This article is written from a British Columbia perspective. It connects the dots between recent developments in the United States, such as A Strategic Agenda to Protect Waters and Build More Livable Communities Through Green Infrastructure released by EPA in April 2011, and comparable initiatives that have been underway in British Columbia for the past decade. A key message is that we are observing a convergence of understanding. On both sides of the 49th parallel, light bulbs are going on about the inter-connectedness of green infrastructure and water sustainability, and the implications for watershed health. We hope that this article will stimulate a cross-border discussion on the relative effectiveness of an educational versus prescriptive approach to leading and implementing change.
The View From British Columbia
In both Canada and the US, there is a growing green infrastructure movement. This reflects a heightened public awareness of the need to build our communities differently. Also, land use and infrastructure professionals increasingly appreciate that effective green infrastructure is at the heart of responsible rainwater management. As a result, there is a shift away from pipe-and-convey solutions to ones that embody “designing with nature” to protect our streams and fishery resource.
Looking back, 2008 was a defining year for green infrastructure on Canada’s west coast. The government of British Columbia put in place a policy framework that is a “call to action” on the part of local governments. This call to action is underpinned by the notion of shared responsibility–that is, everyone needs to understand and care about the goal. If all the players know their role in relation to the goal, then together we can create the future that we all want.
A key message is this: A science-based understanding of the rainfall-runoff process is the foundation for designing with nature and implementing green infrastructure that is truly effective in protecting watershed and stream health.
Similar Vocabulary, Different Goals. From our British Columbia vantage point, it has been fascinating to observe the evolution in American practitioner thinking in recent years. While land-use and infrastructure professionals are using a similar vocabulary on both sides of the border, our goals appear different. The apparent divergence has significant implications for rainwater management in a watershed context. The genesis for this divergence is found in geography and governance:
Geography: British Columbia is primarily a mountainous region. Headwater tributary streams are a predominant feature. Watershed health is very much about protection of aquatic habitat. This contrasts with the water-quality emphasis in the US.
Governance: The American approach is top-down and prescriptive. British Columbia has embraced a bottom-up approach that relies on education, enabling tools and consensus to turn ideas into action.
We are culturally different, yet we can learn from each other, and we each can adapt lessons learned by the other. The power of the enabling approach is the ability to leapfrog ahead when the science leads us to a better way. Cross-border sharing between British Columbia and Washington state, for example, has led to breakthroughs in understanding the cause-and-effect relationship between land use change and stream health.
The approach we have taken in British Columbia differs from that of the United States EPA, due to the nature of the root problems being solved. The critical issue in British Columbia is the damage and loss of habitat caused by development and erosion of the headwater streams. The focus is in direct response to Canada’s Fisheries Act that prohibits damage of fish habitat.
EPA has focused upon water quality in the main stems and coastal waters and seeks to restore the resources of those waters through the goals and objectives of the Clean Water Act. The EPA focus has led to initiatives such as a State Nitrogen and Phosphorus Reduction Framework that states can use to develop strategies that address the degradation of drinking water and environmental quality, developing “pollution diets” for impaired waters, and controlling polluted runoff in the Chesapeake Bay.
Same Science, Different Paths Forward. In this article, we tell the story of how British Columbia and Washington state had the same understanding of the science in the late 1990s, but then moved along diverging pathways. This divergence reflects the markedly different roles played by the federal government in each of our two countries.
Genesis for Cross-Border Collaboration With Washington State
Washington state and British Columbia are geographically similar, with a wet coast and a relatively dry interior separated by mountain ranges. On the coast, Washington’s Puget Sound and British Columbia’s Georgia Basin together comprise the Salish Sea. The bulk of the two populations reside in this Pacific Northwest bioregion. In terms of how rainwater management in a watershed context has evolved, there is a history of cross-border sharing and collaboration.
A Shared Goal to Protect Salmon Habitat. The catalyst for collaboration was the salmon crisis of the 1990s. On both sides of the border, the salmon is an icon. It is also the early warning system that there is a problem. Coastal salmon runs such as coho, chum, and pink spawn and rear in the headwater streams, which are typically small, and their ecosystem value was not fully appreciated a generation ago. The result: streams were being lost as a consequence of rapid population growth and land development. This lack of understanding and respect contributed to the decline of many wild salmon populations. And so the goal of protecting stream health became a driver for action on both sides of the border. An environmental ethic led some water resource practitioners to rethink how we design and build communities.
