Environmental tradeoffs of urban stream restoration in Fairfax County, Virginia

First posted May 18, 2023 For additional information, contact: Director, Virginia and West Virginia Water Science CenterU.S. Geological Survey1730 East Parham RoadRichmond, VA 23228Contact Pubs Warehouse In 2007, the U.S. Geological Survey partnered with Fairfax County, Virginia, to establish a long-term water-resources monitoring program to evaluate the hydrology, water quality, and ecology of Fairfax County streams and the watershed-scale effects of management practices. Fairfax County uses a variety of management practices, policies, and programs to protect and restore its water resources, but the effects of such strategies are not well understood. This report used streamflow, water-quality, and ecological monitoring data collected from 20 Fairfax County watersheds from 2007 through 2018 to assess the effects of management practices, landscape factors, and climatic conditions on observed nutrient, sediment, salinity, and benthic-macroinvertebrate community responses.Urbanization, climatic variability, and an increase in management practices occurred within Fairfax County during the study period. Impervious cover, housing units, wastewater infrastructure, and (or) stormwater infrastructure increased in most study watersheds. Climatic conditions varied among study years; countywide estimates of average-annual air temperature differed by about 3 degrees Celsius, and total precipitation ranged from about 34 to 63 inches per year. The effects of the management practices, implemented to reduce nitrogen, phosphorus, and (or) sediment loads, are considered in this study. These management practices primarily consist of stormwater retrofits and stream restorations; however, stream restorations account for most of the financial investment and expected load reductions. Management practices were implemented in half of the study watersheds, and most practices were installed and reductions credited late in the study period.Changes in hydrologic response during storm events were evaluated over the study period because many management practices that were implemented were designed to achieve nutrient and sediment reductions by slowing or intercepting runoff. The average number and length of storm events was mostly unchanged throughout the monitoring network. Four watersheds with 10 years of streamflow data showed a mixture of trends in stormflow peak, volume, and rate-of-change. Event-mean nutrient and sediment concentrations from these watersheds were evaluated during storm events and generally showed increases in total phosphorus (TP) and suspended sediment and reductions or no changes in total nitrogen (TN).Landscape inputs of nitrogen and phosphorus and the percentage of inputs delivered to streams were estimated for the study watersheds. Estimated phosphorus from fertilizer and nitrogen from atmospheric deposition represented large nutrient inputs in most watersheds; amounts of other nonpoint sources varied based on land use. Estimated nitrogen inputs declined throughout Fairfax County and in most study watersheds from 2008 through 2018; in comparison, phosphorus input changes were relatively small. Most nonpoint-nutrient inputs were retained on the landscape and did not reach streams, with slightly more nitrogen retention than phosphorus, on average. Retention rates were lower for years with more precipitation and streamflow. After adjusting for streamflow, TN and TP loads were generally higher for years with more nutrient inputs. Calculated as a function of flow-adjusted loads, TP retention declined at most stations from 2009 through 2018, in comparison, TN retention was relatively unchanged.Landscape and climatic conditions affected spatial differences and changes in Fairfax County stream conditions from 2009 through 2018. TN concentrations were higher and increases over time were larger in watersheds with elevated septic-system density. TP concentrations were higher in watersheds with more turfgrass; concentrations were lower, but had larger increases over time, in watersheds with deeper soils. Suspended-sediment concentrations were higher in watersheds with greater stream densities. Specific conductance was higher in watersheds with more developed land use and shallower soils. Benthic-macroinvertebrate index of biotic integrity (IBI) scores were lower in watersheds with high road density and had larger increases over time in bigger, more developed watersheds. Annual variability in TN and TP concentrations and benthic-macroinvertebrate IBI scores was affected by precipitation; annual variability in suspended sediment concentrations and specific conductance was affected by air temperature.After accounting for influences from landscape and climatic conditions, expected management-practice effects were not consistently observed in monitored stream responses. These effects were assessed by comparing expected management-practice load reductions with the timing, direction, and magnitude of changes in storm-event hydrology, nutrient and sediment loads, median-annual water-quality conditions, and benthic-macroinvertebrate IBI scores. An important consideration for future investigations of management-practice effects is how to control for water-quality and ecological variability caused by geologic properties, the urban environment, precipitation, and (or) air temperature. The interpretation of management-practice effects in this report was likely influenced by a combination of factors, including (1) the amount, timing, and location of management-practice implementation; (2) unmeasured landscape and climatic factors; (3) uncertain management-practice expectations; (4) hydrologic variability; and (5) analytical assumptions. Through continued data-collection efforts, particularly after management practices have been completed, many of these factors may become less influential in the future.

