Rethinking Storm Water
A MODEL FOR SYNERGICITY
In farm country, the plover has only two real enemies: the gully and the drainage ditch. Perhaps we shall one day find that these are our enemies too.
Aldo Leopold, A Sand County Almanac
Zero-Discharge Masterplan for the University of Wisconsin-Milwaukee
In the fall of 2004, the Milwaukee Metropolitan Sewerage District (MMSD) partnered with the University of Wisconsin–Milwaukee (UWM) to undertake two projects; “UWM as a Zero-Discharge Zone,” a speculative storm water masterplan for the campus, and “the Pavilion Gateway,” an ecological “best management practice” (BMP) demonstration project managing the runoff from a 4-acre portion of the campus (Wasley 2006a, 2006b). The first was the result of an unsolicited proposal by me. The second was in response to a call for proposals that came out before the masterplanning had begun but could not be executed within the time frame of the funding, leading to the fortuitous agreement that the university would use the demonstration funds to plan in detail a more ambitious project and put off the question of construction funding. The two projects essentially became one, with the detailed design study informing the masterplanning process, and vice verse.
The Zero-Discharge Zone (ZDZ) Masterplan that resulted from this intensive investigation provides a road map for transforming UWM’s 90-acre urban campus into a bioregional center for design research into ecological urban storm water management or “green infrastructure.” It provides lessons for the transformation of many postindustrial midwestern cities into SynergiCities in their relationship with the region’s uniquely abundant freshwater.
Storm Water in the Postindustrial City
Postindustrial midwestern cities, such as Milwaukee, are both blessed and burdened by their relation to water. They are blessed because they have abundant supplies of fresh, potable water — a resource that is becoming more precious throughout the world. Many of these cities owe their existence to the transportation corridors and industrial potentials provided by lakes and rivers. The recent ratification of the Great Lakes Compact is further evidence that freshwater is tied to the economic future of the region as well as its past. These cities are at the same time burdened in that their water-management infrastructures are at the limits of their capacities and life spans. The question of how urban environments should relate to their hydrological contexts is one of the most fundamental ecological issues shaping their futures as postindustrial SynergiCities.
Significant political, educational, and economic resources have been applied to postindustrial cities such as Milwaukee to turn a public face toward the rivers and lakefronts that were once seen solely as the domain of industry. However, less attention has been given to ecological urban storm water management, which recapitulates all of the issues associated with the reweaving of rivers and lakefronts into ecological corridors and public parklands that has already commenced in many cities. Postindustrial cities, we believe, are uniquely positioned to solve their storm water problems ecologically. The same logic that applies at the larger scale of river restoration and greenway development — that is, the need to redevelop urban land and to reduce the crushing costs of maintaining traditional infrastructure — opens the door to opportunities to create new amenities that use water as a critical resource and give it new meaning in postindustrial environments.
VISUALIZING STORM WATER SYSTEMS
Nature is resplendent with fractal branching patterns, from the human nervous system to the structure of trees to the landscape’s figuration into drainage basins, streams, and rivers. Within this fractal landscape there is no “smallest branch,” but only branching patterns that diminish in scale. Therefore, virtually every surface of the earth receives water and directs it downstream through branches and tributaries of natural and humanmade watercourses.
Throughout their history, cities have been engineered to channel rainwater away from human settlement through vast networks of underground channels or pipes. This is done to wash away waste, to prevent flooding, to liberate land for human uses, and to reduce the spread of waterborne diseases, among other reasons. Milwaukee, a progressive industrial nineteenth-century midwestern city, was engineered to do all of these things. The construction of a flushing tunnel that pumped water from Lake Michigan to dilute the raw sewerage collecting in the slow-moving Milwaukee River made the city a progressive beacon at the end of the nineteenth century. In fact, public infrastructure was such a high priority for Milwaukee’s socialist leaders during the early twentieth century that they were sometimes derisively called “sewer socialists.” A typhoid scare in 1909 led to the creation of one of the nation’s first sewerage treatment plants at Jones Island in 1925, which innovatively used microorganisms to digest the organic waste (Milwaukee Metropolitan Sewage District 2010).
A century later, the limitations as well as the benefits of this heavily engineered hydrological landscape are now apparent. Like many other aspects of the postindustrial city, the apparent success of infrastructure technology is understood today to have both conceptual flaws and physical limits. This chapter shows that ecological urban storm water management can ameliorate some of the problems introduced by engineered storm water management systems by acknowledging its limitations and implementing new strategies that address storm water before it is collected and redirected to water treatment facilities.
