Where Does All of That Rain Water Go?

TACOMA, Wash. — Where is all of the rain water of the past several weeks ending up, and more importantly to WSU Extension educator Curtis Hinman, how is it getting to its final destination?

How development of once open, plant-covered spaces changes stormwater movement over and through the landscape is one of the greatest threats to water quality, supply and aquatic habitat in the Puget Sound area, according to Hinman, who works at the WSU Pierce County Extension office at Tacoma. One of five Extension faculty working on water issues in the Puget Sound Basin, he researches, designs and monitors low impact development strategies for that region.

“Both resources and attention are turning to stormwater management throughout western Washington,” said Hinman. “We have started to realize that even a small amount of urbanization can dramatically affect the watershed.”

The major challenge of stormwater management is its complexity, he added. “There are literally thousands – maybe even millions – of individual actions that contribute to the issue.”

For example, the transition from meadow to shopping mall increases impervious surfaces such as roads, parking lots, sidewalks, rooftops and compacted soils. Native plants and the upper soil layers that filter, store or allow rainwater to return to the atmosphere are typically removed, creating a “double whammy” with water quality and movement.

“Water quality is impaired as stormwater flowing from impervious surfaces collects oil, grease, heavy metals and other pollutants and is discharged to streams, lakes, wetlands and the Sound,” Hinman explained.

Those same surfaces also cause stormwater to move out of a specific landscape more quickly, altering stream channel form and degrading aquatic habitat and the ability of fish, insects and other stream life to survive.

Properly managing stormwater “comes down to good watershed planning, effective design at the project site and to individual residents,” Hinman said. “It is much more based on the actions of individual property owners; it brings the individual into the ecology of the watershed.”

Low impact development can be a solution, he added. It is a land- use development strategy that emphasizes protection and use of features already on a building site as well as small scale, engineered controls on individual lots and at the subdivision level to manage stormwater.

Specific strategies include minimizing building footprints and road widths to reduce impervious surfaces; using permeable paving wherever possible; creating small “bioretention” areas with appropriate soils and plants to filter and store stormwater; and managing stormwater as close to its origin as possible.