Bioswales in High Point Public Natural Drainage Systems

Bioswales in High Point Public Natural Drainage Systems

By: Fiorella Eduardo-Palomino

Credits: Designed in partnership between the Seattle Public Utilities and Seattle Housing Authority with the participation of MITHUN Architects, Designers and Planners as well as SvR Design Company

Location: High Point, Seattle, Washington. The High point community is located within a sub-basin of the Longfellow Creek Watershed.

Why did you select this design?

I select this one because I was looking for a large design that fits a large area, for example, a street. The photo (Figure 2) where I first saw this place catch my attention because this bioswale looked large and was located in a public area. After search the origin it was part of a big drainage system project, so I decided to research about it.

Brief description:

The High Point Public Natural Drainage Systems (NDS) is part of a large-scale natural drainage system in an urban area environment with a high-density urban setting. It was completed in the fall of 2005 and cover 34 blocks of Seattle’s streets, from 35^th Ave SW to High Point Drive SW and SW Juneau St. to Myrtle St.

One of the goals of the project was to process water in a  similar manner to a forest meadow. This natural drainage system treats about 10 percent of the watershed feeding Long Fellow Creek which is part of the Seattle’s priority watershed. The NDS is a combination of grass-lined and vegetated swales located in the row that receive street and residential stormwater runoff (SvR Company, 2010).

The High Point Public Natural Drainage Systems (NDS) was part of an integral design with the participation of the High point community. It includes the public stormwater control systems and private drainage facilities. The principal function of the public bioswales was a small storm detention the overflows over land or through a grate to the Natural Drainage Systems as well as to enhance the water quality. The public rain garden was also attached to a porous sidewalk as well as the street gutters near to the road pavement (Figure 1). 

Figure 1. Construction detail of the bioswale. Modified from Seattle Public Utilities (2018) by Fiorella Eduardo-Palomino.

Landscape performance benefits:

·         Environmental: Rather than select a street made of pavement with few trees that can flood with rains, they use the space to take advantage of the rain runoff to produce of biomass (plants) as well as naturally filter (bioretention) the pollutants that the runoff might have.

This Bioswale is composed of different kind of plants, some are native and increase the biodiversity of the place. Three groups were identified. Plants for drier conditions, plants for drier and fluctuating condition of water and plants for fluctuating conditions. The designers also consider the use of native plants adapted to the forest meadow conditions, this consideration help to the conservation of plant species of the Long Fellow Creek watershed. The plants (biomass) of the rain garden located in this urban area help to capture the CO₂ that human activities generate in this city, consequently, people might have better air conditions.

Rather than design a concrete sewer in the pavement they decide to use productive soil, mulch and compost. This live soil is also the home of millions of microorganisms that increase the biodiversity of this urban ecosystem. The soil microorganisms can help to transform pollutant substances in less contaminant ions.

·    Aesthetic: Is pleasant to see. The recreation of a forest meadow helps to create a connection between the urban area with the wilderness surrounding the city. Considering trees on the design was an aesthetic benefit. For the design they considered two kinds of herbs. The first was to consider a deeper vegetated zone and second a shallow Grass lined zone (Figure 1). The alignment of the trees helps to give the sense of continuity on the street and help to join the two different herbal areas.

·       Functional: As it is linked to a porous sidewalk this bioswale is also functional to provide a crossing for pedestrians. 

·    Social: People enjoy running around the gardens. This place is more visited due to the landscape that this bioswale generate.

·     Educational: With this project, people learn to appreciate their environment. For visitants and foreign people this project is an example that cities not are only made of pavement, they also can contain beautiful and functional gardens.

·  Economical: The initial investment for the construction of this swales might be higher. Monsoonraingatdens.com mention that the cost of the installation varies between $4500 and $6000, including all designs, labor and materials. However, the benefits for the population were more. The Seattle Public Utilities reported that houses on this place increased their value due to the landscape that this bioswales generate. The Seattle Housing Authority mentions that the average household utility savings each year compared with typical new constructions is $372. The insured value of buildings $ 260 000 000 and the annual property taxes $3 500 000.