FIGURE 8.1. Conceptual drawing illustrating environmental design strategies for developing sustainable urban infrastructures. (Illustration by Paul J. Armstrong. Courtesy of U.S. Pipe/Wheland Foundry and LA Quatra Bonci Associates/Edward Dumont)
In thinking about how storm water relates to the land on which it falls, there is often a disconnection between the “natural” world aboveground and the subterranean and unseen world of the sewers (fig. 8.1). No matter how urbanized the landscape, it is still quite possible to trace the natural flow of water aboveground. As it is pulled by gravity, water flows downhill and runs across every conceivable surface until it is either evaporated, claimed by plants or porous ground, gathered into a body of water, or collected by subterranean sewers. The sewer system is both unseen (out of public sight) and labyrinthine. While its engineering is often complicated by codes, the patterns of streets and buildings, and the subsurface routes of other public utilities, a sewerage system is conceptually quite simple: it is an extension of the flow patterns of the ground surface. A sewer system, therefore, can be compared to the branching structure of a tree in which small branch structures are collected into larger branches and trunks. In many cases the structure underground is actually a transposition of the aboveground patterns, where natural drainage channels and streams have been buried in pipes to free up the urban land surface for other functions. It is not uncommon for an ancient stream or other watercourse to be contained in pipes below the roadways of a modern city.
Like other industrial cities, Milwaukee is served by a combined sewer system (CSS), which means that sanitary waste is carried in the same network of pipes that collect storm water. The branching pattern of a combined sewer system collects storm water and effluent and directs it to trunk lines that lead to sewerage treatment plants, where the treated water can be then safely discharged back into the system itself or into lakes or rivers. The elevation of the city of Milwaukee is slightly above that of Lake Michigan. Therefore, rainfall collects on impervious surfaces, such as rooftops, streets, and parking lots, where it is diverted to rivulets, streams, and rivers that all flow eventually into Lake Michigan. The storm sewer system traces a similar path below ground to the same harbor mouth as surface water. It is here where Jones Island serves as the site for the combined sewerage treatment facility.
In newer or historically less densely developed areas, such as Milwaukee’s postwar suburbs, sewerage and storm water are carried in separate infrastructure pipelines, which are less selfcontained and more closely tied to patterns in the landscape. The branching pattern of the natural landscape is in this case augmented with prosthetic limbs — branches of sewer pipes intertwined with surface flows, providing engineered shortcuts from some specific patch of ground to a once “natural” collecting stream or river.
Though viewed today as economically unfeasible, combined sewer systems arguably are beneficial in that they cleanse both human waste effluent and contaminated urban storm water before returning it to the environment. However, in certain cases, such as a heavy rainfall, the capacity of a storm sewer system can be overwhelmed, and storm water combined with raw sewerage can be released directly into the environment as a “combined sewer overflow” (CSO). In a separated sewerage/storm water system, the capacity of the sewerage system is not intentionally compromised by storm water, yet the ecologically damaging effects of concentrating urban runoff remain. “Best management practice” literature often glosses over the differences between these two systems and their potential impacts for ecological design. The ZDZ masterplan presented in this chapter illustrates the significance of both systems as a key to opening up unexpected design opportunities.
CONCEPTUAL PROBLEMSWITH CONVENTIONAL “HARD-PIPE” STORM WATER MANAGEMENT
From an engineering perspective, storm water management in any form must account for three basic variables: water quality, water quantity, and rate of flow. Each of these variables can assume varying degrees of importance in a given situation, which makes storm water management a design challenge, where specific conditions often trump general principles and counterintuitive solutions are often contained within the problem itself.
Modern urban environments have replaced pervious and vegetated surfaces with impervious surfaces, such as concrete and asphalt, which increases both the quantity of water and its flow rate as it moves downhill. A pervious natural surface, by contrast, often acts as a large sponge by absorbing water into the soil or collecting it into wetlands. Only when these natural systems become overburdened, as during a heavy rainfall, does flooding occur. Excess concentrations of water can degrade local water quality by making water bodies “flashy,” meaning that their water level fluctuates dramatically during a rain event. Concentrated water runoff that is suddenly discharged into a stream not only raises the water level, which can cause erosion and flooding, but also carries with it all of the contaminants that have been collected on impervious surfaces. Contaminants from streets and parking lots, such as oil and chemicals, can no longer be degraded by the slow dispersed workings of sunlight and microbial activity but are swept away by the rushing water in potentially damaging concentrations. This unregulated process also raises the turbidity and temperature of the surface water in ways that can be detrimental to aquatic habitat as well.
