the calculation of sediment transport metrics and stream channel design. Using bedload and suspended load sediment transport measurements collected at 138 sites across the United States, we calculated the effective discharge, sediment yield, and half-load discharge using sediment rating curves over long time periods (median record length = 24 years) with both daily-averaged and sub-daily streamflow records. A comparison of sediment transport metrics calculated with both daily-average and sub-daily stream flow data at each site showed that daily-averaged flow data do not adequately represent the magnitude of high stream flows at hydrologically flashy sites. Daily-average stream flow data cause an underestimation of sediment transport and sediment yield (including the half-load discharge) at flashy sites. The degree of underestimation was correlated with the level of flashiness and the exponent of the sediment rating curve. No consistent relationship between the use of either daily-average or sub-daily streamflow data and the resultant effective discharge was found. When used in channel design, computed sediment transport metrics may have errors due to flow data resolution, which can propagate into design slope calculations which, if implemented, could lead to unwanted aggradation or degradation in the design channel. This analysis illustrates the importance of using sub-daily flow data in the calculation of sediment yield in urbanizing or otherwise flashy watersheds. Furthermore, this analysis provides practical charts for estimating and correcting these types of underestimation errors commonly incurred in sediment yield calculations.

(2017). Urban Floodplains: Changing Climate, Land Use, and River Channels. Regions Magazine: Vol. 306, No. 1, pp. 18-20.

The characteristics of hydroclimatic risk in the 21st Century are rapidly changing. Increases in extreme weather events and population densities alter exposure to floods and droughts. Water infrastructure is unable to keep pace and deterministic models can mislead. Yet, predominant strategies for managing risk continue to follow historical precedent, striving to tame nature's outbursts and mitigate disasters through conventional engineering structures. In this Viewpoint article, scholars from three disciplines address underlying limitations in contemporary risk management, each of which is rooted in the concept of hubris. They argue that effective risk management must extend beyond hubris-thinking to an approach based on humility. Extending from the three types of limitations—described as Disconnect from Nature, Engineers of a Fixed Nature. and Modelers of Nature— a collective and synthetic consideration provides insights into potential pathways forward for both science and practice. More satisfactory strategies for managing hydroclimatic risk will require a shift from a hubris-based paradigm to a more humility-based approach.

Urbanization alters the delivery of water and sediment to receiving streams, often leading to channel erosion and enlargement, which increases loading of sediment and nutrients, degrades habitat, and harms sensitive biota. Stormwater control measures (SCMs) are constructed in an attempt to mitigate some of these effects. In addition, stream restoration practices such as bank stabilization are increasingly promoted as a means of improving water quality by reducing downstream sediment and pollutant loading. Each unique combination of SCMs and stream restoration practices results in a novel hydrologic regime and set of geomorphic characteristics that interact to determine stream condition, but in practice, implementation is rarely coordinated due to funding and other constraints. In this study, we examine links between watershed-scale implementation of SCMs and stream restoration in Big Dry Creek, a suburban watershed in the Front Range of northern Colorado. We combine continuous hydrologic model simulations of watershed-scale response to SCM design scenarios with channel evolution modeling to examine interactions between stormwater management and stream restoration strategies for reducing loading of sediment and adsorbed phosphorus from channel erosion. Modeling results indicate that integrated design of SCMs and stream restoration interventions can result in synergistic reductions in pollutant loading. Not only do piecemeal and disunited approaches to stormwater management and stream restoration miss these synergistic benefits, they make restoration projects more prone to failure, wasting valuable resources for pollutant reduction. We conclude with a set of recommendations for integrated planning of SCMs and stream restoration to simultaneously achieve water quality and channel protection goals.

