Modeling Fate of Pathogenic Organisms in Coastal Waters of Oahu, Hawaii

Abstract

A comprehensive modeling study was undertaken to examine the transport and fate of pathogenic organisms in the coastal waters of Mamala Bay, the southern shore of the island of Oahu, Hawaii. Specifically, two mathematical models were developed, calibrated, and validated in an attempt to understand both the relative contributions of various outfall and shoreline sources to organism counts throughout Mamala Bay and the benefits achieved by various source control options. A three-dimensional hydrodynamic model was constructed to simulate the advective and dispersive processes observed in the bay. A near field plume model was coupled with the hydrodynamic model to realistically incorporate initial mixing dynamics. Results of the hydrodynamic model were then used by a pathogen fate model to predict the distributions of fecal contamination indicator organisms and specific pathogens at several locations throughout the bay. Two sources were identified as primary contributors of contamination within Mamala Bay: the outfall from the Sand Island wastewater treatment plant and the Ala Wai Canal. The relative importance of the sources was dependent on the indicator organism used to assess fecal contamination. Using the fate model results and assuming a seven consecutive day exposure, the maximum risk of infection at Waikiki Beach was estimated to be 1.3/100 for virus and 3.1/10,000 for