Hakai Magazine –
I’m swimming under a sidewalk. The cantilevered slab of concrete is a couple of meters over my head, part of Seattle’s Central Waterfront area that is famous for Pike Place Market and the tourist stroll of chowder houses and souvenir shops. It’s not your average sidewalk: it’s been embedded with translucent glass bricks that allow light to hit the seawater. Like many of the other enhancements to the recently rebuilt sea wall, it’s an act of eco-engineering intended to improve marine habitat in the waters of Elliott Bay, in Washington State.
Thanks to the glass bricks, I can see some of the other subsurface innovations. Most obvious is what’s right in front of me: the concrete face of the sea wall itself, which has a cobbled, river stone texture and angled shelves that encourage the growth of algae and invertebrates. Below me, the seafloor has been built up with mesh bags stuffed with rocks, known as marine mattresses; these reduce the water depth and make the sea wall area more hospitable to juvenile salmon, which are evolutionarily programmed to prefer shallow, nearshore waters. As for the light-delivering sidewalk, it’s intended to boost seaweed growth and create a more inviting passage to shade-avoidant salmon smolts.