urban

=Urban streams: A holistic assessment of Earth’s most precious resource and its struggle to adapt to a developing world =

Abstract
//Rivers have long been a symbol of life, winding untamed through the landscape, providing an essential resource for human survival and diverse habitat for wildlife. Throughout history, from ancient civilizations to modern-day communities, people have not only settled but also thrived along the world's rivers. But while this encroachment of the river's surrounding floodplain has supported human populations to exponential growth, the concrete infrastructure that now dominates the urban landscape has had detrimental effects on river and stream ecosystems. As impervious surfaces replace the natural ground cover of a pre-development era, stormwater runoff has increased, which in turn increases the risk of flooding and intensifies the threat of pollutant loads carried to receiving waters. Urban river restoration practices are an increasingly popular strategy for reversing these negative // //anthropogenic // //impacts. While general restoration techniques have the potential to enhance //// in-stream habitat, improve floodplain connectivity, restore stream complexity, and stabilize stream banks, application to urban streams //// is often constrained by limited land availability and high costs. In order for these constraints to be overcome and for these techniques to be truly successful, urban stream restoration efforts ////must be combined with broader catchment ////management strategies and best management practices. Ultimately, the challenge is to establish criteria for weighing the feasibility of urban river restoration with long-term effectiveness. Only then can the improvement of degraded stream ecosystems become a reality.//

Introduction
 As the world’s population and use of resources expands at an unprecedented rate, it is critical that we develop the knowledge and tools necessary to strike a sustainable balance between natural and human systems. Even more challenging is that this rapid urbanization includes extensive development on floodplains, land that usually acts as a natural overflow area for rivers, resulting in major impacts to the physical, chemical, and ecological processes of urban streams. It is estimated that approximately 75% of the United States population resides in urban areas (Paul & Meyer, 2001). This percentage only continues to grow, along with the urban landscape's ecological footprint. As a result, the number of streams and rivers in the United States being impaired by urbanization is steadily increasing. As Figure 1 shows, the effects of urbanization are extensive in terms of both magnitude and features. Even characteristics of the development itself can impact how an urban stream is modified; for example, the age of infrastructure, type of development, and distribution and location of the development in relation to the stream (EPA, 2012). For example, with regards to the location of development, if urbanization occurs lower in a catchment, storm water flooding from that area can drain faster than from a forested area located higher in the catchment due to increased impervious surface cover. This scenario could result in decreased overall peak flow, yet increased flood duration (Paul & Meyer, 2001). Most often, however, an increase in impervious surface cover in an urbanized catchment corresponds to a higher peak flow from the increase in surface runoff.

However, concerns over urbanization of streams are not solely confined to the hydrologic, ecological, and chemical alterations that negatively impact the health of the stream itself. Instead, a growing concern has risen from the idea that these negative impacts could also pose a threat to the ecological and social services of river systems that human life depends on (Bernhardt & Palmer, 2007). Substantial investment has also been made to stabilizing the plight of the urban stream through practices aimed at reducing the threat to floodplain infrastructure.

This paper aims to: (1) present existing and developing assessment frameworks for classifying urban streams, (2) describe the various ecosystem responses to urbanization, (3) apply the urban stream concept to the middle Rio Grande, and (4) provide a quantitative evaluation of strategies for restoring, protecting, and managing urban streams.



**//Assessment of Urban Streams //**
Within the realm of water resources, there are various assessment frameworks currently available for stream classification, however these are often geared towards natural systems and neglect many of the alterations that have occurred within an urban stream ecosystem. Because urban areas only continue to grow, it is of the utmost importance to assess and expand upon the most recently developed conceptual models and assessment frameworks for the major urban impacts on stream ecosystems. Figure 2 shows one example of how the urban nonpoint source (NPS) pollution process and even best management practices, which are discussed later in the paper, can be integrated into a watershed model.



