Sprawl: Threatened Salmon, Staggering Costs

By Patrick Mazza and Eben Fodor

Across Washington and Puget Sound, streams that once gave birth to abundant salmon runs now witness sharp declines. Across the state, 13 percent of salmon stocks are in a critical or depressed condition. In the greater Puget Sound region where 64 percent of Washingtonians live, fish suffer under sprawling urban development. There, 23 percent of salmon stocks are rated critical or depressed. Recent Endangered Species Act listings of salmon blanket Seattle-Tacoma and Portland-Vancouver, the first large U.S. metro areas to come under the ESA.

The ultimate costs of recovery efforts are unknowable, but they will surely run to hundreds of millions and possibly billion of dollars. The definition of recovery counts for everything, notes Derek Booth of the University of Washington Center for Urban Water Resources. Restoring streamside habitat and relying primarily on planting eggs from hatcheries, a model employed in such Seattle creeks as Thornton or Pipers, would cost roughly $1 billion if applied throughout the urbanized Puget Sound, Booth estimates. Restoring fully self-sustaining runs, even if it were possible, would likely require a level of watershed restoration costing "at least an order of magnitude" beyond that, Booth says.

Another very rough indication comes from an unofficial Department of Community, Trade and Economic Development assessment of local government expenditures on salmon recovery over the next 10 years. Two-thirds of the $2 billion total, $1.3 billion, is to manage urban stormwater. Mitigation for other urban development problems, such as culverts and water pollution, was put at $256 million.

Even with large expenditures, Booth says, "It's not clear that the limiting factor in an urban setting is money. There's a knowledge gap as well as a money gap. The science of salmon living in disturbed watersheds is pretty young."

How Sprawl "Firehoses" Salmon Streams

To comprehend what happens when a forest becomes a subdivision or strip mall, begin by picturing the way a natural forest shapes the flow of water through it. Entering from the sky as rainfall, much moisture is caught in trees and duff, the layer of debris covering the forest floor. The process of evapotranspiration returns almost half the moisture directly to the sky. Water that does make it to streams generally runs beneath the surface, and can take weeks or months to get there.

For salmon down in the streams, that steady subsurface supply is ideal. It keeps waterways from drying up and limits flood surges that scour the gravel where they deposit their eggs. It carries little of the sediment that can clog that gravel and make successful reproduction impossible. The forest also shades waters from salmon-killing heat, and provides a steady supply of dead branches and logs, building materials for pools where many salmon, notably Coho, take shelter.

With urbanization, all that changes. The greatest change nearly always is in how water flows down to streams from the overall drainage. Trees and duff are no longer present to sponge up rainfall. In the place of absorbent vegetation and soft soils come a profusion of hard surfaces--roads and bridges, parking lots, driveways and roofs--off of which rainfall sluices almost immediately.

Water that might have gracefully seeped to streams over months instead arrives in hours. Two to five times more water rolls off during peak rainfall runoffs. Flow magnitudes generally run five to 10 times longer. Flows powerful enough to carry sediment and disturb habitat come 10 times more frequently. All this spells trouble for salmon.

Hydrological engineer Thomas Holz compares increased annual runoff and peak flows to a fire hose. Surging waters dig stream channels deeper and wider, sluicing away pools and other salmon habitat. And there's a double whammy. Since water flows out instead of recharging groundwater, it is no longer available to fill those larger channels during the summer dry spell. That sets up salmon-killing conditions. For salmon, one year of dry streambed is not a statistical blip but a serious threat of extinction.

Patrick Mazza is a writer-researcher for Climate Solutions. Eben Fodor is author of Better Not Bigger: How to Take Control of Urban Growth and Improve Your Community (New Society, 1999). This article is based on a Climate Solutions Report, "Taking Its Toll: the Hidden Costs of Sprawl in Washington State," available at www.climatesolutions.org.

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