In a CSS, the surge of rainwater in a storm event collides with the waterborne human waste stream, which stresses the capacity of the system and sets up the potential for a CSO. When combined sewer overflows were first regulated in the 1970s by the Clean Water Act, the city of Milwaukee responded with the Deep Tunnel Project. The MMSD created 19.4 miles of tunnels that serve as underground storage vaults that follow the natural geography of the three river valleys and expand the trunk capacity of the combined sewer system’s concrete tree (Milwaukee Metropolitan Sewage District 2010). Though Milwaukee’s deep tunnels have greatly reduced the number of CSOS to an average of three per year (half of the federally mandated limit of six per year (Environmental Protection Agency 2009), they are prone to the same water surcharges as any engineered “hard-pipe” network. Further expanding the network’s capacity to capture these statistically less and less frequent storms at some point becomes prohibitively expensive because it takes pipes increasingly larger in diameter to divert proportionately smaller quantities of water. In order to eliminate such overflows, the premise of this study is that it is more cost effective to keep storm water out of the sewer system altogether through ecological management practices than it is to add any more additional storage and/or treatment capacity to already overtaxed systems.
In working with a combined sewer system, the problem to be solved through ecological management often thus centers on the system’s total capacity, where controlling the volume of water entering the system is the primary concern. At other times, the design may be determined not by the total capacity of the system but by the rate of flow that individual branches of the system can accept without backing up. Interestingly, the design of these ecological features doesn’t necessarily turn on issues of water quality, that is, not unless the ecological goal is to discharge water directly into rivers, lakes, or aquifers rather than sending it first to a water treatment facility.
The primary dilemma with any “hard-pipe” engineered system is its ability to meet the changing needs of growing populations in urban areas. As human development covers greater areas of land and surfaces it with impervious materials, more water is channeled into the sewerage system. Since the system is limited and inflexible, because every branch has a fixed capacity, when the system is overcharged, as in a storm-related event, flooding can occur. A second dilemma is that legally prescribed standards for water quality have become more stringent as the science of water quality has evolved. The standards that applied to the nineteenth-century industrial city are not those of the postindustrial city of today. Another concern is that rainfall patterns are changing, due primarily to human practices, such as burning fossil fuels, which have micro- and macro-environmental effects. Global climate change is predicted to increase rainfall in most of the Midwest by 0.6–1.0 inches every 10 years and potentially over 1.5 inches every 10 years in parts of Minnesota, which has thousands of glacial freshwater lakes. These data cast doubt on the efficacies of contemporary municipal ordinances that regulate storm water engineering and the infrastructure of piping and treatment systems that are currently in place to manage both human waste and water.
Finally, both the environmental and economic costs of the treatment process itself are an issue. Conventional sewerage treatment is an energy- and chemical-intensive activity. As we redevelop our postindustrial cities, we also need to consider the ecological relationship between water and energy conservation. Conventional water treatment facilities depend on fossil fuels for energy, which adds carbon-based pollutants to the atmosphere and further affects the climate. The goal of ecological storm water management, therefore, is to reduce the overall negative impacts of water management by employing biological systems and processes to absorb and filter storm water.
THE GOAL OF ECOLOGICAL STORM WATER MANAGEMENT
The practical goal of ecological urban storm water management, especially in a combined sewer system city such as in Milwaukee, is to keep as much storm water out of the sewer system as possible. The stresses on capacity created by expanding urbanization, changing weather patterns, increasingly stringent regulation, and the economic and ecological costs of maintaining the status quo are overwhelming. The holistic goal of an ecologically managed water system, therefore, is to employ natural water treatment processes to their greatest potential while maintaining and enhancing the human environment for livability. The goal, then, is to weave natural water treatment processes organically into the city by applying the same principles that have transformed postindustrial brownfield sites along rivers and lakes into parks, sustainable wetlands, and natural biomes.
To do this, it is necessary to understand the properties of water and its behavior as an interdependent organic system. When water management and treatment is perceived as a holistic, natural system, then we can restore the natural hydrology of a place and design our urban environments to perform as an ecologically balanced system of interrelated parts. When planners and engineers use ecological methods to regulate and treat water, it will result in an environment that is more attuned to the natural world.
