Conservation Magazine Article: How to Build a Living Seawall

20 03 2012

How to Build a Living Seawall

Simple fixes bring marine life back to urban coastlines


In the coming decades, coastal communities will build or reinforce hundreds of miles of seawalls, breakwaters, and other coastal defenses to protect themselves against rising sea levels and increased storms, as well as to accommodate growing populations.

Already, more than half the shoreline in parts of Japan, Europe, the U.S., and Australia is artificial. And that puts the squeeze on intertidal creatures. Seawalls and similar structures truncate the gradual slope of natural intertidal zones and sharply reduce the area available for species that depend on this habitat.

But lately, researchers are making the case that these structures can be compatible with a healthy measure of marine life—and at very little extra expense, says Mark Browne, a marine ecologist at University College Dublin.

Several years ago, Browne—then a postdoctoral fellow at the University of Sydney in Australia—was part of a team of ecologists who bolted ten-liter flowerpots made of cast concrete to the seawall in Sydney Harbour. The vessels retained water at low tide, mimicking the tide pools found on natural rocky shores.

Seven months later, the researchers counted 25 species in the pots that weren’t present on adjacent sections of the vertical seawall, an increase in species richness of 64 percent.1 “We were getting universal increases across the different phyla that we were looking at,” says Browne—large crabs, sea stars, sponges, tube worms, snails that thrive in sheltered habitat, a diversity of seaweeds. A previous experiment in Sydney Harbour was even cheaper. Engineers simply left out a few of the sandstone blocks from a new seawall. This created cavities that soon became home to urchins, sea slugs—even octopus.

“Even quite small modifications to the seawall surface will increase the diversity” of species, adds Richard Thompson, professor of marine science and engineering at Plymouth University in the U.K. Thompson was part of a team that drilled small holes—about the diameter and depth of a coin—into concrete panels and then attached them to a nearby seawall. Where only one or two species of intertidal organisms typically colonized a section of standard seawall, up to 16 might be present on the textured surface, the researchers found. The experimental panels “were a poor comparison” to natural rocky shoreline, Thompson cautions, “but they were far better than the smooth concrete.”

Those results call for a shift in thinking on the part of engineers and designers, who tend to default to smooth, rectilinear structures. “As human beings we want things that are sleek and straight and orthogonal, and that does not help ecology,” says Cristina Bump, a Boston-based architect who has studied efforts to enhance seawall habitat in both Sydney, Australia, and Seattle, Washington—where a multimillion-dollar, twenty-block seawall reconstruction project is getting underway.

For the Seattle study, a team from the University of Washington bolted a number of five-feet-by-seven-and-a-half-feet concrete panels to the seawall. Some of the panels had “steps” or “fins” projecting a foot or two off the vertical surface. Some had an all-over bumpy texture, achieved by casting the concrete in a mold used to make faux-cobblestone patios. “We just used something that was already out there,” says Maureen Goff, who worked on the project as a master’s student. “We looked at trying to place real rocks into concrete, but it was structurally not great, and more expensive.” There’s a learning curve for ecologists in this field, too.

The researchers installed the panels at three sites along Seattle’s downtown waterfront and monitored the marine life that colonized the surfaces over a period of two years. “The overall community was pretty similar to a vertical seawall, but we discovered that certain features are good for certain organisms,” says research ecologist Jason Toft. Mussels found purchase in the spaces between the “cobbles.” Exuberant stands of Fucus, a greenish-brown seaweed that provides habitat for other intertidal species, grew on the horizontal surfaces. Copepods and fly larvae called chironomids congregated above and below the fins and steps, perhaps finding that these spots were sheltered from the waves.

Similar features and textures may be incorporated into the rebuild of Seattle’s seawall. The city would especially like to have more copepods and chironomids around, because these animals provide food for young endangered salmon.

“There’s a lot that lives down there,” Toft says. Even in a highly urbanized stretch of waterfront, a surprising number of species can thrive with just a few, relatively inexpensive tweaks to their habitat. A cobble, a divot, a cranny—sometimes, what nature needs from us
is just a little bump. ❧

—Sarah DeWeerdt, Conservation Magazine

1. Browne, M. and M. Chapman. 2011. Environmental Science & Technology doi:10.1021/es201924b.

Graphic courtesy of Cristina Bump, Associate AIA, LEED AP


Big Move

21 09 2011

I have been a bit MIA lately, mainly because I moved away from Seattle! I have recently relocated to Boston, MA, where I am working at a great architectural firm and getting to know the city.

