Mitigating Salt-Water Intrusion through Hiram M. Chittenden Locks

The Seattle metropolitan area surrounds Lake Washington, a large freshwater 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 current of salt water flows from the lock chamber into the freshwater system resulting in two opposing water-management issues at the locks: salt-water intrusion and water conservation. Several physical structures are present to prevent salt water from propagating upstream with each lake-bound lockage. During heavy use in the summer period, these structures cannot keep up with the amount of seawater entering the freshwater system, and an additional flushing technique is required. Consequently, the U.S. Army Corps of Engineers, which manages the locks, has implemented a "miniflushing" procedure for summer months. Miniflushing is defined as any process that can be temporarily implemented as part of a lockage to minimize salt-water intrusion. Recent field experiments at the locks compare two methods of miniflushing, and a recent improvement in procedure is discussed in this paper.