Selection of a Rotating Screen for Minimizing Impingement and Entrainment

In response to severe water shortages, a 10MGD desalination plant was constructed within the Taunton River in 2008.  The plant withdraws none of its water for cooling purposes; however, regulatory agencies required a final design commensurate with Phase II of Clean Water Act Section 316(b).).  The plant’s intake structure is equipped with a 0.5mm mesh barrier net (Gunderboom®) which has been monitored extensively for impingement and entrainment (I&E) since 2008.  Despite generally good performance (exclusion rates exceed 80% for some species), there are significant maintenance issues in a dynamic tidal environment.  Consequently our team assessed the feasibility of installing a rotating screen technology (Beaudrey® WIP).  This technology has demonstrated good site specific results for juvenile and adult impingement; however, larval impingement mortality was unknown.   In 2011 our team conducted laboratory pilot studies to determine the susceptibility and rate of entrainment, impingement, and survivability of early life stages of fish eggs and larvae in a controlled flume environment.  Preliminary laboratory results indicated that survival rates could be as high as were 86% and 71% for eggs and larvae respectively.  When installed in 2016, the performance of the WIP screen will have applications to other facilities as they consider 316(b) compliant technologies.