From dam damage to improved fishing habitats
By Helen Broemmelsiek and Megan McCarthy, communication students, and Lynn Davis, College of Natural Resources
The 1970’s energy crisis led to an urgent attempt to diversify the country’s energy base. Numerous hydropower projects were built. “And downstream effects were often not considered,” says Don Orth, Virginia Tech fisheries professor.
As a result, hydroelectric dams have threatened the biodiversity and fish living in the southeast United States. Thirty years later, licensees for many of these projects expired. Relicensing agreements are more considerate of environmental consequences of dams.
Orth and his colleagues are monitoring the aquatic habitat of the Cheoah River in North Carolina to determine whether new flow management strategies will correct ecosystem damage. The project is Ph.D. student Ryan McManamay’s dissertation research.
The Cheoah River dam was operated by holding back as much water as possible and diverting it through a mountain to create power. Decades of trapping water and preventing sediment from flowing down the river channel resulted in a change downriver, Orth says.
Prior to the 2005 Federal Energy Regulatory Commission relicensing settlement agreement for the Cheoah River dam, there were no consistent water releases or mandatory flood flows on the river. Because rivers need sediment and high flows to scour and shape the channel, the lack of flow substantially shrunk the channel.
“As a result, woody plants and trees germinated in the middle of the channel and consolidated what little sediments were there. Ultimately, the Cheoah River was transformed into a dry habitat, altering the environment and economy supported by the river,” Orth says.
The goal of the Cheoah River project is to restore a cluster of diverse native species and enhance the population of rare or threatened species. Actions include identifying segments of the river to restore with gravel augmentation, short-term changes in gravel-habitated environments due to scheduled flow releases, analyzing the recovery of target fish species, and monitoring long-term biological responses to habitat change.
Several strategies will be tested and monitored during the study. The relicensing agreement requires the implementation of three elements to improve environmental conditions on the Cheoah River.
The first strategy is restoration of a minimum flow. A continuous release of water from the dam will enhance productive shallow-water habitats. “We predict the fish assemblage in the Cheoah River could then eventually reach a new equilibrium condition with a stable composition,” Orth says.
The second strategy, releasing short-duration high flows, is intended to protect, enhance, and restore the Cheoah River. As with the minimum flow strategy, the flood flows will assist with sediment transport. Additionally, peak flows will permit recreational whitewater kayaking on weekends. The flows are determined by the average daily inflow from the preceding three months, and water releases are scheduled several times throughout the year. By analyzing the impacts that the scheduled flows have on the river, researchers will be able to monitor and evaluate the shortterm restoration benefits of the flood flows multiple times each year.
Gravel augmentation, the third strategy, aims to restore the natural process of streambed mobilization and redistribution of fine materials. The strategy’s success will be measured by comparing two augmented sites to two control sites. According to their research proposal, Orth and his researchers hypothesize that “the gravel augmentation and subsequent redistribution of additional particles will enhance the amount of habitat patches dominated by gravel.”
The Cheoah River research will provide vital information on the effects that humans have had on the ecosystem and will begin the restoration process to address past damages.
Orth, who holds the Thomas H. Jones endowed professorship, also did extensive, long-term research on the effects of hydro-electricity on the Smith River, where the dam drastically altered temperatures and velocity fluctuations, adversely affecting the trout population and local economy. Orth designed a monitoring plant to enable state agency officials to continue to monitor and determine the most effective way to manage the river. He will monitor the long-term effects that the strategies have on the adjustment of the channel.
Restoration of the Cheoah River is a model for addressing concerns about dam impacts on a river ecosystem, community, and economy. Dams can still be an important energy resource without sacrificing river life.