Rising sea levels and growing coastal populations are intensifying interactions at the land-sea interface. To stabilize upland and protect human developments and infrastructure from coastal hazards, property owners commonly emplace hard armoring structures, such as bulkheads and revetments, along the estuarine shoreline. While research regarding the ecological and economic impacts that accompany hard armoring implementation has garnered significant attention, there have been limited efforts to document the extent of hard armoring or identify drivers of hard armoring patterns. This study addresses a knowledge gap in the documentation and understanding of hard armoring patterns and their drivers at the scale of individual landowners, by assessing the distribution of hard armoring along the Georgia coastline. Using a set of environmental and socioeconomic predictor variables in coordination with a novel fine-scale census of hard armoring, we present a parsimonious statistical model that predicts the probability of hard armoring emplacement at the parcel level. Our model has a high correct classification accuracy and we find that a variety of interacting environmental and socioeconomic influences contribute to patterns of shoreline armoring; in particular, the presence or absence of armoring on a neighboring parcel has a strong association with the probability of hard armoring. Our model also suggests that continued sea level rise and coastal population growth could trigger increases in armoring implementation into the future. Thus, we underscore the importance of considering both the current and potential future distributions of hard armoring when evaluating associated impacts of sea level rise on ecological systems and in socioeconomic evaluations. For example, evolving distributions of hard armoring should be considered in predictions of salt marsh sustainability through inland migration. In addition to providing the first parcel-level census analysis of hard armoring at a scope relevant to local and regional government decision-making, this study also presents a methodology adaptable to assessing patterns of hard armoring in other study areas. With improved understanding of hard armoring distributions, SLR response plans can be fully informed to design more efficient scenarios for both urban development and coastal ecosystems.

More than a century of dam construction and water development in the western United States has led to extensive ecological alteration of rivers. Growing interest in improving river function is compelling practitioners to consider ecological restoration when managing dams and water extraction. We developed an Ecological Response Model (ERM) for the Cache la Poudre River, northern Colorado, USA, to illuminate effects of current and possible future water management and climate change. We used empirical data and modeled interactions among multiple ecosystem components to capture system-wide insights not possible with the unintegrated models commonly used in environmental assessments. The ERM results showed additional flow regime modification would further alter the structure and function of Poudre River aquatic and riparian ecosystems due to multiple and interacting stressors. Model predictions illustrated that specific peak flow magnitudes in spring and early summer are critical for substrate mobilization, dynamic channel morphology, and overbank flows, with strong subsequent effects on instream and riparian biota that varied seasonally and spatially, allowing exploration of nuanced management scenarios. Instream biological indicators benefitted from higher and more stable base flows and high peak flows, but stable base flows with low peak flows were only half as effective to increase indicators. Improving base flows while reducing peak flows, as currently proposed for the Cache la Poudre River, would further reduce ecosystem function. Modeling showed that even presently depleted annual flow volumes can achieve substantially different ecological outcomes in designed flow scenarios, while still supporting social demands. Model predictions demonstrated that implementing designed flows in a natural pattern, with attention to base and peak flows, may be needed to preserve or improve ecosystem function of the Poudre River. Improved regulatory policies would include preservation of ecosystem-level, flow-related processes and adaptive management when water development projects are considered.

Phosphorus and fine sediment pollution are primary causes of water quality degradation. Streambank erosion is a potentially significant source of fine sediment and particulate phosphorus to watersheds, but it remains difficult to quantify the magnitude of this loading. A new, easily applied, watershed scale model was used to simulate the potential for future phosphorus and sediment loading from channel erosion in two watersheds: Big Dry Creek, Colorado and Lick Creek, North Carolina. The projected magnitude of loading for phosphorus is about an order of magnitude higher in Big Dry Creek compared to Lick Creek (∼280 kg/yr and ∼50 kg/yr, respectively), while sediment loading results are similar (∼950 ton/yr). In both watersheds, model results suggest that channel erosion will not contribute a significant amount of phosphorus to the watershed (∼1–4% of historic watershed total from all pollutant sources) but will contribute a large amount of sediment (30–100% of historic watershed total). Uncertainty in these estimates is high, but quantifying confidence in model projections is important for understanding and using model results. Importantly, modeling shows no decrease in loading over the 40-year model time frame in either watershed, suggesting that the channels are not adjusting to a new stable state and erosion will continue to be a pollutant source. Lick Creek model results are sensitive to upstream sediment supply while Big Dry Creek's are not, reinforcing the importance of considering alterations to both the hydrologic and sediment regimes when analyzing potential channel changes — at least in vertically active channels. This new modeling approach is useful for estimating historic and future phosphorus and sediment loading from channel erosion, an important first step in effective management to improve water quality.