This is the philosophical underpinning of the ecological storm water research at the UWM campus. This approach does not place the needs of nature against the needs of human settlement but rather enhances a built-up urban environment with rain gardens of various shapes and sizes that treat water as an amenity to be enjoyed rather than an adversary to be controlled. As such, it intensifies the urban qualities of place and exploits the specific attributes of ecological design.
UWM as a Zero-Discharge Zone
The stated goal of UWM as a ZDZ study is to recreate a runoff rate and volume comparable to what would have existed before settlement and development of its 90-acre urban campus. The goal of the Pavilion Gateway Project is to capture as much runoff water as possible within a 4-acre drainage area of the parking lot of the campus power plant, and to transform this service area into a pedestrian storm water interpretive path. This area, in turn, will become a focal point for a recently constructed gymnasium and the Pavilion underground parking structure.
The first project realized from the masterplan in 2008 (fig. 8.2) was the construction of the Sandberg Green Roof, a 32,000-square-foot vegetated roof on the commons building sitting between the four towers of the campus’s high-rise dormitory complex. In 2009, the Sandburg Green Roof was followed by the construction of the first phase of the Pavilion Gateway Project, with a series of demonstration rain gardens known collectively as the Spiral Garden, which collect water from approximately 2 acres of parking and building roofs (fig. 8.3). An observation deck in the center of the Spiral Garden and other sculptural additions and interpretive signage for the project are also being developed. A proposal for an innovative 55,000-square-foot green roof retrofit project on the Golda Meir Library has received over $1 million in MMSD support and will be installed in 2011. And perhaps most significant, the ZDZ Masterplan, a speculative exercise in design research and green campus movement activism, has been adopted as a sustainable prototype model and incorporated into the official UWM campus masterplan.
THE UWM CONTEXT
Although the ZDZ proposal was unsolicited, there was a clear and compelling case for its implementation. In addition, the MMSD had both a vested interest and specific agenda in funding it. So while our agenda was to promote UWM as a bioregional center for urban ecological storm water research and education, the drivers of the project are found in the specific conditions of the surrounding neighborhood as much as in the needs and desires of the university.
To the north of the Milwaukee harbor, the Lake Michigan bluff is separated from the western extent of the city by the Milwaukee River, which flows southward parallel to the lake’s glacial rim for much of its length before finally entering Lake Michigan. The neighborhood between the river and the lake, known as the East Side, is built on a narrow strip of poorly drained clay that also forms the subsoil of the UWM campus. An examination of the local topography points out the subtle but important fact that the Milwaukee Teachers’ College, the original institution on the UWM site, was built on a slight knoll, which in the late nineteenth century was located on the outskirts of the city. While this topography is subtle, it directs the movement of water across the campus, both above grade and in the sewers below. Historical plat maps show that both the southern edge of the campus, now Kenwood Boulevard, and the northern edge, now Edgewood Avenue, were defined by small watercourses that drained into the Milwaukee River. Neither of these original watercourses remains evident above grade, but the northern drainage area is clearly perceptible today as a low point in the terrain.
This dip, marked by Edgewood Avenue, also happens to be the political boundary between the city of Milwaukee and the village of Shorewood. The Edgewood Avenue neighborhood has a long history of basement sewerage backups and local flooding, which is compounded by an undersized sewer infrastructure system that is regulated by two different municipal jurisdictions. In funding the ZDZ Masterplan, it was the MMSD’s intention that an ecological way to contain and filter storm water on the 62-acre UWM campus could be an alternative to a much more expensive process of reconstructing the existing sewer system. Furthermore, an environmentally driven solution would be an example at a prominent public institution for the community at large to follow.
FIGURE 8.2. Site plan of the Pavillion Gateway-Up per Garden on the University of Wisconsin-Milwaukee campus. (Courtesy of James Was ley, University of Wisconsin-Milwaukee, School of Architecture and Urban Planning)
FIGURE 8.3. Rendering of the proposed Pavilion Gateway and Upper Gardens on the University of Wisconsin-Milwaukee campus. (Courtesy of Celia Liu)
Based on modeling projections, the goal was to contain a sudden “spike” of water runoff lasting less than 30 minutes at the north end of the campus. This goal also served as the premise for future proposals. The MMSD’s regulations stipulate that the rate of flow requires that any temporary storm water storage be fully drained and ready for recharge within 24 hours of a rain event. Thus, the ability to detain northward-draining storm water for less than a day is the critical metric for success. Whereas the design study conceptually addresses the entire campus, only the northern half of the campus was modeled in terms of its hydrology. Whereas the MMSD’s literature emphasizes “keeping water out of the deep tunnel,” this was not the central issue for the UWM campus. In other words, while keeping storm water out of the system altogether is good, simply slowing it down solves the critical problem of control. We were aware that storm water from the entire campus flows eventually into the same combined sewer system as the Edgewood neighborhood, and that demonstration projects on the north side of campus would have a local impact very different from those located on the south side.
