When the River Changed Course

A flood in December 1999 caused major damage to Chatham Acres, a small community located on the North Fork Stillaguamish River in Snohomish County, Washington. In a process known as avulsion, the river abandoned its existing path and cut an entirely new 200-foot wide, 800-foot long channel through Chatham Acres before rejoining its original course.

One home was washed away when the river changed its course. Fortunately, the house was unoccupied at the time, and no one was hurt. Ten other residences in the area, however, were immediately threatened by the avulsion.

Most of the homes in Chatham Acres had been constructed in the 1930s, long before the advent of the National Flood Insurance Program, Flood Insurance Rate Maps, and the modern approach to floodplain management. Although no one realized it at the time, the homes were built within the Stillaguamish River’s floodway.

In response to the immediate problem in late 1999 and early 2000, the Chatham Acres Homeowners Association applied for and received approval to construct a section of rip-rap along the affected shore. This was only a temporary solution. Soon after the rip-rap was in place, three more flood events washed away an additional 50 feet of riverbank, and the shoreline behind the rip-rap began to erode, too.

An even larger threat was developing 650 feet upstream where the Stillaguamish River was beginning to migrate into a course that would enter Placid Creek, a parallel stream. The combination of the two watercourses would lead to even greater and more damaging avulsion throughout the area.

In June 2002, an application was filed with FEMA requesting Hazard Mitigation Grant Program (HMGP) funding for the purchase and demolition of the Chatham Acres homes. Acquisition would safeguard the lives and property of those in the endangered area and remove potential problems arising from future flooding and avulsion.

A condition of the HMGP grant was an agreement by the county not to develop the acquired property and to put restrictive easements on the property title to ensure future development would never take place there.

When beginning to plan the project, an assessment of possible losses was calculated to determine whether or not it was financially feasible. The total loss, if nothing were done to resolve the problem and future avulsion continued to occur, was estimated to include the destruction of most if not all of the homes. It was determined by examining previous damages that another overtopping of the river and Placid Creek would almost certainly occur again, virtually guaranteeing the future destruction of some of the properties.

The HMGP grant provided the necessary funding to acquire the threatened properties, and by 2005 the land was acquired and the homes removed. The entire purchase amounted to $1,899,000, with more than $1,400,000 covered by the HMGP grant. The overall lifetime savings accrued by avoiding the flood damages that would have occurred had the area not been purchased was estimated to be nearly $4 million.

While assessing the acquired homes for demolition, the contractor determined that much of the house material could be recycled for future use. This resulted in a significant savings in the cost of the demolition. Additionally, two of the homes designated as historic were saved and relocated prior to the scheduled destruction.

Now that Chatham Acres has been restored to its natural state, the only county maintenance is the educational signage used to inform the public of the area, its history, and its habitat. Thanks to the rules governing these property acquisitions, Chatham Acres will never be developed again. It is only a matter of time before the natural processes completely restore the area.

The river is a migration route for several species of fish, including trout, coho salmon, and steelhead. Many other forms of wildlife live in the vicinity, such as the bald eagle. In addition to protecting property and human lives, removing the homes and restoring the area to its natural condition increased the wild habitat available for these animals.