Among those leading change, Bill Derry has had a profound influence on both sides of the border. In the 1980s, he was one of the first stormwater utility managers in Washington state. He believed so strongly in the need for scientifically defensible research that he convinced his fellow utility managers to organize and fund a research centre at the University of Washington. He was a founding director of the Center For Urban Water Resources Management. Though he is now retired, the mission continues: Currently, Bill Derry is president of People for Puget Sound.
A Science-Based Road Map for Integrated Rainwater Management. In 1996, the Center for Urban Water Resources Management published the landmark findings of Richard Horner and Chris May. Their seminal paper synthesized a decade of research to identify the factors that degrade urban streams and negatively influence aquatic productivity and fish survival. The four factors limiting stream health are shown in Table 1 in order of priority.
When published, this ranking shook conventional stormwater management wisdom in the Pacific Northwest to its foundation. If the goal is protection of aquatic resources, it proved that a water-quality-driven program would not achieve the goal. Figure 1 illustrates the research findings for changes in hydrology (#1) and deterioration in water quality (#4). Two key messages flowed from this research: salmon would already be gone by the time pollutant loading is a factor in salmon survivability; if we get the hydrology right, water quality typically takes care of itself. The four factors provide a road map for integrated rainwater management.
A Springboard to British Columbia’s Guidebook. Derry communicated the science in a way that was easy for his audiences to embrace. His teaching resonated with local governments in British Columbia. A series of workshops and forums in the late 1990s jump-started an ecosystem approach that integrates rainwater/stormwater management and land use planning. In particular, the stream health findings by Horner and May gave British Columbians a springboard to reinvent urban hydrology. Released by the Province in June 2002, Stormwater Planning: A Guidebook for British Columbia is a transformational document. It quickly became a catalyst to implement a “design with nature” approach to rainwater management and green infrastructure.
Stormwater Planning: A Guidebook for British Columbia
The Guidebook advanced this provocative premise: Land development and watershed protection can be compatible. In 2002, this radical shift in practitioner thinking resulted from recognition of how a science-based understanding could bridge the gap between high-level policy objectives and site design practices. A key to the breakthrough in thinking and approach was developing the concept of the rainfall spectrum and translating the concept into an integrating strategy (Figure 2).
The Guidebook was a catalyst for action, providing:
- direction
- science-based principles and objectives
- guidance on how to do integrated planning
It introduced these core concepts:
- rainfall spectrum
- the “retain, detain, convey” integrated strategy
- water balance methodology
- performance targets
- a “learn by doing” adaptive framework
Watershed Restoration Is Achievable. The Guidebook applied a science-based understanding to show that we can lighten the hydrologic footprint, developed the water balance methodology to establish performance targets for rainfall capture, and demonstrated that urban watershed restoration could be accomplished over a 50-year timeframe as and when communities redevelop.
Over the next five years, British Columbia practitioners became comfortable with what “rainfall capture” meant in practice. The evolution in watershed thinking was captured in Beyond the Guidebook: Context for Rainwater Management and Green Infrastructure in British Columbia, released in June 2007. By addressing the relationship between rainfall capture and resulting flow rates in streams, Beyond the Guidebook picked up where the Guidebook left off in 2002. Where the Guidebook emphasizes rainfall capture (volume control) at the site scale, Beyond the Guidebook focuses on the relationship between volume control and resulting flow rates in streams.
Beyond the Guidebook foreshadowed Living Water Smart, British Columbia’s Water Plan and the Green Communities Initiative, both of which were launched by the province in 2008. These established an over-arching provincial “design with nature” policy framework. There is now clear guidance for aligning local actions with provincial and regional goals.
British Columbia and Washington State on Diverging Paths
Later in 2007, a cross-border panel session at a joint Washington State-British Columbia conference held in Seattle created an opportunity to take stock of how each region had progressed a decade after the work of Horner and May had provided a common point of departure. The panel introduced this question: Is rainwater management on diverging paths in British Columbia and Washington state? Subsequently, the panel collaborated on a paper for the American Water Resources Association that reflected on the American top-down prescriptive approach versus a Canadian bottom-up educational approach.
In October 2011, the Salish Sea Conference creates another opportunity to compare notes on what each region has accomplished since 2007.
