Preliminary results of light transmission under residential piers in lake washington, king county, washington: A comparison between prisms and grating

Abstract

During the summers of 2003 and 2004, 11 piers (two public and nine private) were evaluated for their ability to transmit light through the decking to the water surface below. Solid decking produces distinct shading that migrating juvenile Chinook salmon appear to avoid by swimming into deeper water where more potential predators live. Two new types of surface treatments (acrylic prisms and grating) were evaluated and compared to traditionally spaced decking as well as solid decking. Grating (with 37–58% open space) was found to transmit significantly more light to the water surface below (mean = 7.5% of full sunlight) than 23 × 5 cm acrylic prisms (mean = 0.7% of full sunlight). In other words, compared to full sunlight, grating transmits 10 times more light under the pier than acrylic prisms. In addition, light that passes through open grating penetrates the water evenly under the pier. Light transmitted through prisms concentrates beams of light that do not always reach the water surface. © 2006 Taylor & Francis Group, LLC.