The insistent sound of a beating heart throbs through the labyrinthine Monterey Bay Aquarium in northern California as a crowd watches a diver swim through a swaying forest of kelp in a two-story glass tank. The distant heartbeat swells louder and faster, rushing to a wild crescendo. Suddenly the drumming stops and people drift away to look at other exhibits. But in a little while, the heartbeat begins again and builds to the same urgent height.The sound turns out to be the accompaniment for a population map of Earth on which a pinpoint of light sparks up for every million people who appear on the planet. Centuries tick by, and before the new millennium is 50 years old, the United States has become a solid blaze of light. This simple fact is intended to show that ocean ecosystems cannot sustain the harvest demands that will be made by a burgeoning population. But viewers go home having understood a deeper message: Growth in one’s own community is not just a neighborhood phenomenon but part of a global trend from which there will be no escape.The Specter of Increasing ImperviousnessA baby born in the US today will require about an acre of impervious surfaces, according to David Pimentel of Cornell University Extension Service. This 209- x 209-ft. area, about as large as a small city block, includes that baby’s portion of streets, parking lots, stores, services, airports, driveways, workplace, residence, yards, and lawns.Many of us already experience this increasing urbanization through the mounting frustration we experience with rush-hour traffic or through the realization that where we live is sprawling into what used to be the countryside. But not many of us have prowled the downstream end of stormwater discharge pipes to see how urbanization has affected the streams into which the city’s impervious surfaces drain.It can be a harrowing field trip; for in addition to the trash that somehow finds its way into urban drainages, we are likely to be confronted with a channel, streambanks, and riparian margins all out of whack in comparison to undisturbed streams in the area. The channel is likely to be scoured by the sudden and repeated rush of water delivered to it from rooftops, parking lots, and streets by pipes, curbs, and ditches after every rainfall or meltwater event.How Urbanization Affects the Hydrology of Streams and Wetlands
Johnson Creek, Portland, OR, 1934Under ordinary conditions, wetlands and riparian areas have the capacity to store floodwater, thus serving to desynchronize flood events, diminish the erosive power of flood flows, and filter sediments. Slow release of water stored in wetlands recharges groundwater, which feeds streams during dry periods-an essential function in regulating the timing and quantity of runoff and in sustaining aquatic life. Corridors along hydrogeomorphically connected wetlands provide a means for wildlife to move through and between ecosystems. High groundwater also supports a community of plants that is quite different from the vegetation of the better-drained hillslopes above; thus, wetlands support a surprising array of wildlife. The roots of wetland and riparian plants help to stabilize streambanks and shorelines, and this vegetation also takes up nutrients and contaminants in stormwater.Wetland FunctionsPeople, Fish, and Wildlife. Recreation . Vegetation diversity. Endangered species. Shoreline stabilization. Breeding areas for water birds. Habitat for migratory and wintering water birds. Habitat for resident and anadromous fish. Amphibian and turtle habitat. Food-chain support Hydrologic System Support. Groundwater storage. Base flow to streams . Flood storage and desynchronization. Flood energy dissipation. Infiltration. InterceptionWater-Quality Support. Nutrient removal. Detoxification. Processing of inorganic solids. Water-temperature regulation . Sediment trapping. Phosphorus and nitrogen processing Residents, planners, park directors, and public works people are noticing that both channels and channel-margin environments are being degraded by the stormwater burdens that urban streams are forced to carry. Less precipitation is captured by the leaves and needles of trees, absorbed by humus, or infiltrated into the soil. More runs off into gutters and storm drains