Seattle was a great city to learn from and I am looking forward to keeping up to date with the waterfront redevelopment.

I met with the Boston Society of Architects last week and they are interested in showing the ‘Smart Seawalls’ exhibit next year at their new location. I will update as I hear more info!

I will be keeping up to date with the Seattle Waterfront Development so stay tuned!


Catch the Smart Seawalls Show this week before it leaves the Seattle Aquarium!

28 03 2011

Revitalizing Seawalls: An interview in AIA Forum Magazine

17 01 2011


by Dennis Haskell, FAIA

An Interview with AIA Seattle Travel Scholarship recipient Cristina Bump Assoc. AIA, LEED AP

The seawall at McMahon’s Point in Sydney was designed with the intent of providing habitat, in addition to protecting the land. The wall features sandstone blocks with holes that provide shelter for some species, and the omission of a few choice, non-structural blocks create tide pools that serve as habitat.


Why did you select this topic for your application?

After following the Alaskan Way Viaduct redevelopment, I was surprised that the seawall was not a critical consideration: the future of the waterfront relies heavily on improvements to the water’s edge.

Did you do significant research before submitting?

I conducted interviews with several organizations, including SDOT, UW School of Aquatic and Fishery Sciences, Army Corps of Engineers, AIA Seattle, People for Puget Sound, and Puget Sound Partnership, which gave me invaluable information on the current development of the waterfront. After finding limited examples of environmentally friendly seawalls in urban settings, I chose to investigate Australian habitat research in Sydney, Melbourne, and Brisbane.

What were the significant discoveries from your travels?

In Seattle, there are three locations where shallow water development will be considered (Pier 48, the Aquarium, and the Olympic Sculpture Park). The rest of the seawall to be replaced will be vertical due to bathymetric depth and utility locations. For this reason, I focused on studying vertical walls in urban settings and comparing them to the Seattle environment.

Tell us about Sydney

At McMahons Point in Sydney, steel I-beams were hammered to bedrock, then tied back to concrete anchors installed underground. L-shaped precast concrete panels were attached to the steel beams. Sandstone blocks were laid on the bottom section of the L and built vertically. Several non-structural blocks were omitted for environmental purposes. A rock armor was used along the bottom of the seawall to protect against an abundance of wave action. The North Sydney Council asked the University of Sydney’s School of Biological Sciences to design sandstone blocks with inlets that could act as rock pools; holes were drilled into the surface for animals and plants to find shelter.

Salmon, a major part of the Pacific Northwest ecosystem, are a concern as Seattle looks to redevelop its waterfront. According to Jeff Cordell, lead research scientist from the Aquatic and Fishery Sciences Department at the University of Washington, salmon are genetically hardwired to seek horizontal, shallow water habitat. In an urban environment where these shallow water areas have been replaced with vertical, deep water habitat, salmon struggle to find food or refuge. In Seattle, most of the new seawall’s structure will be set in deep water, but a non-structural, environmental component— such as Sydney’s sandstone block tide pools—can be hung off the primary structure at whatever shallow depth will best encourage desired species. This would provide a continuous fish migration corridor along our seawall, providing food and refuge for juvenile salmon swimming out of the Duwamish River.

I learned from Ross Coleman, Director for the Centre for Research on Ecological Impacts of Coastal Cities at the University of Sydney, that if the structural complexity of a seawall is increased, the biodiversity in that habitat will also increase.

What can we learn from Melbourne?

Melbourne went through a period of industrial trade and commerce on the Yarra River. The city effectively turned its back on the river– allowing its banks to become lined with parking lots—and the river soon became contaminated. Birrarung Marr Park, completed in 2002, has transformed the river’s edge, providing an urban place, a public arts space, a pedestrian connection between major city landmarks, and a revitalization of the downtown core. The park reflects the landscape and geology of Australia and celebrates its aboriginal roots.

While Birrarung Marr did not implement an environmentally friendly seawall, it provides an example of smart urban planning and revitalization along a river’s edge.

And Vancouver?

The new Vancouver Convention Centre West incorporates a bioengineered habitat skirt that uses a series of permanent, stepped, pre-cast concrete benches. The five-tiered underwater structure looks like a set of bleachers, consisting of 76 concrete frames weighing more than 36 tons each. The top surface of each bench has a wave pattern of exposed aggregate. A central trough closed at both ends runs along the length of each bench to mimic tide pools.

This variety of surfaces and tidal elevations is expected to encourage initial colonization and long-term use of the bench habitat by a broad range of marine flora and fauna that seek the intertidal zone.