On the basis of analyses conducted by the ZDZ, it was determined that averting the Edgewood Avenue combined sewer expansion was not feasible, since the total catchment area for the north draining area of the UWM campus is not physically large enough to retain enough storm water to prevent it from backing up. This realization did not impact the immediate goals of reducing the spike of water rushing to Edgewood Avenue, and the opportunity for UWM to take a leadership role in demonstrating ecological urban storm water management practices as a whole.
Another site-specific condition that we considered was the layered urban environment in which the UWM campus is embedded. The 90-acre study area includes a public grade school and an adjacent hospital, which will eventually be acquired by the university. Excluding the local streets and the Downer Woods, a small state-protected area of woodland adjacent to the Sandburg residence hall complex, 53% of the campus is comprised of impervious surfaces. In addition, because existing underground fuel storage tanks for the campus power plant were located in the demonstration area for the Pavilion Gateway, ZDZ was required to provide a fuel spill containment strategy. Further complicating our efforts were the underground remnants of the original power plant that serviced the old Downer Teachers’ College. Thus, the site chosen for the Spiral Garden was in reality a subterranean maze of active and abandoned steam tunnels and utilities.
The realization that the site was not ideal only enhanced its potential as a demonstration project. It offered a unique institutional setting that could serve as a laboratory of urban conditions and solutions that could be applied to other drainage areas in the city of Milwaukee and many other prospective postindustrial sites as well.
THE ZDZ MASTERPLAN’S QUANTITATIVE FRAMEWORK
While encompassing many related activities, at its core the ZDZ Masterplan is comprised of a design study of the UWM campus as a site for demonstration projects catalogued by type, and a civil engineering study quantifying the potential impacts of BMP strategies. With the goal of capturing storm water at every opportunity, the approach of the design study was to identify BMPs for all surface types. Each surface type was catalogued into one of three categories: priority, secondary, and not suited for capture. Priority applications were those that had multiple benefits in terms of storm water management, ecological enhancement, scheduling of campus maintenance projects, aesthetic impact, and symbolic value. Together, priority and secondary equal full implementation, which in our analysis represents the maximum feasible extent that capture is possible. Through an iterative process of goal-setting and field evaluation, the masterplan strategy proposed a series of target values for each type of impervious surface. For example, internally and externally drained roofs have a priority implementation target of 40% capture amount of water drained from all roof surfaces, and a full implementation target of 80%. Pedestrian and vehicular hardscapes have priority implementation targets of 20% and full implementation targets of 80%.
On the civil engineering side, a Storm Water Management Model (SWMM) was developed as a graduate thesis project in civil engineering by Elizabeth Locke, under the guidance of her advisor, Professor Hector Bravo. Given the limitations of funding and time, Locke’s SWMM model represents only the critical northern drainage area. Calibrated against actual measurements taken at the Edgewood Avenue interceptor, the SWMM model predicts the impact of transforming the surface-flow characteristics of the campus by the application of the priority and full implementation of the design study’s categories of BMPs.
The goals of the ZDZ Masterplan were twofold: (1) to create a model of the campus that approximates the hydrological and ecological functions of the landscape as it once existed before settlement, and (2) to apply implementation strategies that will retain storm water in an ecological manner comparable to historic natural drainage and retention patterns while maintaining the urban characteristics of the UWM campus. From a regulatory perspective, the MMSD’s targeted release rate for new development is 0.5 cubic feet per second per acre drained (cfs/acre) for a 100-year storm event. By chance or design, this standard also describes quite accurately the peak discharge rate of the northern drainage of the UWM campus as modeled by Locke according to the hypothetical presettlement conditions of the campus, that is, when the campus area was an oak grove. As a result of this convergence, 0.5 cubic feet per second per acre per 100 years emerged as the technical definition of the “zero-discharge” goal.
SOLUTIONS FROM THE TOP OF THE MOUNTAIN DOWN
In describing what could be considered the dawning of his ecological enlightenment, Aldo Leopold writes in A Sand County Almanac of learning to “think like a mountain.” Leopold realized that the human micromanagement of natural processes is often misplaced unless it is subservient to a larger ecological vision.
