Entrainment Abundance and Composition Differ from Source Water Ichthyoplankton at Plant Vogtle, Savannah River, GA

GPC biologists performed an entrainment assessment at Plant Vogtle’s make-up water intake structure in 2008. Intake entrainment was compared to ichthyoplankton samples from Savannah River source water. Semi-monthly sampling was conducted at a mid-depth intake location and an upstream source water transect location during March – July. Source water was sampled with a double 0.5 m plankton net rig equipped with 500-micron mesh nets at 1-m depth intervals on 6-hr nodes over 24 hours.  Entrainment sampling consisted of a submersible pump system (4.6 l/s capacity) sampling at a mid-depth intake canal location about 46 m from the intake screens. Intake waters were sampled through the same net rig used for source water mounted inside the mouths of tandem 208-l plastic drums located beside the intake canal.  Substantial differences in abundance, species composition, and life stage composition were observed between source water and entrainment. Dominant species and life stages in source water differed from entrainment. Source water eggs and larvae were 36.4 times more numerous than entrainment. Source water samples yielded 23 species compared to only seven taxa in entrainment. Eggs were most abundant in source water compared to no eggs in entrainment. Intake pumping was consistent during the sampling. No significant relationships were found between entrainment rate and environmental variables or river discharge. GPC’s 1970s desktop studies concluded that minimal entrainment would result at Plant Vogtle. Disparity between source water and entrainment abundance and composition in this applied study is conjectured as likely due to a combination of physical and hydraulic characteristics of the intake site and structure.