MITIGATING SALT-WATER-INTRUSION THROUGH HIRAM-M-CHITTENDEN-LOCKS

The Seattle metropolitan area surrounds Lake Washington, a large fresh water lake connected to the salt water of Puget Sound by an 8-mi-long ship canal with a lock-and-dam structure at the downstream end of the canal. When raising vessels from Puget Sound to lake level, a strong c urrent of salt water flows from the lock chamber into the freshwater s ystem resulting in two opposing water-management issues at the locks: salt-water intrusion and water conservation. Several physical structur es are present to prevent salt water from propagating upstream with ea ch lake-bound lockage. During heavy use in the summer period, these st ructures cannot keep up with the amount of seawater entering the fresh water system, and an additional flushing technique is required. Conseq uently, the U.S. Army Corps of Engineers, which manages the locks, has implemented a ''miniflushing'' procedure for summer months. Miniflush ing is defined as any process that can be temporarily implemented as p art of a lockage to minimize salt-water intrusion. Recent field experi ments at the locks compare two methods of miniflushing, and a recent i mprovement in procedure is discussed in this paper.