YOUR DRIFT CELL
Your beach is made of sand and gravel from rivers or from other beaches or bluffs. A drift cell is a segment of coastline with one or more sources of sediment, usually including a bluff, that supplies the nearby beaches. Wind and waves cause a cyclical replenishing of beaches, helped along by rainwater that flows over the surface and into the ground and by seasonal freezing and thawing.
The process is often gradual. Some sites can have minimal erosion and then experience a dramatic event such as a landslide during a wet winter. Nevertheless, overall erosion rates are low along Puget Sound.
Bluffs are vital to replenishing beaches with sand and sediment.
Bluffs are especially vital to replenishing beaches with material—which is why some of these naturally eroding landforms are known as “feeder bluffs.”
Little by little–or sometimes in a big chunk–bluffs break down and deposit rich glacial sediment onto the beach below.
In the Puget Sound area, feeder bluffs range in height from a few feet to more than 300 feet. As sea levels rise due to climate change, naturally-eroding bluffs will help build up higher beaches.
Drift cells can overlap, but the eroding material usually stays within a discrete zone. Puget Sound has more than 800 drift cells; you can get information about yours by consulting the Washington State Coastal Atlas.
When waves hit the shore at an oblique angle, they can move the sediment along in one direction. Some of the sediment is carried into deeper water, and the rest is deposited on a beach, sand spit, or point.
See how drift cells interact in different locations around Puget Sound–including Eagle Point, Dungeness Spit, West Beach, Maxwelton, and Magnolia Bluff–in the animations below.
The constantly replenished beaches—and the estuaries, lagoons, and marshes behind them—provide valuable habitat for marine life, shorebirds, and insects. In shallow waters shaded by vegetation, smelt and herring feed on plankton and spawn among eelgrass and kelp. Young salmon feed on these smaller fish, as do shorebirds that nest in nearby trees. Oysters grow in shallow bays and estuaries, filtering toxins from the water and forming reefs that shelter crabs and other shellfish. Insects that are food for fish, birds, and other wildlife live in drift logs and other organic beach debris.
The tide flats of Puget Sound are populated by an abundance of creatures.