Physical habitat recovery in a former dam impoundment

This study examines the recovery level of physical habitat in the former impoundment of the Gunpowder Falls River behind the Gunpowder Paper Mill Dam. Recovery is examined at three temporal/spatial scales. A biological time scale of less than two years and the spatial scale of the streambed substrate in a channel cross-section are used to assess recovery for the macroinvertebrate habitat. An historical time scale and a watershed spatial scale are utilized to examine landuse history and its impacts on the riparian tree community in the former impoundment. A geomorphologic time scale coupled with a channel and valley cross-section morphology spatial scale provide the intermediate link between the coarse watershed scale and the fine macroinvertebrate habitat scale. The temporal evolution of stream morphologic and habitat recovery after dam removal is studied by examining the recovery of the former impoundment at an historically failed dam site as a surrogate for an intentional dam removal situation.; This study shows that one habitat, the streambed macroinvertebrate habitat, may have fully recovered at one temporal/spatial scale and another, the riparian tree community habitat, may still be significantly impaired at another temporal/spatial scale. The recovery of the one and the continued impairment of the other have both been controlled by a common watershed landuse history. Clarification of the inter-scale connections and the intra-scale processes inherent in a fluvial landscape is essential to making effective dam removal or other stream restoration decisions.; Field data collection methods employed are those in common usage by stream restoration technicians and watershed planners. Analysis subjects the data to more rigorous methods. The results suggest that the types of data commonly collected can provide much more information about stream morphology and habitat recovery than is typically garnered. This additional information may help stream restoration decision-makers better identify what component of a stream's morphology or habitat needs restoration and what components may be recovered or able to recover without intervention. In the case of dam removal stream restoration, this study provides some insight into the time frame in which recovery may take place.