Abstract: Rapid population growth and land use changes have severely degraded streams across the United States. In response, there has been a surge in the number of stream restoration projects, including stream restoration for mitigation purposes. Currently, most projects do not include evaluation and monitoring, which are critical in the success of stream restoration projects. The goal of this study is to review the current status of assessment methodologies and restoration approaches for streams in Virginia, with the aim of assisting the res-toration community in making sound decisions. As part of the study, stream restoration projects data from a project in Fairfax County, Virginia was assessed. This review revealed that the stream assessment methodologies currently applied to restoration are visually-based and do not include biological data collection and/or a method to incorporate watershed information. It was found from the case study that out of the twenty nine restoration projects that had occurred between 1995 and 2003 in Fairfax County, nineteen projects reported bank stabilization as a goal or the only goal, indicating an emphasis on a single physical component rather than on the overall ecological integrity of streams. It also turned out that only seven projects conducted any level of monitoring as part of the restoration, confirming the lack of evaluation and monitoring. However, Fairfax County has recently improved its stream restoration practices by developing and incorporating watershed management plans. This now provides one of the better cases that might be looked upon by stakeholders when planning future stream restoration projects.

Costs of Meeting Water Quality Goals under Climate Change in Urbanizing Watersheds: The Case of Difficult Run, Virginia

Reducing nutrient loadings in urban areas is important for water quality improvement programs in many watersheds. Urban nutrient loadings are expected to increase and become more variable under climate change (CC). In this study, a water quality simulation model (SWMM), land cover data layers, and mathematical programming models were used to compare costs of abating nutrient loads under CC in the Difficult Run Watershed located in Fairfax County, Virginia. Predicted costs of abating mean total nitrogen (TN), total phosphorus (TP), and total suspended sediment (TSS) loadings under current climate conditions were compared with those for CC under certainty with a Cost Minimization Model and under uncertainty with a Safety First Model. Total nitrogen loadings abatement had the highest cost followed by TP and TSS abatement in that order. Costs of controlling TP and TSS increased with CC, whereas there was little change in TN control costs. Introducing uncertainty of loadings caused control costs to increase substantially for all three pollutants. The preferred pollutant control strategy was urban stream restoration. Policy makers seeking to meet water quality goals over a multiyear horizon should consider front-loading supplemental best management practices (BMPs) to offset the changes in nutrient loadings predicted for CC.

Restoration of hydrologically, morphologically and ecologically degraded urban streams is an essential activity in any conurbation that aspires to becoming a Blue–Green City. Appropriately restored urban streams constitute a valuable form of multifunctional blue–green infrastructure capable of generating a raft of economic, social and ecosystem benefits. In addition, they also create flood ways that can be used to transfer stormwater sustainably and interoperably with other urban systems, and greenways that facilitate the safe movement of people (walking, running or bicycling) and wildlife (swimming, burrowing, crawling, running or flying), even in densely developed city centres and disadvantaged neighbourhoods. In this chapter we frame urban streams as natural capital assets, and briefly review the types of urban restoration projects undertaken to date in the UK with a view to conserving those assets. Methodologically, urban stream restoration has lagged behind rural restoration, but frameworks for urban stream assessment, prioritisation and restoration design are becoming available. We review two such frameworks, one developed in Europe and the other in North America. However, the main contribution of this chapter lies in lessons learned from three case examples (two from England and one from the USA). These examples have been selected to highlight the importance of adopting a holistic approach that re-naturalises urban streams within the constraints imposed by the urban and societal contexts, considers the values and preferences of beneficiary communities, and levers resources through partnership working between different stakeholder agencies. The case studies demonstrate how barriers to innovative urban stream restoration can be overcome, allowing recreation of streams that have high functionality, but low maintenance requirements. These case studies should embolden flood and water management practitioners in challenging those who insist that ‘blue–green approaches would be good, but they can’t be applied here’. As the case studies make clear, in a future characterised by climate change and increasing disparities between the rich and the poor, blue–green approaches to urban stream restoration that are sustainable, resilient and socially just can, and should, be applied everywhere.

