Effects of a Small, Century-old Dam on a Second-order Stream in the Virginia Piedmont

The geomorphology, hydrology, and ecology of a second-order stream in central Virginia were compared to that of an adjacent reference stream in order to determine the impact of a small, 100-yr-old dam. The dam had little effect on stage hydrographs, but surface release of water resulted in temperatures 2-5 degrees C warmer than the reference stream during spring and summer months. Stream geomorphology was not highly altered by the dam, being influenced more strongly by valley geology and topography, but riffle sediment size distributions were affected by sediment trapping in the reservoir. Macroinvertebrate populations just below the dam appeared impaired, while sites 8 km downstream and on the reference stream scored well on ecological metrics. Bluegill fish (Lepomis macrochirus) which likely originate in the lake were abundant in the dammed creek, whereas the reference stream was dominated by native dace (Phoxinus and Rhinichthys spp.) and creek chubs (Semotilus atromaculatus). Overall, the impact of the dam on the creek is only moderate and declines significantly within 8 km downstream.