What Is Holding Washington State Back? Ed O’Brien, representing the Washington State Department of Ecology on the panel, posed and answered this question in 2007: What is holding Washington state back? “Locally, our knowledge was and still is way ahead of the federal game because of Puget Sound Plan initiatives and a few forward-thinking local governments. The federal rules impede our progress in implementing strategies and requirements that we know are necessary.
“In Washington State, we cannot achieve environmental protection using current methods of development. Not many new developments are applying low impact development techniques. There isn’t a land use dictator who can demand change. It will take public education to instill a culture change for us to have any hope that we can protect aquatic resources in the urban environment,” concluded O’Brien.
In 2011, Derry reflected on the Washington state situation as follows: “In the late 1970s and 1980s, Washington state jumped out ahead of most of the nation because several stormwater utilities were formed (the first in the nation). Formation of the stormwater utilities resulted in financial, technical, and staff resources that were focused on stormwater issues. Local stormwater managers recognized the need for more technical information to help make more informed stormwater management decisions. This led to the formation of the Center For Urban Water Resources at the University of Washington. This Center conducted and disseminated the seminal body of work now used internationally by stormwater managers. Many municipalities used this information to update their regulations and management practices. But there was a wide disparity between local municipalities in their regulations and management practices.
“Due to political pressures many jurisdictions will not adopt the necessary programs to protect environmental resources until required to do so. Once a state permit program was initiated, the previously cooperative approach between the state and local municipalities became adversarial. There are extended negotiations over the requirements of the permits. Now after several years of living with state municipal stormwater permits there is more consistency between jurisdictions, but the bar has been lowered for environmental protection. For example, a recently proposed regulation to require Low Impact Development (mandated by court order) is so full of exemptions that it is essentially voluntary.
“The American system seems based on political compromise which means that with each compromised decision environmental resources lose some more,” concluded Derry.
How British Columbia Is Creating Change. Kim Stephens provided this British Columbia perspective in 2007: “We are creating change through on-the-ground partnerships. Finding the right solution is an outcome of sharing a vision about what we want our communities to look like, not because a government agency prescribed a regulation. For us, designing with nature has become a rallying cry. In British Columbia, we have made a conscious decision to go the educational route. It is all about establishing expectations and creating an environment that encourages innovation and gets practitioners excited about what they are doing. The culture is changing.”
Take Stock and Look Ahead. Our impression is that the efforts of both EPA and British Columbia may be moving closer. The National Lakes Assessment, the first-ever comprehensive assessment of lakes in the United States, found that habitat loss and nitrogen and phosphorus pollution are leading causes of impairment. Similarly, the objectives of A Strategic Agenda to Protect Waters and Build More Livable Communities Through Green Infrastructure could lead the United States to pay closer attention to the pioneering work of Horner and May and others. Perhaps when EPA focus shifts from water quality to include habitat loss, the lessons learned in British Columbia can be reviewed and incorporated into the policies and objectives of EPA.
In British Columbia, our focus has been on stream habitat (for the reasons explained earlier in this article). Looking ahead, our emphasis may shift to include water quality once the efforts to mitigate habitat damage become universal and effective practice. This could lead to the next evolution in creating a greener and more sustainable environment for each unique watershed.
“Cross-border communities, stream keepers, and First Nations (Tribes) have been meeting to discuss shared waters issues and to share information since the 1990s. Some combined projects have gone forward looking at circulation and pollutant transport pathways plus coordinated monitoring specifically for data sharing. By working together with available resources and sharing findings, we can better meet watershed goals of improved water quality and ecological health on both sides of the border,” observes Carrie Baron, manager of Drainage and Environment with the City of Surrey, British Columbia’s second largest city.
Science-Based Foundation for Designing With Nature
In British Columbia, we have built on the foundation provided by the pioneering work of Horner and May and others, including Derek Booth, R. Christian Jones, John Maxted, Craig MacRae, and Ivan Lorent. They questioned common wisdom, they undertook original research, and they provided us with a science-based understanding of the importance of changes in hydrology. Their work yielded guiding principles that are standing the test of time. We continue to enhance their pioneering work.