Abstract. An improved understanding of sources and timing of water, carbon, and nutrient fluxes associated with urban infrastructure and stream restoration is critical for guiding effective watershed management globally. We investigated how sources, fluxes, and flowpaths of water, carbon (C), nitrogen (N), and phosphorus (P) shift in response to differences in urban stream restoration and sewer infrastructure. We compared an urban restored stream with two urban degraded streams draining varying levels of urban development and one stream with upland stormwater management systems over a 3-year period. We found that there was significantly decreased peak discharge in response to precipitation events following stream restoration. Similarly, we found that the restored stream showed significantly lower (p < 0.05) monthly peak runoff (9.4 ± 1.0 mm day−1) compared with two urban degraded streams (ranging from 44.9 ± 4.5 to 55.4 ± 5.8 mm day−1) draining higher impervious surface cover, and the stream-draining stormwater management systems and less impervious surface cover in its watershed (13.2 ± 1.9 mm day−1). The restored stream exported most carbon, nitrogen, and phosphorus at relatively lower streamflow than the two more urban catchments, which exported most carbon and nutrients at higher streamflow. Annual exports of total carbon (6.6 ± 0.5 kg ha−1 yr−1), total nitrogen (4.5 ± 0.3 kg ha−1 yr−1), and total phosphorus (161 ± 15 kg ha−1 yr−1) were significantly lower in the restored stream compared to both urban degraded streams (p < 0.05), but statistically similar to the stream draining stormwater management systems, for N exports. However, nitrate isotope data suggested that 55 ± 1 % of the nitrate in the urban restored stream was derived from leaky sanitary sewers (during baseflow), statistically similar to the urban degraded streams. These isotopic results as well as additional tracers, including fluoride (added to drinking water) and iodide (contained in dietary salt), suggested that groundwater contamination was a major source of urban nutrient fluxes, which has been less considered compared to upland sources. Overall, leaking sewer pipes are a problem globally and our results suggest that combining stream restoration with restoration of aging sewer pipes can be critical to more effectively minimizing urban nonpoint nutrient sources. The sources, fluxes, and flowpaths of groundwater should be prioritized in management efforts to improve stream restoration by locating hydrologic hot spots where stream restoration is most likely to succeed.

In recent years, local governments have invested heavily in management practices to reduce nutrient and sediment loads. These practices provide localities with nutrient and sediment regulatory reduction credits; however, their effects on water quality are poorly understood at the watershed scale. Long-term watershed-scale monitoring is essential for assessing progress toward water-quality goals, yet it has historically been lacking in urban watersheds. Since 2007, Fairfax County, Virginia, has partnered with the US Geological Survey to monitor and evaluate water-quality conditions in 20 small urban streams. This study assessed nutrient and suspended sediment loads, trends in concentration, and trends in load. Trends in load are affected by streamflow-induced variability that must be removed through a process called “flow-normalization;” however, existing methods have neither been applied to small urban watersheds nor to loads computed on a sub-daily timestep. In this study, four such methods also were assessed, and an adaptation of the weighted regressions on time, discharge, and season approach was found to be most effective. Loads, concentrations, and trends in load were spatially and temporally variable. Differences were attributed to physical watershed features such as geology, soils, and channel geomorphology, as well as urban sources such as turfgrass fertilization and septic infrastructure. Most notably, flow-normalized suspended sediment, nitrogen, and phosphorus loads decreased in two watersheds with completed stream restorations and increased in those with few implemented practices.

