Neighborhood tries to honor Mother Nature's runoff rules
Seattle Times staff reporter
The tract of raw dirt and pavement crisscrossed by bulldozers at the High Point housing project in West Seattle doesn't look much like a meadow.
But when it rains, it's supposed to act like one.
The 120-acre site, slated to eventually hold 1,600 apartments and houses, is among the most ambitious attempts in the region to reshape what happens to raindrops after they hit the ground in cities and suburbs.
Using everything from concrete that soaks up water like a sponge to ditchlike gardens that channel water off streets, High Point's creators are using innovative engineering tricks to imitate nature.
The experiment there, and similar ones scattered around the Puget Sound and the country, could change how neighborhoods look and how development affects surrounding ecosystems. If the experiments are successful, future subdivisions could have narrow, winding streets without curbs, cascading artificial streams instead of storm drains, and intensive landscaping rather than massive water-detention ponds.
"You're never going to be able to replace that forest, but what you can do is mimic the functions of the forest," said Denise Andrews, a Seattle Public Utilities manager.
For decades, rainwater in urban America has been handled much like water flushed down a toilet. It's funneled from homes and streets into pipes. In most modern developments, it's stored in artificial ponds and gradually poured into a nearby creek or lake.
The new High Point project is being constructed on the same site as an older housing project that was built during World War II. In typical fashion of the time, stormwater was channeled through open ditches, out a pipe and into Longfellow Creek, then on to the Duwamish River and to Puget Sound.
While such old-fashioned setups get rainwater out of sight, there's growing recognition that they take a toll.
In a forest, rain soaks into the ground and seeps gradually to streams. But housing developments cause streams to flow too high or too low. In the wet months, water runs off roofs, roads and sidewalks and is flushed straight to the stream instead of becoming groundwater. Then, during the dry season, there's less groundwater to leak into the streams.
Too much water means erosion that clogs streams and hurts salmon, aquatic insects and other species. Too little water makes creeks too shallow and warm for the creatures that live there.
In Longfellow Creek, for example, years of stormwater have polluted and eroded the stream, leaving a concretelike streambed in some places.
"As far as the freshwater habitat, streams and wetlands around the Puget Sound, stormwater is a major issue and a very challenging one," said Curtis Hinman of the Washington State University extension office in Pierce County. Hinman has written a manual for new, low-impact stormwater systems.
"People are used to, 'It goes down the drain and what else do we need to know?' It's been kind of out of sight and out of mind."
Other Seattle projects
The solutions can be as simple as rain-absorbing gardens. They can be as complex as heavily landscaped canals, artificial creeks and narrow, winding roads devoid of conventional curbs.
Many of the ideas were pioneered in places such as Maryland, which was trying to clean up Chesapeake Bay. Seattle has taken the lead in this region.
Several projects in the Broadview neighborhood in northwest Seattle are already finished. But High Point is the most extensive use of the system with densely packed homes. Officials also plan to use the new techniques to overhaul several blocks near Thornton Creek, in the Pinehurst neighborhood.
At High Point, the Seattle Housing Authority, which is redeveloping the site, has tried to make the novel features as invisible as possible.
Streets are tilted to one side instead of sloping from the center toward each shoulder. The design directs rainwater through cuts in the curbs, where it flows to landscaped and grassy depressions, like shallow ditches. Designed with rich, porous soil and a bed of gravel underneath, these swales absorb much of the water.
On the homes, gutters feed water into tiny concrete troughs that lead to landscaped areas designed to absorb water. Other gutters lead to buried, perforated pipes that gradually leak the water into the ground. Porous sidewalks, like glued-together gravel, also soak up water.
With a lot of houses and pavement, engineers have also had to build a conventional stormwater system — pipes and a pond — for infrequent but heavy storms that might overwhelm the new features.
The new system is expected to cut the runoff into Longfellow Creek during regular storms by roughly 80 percent compared with a conventional system, according to a report from SvR Design, the firm designing the stormwater network. That's similar to a meadow, and slightly more runoff than a forest.
The dual stormwater systems will cost $3 million more than using a conventional setup alone. Seattle Public Utilities is paying for it to test the new water-control strategies on a large scale and to improve Longfellow Creek.
While the High Point system is meant to attract little notice, a similar project completed in the last couple of years in the Broadview neighborhood is easy to see.
Narrow, north-south streets wind down blocks. One side of each street is lined by a sidewalk and a curb only 2 inches high. On the other side, there is no curb. Instead, water runs into deep, rocky depressions like empty ponds, planted with grasses and shrubs. At the end of the block, the ponds feed into a series of rock-filled basins, which cascade down the edge of the steep street like a creek. Water can collect and soak into the ground there. Whatever makes it to the bottom feeds Pipers Creek.
Craig Myers, who lives at First Avenue Northwest and Northwest 107th Street, likes the changes. When it rains, he's startled by how much water pours into the rock basins, turning into a small stream. Some neighbors have complained about a loss of parking space. But Myers is happy because his basement doesn't flood anymore.
98 percent less runoff
Tests on a nearby block with similar features showed the system cut runoff by 98 percent.
A few similar efforts are under way in projects in King, Pierce and Thurston counties, as developers and government agencies test whether they want to embrace them more wholeheartedly.
Meanwhile, though, there is apprehension among developers about new methods that could be expensive, said Tim Attebery, a lobbyist for the Master Builders Association of King and Snohomish Counties.
"Not every builder understands it and not every builder is doing it, but there's interest in the industry," he said. "Like anything that is a new development strategy, people are going to ease into it."
Another major hurdle for the new systems is that many communities have no rules for them, so developers need special approval, said Andrews, of Seattle Public Utilities.
So don't expect the features to show up on new developments overnight, said Hinman, the WSU extension office's stormwater expert.
The new systems may become the norm someday. But right now, as for any innovation, there are tests to run and results to monitor.
"The general feeling I get is, 'Well, let's move ahead, but let's not wholesale change over to a whole new system of stormwater management,' " Hinman said.
Warren Cornwall: 206-464-2311 or email@example.com
Copyright © 2005 The Seattle Times Company