and is discharged immediately to streams. Common stormwater pollutants, such as pesticides, oil, grease, and metals shed from cars, can contribute to this degradation. Urban homeowners apply three times more pesticides per acre than farmers, according to Pimentel.As increasing imperviousness hastens runoff, the hydrology of local streams changes. During the wet season, streams convey higher flows more frequently than in predevelopment conditions. During the dry season, the flows are lower because there is less groundwater available to recharge them. Repeated high flows are eroding streambeds and banks. The eroded sediments are transported downstream and deposited in reaches with lower velocities. These sediments often are remobilized by high flows and deposited overbank in stream margins during flood events, often at rates far exceeding those of undisturbed stream systems. The sediment takes up volume that otherwise might be occupied by water during high-flow events and diminishes the ability of channel-margin vegetation to filter suspended sediments from flood waters.How Streams Disappear: A Case Study
Typical planning for western frontier cities involved careful platting–in this case, over extensive sloughs and wetlands of the dynamic Willamette River floodplain (1874).Local governments are beginning to look for softer, greener fixes in cities where increased flooding is occurring as a result of the efficiency of stormwater conveyance systems. Some have begun this search by endeavoring to understand the presence and extent of local rivers, streams, and wetlands before people settled in these landscapes. In the Willamette Valley of Oregon, home to the nation’s 10th-largest river, Oregon State University researcher Patricia Benner and colleagues found that on a 65-mi. stretch of the mainstem, 53% of the channel length had been eliminated during the 121 years priorto 1975.Archival maps and photos tell a story that can be repeated for most “working-river” cities of the country: Extensive wetlands formerly in the margins of the Willamette River in the Portland area were filled as the city became a major West Coast port and the hub of the state’s heavy industrial activities. Crops, logs, and raw materials for domestic and international markets were shipped to the city via the Columbia River from a vast, productive hinterland east of the Cascade Mountains. Manufactured goods from all over the world were offloaded at Portland’s docks. Floodplains and sloughs at the river’s edge were filled to accommodate the water-dependent commerce that resulted. A nexus of continental railroads and highway systems sprang up to serve these industries, and a nested “break-in-bulk” economy was created.
Little streams vanished as neighborhoods sprang up and were sewered. Shown here is the Rhone Street Sewer, Portland, OR, 1926. Portland thrived and, as done in cities all across the nation, Portlanders continued to rearrange the landscape as people settled and neighborhoods sprang up. They leveled high points, put streams in pipes, and filled-in stream canyons and wet areas to make way for platted neighborhoods, roads, and streetcars. As the city grew, riparian gallery forests of cottonwood, alder, and Western red cedar that had shaded the area’s streams all but disappeared. The loss of floodplains and channel-margin wetlands on many local streams occurred in the context of public works projects to improve storm drainage and flood protection.By the mid-1990s when Metro, Portland’s regional government, began to research the original stream conditions, it determined that 400 mi. of the region’s streams had simply “disappeared”-been piped or filled in the process of the area’s relatively quick 150 years of urbanization. A few years later, 12 species of salmon and trout that use the Columbia, Willamette, and tributary streams in the Portland region were listed as threatened under the Endangered Species Act. Watershed councils completed stream inventories and found that culverts barred these fish from gaining access to tributaries. For the most part, these tribs had become too warm, too burdened by sediments and other pollutants, and too “blown out” by urban flow regimes for cold-water fish to spawn, their eggs to mature, or young to survive.
