South Fork McCorkle Creek Drainage Evaluation

Client: Lexington Flood Control Zone District, Cowlitz County, Washington

The South Fork McCorkle Creek Detention Structure was constructed in the 1990s. The structure provides flood protection to the lower McCorkle Creek watershed and area residents. Although the structure worked well initially to reduce flooding, the District reported several storm events that resulted in water over the spillway structure.

Gibbs & Olson was hired to perform a hydrologic/hydraulic drainage evaluation to determine if raising the height of the existing detention structure would provide improved flood protection at a reasonable cost. The modeling results showed that raising the detention structure will detain enough water to allow the downstream McCorkle Creek Pump Station to keep up with the runoff from the remainder of the McCorkle Creek watershed during the 24-hour, 100-year design storm. The detained water can then be slowly released after the runoff from the rest of the watershed has been pumped to the Cowlitz River.

Subsequently, Gibbs & Olson was hired to provide permitting, surveying, design, and construction phase services for the recommended Detention Structure Modifications.


Working with Gibbs & Olson feels like working with a real partner who is an extension of my own office and I appreciate that we can have combinations of short easy conversations or in-depth complex ones.  When we have worked with, or presented to, our elected officials or the general public, their ability to communicate clearly always impresses me and enables us to achieve our objectives.

—Patrick Harbison, PE, Utilities Manager, Cowlitz County Public Works