Following a devastating flood in 1931, the Army Corps of Engineers channelized a free-flowing stream known as Mill Creek, which flows through downtown Walla Walla, Washington. The Mill Creek Flood Control Channel in Walla Walla, Washington has successfully mitigated flooding issues since then, but after decades of wear and tear, the Channel’s infrastructure is crumbling and high water levels are once again threatening the city. The Mill Creek Flood Channel runs underneath or adjacent to historic buildings, businesses, and public facilities in the downtown Walla Walla area, protecting over 23,000 Washingtonians and almost 10,000 structures with a property value of $3 billion.
If the Channel continues to deteriorate, an inevitable collapse would result in the significant loss of property, potential loss of life, and flooding of critical facilities including hospitals, schools, and fire stations. Contributing to the problem is a water management decision by the Corps of Engineers necessitating the release of more water from Bennington Lake into Mill Creek during periods of high water due to reduced storage capacity in the Lake itself. The Mill Creek Channel received a “minimally acceptable” rating during a periodic inspection in 2010, leading Walla Walla County, the City of Walla Walla, the Port of Walla Walla, and the Downtown Walla Walla Foundation to form the Mill Creek Coalition in 2013. This coalition of interests partnered with Summit Strategies to seek funding from the US Army Corps of Engineers for a General Investigation (GI) Study to evaluate Mill Creek’s safety, viability, and need for stabilizing improvements.