Sawmill Creek, Anne Arundel County, MD Fish Passage - Study & Design

Through an open-end agreement environmental contract with Anne Arundel County, Department of Public Works, Environmental Systems Analysis, Inc. (ESA) performed a study and subsequent design of a fish ladder and step pool to allow migration opportunities for anadromous spawning fish. A four-foot concrete weir located on Sawmill Creek (a tributary of Furnace Creek and Curtis Bay in Baltimore) at 8th Avenue and a USGS gauging station at Maryland Route 648, represent impediments to shad, herring, alewife and perch.

The objective of fish passage is to provide a gentle slope or gradient and reduce water velocity so that upstream navigation is within a fish's physical capability. The simplest method to provide fish passage is to remove all or part of the in-stream obstruction, which may involve creating an opening or notch (breaching). Where possible, removing an impediment such as a dam may often be the better option because it restores the natural free-flowing condition of the stream as well as permitting fish passage. Other structures such as exposed utilities, culvert aprons or gauging stations may be retrofitted to provide the necessary gradient and flow for fish passage.

Another solution is to construct fishways (called 'ladders') to allow fish to pass over or around an obstruction. Fishway designs are unique to the type and size of the blockage, the number of fish they will pass (based on available upstream habitat), and fluctuations in stream flow. Common types of fishways include vertical slot and denil lifts (and modifications of such). Both fishways are passive flume-like (inclined water chute) structures equipped with a series of baffles or weirs. Fish negotiate a ladder at their own pace, just as they would negotiate natural rapids.

Working with local officials and Maryland Department of Natural Resources, ESA with specialized engineering assistance, performed the necessary hydrology, hydraulics and environmental studies to design preferred retrofits. Ladder and step pool designs required detailed evaluation of flow patterns, resting pools, 'attraction water' and slope of the structures. Construction is proposed for late 1999 or early 2000 with funding through matching county and federal grants.