Given the foregoing frame of reference, the authors of this article wish to inform or remind today’s water resource practitioners of the lasting value of this pioneer work. This is the foundation of our evolving knowledge of the impacts of urban development and the impacts upon the aquatic environment. Our understanding of the current state of knowledge allows us to question our common wisdom and to apply corrections where appropriate. In this manner we are continuously improving and including sound reasoning backed up by demonstrable science.
Next, we introduce and briefly describe building blocks that constitute the science-based foundation for rainwater management in a watershed context. We:
- highlight the significance of the pioneer research,
- elaborate on how the concept of the rainfall spectrum has led us look at rainfall differently in British Columbia,
- examine the hydrograph for a typical year,
- describe the relationship between stream erosion and stream health, and
- explore the implications of disrupting how rainfall reaches the stream.
Truly understanding the rainfall-runoff process allows us to implement “design with nature” designs that soften the footprint of development.
Learn from the Pioneers. 1996 stands out as a year of breakthroughs. We have already discussed the significance of the Horner and May contribution in demonstrating the order-of-priority for factors limiting the ecological values of urban streams. In that same year Jones, Maxted, MacRae, Horner, Booth, Azous, and May presented papers at an Engineering Foundation Conference sponsored by the Urban Water Resources Research Council of the American Society of Civil Engineers. Their research findings are important because:
Jones and Maxted indicated that the biological stream community were impacted by urban development in spite of the engineering application and implementation of stormwater best practices.
MacRae indicated that the use of detention basins to simply restrict flows to predevelopment rates would increase the rate of stream erosion and that different criteria were needed, and proposed an alternative based upon maintaining the distribution of shear stress across the channel from pre to post development conditions.
Horner, Booth, Azous, and May condensed the findings of a number of studies to conclude that coho salmon populations were greatly affected by development that included less than 10% impervious area, and water quality and concentration of metals in sediments did not change much until imperviousness approached 50%. As urbanization increases above the 60% impervious level, water and sediment chemistry will become biologically more important.
The findings by MacRae validated the earlier work of Ivan Lorent, published by the Ontario Ministry of Natural Resources in 1982. Lorent undertook a study to clarify the understanding and the processes involved in stream erosion. He questioned the common wisdom that suggested matching pre- and post-development discharge rates was an adequate method of avoiding environmental impacts. In 1982, Lorent demonstrated that the design standard using rate control to match post-development flow rates to predevelopment rates could result in increased stream erosion.
Understand the Rainfall Spectrum. Figure 2 shows the rainfall spectrum graphic that is the branding for the Water Balance Methodology presented in the Guidebook. This was the outcome of looking at rainfall differently in British Columbia. Our reassessment of rainfall has led us to a better understanding of how rainfall fits into the overall picture:
Typical Frequency Distribution of Annual Rainfall: Figure 3 shows the number of days with rainfall. These are divided into three volume categories based upon the mean annual rainfall (MAR) event. The vast majority of wet days would have small amounts of rainfall, and statistically only a single day would typically equal or exceed the MAR amount. This underscores that the impacts to streams are driven by small events, not those used in designing drainage conveyance systems or flood protection works.
Typical Volume Distribution of Annual Rainfall: When we compare the volume of rainfall associated with the size of the event in Figure 4 we can see even more interesting indications of the source of the impacts. The majority of the rainfall volume occurs in very small events, with only about 5% coming from the larger return period events that might be approaching the size of those used for design of drainage systems and flood protection.
The insight gained from examining rainfall patterns leads us to ask whether it is appropriate, or even correct, to use less-frequent events with a greater return period to examine the impacts to streams. A typical year of rainfall and stream discharge is shown in Figure 5. This illustrates a core concept underpinning Beyond the Guidebook.
Understand What Happens During a Typical Year. Figure 5 shows that the larger of two rainfall events resulted in much less runoff. The smaller event was preceded by a period of wet weather such that more runoff resulted. The hydrograph also shows that 90% of the total annual runoff volume corresponds to a very small runoff rate. The implication of this finding is that the 90% can easily be managed through rainfall capture measures. For the other 10%, it is a matter of detaining and conveying in accordance with the integrated strategy for managing the complete rainfall spectrum (Figure 2).
Additionally, retaining 90% on site would have little effect on peak runoff rates unless other practices are brought to bear. This implies that retaining 90% of the rainfall is only a part of the requirement for an effective rainwater management system. This underscores the need to manage the complete rainfall spectrum.