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">With a growing awareness for the importance of stream health, some assessment frameworks are starting to be developed through alteration of existing frameworks for natural streams. One such framework, developed by McBride (2001), tests the response of certain physical attributes to urbanization and compiles them into the Physical Stream Conditions Index (PSCI). These parameters, including channel size, large woody debris (LWD) abundance, bank stability, structural complexity, embeddedness, and cementation, are listed in Table 1 along with descriptions and their respective scoring criteria with 1 corresponding to a poor condition and 4 corresponding to an excellent condition. These unique parameters were chosen as indicators of an urbanized stream due to their known variance with human influence and their known response to urbanization (Carnegie, 2006; McBride, 2005). Ultimately, the PSCI suggests that urbanization effects on physical stream conditions are often influenced by spatial scale and landscape patterns.



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Building off of the framework from McBride (2001), Carnegie (2006) developed an Urban Stream Assessment Framework that evaluates the following variables: Channel Alteration, Number of culverts/road drains entering channel, Type of Energy Dissipation Mechanism, Type of Riparian Vegetation, Riparian Width, Impervious Surface Cover, Bank Stability, Sediment Deposition, Type of Urban Debris, and Stream Complexity. Through testing the framework on the heavily modified Schneider Creek located in Kitchener, Ontario, it was concluded that only Channel Alteration, Riparian Width, and Type of Riparian Vegetation could be accurately analyzed from a geomatics database, while the variables Bank Stability and Sediment Deposition were most difficult to detect (Carnegie, 2006).

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Regardless of the framework used in assessing the condition of an urban stream, it is most important to use the gained knowledge of urban stream processes to not only recommend appropriate best management practices (BMPs) and restoration goals for rehabilitation, but also to raise awareness to surrounding communities of the direct effect that urbanization has on the surrounding landscape.

//<span style="color: #1f487d; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Stream Process Response to Urbanization //
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">After a stream has been exposed to urbanization, it is important to identify the specific ecosystem responses in order to understand the relationship between processes and to develop ways in which to mitigate these changes. Impacts of river modification can be categorized into three categories: physical, chemical, and biological/ecological (Paul & Meyer, 2001). These responses have more recently become known as the symptoms associated with streams inflicted with "urban stream syndrome" (Walsh, et al., 2005). Common symptoms (i.e., responses) of a stream affected by urbanization are shown in Table 1.



<span style="color: #8ab800; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Physical <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Rapid and dramatic urbanization in a watershed results in major hydrogeological and geomorphologic changes. In particular, land cover change (e.g., deforestation and paving), most often characterized as an increase in the percent impervious surface cover, significantly influences the hydrology of the watershed by decreasing infiltration rates and therefore increasing runoff. These changes are evident in the shifting of the stream's hydrograph to having an increased magnitude of high flows combined with a decreased lag time to peak flow. In other words, the hydrograph of an urban stream is flashier than that of an unaltered stream. Not only are larger flow events occurring more frequently as indicated by the taller hydrograph peaks, but the runoff is accumulated and transported to the stream quicker, as indicated by the steep ascending and descending limbs of the hydrograph.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The increased frequency of these flashy, high flow events corresponds to increased frequency of erosive flow, causing channel incision, bank erosion, and overland flow. Figure 3 best illustrates the progression of the various stages of channel changes associated with urbanization and the resulting consequences to the stream. As depicted in the "Erosional Phase" in Figure 3, erosive flow eventually changes channel morphology as well by increasing channel width, increasing scour, and decreasing channel complexity. Bank erosion occurring in this phase increases the concentration of suspended sediments in the water. This process, known as "siltation", causes sediment to behave as a pollutant, greatly affecting both the distribution of clean water and the health of aquatic species that are sensitive to sediment loads. Suspended sediment can also serve as a mechanism for chemical pollutant transport, as will be discussed in further detail in the following section (Kibler, 1982).

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Morphologically, urbanization's strongest impact is the alteration of drainage density, calculated as the total length of all streams in a drainage basin divided by the total drainage basin area. Generally, drainage density is an indicator as to how well stream channels drain a watershed. That is, a high drainage density indicates faster runoff removal rates. In the case of artificial channels and as might be expected from the urban stream's flashier hydrograph, densities can increase from impervious surfaces such as roads and roofs transporting runoff faster than in a forested watershed. On the other hand, in the case of natural channels, drainage densities can decrease because of the filling of small streams (i.e., decreased total stream length) that often occurs for the sake of urban development (Paul & Meyer, 2001).



