Prepared 10 March 2010 for Prof. Madhav Badami (URBP506, McGill University).
————— —— —————
In this paper:
With ever-confining constraints on budgets for capital projects, municipalities must increasingly consider the most efficient and cost-effective means to accommodate anticipated usage demands while also meeting compliance with stronger environmental regulation. For storm water and wastewater management, the century-old engineering methodology of straightening and burying indigenous waterways and tributaries is being reconsidered as major flooding events, complications from street pollution runoff, and the deterioration of drainage conduits strain ageing subterranean infrastructure. As well, increased citizen concern for the ecological health of their surroundings contrasts against the old stigma of creeks and streams serving as magnets for open sewage and illegal dumping.
Stream daylighting, the practice of “expos[ing] some or all of the flow of a previously covered river, creek or storm water drainage” is restoring once-buried watersheds to surface, allowing them to assume the manifold role of absorbing and slowing discharge from major rainfall events, mitigating polluted effluent from street runoff, and re-introducing recreational watershed spaces for cities. Given ongoing costs incurred by infrastructure upkeep and replacement, daylighting may also present long-term, cost-saving advantages relative to traditional storm water collector installation — once ancillary benefits are figured into cost-benefit analyses.
1) Improving local watersheds and meeting stricter water quality regulations.
Sediment, bacteria, and excessive nutrients from water runoff — collected by and directed through conventional storm water conduits — ultimately find their way into estuaries, rivers, lakes, and bays. Unless this water is actively treated by a municipal water treatment facility, then these contaminants are aggregated and released at once. This can result in disruptive, toxic conditions which negatively affect riparian and marine habitats and render beachfronts and other public recreational facilities into hazardous zones. This produces what is known as the “shock-loading” of a water ecosystem. In addition, hypoxic “dead zones” in places like the Gulf of Mexico, agitated by excessive nitrogen (runoff from lawn fertilizers), phosphorus (detergents and surfactants), and “non-point” hydrocarbons are also traceable to urban water discharge.
By contrast, the filtering of those sediments and pollutants (through the engineering of grass swales, wetlands, and bogs, as integrated into daylighted creeks or streams) discharges water only once it undergoes staged filtration — spreading those surplus nutrients over a broader area and allowing indigenous microorganisms to help break down runoff contaminants. Deployed properly, for example, this process of bio-retention absorbs and breaks down significant levels of phosphorus. As well, the anoxic conditions endemic to wetlands helps to convert nitrogen-laden runoff by freeing nitrogen back into the atmosphere. An imperative to take responsibility over local water quality stems from distinct, but interrelated concerns: public health; adherence to stronger water quality regulations; and cost-optimization by letting natural processes replace the engineering and upkeep of underground retention basins while reserving the role of water treatment facilities for raw sewage treatment.
2) Preparedness for absorbing discharge overflow during intense rainfall events.
It is not uncommon for water management districts to merge storm water and sanitary sewage lines into the same collector lines for centralized sanitary treatment. In addition, the practice of burying former creek beds and re-routing water to underground pipelines for this purpose is problematic for three reasons.
First, as water is re-routed from impervious surfaces (e.g., pavement, rooftops, etc.) to storm water drainage pipes, this simultaneous runoff tends to overwhelm drainage infrastructure. This can result in street- and flash-flooding events. This is due to the excessive presence of impervious surface coverage for urban paving applications. Second, as storm water is channelled through storm sewer lines, the generally straightened pathways afforded by these pipelines dramatically boost water velocity and volume throughput. Once discharged, the wakes of these outflows can mimic jet exhaust — rapidly eroding soil in its wake, creating sinkholes, and severely damaging aquatic and riparian ecosystems. In other words, urban watersheds — re-engineered to absorb massive amounts of storm water discharge — are rendered into “gutters” where indigenous ecological activity is virtually forced from the picture; consequently, the natural capability to recharge groundwater is defeated. During lulls in precipitation, these output streams can run dry, preventing the relatively steady levels required to sustain a diversified ecosystem. Third, creating a ring of retention basins around a city for interim floodwater storage — until a water treatment facility is able to absorb the overflow — is cost-prohibitive and can require decades to plan, finance to build, and bring completely online.
3) Approaches for enhancing public space and creating habitat corridors.
Urban recreational space offers a soft asset for citizens and neighbourhoods by linking the city to natural ecological activity. How these spaces are configured is also relevant: a park designed either as an afterthought or from a master plan can fail as an attractor for recreational participation because the scale, intended purpose, or quality of scenery might not resonate with what citizens find to be desirable. By the same token, treating green space as a luxury amenity rather than a public health necessity passes over special opportunities to enrich a locality’s quality of life.
One distinctive characteristic of a daylighted stream is that it restores a natural waterway corridor where before it lay buried underground, invisible, and possibly forgotten. By combining the primary function of filtering and cleaning storm water runoff with the re-introduction of public spacing — an “ecological park” — it rewards citizens with new ways to see, experience, and engage with a riparian habitat within the city. In settings where a proposed daylighting project would cut through a densely urbanized area — restricting its ability to meander — it is still possible to develop public promenades to run alongside a corridor. Whereas a daylighted stream is restoring the siting of a historically significant waterway, the use of landscape design can additionally emphasize its aesthetic features by integrating these with its primary role as part of a storm water management regime. Likewise, the introduction of a daylighted waterway through an urban centre may function as an economic incentive to attract businesses and residences desiring proximity to an attractive water corridor.