The UWM campus may be relatively flat, but “thinking like a mountain” in this context means literally following every rivulet of water as it flows from high ground to low elevations as it seeks ecological equilibrium. The basic strategy of the ZDZ study was to analyze the hydrological cycle beginning with the rain cloud overhead, and to measure and evaluate each horizontal surface of the campus for its potential to capture storm water. The goal was to collect and disperse the water throughout as much of the campus area as possible. Where hard-pipe engineering seeks an efficient solution by gathering and concentrating water through a network of pipes and directing it to treatment facilities, our “soft engineering” or ecologically informed design approach seeks to mimic the distributed, fractal behavior of the natural landscape. Tracing the downward flow of water, we catalogued water surfaces into the following domains.
INTERNALLY DRAINED ROOFS
Internally drained roofs are flat or low-slope roofs with drains running within the building directly into the storm system. Approximately 23 acres or 20% of the total area of the UWM campus is covered by the barren surfaces of these roofs. These are evaluated for their suitability to be retrofitted with “green roofs” or engineered vegetated roof systems. We have assumed lightweight “extensive” green roof systems 4 inches deep and planted with low-maintenance sedum. A priority design target was established retrofitting 40% of the campus’s low-slope roofs with a full-coverage target of 80%. The ensuing analysis justified actual coverage values of 37% and 73%, respectively, based on accessibility, visibility, structural adequacy, and similar constraints.
Quantifying the impact of the study, the now completed Sandburg Commons Green Roof accounts for 32,000 square feet of the entire 423,000 square feet of the northern drainage area. When the 55,000 square feet Golda Meir Library vegetated mat retrofit is complete in 2011 we will have installed green roofs on 20% of the Northern Drainage Demonstration Area’s internally drained roofs.
EXTERNALLY DRAINED ROOFS
Externally drained roofs are roofs drained to gutters and downspouts, which are often accessible for diversion into rain gardens and other engineered landscape features. Approximately 7 acres or 6% of the campus area is represented by pitched roofs. The ZDZ catalogues the potential disconnection of 40% and 86%, respectively, captured by rain gardens all located to avoid the removal of existing trees.
The first rain garden demonstration project captured water from the 1,000-square-foot surface of the Sabin Hall roof and was undertaken by the Ecotone student group during the masterplanning process. As a part of the Spiral Garden Project, my graduate studio will be disconnecting downspouts constituting another 16,000 square feet of roof surface drainage at Holton and Merrill Halls and the Norris Health Center, which is approximately 15% of the campus total. To dramatize the water runoff and integrate it into the landscape of the campus, the Norris Health Center downspout disconnections will feed two rivulets that will tumble downward from garden to garden along a newly constructed stairway from the main entry of the building to the Spiral Garden below.
PEDESTRIAN HARDSCAPE
Approximately 20 acres or 17% of the total campus area is dedicated to pedestrian hardscape, though the ZDZ analysis identifies and excludes the quarter of that total that drains to the landscape and not directly to the storm sewer system. Here the variety of recommended BMPs multiplies in response to a myriad of local conditions. Every local topographical relationship that could be used to drain water by gravity and absorbing it into the landscape has been exploited. For example, the Hartford Avenue School Planter Bench addresses the largest single pedestrian hardscape area to date and best demonstrates the principle of “following the flow.” The Hartford Avenue public grade school is embedded within the UWM campus and is surrounded by a traditional asphalt playground. The playground is elevated 5 feet above the grade of an adjacent sidewalk, which is wide enough to allow children to queue for school buses. A planter bench will provide gravity-fed storage for water collected from the playground, as well as a place for the students to sit. Together with a proposed dry well at the far end of the playground, this project alone will capture 62,500 square feet or 11% of the total sewer-serviced pedestrian hardscape.
Pervious paving is considered as part of the mix of strategies appropriate for the campus, but only where the option of having the storm water remain above grade and interact with plants is not available. This choice reflects our belief that storm water management should have an aesthetic and ecological benefit as well as an engineering benefit wherever possible. On the other hand, pervious paving BMPs create underground storage capacity that generally cannot be matched by aboveground features. This inherent storage capacity accentuates the impact of these BMPs in relation to all others, especially when modeled for the extremes of a 100-year storm event, making them a potential buffer component in any comprehensive solution.
