Statistical analyses of the effects of a coastal power plant cooling system on underwater irradiance

Abstract

The authors estimated the effects of a cooling water discharge from a coastal power plant on underwater light levels using 6 years of integrated hourly irradiance measurements which were taken at the sea bottom in water depths of 10–14m. They applied a before-after-control-impact design (BAC1) to the irradiance recordings. The basic BAC1 design estimates the power plant effect as the difference between the means of impact-control differences observed in separate periods after and before the power plant began operation. This design subtracts out constant spatial differences and uniform temporal changes, leaving only the time-by-location interaction which is the power plant effect. They modified the basic BACI analysis in several ways to deal with high natural variability, serial correlation in the data, and the effects of current direction. The daily irradiance data were divided into two sets of days in which the impact stations were downcurrent or upcurrent from the power plant discharge. For downcurrent days, the authors found significant ( p < 0·0.016) reductions in irradiance ranging from 20 to 28% at three impact stations. For the upcurrent days, they found insignificant increases of about 14%.