Letter to the Editor: Why Dredging Is Not the Answer to Flooding in the Chehalis Basin

Posted

Recently, a well meaning individual stated his belief that the true solution to flooding in the Chehalis Basin was simply dredging the entire river. When solving physical problems, belief, feelings and emotion afford few if any components to real solutions.These types of solutions require investigation producing data and facts which then produce feasibility or failure of the proposal.  

Early on in the effort to solve our flooding problems, dredging was thoroughly studied by the Army Corps and engineers contracted by what has become the Chehalis River Basin Flood Control Zone District. Three main factors disqualified dredging as a workable option. 1. There is not sufficient elevation drop in the river as it works its way to the Pacific for dredging to increase flow rate even if the river bed were "cleaned" up. True, a deeper river bed would hold more water even if it didn't move faster, but it was found that to hold enough water to make a significant improvement in flood levels, the dredging would have to be unreasonably deep  2. At the time the studies were completed, the dredging cost estimate was $400 to $600 million. This high cost is partially due to the presence of the solid rock Centralia hump in the river north of the Mellen Street bridge. That would have to be removed necessitating the creation of a diversion channel used during demolition of the rock barrier. Most residents are familiar with how in most summers a "lake" is created in the river south of the bridge that is usually covered by algae indicating extremely low flow which is  caused by the rock hump. Further engineering has determined that the proposed retention facility in the upper basin would cost a similar amount to the dredging with much greater long term benefit. 3. Dredging would all but destroy fish habitat which is absolutely not acceptable. This factor alone would eliminate any thought of proceeding with dredging. 

All full or partial solutions are being investigated and no one of them is the "be all, do all." It is recognized that there are many facets to address as we attempt to make the basin flooding something we can tolerate. No one solution covers it all. Some proposals accomplish much more than others, but that still means we consider the merits of all those offering  some meaningful improvement. To keep abreast of progress and proposals on this matter please visit the web site: chehalisriverbasinfczd.com   



Dr. John Henricksen,

Chair of Chehalis River Basin Flood  Control Zone District advisory committee