VEHICULAR HARDSCAPE
Vehicular areas, such as streets, parking lots, and building service areas, are evaluated first with respect to the capacity of the surrounding landscape and second as candidates for pervious paving. First we must ask: are there adjacent down-slope areas where runoff can be diverted to rain gardens? Can these lots be redesigned to incorporate bioretention within their given footprints? With only 9 acres of total vehicular hardscape on the campus, nearly 5 acres is required for loading dock access, disabled parking, and other critical uses that cannot be displaced. Using a bioretention area design standard of 5% of the area to be served, the ZDZ established priority and full implementation target values of 20% and 80%, and verified the design potential to accommodate 19% and 71%.
The construction in 2009 of the Spiral Garden Project represents the first implementation of a parking lot disconnection from the storm sewer, which captured surface runoff from an acre of asphalt, or approximately 18% of the vehicular hardscape at the northern drainage area of campus.
Eliminating the Dunce Cap: Storm-Pipe Daylighting
According to the analysis provided by Locke’s SWMM model, the volume of storm water draining into Edgewood Avenue in a 100-year storm is approximately 5.6 acre-feet. The peak flow rate, which is the critical variable in terms of the interceptor’s capacity, would be 120 cubic feet per second in that situation. Full implementation of all of these surface strategies throughout the northern drainage would reduce this total by 54% to 2.6 acre-feet, with a peak flow reduction of 44% to 67.5 cubic feet per second. These are sizable reductions but do not meet the 100-year zero-discharge standard of 0.5 cubic feet per second per acre, which translates to 30 cubic feet per second across the 60 acres of the Northern Drainage Area. Graphically, this results in a “dunce cap,” a small red spike in the volume/time graph representing water leaving the Northern Drainage Area into the Edgewood Avenue interceptor at a rate greater than 0.5 cubic feet per second per acre. With every horizontal surface accounted for, the ZDZ Masterplan has failed thus far to achieve its stated objective.
In response to this shortfall, the final strategy explored will be “daylighting” water that has already entered the drainage system. Here we are seeking to coin a new usage for the term “daylighting,” extrapolating from the concept of “stream daylighting.” Whereas stream daylighting refers to restoring large urban waterways that have been encased in underground pipes to the surface, storm-pipe daylighting implies capturing stormwater that has already entered the smallest branches of the same underground system and retaining it in rain gardens, filter strips, and other biomes. The goal in both instances is once again to bring water as a visible feature into the human-experienced environment, where it can serve both ecological and aesthetic functions (fig. 8.4).
Here a final specificity of the UWM campus becomes critical — while the campus is situated within the combined sewer district of the city, the piping infrastructure on campus is designed to keep storm water and sewerage separated. It is only when the campus storm sewers tie into the adjacent streets that they are combined.
Taking the concept of daylighting water that is already within the storm drainage tree as the starting point, the masterplan goes on to analyze several distinct categories of storm-pipe capture. Liberating storm water from internally drained roofs, capturing water running through accessible plumbing in underground parking structures, and directing storm water from existing detention pipes into engineered wetlands were all explored. Furthermore, the campus’s storm drains remain separated until they join the streets that define the perimeter of the campus and its lowest elevation. This realization led to the idea of creating a “moat” of rain gardens comprised of water-loving flowers and pervious sidewalks that will ring the entire campus. Water in the moat will be replenished by sump pumps located just upstream of each of the connection points between UWM’s subterranean concrete storm water trees to those of the combined sewer system.
Capturing water that has already entered the labyrinth turns out to be the only viable way to meet the 100-year ZDZ goal. However, once this possibility has been realized, there are many other locations on campus that will allow us to combine easy access to captured water with landscape features to manage water runoff and enhance human interaction. The essential idea of the Pavilion Gateway, for instance, is to create an interpretive path starting at the newly constructed Pavilion parking structure on Edgewood Avenue and progressing uphill to the top of the knoll at the center of campus. This interpretive path is metaphorically seen as a stream, gathering storm water from every possible surface in its discrete drainage basin. As we sought to capture water from an internally drained roof, which represented the highest point on campus, this led us to the realization that even after this water was underground there was enough topographical change along the path that the campus storm sewer could actually be daylit as the headwaters of the Pavilion Gateway’s storm water garden system, similar to an Italian Renaissance grotto. Likewise, a lower internally drained roof on the same building could have its plumbing rerouted to daylight high on an exterior wall, where a sculptural scupper could be installed to mark the presence of the hidden grotto and the start of the garden path below.
