Remnant Log Drive Dams: A Legacy of Hydraulic Checks

Remnant dam sites and their impacts are an overlooked legacy on the Maine landscape. As part of our habitat restoration program, Project SHARE is documenting and removing historic log drive dams. While remnant dam sites generally do not present a major barrier to fish passage, habitat alterations remain long after the dam was breached. Stream reaches immediately upstream of historic dam locations typically do not possess habitat attributes suitable for Atlantic salmon spawning or parr rearing. Site specific assessments include longitudinal profiles and transects, pebble counts, temperature monitoring and fish community structure. Aerial photography reveals the presence of over-widened channel associated with historic reservoirs. Longitudinal profiles reveal the presence of hydraulic checks where dams were not completely removed to the natural stream bottom. Impacts to stream function include: decreased current velocities, increased temperature, and sediment transport. Short-term impacts from complete removal include: decreases in wetted width, increased current velocity, mobilization of fine sediments, and renewed use of recovering salmon habitat. We recommend that the potential presence and impacts of remnant dam sites be a part of holistic, process based habitat restoration programs.