Thurston County Connection Newsletter
Thurston County Connection
Thurston County Connection
September, 2014
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This Month's Articles

Back-to-School Safety 101:

Hope for the Best…..Prepare for the Worst!

Telephone Alerts Available for Flooding Hazards

The War on Food Waste

Little Red School House Drive a Big Success!

A Herd of Folks at the Thurston County Fair

Making it in the Dry Years

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 There’s More Than One Type of Flood.

Are you prepared?

When we think of flooding, we often envision the type of flooding that occurred along the Chehalis River in recent years. However, Thurston County also experiences other types of flooding.

Much of the soil in southern Puget Sound is glacial outwash, loamy sand or gravelly-sandy soils that drain well. The loose soils, however, allow water to travel in both directions. The very soils that allow water to easily soak into the ground also allow the water to rise back up to the surface if it hits an underlying layer of compacted soil or rock. This often results in overland surface flows during heavy storms.

In some areas of the county, the gravelly-sandy soils drain into underground water tables, which can rise and flood low-lying land. If the water tables are naturally close to the surface of the land to begin with, heavy, prolonged rainfalls are more likely to cause the water tables to rise and cause flooding. These areas, called “high groundwater hazard areas,” are identified on Thurston County’s Geodata Website.

The size and steepness of a watershed also contributes to the timing and severity of floods. The Salmon Creek Drainage Basin, south of Tumwater, is very large and flat, so it drains slowly. Storms that cause “gullywashers” in smaller, steeper watersheds can leave water sitting beneath these properties, waiting for the next storm and the next.

Properties in these areas are identified and protected through land-use planning and zoning regulations. The major groundwater flooding areas are the drainage basins of the following creeks: Salmon, Chambers, Yelm, Thompson and Scatter.

Even if your property isn’t in a high groundwater area, check out soils and landscape position in the watershed. Homes located in tight clay soils may flood during and following heavy rain.

By Keith Eisner

South county flooding in 1995. South county flooding in 1995.