Living Roofs in Integrated Urban Water Systems

Daniel Roehr, Elizabeth Fassman-Beck

• Publisher: Routledge
• Year: 2015
• ISBN:
  9781317537021
• Edition: 1
• Topic: Architecture
• Subtopic: Urban Planning & Landscaping

With the infrastructure to manage storm water threats in cities becoming increasingly expensive to build or repair, the design community needs to look at alternative approaches. Living roofs present an opportunity to compliment ground-level storm water control measures, contributing to a holistic, integrated urban water management system.

This book offers tools to plan and design living roofs, in the context of effectively mitigating storm water. Quantitative tools for engineering calculations and qualitative discussion of potential influences and interactions of the design team and assembly elements are addressed.

Chapter 1: Introduction

1.1 WHY WORRY ABOUT WATER? WATER AS A DRIVER FOR LIVING ROOF IMPLEMENTATION

Water is crucial for life on earth. It is our most precious resource. In many parts of the world, water scarcity causes immense hardship for human, animal and plant life. The extent of these areas is steadily increasing (International Water Management Institute 2000; Rijsberman 2005; UN Water, Food and Agriculture Organization of the United Nations 2007). The quality of water has been degrading rapidly since the Industrial Revolution, a situation which has been accelerated by the immense increase in population over the last 40 years (Albiac 2009; Carr and Neary 2009; Nienhuis and Leuven 2001). In the Western world, concerns over water extend beyond basic infrastructure to now address the preservation of ecosystems and ecosystem services. With increasing urgency, urban development professionals including architects, landscape architects, engineers and planners are researching and implementing various methods to recycle, store and reuse water, improve its quality, and protect or restore the natural resource base from which it is extracted (Margulis and Chaouni 2011; Planning Institute Australia 2003).

What we do with water use (how much) and its management (quality, where it ends up, and how fast it travels) at a local level always impacts a larger system, which in turn, feeds back to the availability and quality of water in our cities. Of the many forms that water takes, this book is concerned with urban stormwater runoff. It examines the role and design of living roofs to mitigate runoff’s environmental and infrastructure impacts, while creating productive urban spaces. Living roofs have to be seen from two sides: the pragmatic/technical side from an engineer’s point of view alongside the environmental, social and/or aesthetic/experiential side from a designer’s point of view. Designers try to create a human experience resulting in a higher quality of life but this cannot happen without the engineer’s objective to protect water resources for creating and sustaining life.

Urban stormwater runoff poses a suite of receiving water and infrastructure impacts that threaten public health and welfare as much as ecosystem services, but also offers an opportunity of a resource to be captured for beneficial uses. The historic focus of an urban drainage system was to expediently remove or dispose of runoff so as not to disrupt urban activities, damage structures or threaten public safety. Expedient removal is no longer the only goal or cost. In some cases, it is not the goal at all. Almost every aspect of the hydrologic cycle (water’s distribution and flux in a watershed) is modified by urban development. In a natural forested condition, 10–20 mm of precipitation may be intercepted by the vegetated canopy and infiltrated (soaked) into the ground before stormwater runoff is generated at the surface. In an urbanized condition, runoff may be generated from as little as 2 mm of rain. Thus, in urban settings, flows are generated almost every time it rains, and pollutants are transported to receiving waters such as streams, rivers, lakes, estuaries, bays and harbors. Increased flow rates, runoff volumes and occurrence of runoff along with how quickly runoff is initiated contribute to channel erosion and instability, which degrades both physical and biological habitat structure by a process known as hydromodification (US EPA 1993). Studies show that marked alteration of channel flow processes is associated with declining ecological health, or degradation of the physical channel attributes required for normal ecological functioning (Gippel 2001). Across the United States, receiving water quality has largely been considered “degraded” for decades; pollutants carried by urban runoff are largely discharged without treatment. Altogether, hydromodification and pollutant loadings compromise aquatic habitat, infrastructure and property almost every time it rains.