Land-Use Planning Holds Promise of Livable FutureThe Environmental Protection Agency’s recent study of research on the efficacy of urban stormwater BMPs (www.epa.gov/OST/stormwater) concluded that, in areas undergoing new development and redevelopment, the most effective method of controlling impacts from stormwater discharges is to limit the amount of rainfall that is converted to runoff. This opens the door wide for land-use planning as a means to require a whole new generation of design and construction standards.Most of us are already familiar with the stormwater best management practices (BMPs) that became a regular part of business when the National Pollutant Discharge Elimination System Phase I made its appearance. These BMPs include erosion control measures and a range of infiltration, detention, and pollutant uptake facilities designed to protect the quality of stormwater runoff during and after construction. The new standards we will be seeing will apply to the basic framework of development itself and will include a narrowing of road widths and a move toward permeable materials; shoulder treatments that are short on pesticides and long on infiltration; sidewalks on only one side of the street; smaller footprints for structures; greater attention to the functions of landscape materials; more and wider buffer widths for streams and standards for plantings in this zone; fewer incursions into streams by roads, culverts, and bridges; limits on total impervious surfaces; and standards that minimize site disturbances during construction.Watershed Zoning Is the Toolbox
Dredge discharge filling Guilds Lake in the Willamette River floodplain. Zoning is the toolbox that will result in the implementation of this remarkable range of practices. To devise watershed-based zoning, Tom Schueler of the Center for Watershed Protection in Ellicott City, MD (www.cwp.org/), recommends that the community undertake a comprehensive physical, chemical, and biological monitoring program to assess the current quality of its streams and identify the most sensitive stream systems. Existing and future impervious surfaces in each watershed should be mapped, and the relationships between stream condition and imperviousness should be reviewed. The desired future condition of each stream is then determined. Based on these resource objectives for streams and watersheds, policies are developed that address buffer widths, limits on impervious cover, and other BMPs to support the desired future condition of the resources. These policies and practices are then applied to future development projects.
Dredge Clackamas discharging on the east bank of the Columbia River. This approach, according to Schueler, provides managers with greater confidence that resource-protection objectives can be met as development proceeds. It also forces hard choices about which resources will be protected. But it requires a monitoring protocol for assessing the effectiveness of zoning BMPs on resource quality. Schueler suggests a rapid sampling program to collect consistent data on the variables of hydrology, morphology, water quality, habitat, and biodiversity in each subwatershed. These data are compared to data from streams of undisturbed reference watersheds.
Stream Buffers Are a Major ToolOne of the most critical components of watershed zoning is the stream buffer. According to Schueler, buffers act as rights of way for streams, function as integral parts of stream ecosystems, and are instrumental in removing stormwater pollutants entering them as sheetflow or shallow groundwater from outside areas. The buffer should be designed according to 10 performance criteria:1. Establish minimum width. Recommended: 100 ft.2. Establish three buffer zones. A streamside zone; a middle zone that can include paths, stormwater BMPs, and maintenance access; and an outside setback zone of 25 ft. 3. Establish a goal for the vegetation in the buffer. In most cases, the goal is reestablishment of a mature, predevelopment riparian plant community in the buffer.4. Allow for buffer expansion and contraction. Mechanisms are put in place to expand the middle zone by including wetlands and critical habitats, the full extent of the 100-year floodplain, and undevelopable steep slopes (at least 25%). In some places, the buffer is contracted to accommodate historical development patterns, shallow lots, stream crossings, stormwater ponds, or streams of higher order in a downstream direction.5. Delineate the buffer. Determine the mapping scale (1:24,000), point of origin of first-order streams (when channelization begins), and point of inner edge of buffer (centerline for first-order streams, top of bank for others).6. Establish policy for buffer crossings. Determine standards for allowing incursions into the buffer, including roads, bridges, fairways, underground utilities, storm drains, and outfall channels. Such standards include crossing width, angle, frequency, and elevation and the use of spans and bridges instead of culverts and pipes.7. Allow facilities for treatment of stormwater runoff. Determine standards for the use of buffers for stormwater treatment and the location of stormwater ponds and wetlands.8. Incorporate into plan review and construction sequence. Delineate buffers on preliminary and final concept plans; verify stream delineation in field; check computations and mapping of buffer expansions; check suitability of buffer for stormwater treatment; ensure other required buffer BMPs are integrated properly; examine buffer crossings for problems; mark buffer limits on plans used during construction; conduct preconstruction stakeout; mark limits of construction disturbance, including equipment maneuvering and stockpiling of earth; and familiarize contractors with disturbance limits during preconstruction walk-through.9. Educate and enforce. Mark buffer boundaries with signs describing allowable uses, educate buffer owners, ensure new owners are informed, engage residents in stewardship programs, and conduct annual buffer walks to check on encroachment.10. Buffer flexibility. Allow for economically beneficial use of properties affected by the buffer by incorporating flexibility into the land-use regulation. Flexible techniques include buffer averaging, density compensation, conservation easements, and variances.“Working Green Infrastructure” Can Contribute to Quality of Life
Sand is dredged from river shoals and discharged in a slurry at the river margin. Most people look to decreased density as a way to lessen the impacts of imperviousness on stream quality. But this assumption is giving way to new thinking. This summer, ground will be broken on a 500-ac. site in Surrey, BC, that will accomplish high density (10 structures per acre) while achieving low effective impermeable surface. Dubbed Headwaters Sustainable Development Demonstration Project, the 15,000-member community endeavor is championed by Patrick Condon, director of the University of British Columbia’s Landscape Architecture Program and chair of UBC’s Landscape and Livable Environments.
