Proposed Retention Project

Chehalis River Basin flood damage reduction project

The Chehalis River Basin Flood Control Zone District is proposing to construct a new flood retention facility and temporary reservoir near the town of Pe Ell, Washington, and levee improvements around the Chehalis-Centralia Airport in Chehalis, Washington. See the Vicinity Map. The proposed project is intended to reduce flood damage in the Chehalis River Basin and includes:

A flood retention facility and associated temporary reservoir near Pe Ell to reduce damages during a major flood. It will not protect communities from all flooding, nor is it designed to stop regular annual flooding from the Chehalis River. The facility would only store floodwater during major floods and then slowly release retained floodwater when it is safe to do so and over a period of time. Most of the time, the Chehalis River would flow through the structure’s low-level outlet works at its normal rate of flow and volume—and allow fish to pass both upstream and downstream. See the Scoping Meeting Board on the Flood Retention Facility – Expandable (FRE) for more details.

A major flood in the Basin (an event with greater than 38,800 cubic feet per second at the Grand Mound gage located along the Chehalis River) has a 15% probability of occurring in any given year (an approximate 7-year recurrence interval).

Fish passage facilities at the flood retention facility to allow fish to pass both upstream and downstream during:

  • Construction using a river bypass tunnel
  • Normal flows through low-level passageways that would remain open during normal conditions and smaller floods
  • Major floods, using a fish collection, handling, transport, and release facility (trap and haul) when the structure’s outlets are closed

See the Scoping Meeting Board on the Flood Retention Facility Fish Passage for more details.

Airport levee improvements to protect the Chehalis-Centralia Airport, local businesses, and area transportation from damage from a 100-year flood. In addition to raising the existing levee around the Chehalis-Centralia Airport, 1,700 feet of Airport Road would be raised to meet the airport levee height along the southern extent of the airport. See the Scoping Meeting Board on the Airport Levee Improvements for more details.

For more information

map of flood vicinity
illustration of proposed flood retention facility
map of airport levee improvements