Reducing or avoiding impacts from “everyday” rainfall events is increasingly incorporated into policy, but has not historically been the focus. Since 2001, US state and municipal agencies in Portland, Philadelphia, Seattle, Atlanta, Chicago, New York, Pittsburgh, Washington State, California, Maryland, Vermont and Virginia have introduced policies and related design requirements. Significant legislation enacted in 2007, Section 438 of the USA Energy Independence and Security Act, requires extensive on-site runoff control from “everyday” events for federal facilities undergoing new or redevelopment. Living roof technology is perfectly suited to mitigate these sorts of storm events.

In many older cities, “everyday” stormwater impacts to receiving environments are exacerbated or even superseded by combined sewer overflows (CSOs). Combined sewers are intended to carry sanitary sewerage and stormwater runoff through the same pipes to a municipal wastewater treatment plant. In many major cities around the world, urban infill and densification now generate flows well exceeding the carrying capacity of the combined sewer network. By design, overflow points discharge untreated runoff and sanitary sewerage into receiving environments when the capacity of the sewer is exceeded during wet weather (e.g., rain or snowmelt). While the intention is to prevent overloading the municipal wastewater treatment facility, and causing even greater volumes of untreated wastewater discharge, the impacts to local receiving environments can be devastating. In Brooklyn, NY, modeling predicts CSO events to occur almost every time it rains, without intervention (City of New York 2008). In New Jersey, the state with the highest population density in the United States, as little as 5 mm of rain regularly causes CSOs (NY/NJ Baykeeper.org 2013). Philadelphia is served by 164 permitted CSO discharge points, serving 48 percent of the city (PWD 2011). While larger storms cause the greatest volume of CSO, smaller storms create the greatest number of CSO events. In many areas of the United States, these sorts of discharges are in violation of the 1972 Clean Water Act and its amendments (including the 1994 Combined Sewer Overflow Control Policy) and/or the Wet Weather Water Quality Act of 2000. In the Pacific Northwest, CSOs and runoff contaminants including the elevated temperature of untreated stormwater runoff threaten salmonids protected by the 1973 Endangered Species Act. Environmental regulation and impending lawsuits and/or fines, exacerbated by shifting public awareness and opinion, is causing municipalities and water utilities to invest significant resources in reducing the frequency and volume of CSOs, and restoring degraded waterways.

Upgrading buried infrastructure is increasingly found to be uneconomical and impractical compared to surface-level action. Rigid grey infrastructure (pipes, pumps, tanks and centralized treatment plants) lacks resilience. Alternatively, small and large cities around the world are developing or are already implementing green infrastructure (GI) solutions for stormwater management. Although many definitions of GI have been proposed, a useful compilation is “Natural and engineered ecological systems which integrate with the built environment to provide the widest range of ecological, community, and infrastructure services” (greeningofcities.org 2012). The term green stormwater infrastructure (GSI) is specifically used to identify approaches for runoff management.

Decisions defending GI and GSI adoption cite economics, inability to achieve technical objectives using grey infrastructure, and multi-functionality over and above provision of ecosystem services, particularly with respect to human health and social capital. Across the world, the two largest municipal investments in GSI were recently introduced in Philadelphia and New York City, specifically to address CSO control and receiving water quality improvement. After a comprehensive alternatives analysis, the Philadelphia Water Department (PWD) determined that traditional grey infrastructure would be “cost prohibitive while also missing the restoration mark.” Instead, the PWD is investing US$1.2 billion (2009 net present value) in GSI and in excess of US$3 billion in GI over 25 years “towards greening the city as a means to provide specific benefits … while meeting ecological restoration goals” (PWD 2011: 3). Implementing GI across New York City is projected to eliminate $1.4 billion and defer $2 billion from the municipal government’s budget for state-mandated grey infrastructure projects (City of New York 2012).