The continually increasing global population residing in urban landscapes impacts numerous ecosystem functions and services provided by urban streams. Urban stream restoration is often employed to offset these impacts and conserve or enhance the various functions and services these streams provide. Despite the assumption that "if you build it, [the function] will come," current understanding of the effects of urban stream restoration on stream ecosystem functions are based on short term studies that may not capture variation in restoration effectiveness over time. We quantified the impact of stream restoration on nutrient and energy dynamics of urban streams by studying 10 urban stream reaches (five restored, five unrestored) in the Baltimore, Maryland, USA, region over a two-year period. We measured gross primary production (GPP) and ecosystem respiration (ER) at the whole-stream scale continuously throughout the study and nitrate (NO3 - -N) spiraling rates seasonally (spring, summer, autumn) across all reaches. There was no significant restoration effect on NO3 - -N spiraling across reaches. However, there was a significant canopy cover effect on NO3 - -N spiraling, and directly comparing paired sets of unrestored-restored reaches showed that restoration does affect NO3 - -N spiraling after accounting for other environmental variation. Furthermore, there was a change in GPP : ER seasonality, with restored and open-canopied reaches exhibiting higher GPP : ER during summer. The restoration effect, though, appears contingent upon altered canopy cover, which is likely to be a temporary effect of restoration and is a driver of multiple ecosystem services, e.g., habitat, riparian nutrient processing. Our results suggest that decision-making about stream restoration, including evaluations of nutrient benefits, clearly needs to consider spatial and temporal dynamics of canopy cover and trade-offs among multiple ecosystem services.

Assuring healthy streams in the urban environment is a major goal for restoration scientists, urban planners, and city practitioners around the globe. In South Korea, many urban stream restoration efforts are designed to provide safe water to society and enhance ecological functions. We examined the extent to which the individual interests and different values of multiple stakeholders were considered in previous decision-making in two urban stream restoration projects. The relevant data on stream restoration were collected through the nominal group technique (NGT) and the analytic hierarchy process (AHP) for the two stream cases of a populated inland area and a coastal region in South Korea. The AHP results provide information about the comparative weights of the values of ecological restoration (priority score: 0.487), social restoration (priority score: 0.231), and landscape revitalization (priority score: 0.279) of the Ahn-Yang stream and ecological restoration (priority score: 0.527), social restoration (priority score: 0.182), and landscape revitalization (priority score: 0.290) of the Sahn-Jee stream. The stakeholders of the populated metropolitan area had a relatively high awareness of their role in environmental restoration, thus it was natural for them to place a high value on social restoration.

Stream and river restoration practices have become common in many parts of the world. We ask the question whether such restorations improve freshwater biotic assemblages or functions over time, and if not, can general reasons be identified for such outcomes. We conducted a literature survey and review of studies in which different types of stream restorations were conducted and outcomes reported. These restoration types included culvert restoration; acid mine restoration or industrial pollutant restoration; urban stream restoration; dam removal, changes in dam operation, or fish passage structures; instream habitat modification; riparian restoration or woody material addition; channel restoration and multiple restorations. The streams ranged from headwater streams to large rivers, and the regions included North America, Europe, Australia and New Zealand, and a small number of sites in Asia and Africa. In this part of the review, we describe the methods used for the review and present reviews for the first three types of stream restorations. For culvert restorations, the small sample size and variable study design and biotic responses limited generalizing about temporal and spatial scale effects for that restoration type. The complex and often lengthy time to restore streams from acid mine drainage and industrial pollutants often resulted in positive biotic responses, but restored sites had reduced responses compared to reference sites. Most urban stream restorations had minimal or mixed improvements in biotic responses, with one mismatch in spatial scale evidenced by hydraulic structures used in a restoration unable to withstand peak discharge.

Urban stream restoration continues to be used as an ecological management tool, despite uncertainty about the long‐term sustainability and resilience of restored systems. Evaluations of restoration success often focus on specific instream indicators, with limited attention to the wider basin or parallel hydrologic and geomorphic process. A comprehensive understanding of urban stream restoration progress is particularly important for comparisons with nonurban sites as urban streams can provide substantial secondary benefits to urban residents. Here, we utilize a wide range of indicators to retrospectively examine the restoration of Nine Mile Run, a multi‐million dollar stream restoration project in eastern Pittsburgh (Pennsylvania, USA). Examination of available continuous hydrological data illustrates the high cost of failures to incorporate the data into planning and adaptive management. For example, persistent extreme flows drive geomorphic degradation threatening to reverse hydrologic connections created by the restoration and impact the improved instream biotic communities. In addition, human activities associated with restoration efforts suggest a positive feedback as the stream restoration has focused effort on the basin beyond the reach. Ultimately, urban stream restoration remains a potentially useful management tool, but continued improvements in post‐project assessment should include examination of a wider range of indicators.