Until funding is available and this proposed upper garden can be realized, we have fabricated a prototype for a sculptural scupper that will direct the entire 13,000 square feet of water from the internally drained roof of the UWM power plant into the largest garden in the Spiral Garden chain. It will mark the downstream gateway into the project. Incidentally, this last gesture was completely overlooked until the Spiral Garden was constructed and it became clear that the final garden was not being used to its capacity. If evidence of good design is in the details, then the evidence of good ecological design is in the exploitation of every niche, the interconnection of every node, and the elaboration of every system. While the ecological management of storm water may seem exotic, the Pavilion Gateway demonstration project has shown that it is a strategy that has both practical and aesthetic potential.
Conclusions
Several insights emerge from this research that might guide postindustrial cities everywhere seeking to sustainably and ecologically reweave storm water management systems back into their urban fabrics. The first insight is to find creative solutions in the complex mesh of existing urban landscapes by analyzing and understanding the intertwining worlds of free-flowing water in natural habitats and that of the engineered sewerage system, and to be specific about the problems to be solved at each juncture. The flow of storm water in cities is a tangle of site-specific conditions, but when they are untangled they reveal unexpected opportunities. The liberation of water from the campus storm water system through storm-pipe daylighting is possible only because this small catchment area has been separated from the combined sewer system into which it flows. The fact that the combined sewer system at Edgewood Avenue creates a local bottleneck that promotes flooding is due not to the amount of stormwater runoff but to the timing of its arrival, which means that we can use surface containment methods to solve the immediate runoff problem. Our research shows that rain gardens and filter strips work, even though the campus is situated on impervious clay and water may never reliably infiltrate into the ground and be absorbed into the water table below.
FIGURE 8.4. Spiral Garden project at the University of Wisconsin-Milwaukee campus. Storm water is directed in a spiral path toward a retention area with aquatic native plants and natural features (as shown in the photograph). (Courtesy of James Wasley)
A second insight rooted in this view of sustainable storm water management is the realization that the same limits that apply to hard-pipe solutions in terms of the law of diminishing returns also apply to ecological storm water BMPs. Designing a single rain garden to have the capacity to hold water from a 100-year storm means that much of that capacity is going unused most of the time. All storm water systems are designed to have reservoir capacities, and the best way to think of them working efficiently is to think of the combined system working together in a truly distributed fashion — the greater the distribution in an area, the more likely that there are situation-specific ways that each individual system can support the other. Our research has shown that the best solutions of storm water management for the postindustrial city are truly ecological ones, in which an organic network of biological water channels and nodes are artfully woven into urban landscapes. This is also the lesson that can be extrapolated from sitespecific research and applied to the postindustrial city. When stormwater is managed in an enlightened and sustainable manner, it creates synergy that enhances our experiences of both the natural and humanmade environments. It provides a new form of infrastructure for the development of economic, social, and environmental opportunities that will allow postindustrial cities to prosper and evolve into global SynergiCities.
References
Environmental Protection Agency. 2007. Report to Congress on Combined Sewer Overflows in the Lake Michigan Basin. Executive Summary. Available at the website of the Environmental Protection Agency, www.epa.gov/npdes/pubs/cso_reporttocongress_lakemichigan.pdf.
Leopold, Aldo. 1966. A Sand County Almanac with Essays on Conservation from Round River. New York: Ballantine Books.
Milwaukee Metropolitan Sewerage District. 2010. History. May 2009. Available at the website of the Milwaukee Metropolitan Sewerage District, http://v3.mmsd.com/history.aspx. Retrieved January 2, 2012.
Milwaukee Sewer Socialism. 2010. Available at the website of the Wisconsin Historical Society, www.wisconsinhistory.org/turningpoints/tp-043/?action=more_essay. Retrieved January 2, 2012.
National Weather Service. 2010, May. National Weather Service Climate Prediction Center: U.S. Temperature and Precipitation Trends. Available at the website of the National Weather Service Climate Prediction Center, www.cpc.ncep.noaa.gov/anltrend.gif.
Wasley, James. 2006a, May 5. The Pavilion Gateway Demonstration Project. Available at the University of Wisconsin at Milwaukee PantherFile website, https://pantherfile.uwm.edu/xythoswfs/webui/_xy-39703776_1-t_cuPZank6.
———. 2006b. UWM as a Zero-Discharge Zone: A Stormwater Masterplan for the UWM Campus. Available at the University of Wisconsin at Milwaukee PantherFile website, https://pantherfile.uwm.edu/xythoswfs/webui/_xy-39703775_1-t_cuPZank6.