On a smaller scale, site or block-level initiatives are often instigated by municipalities in response to neighborhood complaints. Many successful stories and/or pilot projects are emerging from Seattle, Portland, Lancaster (Pennsylvania), New York City and Washington, DC where GI solutions for stormwater are integrated into street or intersection redevelopment to improve traffic and pedestrian safety. Addressing runoff problems at – or close to – the source with GI eases the burden on the overall network and reduces the demand for inflexible grey infrastructure and large downstream flood management facilities.

GI fundamentally couples better community design with technological function. From a landscape architecture perspective, Fredrick Law Olmsted’s work can be seen as the genesis of design and planning that combines open space with infrastructure services. As the designer of New York City’s Central Park and the 1893 Chicago World Exhibition, Olmsted was the most prominent North American landscape architect in the nineteenth century. He understood that accessibility to green public open space close to the polluted dense city centers would have tremendous health and social benefits for city dwellers. In Boston’s Emerald Necklace, Olmsted developed a park system connected by so-called “parkways.” These parkways (wide green path systems lined with trees) made the open spaces accessible to the visitors on foot, horses and carriages, but also provided stormwater mitigation through an interconnected swale and lake system (Hellmund and Smith 2006). In the nineteenth century, Olmsted, Henry David Thoreau and John Muir were strong advocates that green open space would be very important for the physiological, physical and spiritual health of the city dweller (Fischer 2010; Martin 2011; Thoreau 1851). Only recently this has been scientifically proven with rigorous experiments and peer-reviewed journal publications (Kellet and Rofe 2009; Kuo 2010; Ulrich 1984).

Visual and physical access to GI is documented as being responsible for improvements in human mental and physical health; decreases in instances of crime; and other social benefits, such as fostering connection to place and increasing economic value (increased property values and economic activity) through the improved aesthetic appearance of neighborhoods (Coley et al. 1997; Cox 2012; Forest Research 2010; Kuo 2010; Wooley and Rose 2004). These potential benefits should motivate urban development professionals to advocate and integrate GI at all scales: regional and municipal masterplans, individual building lot designs, open spaces, and in new or retrofit projects. Precedent for widespread successful living roof implementation is found in Portland (Oregon), Linz (Austria) and Stuttgart (Germany) (Lawlor et al. 2006). Technology, urban design, planning, ecology and associated disciplines have evolved to provide a suite of tools that build upon Olmsted’s parkways. Infrastructure designed with a systems approach merges technical know-how with architectural design to successfully create healthy urban environments.

Figure 1.1
Living roofs: a tool and system component

Within the context of GI, resilient urban stormwater solutions rely on a holistic approach to managing the hydrologic cycle and improving water quality. Green Stormwater Infrastructure (GSI), Low Impact Development (LID), Environmental Site Design (ESD), Water Sensitive Urban Design (WSUD), or Sustainable Urban Drainage Systems (SUDS) are common terms around the world to summarize this design approach. Regardless of the name, the design paradigm combines land-use planning with engineered stormwater control measures (SCMs) to create a functional landscape that minimizes changes to site hydrology and limits pollutant discharges (e.g., Figure 1.1). Equal attention is paid to runoff quality and quantity. From a philosophical and technical perspective, prevention (source control limiting runoff-or contaminant-generating surfaces) is more effective than a “cure” (capture and treat) (National Research Council 2009).

Thoughtfully designed living roofs provide an excellent opportunity to effectively prevent or significantly dampen runoff generation from the traditionally impervious rooftop, yet form does not always complement function. The landscape architect’s objective is to make these planted spaces visually attractive, accessible, noticeable (or invisible) and usable as well as maintainable from an environmentally responsible standpoint. Clients are heavily influenced by garden design magazine images in their perception of living roof appearance. Landscape architects are pressured to produce a “green” roof appearance foremost for the client, whereas lack of connection to the ground means that living roofs are extreme places, (hu)man-made and artificial – thus potentially requiring significant intervention. Designers need to responsibly balance appearance with the long-term environmental benefits, where the premise of the living roof assembly and runoff mitigation capacity might (or should) override the appearance. Exploring the interdependence of the visual impact and techn...