Proceedings of an international symposium on the restoration and protection of streams, held in conjunction with the 2003 World Water and Environmental Resources Congress in Philadelphia, Pennsylvania, June 23-26, 2003. Sponsored by the Urban Streams Technical Committee of the Urban Water Resources Research Council and the Urban Stream Restoration Technical Committee of the Watershed Council of the Environmental and Water Resources Institute of ASCE. This collection contains 48 papers promoting interdisciplinary scientific and ecological approaches for the planning and design of stream restoration projects with a special emphasis on urban environments. The health of streams can deteriorate as a result of channel degradation, channel instability, loss of habitat, loss of infrastructure, and poor water quality. Communities and watershed managers need scientifically, ecologically, and economically sound approaches to mitigate the impacts of urbanization on city watersheds. Topics include: legislative and regulatory setting: federal, state and local programs; master planning: urban drainage and stream protection; case studies: planning projects, successful programs and examples, management tools, decision making, and monitoring programs; defining the desired stream condition: physical, chemical and biological; monetary and value-based tools for assessment, analysis and design: physical, chemical and biological; interdisciplinary integration management tools: stream buffers and low impact design; design criteria for urban stream restoration; monitoring: how to measure performance; and research needs: institutional and funding needs.

Kenney, Melissa A., Peter R. Wilcock, Benjamin F. Hobbs, Nicholas E. Flores, and Daniela C. Martínez, 2012. Is Urban Stream Restoration Worth It? Journal of the American Water Resources Association (JAWRA) 48(3): 603‐615. DOI: 10.1111/j.1752‐1688.2011.00635.xAbstract: Public investment in urban stream restoration is growing, yet little has been done to quantify whether its benefits outweigh its cost. The most common drivers of urban stream projects are water quality improvement and infrastructure protection, although recreational and aesthetic benefits are often important community goals. We use standard economic methods to show that these contributions of restoration can be quantified and compared to costs. The approach is demonstrated with a case study in Baltimore, Maryland, a city with a legal mandate to reduce its pollutant load. Typical urban stream restoration costs of US$500‐1,200 per foot are larger than the cost of the least expensive alternatives for management of nitrogen loads from stormwater (here, detention ponds, equivalent to $30‐120 per foot of restored stream) and for protecting infrastructure (rip‐rap armoring of streambanks, at $0‐120 per foot). However, the higher costs of stream restoration can in some cases be justified by its aesthetic and recreational benefits, valued using a contingent valuation survey at $560‐1,100 per foot. We do not intend to provide a definitive answer regarding the worth of stream restoration, but demonstrate that questions of worth can be asked and answered. Broader application of economic analysis would provide a defensible basis for understanding restoration benefits and for making restoration decisions.

The term “urban stream syndrome” describes the consistently observed ecological degradation of streams draining urban land. This paper reviews recent literature to describe symptoms of the syndrome, explores mechanisms driving the syndrome, and identifies appropriate goals and methods for ecological restoration of urban streams. Symptoms of the urban stream syndrome include a flashier hydrograph, elevated concentrations of nutrients and contaminants, altered channel morphology, and reduced biotic richness, with increased dominance of tolerant species. More research is needed before generalizations can be made about urban effects on stream ecosystem processes, but reduced nutrient uptake has been consistently reported. The mechanisms driving the syndrome are complex and interactive, but most impacts can be ascribed to a few major large-scale sources, primarily urban stormwater runoff delivered to streams by hydraulically efficient drainage systems. Other stressors, such as combined or sanitary sewer overflows, wastewater treatment plant effluents, and legacy pollutants (long-lived pollutants from earlier land uses) can obscure the effects of stormwater runoff. Most research on urban impacts to streams has concentrated on correlations between instream ecological metrics and total catchment imperviousness. Recent research shows that some of the variance in such relationships can be explained by the distance between the stream reach and urban land, or by the hydraulic efficiency of stormwater drainage. The mechanisms behind such patterns require experimentation at the catchment scale to identify the best management approaches to conservation and restoration of streams in urban catchments. Remediation of stormwater impacts is most likely to be achieved through widespread application of innovative approaches to drainage design. Because humans dominate urban ecosystems, research on urban stream ecology will require a broadening of stream ecological research to integrate with social, behavioral, and economic research.

Urban stream restoration in Korea: Design considerations and residents’ willingness to pay