Understand the Relationship Between Stream Health and Stream Erosion. Stream health is a function of streamflow duration, and therefore correlates with stream erosion. Flow duration is something that we can measure and verify. We can also assess the potential for erosion or sediment accumulation within a watershed.
Several quantitative indicators can be utilized in assessing the potential for erosion or sediment accumulation within a watershed. The methodology is based upon shear stress as applied to the stream bed and banks over time. This is a measure of the energy available to cause erosion in a stream. Continuous hydrologic simulation is the key to evaluating multiple development scenario comparisons.
Using long-term climate records to calculate stream discharge means that the durations and frequencies of various occurrences within the watershed and stream can be estimated easily. Also, this approach leads us into examining the hydrograph for the entire year, not just one or two big events that may be associated with flooding.
Continuous hydrologic simulations and this methodology have been used as the basis for developing the Water Balance Model as part of an ongoing process to advance the science of environmental mitigation.
Understand How Water Reaches the Stream. If rainfall is captured to reduce site discharge, how does the water then get to the stream, and what are the processes and timelines? Figure 2 shows the generalized flow patterns of natural and post developed conditions.
“Rainwater management has developed far beyond the simplistic assumptions that created the detention ponds of the 1980s. It is now time to take another leap forward, albeit by moving sideways, and recognize near surface lateral water flow, otherwise known as “˜interflow’,” states Alan Jonsson, habitat engineer with Fisheries and Oceans Canada.
“Interflow is often the dominant drainage path in glaciated landscapes of British Columbia. Even undeveloped sites that are founded on till and bedrock rarely show overland flow because of interflow pathways. Interflow has been traced flowing at velocities that are 1/200th as fast as channel flows on a similar gradient. It is not hard to imagine the beneficial effect that this has in prolonging flows from rainfall to first-order streams.
“Unlike deeper aquifer fed groundwater, interflow water is often rich in dissolved organic carbon and other nutrients. It is this flow that feeds hundreds of small ephemeral streams throughout the Lower Mainland (in the southwest corner of British Columbia) where more than half the population resides. Such streams provide important salmonid food supply and rearing habitat. In some cases, they may even support Coho spawning.
“When we acknowledge the role of interflow and its incredible ability to absorb and slowly discharge precipitation, we are led to the realization: a watershed’s hydrology can be severely degraded without any increase in impervious area. All that is required is a loss of functional soil layer and/or the addition of ditches or perforated pipes and presto, one “˜urbanized’ watershed. Conventional watershed health metrics such as total impervious area can under estimate impacts where interflow dominates.
“Unfortunately, it is a rare thing to find a rainwater management practitioner that ever “˜thinks sideways.’ How many times have we all heard “˜There’s no infiltration on this site’? The challenge for engineers is to determine the influence of interflow on a site and then design and implement techniques that replace or restore it. Our present patterns of land development often seem perfectly suited to ensuring the elimination of interflow. Utility trenches, basements, discontinuous soil, and highly compacted soils all work together to deprive small streams of water. Without a significant change in development practices and standards, based on watershed-specific understandings, we cannot maintain stream health and productivity.
“The lesson is that the interflow system is an incredibly important and yet fragile component of a watershed. It is critical for maintaining stream health and our fishery resource. Where the system is still operating it must be protected; where human activity will cause an alteration to its function, then replacement systems must be created that will mimic its operation to prevent any additional impacts to the stream and our resource,” concludes Jonsson.
These observations further emphasizes the need to evaluate the impacts of diverting 90% of rainfall by infiltration into deep groundwater. Such practices could eliminate base flows in the headwater streams and result in even greater unanticipated and unwanted environmental impacts.
Synopsis of What We Have Learned. We have distilled the foregoing technical discussion into a set of seven conclusions:
- Impacts to the headwater streams of the Pacific Northwest are evidenced by erosion and habitat loss well before water quality becomes an issue.
- Traditional engineering approaches may not result in impact mitigation–for example, discharge rate control may not result in the expected benefits.
- Evaluation of the rainfall spectrum allows us to see new connections.
- Simply capturing and deeply infiltrating rainwater may not be the best solution for a stream.
- Simply capturing 90% of rainfall may not be beneficial to the stream.
- Introduction of stream energy provides us with an additional tool to evaluate and mitigate stream impa