Low Impact Development (LID) is an alternative to conventional urban stormwater management practices, which aims at mitigating the impacts of urbanization on water quantity and quality. Plot and local scale studies provide evidence of LID effectiveness, however, little is known about the overall watershed scale influence of LID practices. This is particularly true in watersheds with a land cover that is more diverse than that of urban or suburban classifications alone. We address this watershed-scale gap by assessing the effects of three common LID practices (rain gardens, permeable pavement, and riparian buffers) on the hydrology of a 0.94 km2 mixed land cover watershed. We used a spatially-explicit ecohydrological model, called Visualizing Ecosystems for Land Management Assessments (VELMA), to compare changes in watershed hydrologic responses before and after the implementation of LID practices. For the LID scenarios, we examined different spatial configurations, using 25%, 50%, 75% and 100% implementation extents, to convert sidewalks into rain gardens, and parking lots and driveways into permeable pavement. We further applied 20 m and 40 m riparian buffers along streams that were adjacent to agricultural land cover. The results showed overall increases in shallow subsurface runoff and infiltration, as well as evapotranspiration, and decreases in peak flows and surface runoff across all types and configurations of LID. Among individual LID practices, rain gardens had the greatest influence on each component of the overall watershed water balance. As anticipated, the combination of LID practices at the highest implementation level resulted in the most substantial changes to the overall watershed hydrology. It is notable that all hydrological changes from the LID implementation, ranging from 0.01 to 0.06 km2 across the study watershed, were modest, which suggests a potentially limited efficacy of LID practices in mixed land cover watersheds.

Instream and floodplain wood can provide many benefits to river ecosystems, but can also create hazards for inhabitants, infrastructure, property, and recreational users in the river corridor. We propose a decision process for managing large wood, and particularly for assessing the relative benefits and hazards associated with individual wood pieces and with accumulations of wood. This process can be applied at varying levels of effort, from a relatively cursory visual assessment to more detailed numerical modeling. Decisions to retain, remove, or modify wood in a channel or on a floodplain are highly dependent on the specific context: the same piece of wood that might require removal in a highly urbanized setting may provide sufficient benefits to justify retention in a natural area or lower-risk urban setting. The proposed decision process outlined here can be used by individuals with diverse technical backgrounds and in a range of urban to natural river reaches so that opportunities for wood retention or enhancement are increased.

Evaluating and designing channel spanning structures for successful fish passage requires description of hydraulic conditions at scales meaningful to fish. We describe novel approaches combining fish movement data and hydraulic descriptions from a three-dimensional computational fluid dynamics model to examine the physical processes that limit upstream movement of trout across 3 unique in-stream structures at a whitewater park (WWP) in Lyons, Colorado. These methods provide a continuous and spatially explicit description of velocity, depth, vorticity, and turbulent kinetic energy along potential fish swimming paths in the flow field. Logistic regression analyses indicate a significant influence of velocity and depth on limiting passage success and accurately predict greater than 87% of observed fish movements. However, vorticity, turbulent kinetic energy, and a cost function do not significantly affect passage success. Unique combinations of depth and velocity at each WWP structure reflect variation in passage success. The methods described in this study provide a powerful approach to quantify hydraulic conditions at a scale meaningful to a fish and to mechanistically evaluate the effects of hydraulic structures on fish passage. The results of these analyses can be used for management and design guidance, and have implications for fishes with lesser swimming abilities.

Whitewater parks (WWPs) are increasingly popular recreational amenities, but the effects of WWPs on fish habitat and passage are poorly understood. This study investigated the use of a two-dimensional (2-D) model as compared with a three-dimensional (3-D) hydrodynamic model (FLOW-3D ® ) for assessing effects of WWPs on fish habitat. The primary aims of this study were to (1) examine the utility of 3-D modelling versus 2-D modelling in a hydraulically complex WWP and (2) compare modelled habitat quality for resident fishes with actual fish abundance and biomass generated from field sampling surveys. Two reaches of a wadeable river in Colorado were modelled: a natural reach and a reach containing a WWP. A 2-D habitat suitability analysis for juvenile and adult brown trout, juvenile and adult rainbow trout, longnose dace and longnose sucker predicted the same or higher habitat quality in the WWPs than the natural pools for all four species and for all modelled flow rates; however, results from fish sampling found significantly higher fish biomass for all four species in natural pools compared with WWP pools. All hydraulic metrics (depth, depth-averaged velocity, turbulent kinetic energy, 2-D and 3-D vorticity) had higher magnitudes in WWP pools than in natural pools. In the WWP pools, 3-D model results described the spatial distribution of flow characteristics or the magnitude of variables better than 2-D results. This supports the use of 3-D modelling for complex flows found in WWPs, but improved understanding of linkages between fish habitat quality and 3-D hydraulic descriptors is needed. Copyright © 2015 John Wiley & Sons, Ltd.