<span style="color: #8ab800; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Chemical
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Runoff from urban areas flows directly into nearby streams, without treatment, carrying varying amounts and types of chemical pollutants. This increased load of pollutants, at any level of concentration, poses a serious threat to water-quality and therefore the delicate balance maintained by such a diverse ecosystem within the stream. In recognition of the dangers of water pollution to the environment and public health, Congress passed the Clean Water Act (CWA) in 1972. The law, an amended version of the Federal Water Pollution Control Act of 1948, places regulations on pollutants being discharged into waterways of the United States. The CWA emphasizes the importance of water quality standards and also includes the National Pollutant Discharge Elimination System (NPDES) program. This program regulates point source pollution (i.e., polluted water discharged from a direct source such as pipes or sewers) and requires all facilities, including industrial and municipal, to obtain a permit before discharging pollutants into nearby surface waters (Cappiella et al., 2012).

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Pollutants of interest when evaluating water quality include but are not limited to: nitrogen, dissolved solids, phosphorus, dissolved oxygen, bacteria, and metals such as lead, arsenic, silver, and zinc. (Adler, et al., 1993). Perhaps most common are nutrients like nitrogen and phosphorus, however, before addressing how to decrease the amount of pollutants being discharged into receiving streams from urban runoff, it is necessary to first identify the source of these pollutants. Generally, urban runoff pollutants originate from three primary sources: (1) impervious land surfaces, (2) catch basins, and (3) combined sewer system overflows (Kibler, 1982). While a wastewater treatment plant (WWTP) is designed to remove chemical constituents before discharging its effluent into any nearby body of water, not all plants are equipped with the expensive technology required to remove 100% off constituents such as chemicals from certain household cleaning products, agricultural pesticides, pharmaceuticals, and hormones (Liney et al., 2006). Chemicals such as these, often identified as endocrine-disrupting chemicals (EDCs) pose a serious threat to fish residing in the effluent receiving waters and have even been shown to cause kidney damage and feminizing effects in fish (Liney et al, 2006).

<span style="color: #8ab800; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Biological/Ecological
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">While urbanization greatly affects the hydrology, chemistry, and morphology of a stream system in unique ways, perhaps no greater indicator of the negative affects of urbanization exist than through the response of fish, invertebrates, and condition of the overall ecological habit. Due to the complex role of fish and invertebrates in nutrient cycling, even a small shift in water quality from a wastewater or stormwater discharge can drastically alter the ecological balance of a stream ecosystem (Kibler, 1982).

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Actions associated with urban development such as riparian clearing, channel modification, water use, and pollutant discharge greatly affect various aspects of the stream ecosystem including habitat structure, flow regime, water quality, energy sources, and biotic interactions (Konrad & Booth, 2005). As shown in Figure 4, changes to these aspects result in subsequent biological responses of lotic communities such as changes in diversity, behavior, and trophic structure. For example, shifts in the timing, rate, and source of streamflow can directly affect structure, productivity, and composition of living organisms in river ecosystems by modifying food source availability and habitat conditions (Konrad & Booth, 2005). This integrative process illustrates the strong inter-dependency that exists between hydrologic flow conditions, chemical composition, habitat structure, and biological diversity.



//**<span style="color: #1f497d; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Regional Application: Within the Context of New Mexico **//
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">In evaluating the symptoms associated with urban stream syndrome, one might recognize the Rio Grande as a prime subject for diagnosis. The Rio Grande is quite literally the lifeline of the Southwest. No longer comforted by the abundance of an aquifer, the growing city of Albuquerque must now look to its already struggling river that once dominated the desert landscape but is now dominated by concrete infrastructure. The portion of the river arguably most directly affected by urbanization is the middle Rio Grande, the stretch of river between Cochiti Dam and Elephant Butte Reservoir. In fact, the Middle Rio Grande Basin has been greatly altered by activities ranging from not just urbanization, but also timber harvesting, livestock grazing, mining, and irrigation (Finch & Tainter, 1995). Therefore, for the purpose of this paper, only the middle Rio Grande portion will be considered in approaching the urban stream concept from a localized perspective.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Restoration goals are often focused on the needs of endangered species, and projects within the middle Rio Grande are no exception. Restoration in the middle Rio Grande is most concerned with improving critical habitat for two endangered species: the Rio Grande silvery minnow (RGSM) and southwestern willow flycatcher (SWFL). For both species, this includes aquatic habitat and riparian vegetation restoration. Dams, channelization, levees, and invasive plant species like the salt cedar pose a serious threat to the regeneration of native riparian vegetation like the cottonwood and willow (Finch & Tainter, 1995).

