Gregory Stewart

Geomorphic and ecological effects of dam removal

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, local communities, and environmental groups. 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 dam removal decision-making (Doyle et. al. 2003).

As part of my Ph.D. research, I investigated the geomorphic and ecological consequences of two small dam removals at Maple Gulch and Dinner Creek; in southern Oregon while at the same time attempting to predict the trajectory of sediment following the removal of Marmot Dam on the Sandy River, OR. While the papers are being finalized, an excellent overview of the work can be found at:

http://www.fsl.orst.edu/geowater/DamRemoval/

Use of two-dimensional models to assess fish habitat

The quantity of water that should be retained in streams and rivers for the benefit of fish during periods of water scarcity is a question of considerable interest to river managers and biologists. The most common type of instream flow methodology utilizes empirically derived habitat suitability indices and flow models to predict the effects of flow changes on individual fish species and life-stages. Although these instream flow methodologies have existed since the 1970’s, no single method has been widely accepted for use on large warm-water rivers because of their high species richness and generalized fish habitat use patterns.

In coordination with the Colorado Division of Wildlife, a methodology was developed that utilizes two-dimensional flow models and meso-habitat fish community biomass estimates to evaluate the effects of flow alteration on Western Colorado rivers. Data collected from the Colorado and Yampa Rivers are used to develop habitat suitability criteria for bluehead and flannelmouth sucker (Catostomus discobolus, Catostomus latipinnis) by comparing adult biomass in individual meso-habitat units with modeled depths and velocities.

Stewart, G., Anderson, R. and Wohl, E., 2005. Two-dimensional modelling of habitat suitability as a function of discharge on two Colorado rivers. River Research and Applications, 21(10): 1061-107

Recreational Activities