As nature's buffers disappear, flooding becomes routine in Puget Sound region

Winter flooding has become nearly as predictable as the rain in the Puget Sound region, where an ever-less natural landscape has lost its ability to absorb big storms.

"Just when you get over one, you are in another," King County Executive Ron Sims said of the floods. "I would like to think this isn't going to be as frequent, but these are going to be events not separated by decades, but by years."

Josh Baldi, who is helping to lead Puget Sound policy for the state Department of Ecology, sees in last week's flooding a legacy of land use that is exacting a predictable punishment.

"Every year it is like we have forgotten what happened the year before," Baldi said. "We have seen a crisis response, but not a policy response.

"You have to ask, how do we get out in front of this, what should we be doing differently?"

The floods show the need to protect what's left in the Puget Sound basin of nature's way of running water downhill in big storms, experts say.

Everything in the natural landscape slows and absorbs runoff, beginning with trees and soils. Western Washington's low-elevation forests are among the best in the world for timber production — and better than shopping malls, subdivisions, or roads at slowing and absorbing rain.

Yet as development presses out into the suburbs, we are losing lowland forests in the Puget Sound region.

"You fly over Snohomish County, and it looks like a forest by day, but by night, you see all the lights," said Brian Boyle, former state commissioner of public lands. "It's been subdivided.

"Kitsap County is gone. The forest may look like trees, but it's not a forest."

Statewide, about 1.2 million acres of forestland, almost all of it privately owned, converted to other land uses including development from the late 1970s to 2002, a little more than the acreage of Olympic and Mt. Rainier National Parks combined, according to the state Department of Natural Resources.

Every year in Western Washington, about 24,000 acres, or an area of working forests almost half the size of Seattle, mostly on private land, is converted to rural-residential and urban development, according to Luke Rogers at the UW College of Forest Resources.

The rivers themselves also have been altered, reducing their ability to manage high water. In King County alone, more than $7 billion worth of development was built over time in the floodplain, according to a county estimate in 2007.

King County has since been changing its development policies to greatly restrict development in the floodplain, and to buy out and remove some homes and mobile-home parks to move residents out of harm's way.

The county has also adopted a more work-with-nature approach to flood management, even taking out some levees to give rivers room to move.

But with so much valuable development already here, there is limited opportunity to restore natural conditions.

Rivers used to meander and to be able to stretch out in high water, filling their floodplains. And they used to be filled with large logs that created thousands of waterfalls in the main channel, dissipating the water's energy as it flowed to Puget Sound.

Not anymore.

Straightened, cut off from their side-channels, and straitjacketed in levees, their floodplains diked, filled, and developed, urban rivers like the lower Puyallup today are more ditch than river.

Less forestland, more development and altered rivers mean when big storms come, the natural landscape can't slow down the water, and soak it up. Instead of dissipating into the ecosystem over days, the rain becomes a flood of runoff, sluicing and blasting off roofs, pavement, and barreling down — and out — of rivers with no where to put it all.

"Every couple of years we have this, and I tell the same story," said Robert Naiman, a University of Washington professor and an expert on rivers. "Yet we continue to build and allow expensive structures and roads into floodplains, and we try to unnaturally constrain the rivers into something they won't do."

To some, the floods are a wake-up call from a stressed ecosystem. "There is such a legacy of how we developed the land in the 1950s, and we are not talking about a few missteps, we are talking about decades," said Derek Booth, a hydrologist and UW affiliate professor in geology and civil engineering.

"We don't notice the everyday degradation of our waterways," Booth said. "But we sure notice it when everything busts out."

Some experts predict the situation could get worse as the climate warms, bringing more rain, less snow. Cutting forests and paving lowlands also means more, and faster runoff.

"A warming climate shifts the mix of precipitation from snow to more rain," said State Climatologist Philip Mote. "And if you cut down all the trees and turn meadows into Wal-Mart parking lots, you are going to increase flood risk, no matter what the climate does. You can't say how the flood risk will change in certain areas, but the prudent thing to do now is allow for a range of possibilities before pouring concrete."

Lynda V. Mapes: 206-464-2736.