The topic of dam removal has garnered national attention and has been the focus of special sessions at numerous recent national scientific meetings. A common theme in all these meetings has been the need for additional scientific research on the ecological and geomorphic affects of dam removal (Aspen Institute 2002, Heinz Center 2002, Hart et al 2003). Dams across America are continuing to age and their management is a pressing issue for resource agencies. Given the scientific uncertainties surrounding dam removal, it has been vigorously argued that the removal of small dams should be viewed as research opportunities that can guide future decision-making (Doyle et al 2003). As part of his PhD research, Gregory Stewart is investigating the geomorphic consequences of the removal of two small dams at Maple Gulch and Dinner Creek in southern Oregon.

Maple Gulch was a 3.4-meter (11.0 feet) high dam located on BLM land near Medford, approximately 0.3 miles upstream of its confluence with Evens Creek. Maple Gulch dam was built in the early 1900’s to supply water to a local schoolhouse, but dam had long since filled with sediment and no longer served any purpose. The dam remained, however, a barrier to fish passage.

During the summer of 2002, the BLM had Maple Gulch dam mechanically removed, leaving behind approximately 750 cubic meters of sediment. During the winter of 2002/2003, a knickpoint formed in the reservoir sediments and quickly eroded a channel. We have been using repeat surveys to estimate the volume and timing of sediment export from behind the dam. This data along with process information is expected to result in a conceptual model for erosion following dam removal. This information provides guidance to future dam removal efforts.

Dinner Creek Dam is a 2.4 meter high, concrete, gravity dam structure located approximately 150 meters upstream from the confluence of Layng and Dinner Creeks within the Layng Creek Watershed, a municipal watershed for the City of Cottage Grove. The dam is estimated to have been built in 1925 and has long since filled with sediment. Both water and sediment now pass over the top of the structure. Dinner Creek dam blocks upstream migration of fish and other aquatic species including native cutthroat trout, speckled dace, long nose dace, and several species of sculpin (Bernstein 2002).

In August 2003, Dinner Creek dam will be mechanically removed by the U.S. Army to allow for fish passage. The removal of Dinner Creek dam will result in the release of approximately 4000 cubic meters of coarse sand, gravel, and cobble into the downstream channel. The planned release of such a large quantity of sediment into a municipal watershed has raised water quality concerns and is predicted to significantly alter aquatic habitat in the area immediately upstream and downstream of the dam.

An interdisciplinary group of Oregon State University researchers are prepared to document key changes associated with the Dinner Creek Dam removal including impacts on: sediment transport, turbidity, channel morphology, hyporheic exchange, water quality, and aquatic macro-invertebrate community composition and abundance.