Gravel addition as a habitat restoration technique for tailwaters
Abstract
We assessed the efficacy of passive gravel addition at forming catostomid spawning habitat under various flow regimes in the Cheoah River, a high-gradient tailwater river in North Carolina. The purpose was to provide a case study that included recommendations for future applications. A total of 76.3 m3 (162 tons) of washed gravel (10-50 mm) was passively dumped down the streambank and into the channel in four locations. Gravel sites differed in terms of average reach slope, bank slope, and the initial volume of gravel added, which could have influenced gravel entrainment. Maps of gravel movement under various flows suggested that large-magnitude discharges (=113 m3/s) caused extensive migration; however, less obvious, smaller discharges (~28 m3/s) still caused substantial shifting, which may influence the stability of catostomid spawning substrates. Following gravel addition, the proportion of gravel in the streambed was significantly higher at all gravel sites. However, comparisons of sites to reference stream reaches suggested that sand, gravel, and cobble were still extremely deficient. Additionally, the volume of gravel was inadequate to create gravel depths that provided suitable habitat for catostomid spawning. Although periodic, passive gravel additions may take years to provide suitable spawning habitat for some fish species, we found that river chub Nocomis micropogon utilized the newly added gravel for spawning.