- Conventional storm water management requires extensive planning, engineering, and implementation, yet lacks the ability to remove non-point pollutants which create hypoxic dead zones in major water bodies;
- Stream daylighting as an alternative to conventional storm water management introduces demonstrably thorough ways to filter nitrogen-based nutrients and phosphates naturally, as well as hydrocarbons typically found in urban water runoff; filtering these pollutants helps to meet increasingly strict water quality standards;
- Daylighting also offers greater responsiveness for absorbing exceptional rainfall events,
whereas conventional storm water management methods may result in flash flooding, land
erosion, and sinkholes; and
- Re-introducing surfaced watersheds within urban zones benefit citizens with greater
connections to healthy ecological activity and surroundings — opening possibilities for promenades, recreational spaces, and increased interest in nearby real estate.
Stream daylighting is considered a “Low Impact Development” approach for managing storm water runoff and reducing primary pollutants typically ascribed with urban activity. Depending on the specific needs and constraints for a candidate site, the amount of pollution removal from water runoff can dramatically exceed conventional water treatment methods. One significant consideration is the capital costs associated with the engineering and construction of a daylighting project: initial costs to prepare a site may run higher than with conventional methods as, for example, land rights-of-way may first need to be secured. Amortized over time, however, these costs can be recovered as the necessity for repairing underground infrastructure and upgrading active wastewater treatment equipment is no longer necessary. Further, stream daylighting, as part of a turnkey water management strategy, can (depending on the project’s specific requirements) be deployed more quickly than conventional piping conduits.
- Pinkham, Richard. 2000. Daylighting: new life for buried streams. Snowmass, Colo.: Rocky Mountain Institute, iv.
- Pinkham, 2000, iv–v.
- Jencks, Rosey and Rebecca Leonardson. 2004. Daylighting Islais Creek: a feasibility study. Berkeley: UC Berkeley Water Resources Center Archives, 20.
- U.S. Environmental Protection Agency. 2003. Protecting water quality from urban runoff. Washington: U.S. EPA, 1. Also Dwight, Ryan H., et al. 2002. Association of urban runoff with coastal water quality in Orange County, California. Water Environment Research, January/February, 74(1), 86.
- Yazdi, S. Kazemi and M. Scholz. 2010. Assessing storm water detention systems treating road runoff with an artificial neural network predicting fecal indicator organisms. Water, Air, and Soil Pollution, 206(1–4), 35.
- Rabalais, N.N., et al. 2010. Dynamics and distribution of natural and human-caused hypoxia. Biogeosciences, (7) 603. Also Larkin, G.A. and K.J. Hall. 1998. Hydrocarbon pollution in the Brunette River watershed. Water Quality Research Journal of Canada, 33(1), 73.
- Benedict, Mark A. and Edward T. McMahon. 2001. Green infrastructure: smart conservation for the 21st century. Washington: Sprawl Watch Clearinghouse, 18.
- Scholz, Miklas, et al. 2010. Monitoring of nutrient removal within integrated constructed wetlands. Desalination, 250(1), 356. Also Hsieh, Chi-hsu and Allen P. Davis. 2005. Evaluation and optimization of bioretention media for treatment of urban storm water runoff. Journal of Environmental Engineering, November 131(11), 1521.
- Scholz, Miklas. 2006. Wetland systems to control runoff. Amsterdam: Elsevier, 97.
- Smith, Brooke Ray. 2007. Assessing the feasibility of creek daylighting in San Francisco, part II: a preliminary analysis of Yosemite Creek. Berkeley: UC Berkeley Water Resources Center Archives, 2–3.
- U.S. EPA, 2003, 1.
- Bernhardt, Emily S. and Margaret A. Palmer. 2007. Restoring streams in an urban world. Freshwater Biology, (52), 738. Also Moerke, Ashley H. and Gary A. Lamberti. 2008. Restoring stream ecosystems: lessons from a Midwestern state. Restoration Ecology, 12(3), 327.
- Smith, 2007, 2–3.
- Jacobs, Jane. 1961. The death and life of great American cities. New York: Random House, 106.
- Groenewegen, Peter P., et al. Vitamin G: effects of green space on health, well-being, and social safety. BMC Public Health, 6(149). Retrieved 10 October 2007.
- Fitzsimmons, Matthew James. Rediscovering nature: daylighting an urban stream (Gwynns Run, Baltimore, MD) (Masters thesis). ProQuest UMI, (2148), 98.
- Simpson, Jacob T. 2004. Rediscovering the River Bièvre: the feasibility of restoring ecological functions in an urban stream (Masters thesis). Massachusetts Institute of Technology, 22–4.
- Pinkham, 2000, 32.
- Doran, Sherrill and Dennis Cannon. 2006. Cost-benefit analysis of urban stormwater retrofits and stream daylighting using low impact development techniques. Water Environment Foundation, 3833–4.