Vast wetlands at the Willamette River’s margin were filled to accommodate what is now Oregon’s most dense industrial area. On a recent lecture tour of the Portland metropolitan region, where the regional government is working with stakeholders to develop a regional stream-protection program, Condon noted that lower densities encourage sprawl, create inordinate costs and burdens of providing infrastructure, price lower-income citizens out of the market, create segregation by income, and result in flight from the urban center, longer commutes, higher gas consumption, and more air pollution. Older developed areas have about a quarter the amount of infrastructure per person as suburban areas, he observed.“The health of individual sites has everything to do with the ecological health of a region,” remarked Condon, adding that standards for community design should consider air quality as well as water quality. He proposed six development policies to achieve community environmental health:1. Provide different dwelling types in the same neighborhood. Achieve this through small residential lots and multistory, mixed-use commercial and residential development. Older commercial developments are approaching redevelopment and will be future valuable land resources in urban areas.2. Ensure that everyone should have access to transit and shops within a five-minute walking distance. Achieve this with 10 dwelling units per acre (25 people) and mixed-use development.3. Require dwellings to present a friendly face to the street.4. Plan interconnected street systems that give way to natural systems. Circulation systems should allow pedestrians to cross streams but keep road crossings to a minimum. Dispersed surface traffic should be encouraged by providing a system of interconnected roads.5. Develop lighter, greener, cheaper, smarter infrastructure. Minimize road widths and structure footprints and maximize infiltration opportunities. Aim for 300-ft. blocks and 50-60% canopy in the developed area. Outslope streets to drain to an infiltration BMP that performs at 0.04 in./hr. during winter conditions. Provide 130-ft. greenways to buffer artificial surface drainages in linear riparian parks that also serve as bike and pedestrian pathways. Use open-graded street pavements, soft shoulders, and graveled common driveway lanes. Use “wet roofs” to hold rainfall and evaporate it back into the atmosphere. Avoid curbs and piped drainage systems.6. Develop natural drainage systems where surface runoff infiltrates back into the soil. A 200-year-old Douglas fir tree can hold a thousand gallons of stormwater on its needles. Dennis King and Lisa Wainger of the University of Maryland’s Center for Environmental Science have devised a method to identify and determine the economic values of “services” such as stormwater detention, provided by natural resources (www.ecosystemvaluation.org/). In addition to the production and recreation services that natural resources provide, King and Wainger count municipal uses such as groundwater recharge, purification of drinking water, and pollution prevention. To this mix of active services, they add aesthetics and opportunities for research and education. But the list gets more interesting when passive services are considered; for example, the avoided costs of flooding, the avoided costs of health care, and the regional effects of natural resources on regulating climate and air quality.
One-hundred years after this 1884 photo, Sullivans Gulch is occupied by an interstate freeway in Portland, OR. As the decades of the new century rush by and increasing numbers of people need places to live and work, the very quality of life in our cities will depend on how we have valued the natural resources that sustain these urban environments. The urgently beating hearts will be the hearts of our own children, and the new lights sparking up on the vast landscape are the communities of a future that is beginning today.