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">In an attempt to address these issues, Rio Grande water managers have based their ecosystem management model on the Flood Pulse Concept that claims floodplain riparian production is carried and assimilated into the aquatic food web as floodwaters recede. (Turner, 2012; Junk et al., 1989). This proves that not only have the dams, levees, and bank-stabilization structures placed along the middle Rio Grande lessened the frequency and duration of over bank flooding, but this has also caused a reduction in allochthonous input to the aquatic food web (Turner, 2012).

//**<span style="color: #1f487d; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Urban Stream Restoration **//
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Urban stream restoration not only presents an opportunity for improved understanding of the physical, chemical, and ecological processes within a stream ecosystem, but also bridges the gap between the natural world and urban life by raising awareness to the impacts of human action. In order to minimize the negative anthropogenic influences of urbanization, priority needs to be placed on developing strategies for restoring, protecting, and managing urban streams. While pre-development stream conditions may never be achieved through restoration practices alone, the implementation of Low Impact Development Best Management Practices (LID-BMPs) and green infrastructure can effectively reduce urban stormwater runoff, a major consequence of hydromodification.

<span style="color: #8ab800; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Restoration
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Restoration projects can generally be characterized as either passive or active restoration. Passive restoration is a more hands-off approach, allowing the system to adapt naturally to changes, while active restoration entails more engineered methods to achieve a desired structure. Bernhardt and Palmer (2007) suggest that active in-channel manipulations, such as channel form alteration or channel structure addition, be used to achieve goals that include increasing habitat diversity, raising the water table in the riparian zone, and achieving leaf litter and woody debris inputs similar to those of non-urban streams. Whether active or passive restoration is implemented to counter the negative impacts of urbanization on streams, it is extremely important to combine short-term solutions with practices that encourage long-term sustainability.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">With regards to riparian ecosystem restoration, Finch and Tainter (1995) suggest water managers seek information on the following topics: 1) tolerance of native riparian vegetation to natural and anthropogenic disturbances, 2) regeneration of ecology, 3) effects of abiotic factors (e.g., climate, water quality, and channel geomorphology) on vegetation development and health, 4) potential ecological linkages between riparian dynamics and upslope processes, 5) responses of animal communities to historical and recent riparian changes, 6) effects of flooding and surface water-groundwater interactions on ecological processes (e.g., nutrient cycling, primary production, and decomposition), and 7) classification models to predict animal species diversity, habitat use, and population change based on riparian plant associations.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">In order to achieve management goals, certain constraints must be overcome in order to apply typical restoration techniques to urban restoration projects. For example, site selection is limited by the high expense and limited availability of urban land (Bernhardt & Palmer, 2007). Infrastructure not only limits site location but also reduces reach connectivity, which negatively impacts recruitment of stream biota dependent on upstream-downstream dispersal (Bernhardt & Palmer, 2007). To minimize these constraints, urban stream restoration goals must arise from a holistic and multi-disciplinary perspective, so that restoration needs compliment those of the overall catchment.

<span style="color: #8ab800; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">LID-BMPs
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Because urbanization is projected to increase in the future, a major area in which urban streams can be protected is in the development phase of urban structures through low impact development (LID) techniques and the implementation of a Stormwater Pollution Prevention Plan (SWPPP) during construction. Management goals in relation to construction may include: 1) restricting development in undisturbed watersheds, 2) encouraging reuse of urban areas, and 3) reducing forest clearing during development (Cappiella et al., 2012).