Analytical channel design tools have not advanced appreciably in the last decades, and continue to produce designs based upon a single representative discharge that may not lead to overall sediment continuity. It is beneficial for designers to know when a simplified design may be problematic and to efficiently produce alternative designs that approximate sediment balance over the entire flow regime. The Capacity/Supply Ratio (CSR) approach, an extension of the Copeland method of analytical channel design for sand channels, balances the sediment transport capacity of a design reach with the sediment supply of a stable upstream reach over the entire flow duration curve (FDC) rather than just a single discharge. Although CSR has a stronger physical basis than previous analytical channel design approaches, it has not been adopted in practice because it can be a cumbersome and time-consuming iterative analysis without the use of software. We investigate eighteen sand-bed rivers in a comparison of designs based on the CSR approach and five single-discharge metrics: the effective discharge (Qeff), the 1.5-year recurrence interval discharge (Q1.5), the bankfull discharge (Qbf), and the discharges associated with 50th (Qs50) and 75th (Qs75) percentiles of the cumulative sediment yield curve. To facilitate this analysis we developed a novel design tool using the Visual Basic for Applications (VBA) programming language in Excel® to produce stable channel slope-width combinations based on the CSR methodology for both sand- and gravel-bed streams. The CSR Stable Channel Design Tool’s (CSR Tool) code structure was based on Copeland’s method in SAM and HEC-RAS (Hydrologic Engineering Center’s River Analysis System) and was tested with a single discharge to verify outputs. The Qs50 and Qs75 single-discharge designs match the CSR output most closely, followed by the Qbf, Qeff, and Q1.5. The Qeff proved to be the most inconsistent design metric because it can be highly dependent on the binning procedure used in the effectiveness analysis. Furthermore, we found that the more rigorous physical basis of the CSR analysis is potentially most important in designing ‘labile’ channels with highly erodible substrate, high perennial flow ‘flashiness,’ low width-to-depth ratio, and high incoming sediment load. The CSR Tool provides a resource for river restoration practitioners to efficiently utilize in-depth design techniques that can promote sediment balance in dynamic fluvial systems.

Traditional approaches to water resource engineering have sought to maintain a static, optimized state of system performance in providing reliable water supplies, energy, and flood protection. However, delivery of these services has been associated with the disruption of freshwater ecosystem functioning, driving global-scale declines of biodiversity and the loss of ecosystem services. Climate change is presenting new challenges for water and ecosystem managers alike. Yet, climate change is also creating new opportunities to consider ecological resilience in the design and management of water systems. Here, we describe a set of climate-informed ecological resilience principles and associated indicators, which can support integration of ecosystem needs within water resource engineering decision-making. These have the potential to guide climate-adaptive water resource management while also provisioning broad benefits to both people and ecosystems in a shifting operating environment.

Nutrient pollution is a pervasive water quality problem. Stream restoration has been proposed as a novel approach to reduce loading and increase nutrient processing within streams. We summarize evidence from the literature on the efficacy of stream restoration for reducing nutrient loading and increasing nutrient removal in stream ecosystems. We also analyze published data on streambank phosphorus concentrations and riparian and stream denitrification rates to improve understanding of the potential benefits of stream restoration for phosphorus retention and nitrogen removal. Finally, we discuss the role of stream restoration in nutrient management and provide recommendations for practice and future research.