Have you been able to get directly involved in the City of Seattle’s process?

Several City Council members have visited the Smart Seawall exhibit. Tetratech, the seawall consultant team, has used images and information from the same. I was also interviewed by the History Channel in their new show airing in November 2010 about America’s infrastructure. I was encouraged at the City of Seattle’s Seawall Open House and pleased that environmental factors are at the forefront of their planning, and that the UW is still monitoring their seawall test panels.

I am involved in the AIA Viaduct Taskforce and the Peoples Waterfront Coalition. My goal is to stay involved in the Seattle seawall process and raise awareness about this once-in-a-lifetime opportunity to make an incredible waterfront.

What other ways are you going to share your experience?

I created a travel blog which outlines my adventure in Australia and follows the political process in Seattle.

I conducted a waterfront tour with the Seattle Architecture Foundation (SAF) where we examined the past, present, and future of the Seattle waterfront with the help of local experts. SAF is picking up the tour for their regular schedule:

AIA Seattle is sponsoring a model, video, and print exhibition about my research and findings called “Smart Seawalls: A Travel Study on the Future of the Seattle Seawall”. Of special interest will be large-scale physical models of the different “smart” seawalls studied and how they could be applied to Seattle’s habitat, ecosystem, and tidal patterns. This exhibit will then travel to several other venues including Mithun and the Seattle Aquarium to reach a wider audience. The exhibit is now at the Seattle Aquarium.

Cristina Bump Assoc. AIA is a designer for Mithun and 2009 recipient of the AIA Seattle Emerging Professionals Travel Scholarship.


Visit the Seattle Aquarium over the Holidays!

14 12 2010

And check out the Smart Seawalls exhibit!


Seattle Aquarium: Smart Seawalls Exhibit

22 10 2010

Thanks to all who came out to the Smart Seawall Exhibit reception last night at the Aquarium. Bob Davidson and his staff from the Aquarium provided an incredible venue! And thanks to the sponsorship from MITHUN and AIA.

The show is up at the Seattle Aquarium indefinitely, meaning you can still go check it out: 9:30 – 5 daily! The exhibit is towards the back right near the Hawaiian fish exhibit.

Seattle Met Article: Sometimes a Seawall Isn’t Just a Seawall

21 10 2010


Message meets models in an eye-opening installation at the aquarium


Here’s how Sydney did it.
Courtesy Cristina Bump

Usually when we talk about Seattle’s downtown seawall we lament how it’s crumbling and threatening to plunge the waterfront, the viaduct, and all the utilities running alongside into disaster. And how Mayor McGinn’s been pushing a bond issue to rebuild it, but everyone thinks he’s trying to end-run the waterfront tunnel so nothing gets done.

Rookie architectural designer Cristina Bump set aside these debates and asked some other questions: Just what kind of seawall should it be, and how should it fit into the marine shore environment? These questions came naturally: Mithún, the architectural firm where she works, sits on a historic waterfront pier. She got an American Institute of Architects travel fellowship and headed off to Vancouver, Sydney, Brisbane, and Melbourne to see what they’d done with their seawalls. Now she’s showing the results in Smart Seawalls, a little exhibit at the Seattle Aquarium that’s both beguiling and enlightening—with an opening reception this Thursday.

Here’s what Cristina bumped into in her travels: Sydney cut the cost of rebuilding its crumbling seawall 50 to 75 percent by squirting cement grout behind the existing sandstone—a trick that might not work in Seattle, but ought to be considered. It created new marine habitat—vertical tidepools—by adding niches, reef balls, and concrete extrusions, plus boulders in front to cushion the waves. Brisbane has no such smart seawall, but it’s kept a mangrove margin and managed to connect pedestrians to shoreline parks despite what looks like even thicker waterfront traffic than Seattle’s. And so on….

All these findings are clearly presented with the usual photos and wallboards (thought they could use a little proofreading). But the treat is the old-fashioned three-dimensional, cross-sectional models Bump made of the seawalls she studied. Alas, the aquarium’s hung them by the play area near the Hawai’ian fish tanks, and the kids pull off pieces faster than she can refabricate them. So make allowances and check it out at the Thursday opening, 6:30-8:30pm (RSVP to or in the coming weeks.

Bump’s installation will remain up indefinitely. And she may not be over seawalls yet. Mithún’s been picked to work with the renowned New York landscape architect James Corner, who will design a new waterfront for Seattle.

Posted by: Eric Scigliano on Oct 20, 2010