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The advantage of LID is its ability to be used as a retrofit technique for already existing buildings. However, Bernhardt & Palmer (2007) assert that even though manipulation of physical structures within and adjacent to stream channels is an important technique for restoring environmental conditions for stream biota, many of these techniques can only have long-term success through effective stormwater management. One method of urban stream restoration through stormwater management practices involves integration of stormwater systems into the landscape (Bernhardt & Palmer, 2007). This includes localized detention ponds that mimic natural processes in their treatment of stormwater. If placed in series as a treatment train of sand filters, constructed wetlands, or grass swales, this method can also be effective in improving water quality on a larger scale (Bernhardt & Palmer, 2007).

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Because stormwater runoff in urban areas is largely due to the high percentage of impervious cover, LID techniques should be applied to the areas that are known to increase runoff the most: parking lots, roofs, and roadways. Rushton (2001) suggests that for parking lots this may include using swales, vegetated open channels that infiltrate and direct runoff waters. For roadways, vegetated medians and pervious pavements can help absorb and in the case of vegetation, naturally filter runoff. Improvements to building infrastructure include features such as green roofs, essentially a thin-layered vegetated roof system that serves as a stormwater management tool by replicating the interception and evapotranspiration aspects of the hydrologic water cycle in a natural system (Carter & Jackson, 2007). By reducing peak runoff flow volumes, green roofing systems can also provide an economic benefit by decreasing the size of storm sewer systems designed for large storm events in urban areas (Carter & Jackson, 2007).

//**<span style="color: #1f487d; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Conclusion **//
<span style="font-family: Palatino Linotype,Book Antiqua,Palatino,serif;">Scientific understanding of urban stream channel processes is complex, yet ever evolving (Cappiella et al., 2012). While by definition, restoration implies the return of a stream to pre-development condition, this is extremely difficult to achieve in practice because of the complex interactions between the physical, chemical, and ecological responses of an urbanized stream. Even more challenging is finding ways in which to measure restoration success. Because every urban stream is subject to its own unique set of restoration needs and constraints, management goals should be determined on a stream-by-stream basis. In developing these goals it is also important to recognize that regional differences in climate, geography, and land-use patterns result in different stream responses to urban development (Cappiella et al., 2012). Ultimately, the goal of mitigating the effects of urbanization can only be achieved through a combination of efforts from scientists, engineers, city planners, and government programs.

//**<span style="color: #1f487d; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Literature Cited **//
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<span style="font-family: Palatino Linotype,Book Antiqua,Palatino,serif;">McBride, M. 2001. //Spatial effects of urbanization on physical conditions in Puget Sound Lowland streams.// Doctoral dissertation, University of Washington.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">McBride, Maeve and Derek B. Booth. 2005. Urban impacts on physical stream condition: effects of spatial scale, connectivity, and longitudinal trends. Journal of the American Water Resources Association (JAWRA) 41(3): 565-580.

<span style="background-color: #ffffff; color: #222222; font-family: Arial,sans-serif;">Rushton, B. T. 2001. Low-impact parking lot design reduces runoff and pollutant loads. //<span style="background-color: #ffffff; color: #222222; font-family: Arial,sans-serif;">Journal of Water Resources Planning and Management //<span style="background-color: #ffffff; color: #222222; font-family: Arial,sans-serif;">, //<span style="background-color: #ffffff; color: #222222; font-family: Arial,sans-serif;">127 //<span style="background-color: #ffffff; color: #222222; font-family: Arial,sans-serif;">(3), 172-179.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">“The urban stream syndrome.” EPA. Environmental Protection Agency, 31 July 2012. Web. 10 Mar. 2014. <http://www.epa.gov/caddis/ssr_urb_urb2.html>

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Turner, T.F., & M.S. Edwards. 2012. Aquatic foodweb structure of the Rio Grande assessed with stable isotopes. Freshwater Science 31: 825-834.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Walsh, C. J., Roy, A. H., Feminella, J. W., Cottingham, P. D., Groffman, P. M., & Morgan II, R. P. 2005. The urban stream syndrome: current knowledge and the search for a cure. Journal Information, 24(3).