The river management and restoration community has devoted much effort to predicting the bankfull discharge, Qbf, and associated channel geometry at Qbf for the purposes of channel study, classification, and design. Four types Qbf prediction methods predominate: (1) direct estimation based on field indicators of bankfull stage, (2) downstream hydraulic geometry equations, (3) a flood peak discharge with a specified return interval based on the annual maximum flood series (e.g., the 1.5- to 2-year flood) or regional flood peak statistical relations, and (4) process-based approaches that incorporate the magnitude and frequency of sediment transport such as the most effective discharge Qeff. Process-based Qbf predictors are calculated using sediment transport data from 95 gauged sites across the United States including coarse, bed load–dominated channels and fine, suspended load–dominated channels with drainage areas ranging from 6 to 1.4×105 km2. These values are compared with observations of Qbf m...

Relationships between changes in streamflow and changes in biological condition are important considerations for water resources management decisions. The Ecological Limits of Hydrologic Alteration (ELOHA) framework offers a way to protect stream health by managing flow conditions. We demonstrate application of a regionally derived ELOHA framework to inform stakeholder defined management challenges in the San Diego River Watershed in southern California, USA—a large semi-urbanized watershed that is undergoing land use changes. Using previously defined flow-ecology relationships based on benthic invertebrate community composition, we: 1) assess how future land use changes will affect flow conditions and impact biological endpoints in the watershed; 2) demonstrate how flow–ecology relationships can be used to prioritize regions of the watershed into various flow management classes that can inform future planning decisions; and 3) evaluate how two future management decisions (specifically, modification of reservoir operations and implementation of low impact development strategies to reduce stormwater runoff) will affect in-stream flow conditions in the watershed. Our study shows a successful transition of regionally derived flow targets to inform local decisions at a catchment or watershed scale, thereby avoiding the need to develop local flow–ecology relationships for every stream of interest (as would be required by other instream flow methods). Case studies are a critical bridge between the science of flow-ecology and real-world implementation and this work illuminates an example of how to navigate technical and management challenges and provide road maps for broader applications by including local stakeholders in defining, interpreting, and implementing products of flow-ecology analyses

This study explores the current state of knowledge with respect to the effects of wet weather flows from urban areas on the physical character of aquatic habitat. It identifies knowledge gaps with respect to our ability to define the cause-effect relationships, examines the comprehensiveness of the data used in support of the published literature in the subject area, and makes a qualitative determination of the usefulness of those data for further analysis to increase our knowledge in the subject area. Finally, it recommends further research studies that will increase our knowledge in the subject area, with emphasis on pilot-scale projects that can be used to develop practical protocols for preventing or mitigating the effects. Major findings and conclusions are: 1) we lack a solid conceptual framework for predicting the impact of large-scale watershed modifications and wet weather flows on ecological processes that influence stream communities; 2) there is a need for longer-term monitoring; 3) there is no widely accepted system for quantifying geomorphic instability and degradation of physical habitat; 4) there is a need for process-based stream classification; 5) specific links between urbanization characteristics and stream degradation are lacking; 6) there is a need for urban best management practice (BMP) assessment standards; and 7) developing a multi-scale understanding of habitat potential in human-dominated watersheds is needed. The report recommends a research program that first and foremost, includes comprehensive, long-term monitoring augmented with mathematical modeling of the linkages between development style/drainage system design, flow regime, and multi-scale changes in physical habitat and biotic response. Improved diagnosis and predictive understanding of future change require multifaceted, multiscale, and multidisciplinary studies based on a firm understanding of the history and processes operating in a drainage basin. Detailed long-term analyses of the influence of hydrologic regime and channel morphology on differences between communities in recruitment, immigration/emigration, mortality, and age structure are also needed. Finally, future research should directly examine tradeoffs between: 1) flood mitigation versus channel roughness, habitat heterogeneity, debris inputs, and riparian protection; 2) chemical water quality improvement through extended detention versus geomorphically-based flow regime controls; and, 3) rehabilitation of aquatic habitat using static features versus allowing the potential for dynamic adjustments in channel form and habitat structure. It is extremely important that the research be pragmatic, and focus on developing pilot/demonstration studies that will lead to design guidance that municipalities can use to design new systems, or improve existing systems, that will protect not only the safety and welfare of the citizenry that it serves, but also the aquatic ecosystems in the streams that receive the wet weather discharges from these urbanized sites. This title belongs to WERF Research Report Series ISBN: 9781843396482 (Print) ISBN: 9781780403243 (eBook)