Fine Slot and Mesh Size Screen Alternatives for Protecting Fish Eggs and Larvae at Cooling Water Intakes

State and Federal regulators are in the process of implementing major changes to the regulations that apply to existing cooling water intake systems with the goal of further reducing injury to fish at these facilities.  These regulatory changes have been met with increased interested in fish protection technologies, other than very costly cooling towers, that can achieve the required reductions.  Facility owners face many challenges as they work to determine exactly which technologies and/or operational measures to implement at their facilities.  An important area of compliance alternative selection is estimation of the site-specific fish protection performance that can be achieved by each alternative technology being considered. This paper compares and contrasts two potential retrofit technologies – narrow slot wedgewire and fine mesh travelling screens – that have the potential to meet the anticipated performance standards for entrainment and impingement reductions.  Because of the small size of eggs and larvae, the slot size/mesh size of the screens must be on the order of 2.0 mm or smaller in order to meet the targeted reductions in entrainment.  Innovative approaches to estimating pre-installation entrainment and impingement reduction performance were developed to make predictions about each technology’s potential to meet the standards.  Similarly, screening technology design, configuration, operation and maintenance solutions were developed along with cost estimates as a part of the technology selection process.  Trade-offs in terms of fish protection, operational reliability, and costs are examined.