·         Psychological: People living in this area might have less stress when they saw this nice environment outside their homes (Figure 2) and they might less worried about floods and runoff.

Figure 2. Bioswales part of the High Point Natural Drainage System in Seattle, WA.

Source: Staeheli, P. and Gwilym, K. (2010)

Additional information: For the maintenance of this bioswale they must be kept clear of sediment, debris and other obstruction at all timer to facilitate the movement of the stormwater (SvR Company, 2010). Some considerations for their maintenance are:

• Remove any sediment within the overflow channel when the accumulation exceeds a depth of 1 inch.
• Maintain grass and vegetation within the bioswale. Replace any damaged vegetation with the adequate plant material when the vegetation is excessively worn.
• Prune if the vegetation across the pedestrian berm is excessively abundant. 

Personal evaluation of the project:

In my opinion, this project is an example of how Bioswales can work on a large scale and how this project can provide services (aesthetics, biodiversity, bioretention and CO₂ capture) for an entire community.

Some questions about the replicability of this project were found during the information research. In 2010 the Seattle Public Utilities develop a similar project in another area of Seattle called Ballard. The results of this project were not positive due to the gardens became muddy ponds and Seattle government had to expend $500 000 to fix the rain gardens (Stiffler, 2011). This made me think that the establishment of rain gardens could take more time in other places. Maybe more research on the place was needed, or technical considerations such as soil infiltration, water table depth or extreme rainfall data could help to overcome this kind of eventualities.

All these problems don't take away the value that bioswales and rain gardens generate on the environment and the potential they had to improve the life quality in many urban areas. On the contrary, this kind of failures can become lessons to learn how to design better bioswales and rain gardens.

This post was part of a research in the Sustainable Landscapes course of Southern Illinois University. If you like it please comment below and share. There are more sustainable constructions that I want to share with you in the following weeks so stay tuned.

References:

Lenth, J., Rheaume, A., Tackett, T. (2015). Lessons Learned from Monitoring Bioretention Swales in West Seattle's High Point Neighborhood. Retrieved 01/24/2018 from: http://www.seattle.gov/util/cs/groups/public/@spu/@usm/documents/webcontent/spu02_020015.pdf

Reiners, J. (2008). Vegetation Growth and success as a function of soil moisture condition in bioretention cells. Retrieved 01/24/2018 from: http://www.seattle.gov/util/cs/groups/public/@spu/@usm/documents/webcontent/spu02_020010.pdf

Staeheli, P. and Gwilym, K. (2010). Rain Gardens and permeable paving systems. Presentation for the Green factor Workshop. S v R Design Company. Retrieved 01/24/2018 from: http://www.seattle.gov/dpd/vault/cs/groups/pan/@pan/documents/web_informational/s040952.pdf

Stiffler, L. (2011). Ballard's rain gardens: A green experiment gone wrong. Seattlepi.com. Retrieved 01/24/2018 from: http://www.seattlepi.com/local/environment/article/Ballard-s-rain-gardens-A-bad-green-experiment-1345766.php

Seattle Public Utilities, (2018). High Point Natural Drainage System. Retrieved 01/24/2018 from: http://www.seattle.gov/util/EnvironmentConservation/Projects/GreenStormwaterInfrastructure/CompletedGSIProjects/HighPointNaturalDrainageSystem/index.htm

SvR Company, (2010). High Point Community Landscape Maintenance Guidelines. Retrieved 01/20/2018 from: https://www.seattle.gov/util/cs/groups/public/@spu/@usm/documents/webcontent/spu02_020022.pdf

Plains : http://www.seattle.gov/util/cs/groups/public/@spu/@usm/documents/webcontent/spu02_020001.pdf