Duwamish Waterways Navigation Improvement Study: Analysis of Impacts on Water Quality and Salt Wedge Characteristics.
Abstract
A review of historical water quality data and studies in the Duwamish Estuary has revealed that several changes in water quality conditions have occurred since the mid-1960's. Surface water D.O. concentrations have dropped near the head of navigation in response to nitrification of increased ammonia discharged from the Renton Wastewater Treatment plant (RTP). However, salt-wedge D.O. concentrations, which historically have been depressed to 1 mg/1, have increased markedly following sewage diversion from the estuary in the late 1960's. This improvement was found to be principally due to decreased oxygen consumption in the wedge. Based on a comparison of total saltwater wedge consumption (calculated) and sediment oxygen demand (SOD) measurements taken during August 1973, wedge D.O. uptake was found to be almost solely benthic (bottom-related). Other factors influencing wedge D.O. (freshwater input, tidal exchange and seawater inflow concentration) have not changed significantly since 1966. Since oxygen demand is primarily benthic, a dredging project which only increases wedge depth (area constant) will have minimal effect on wedge D.O. concentrations because the longer residence (reaction) time will be offset by the increased dilution of SOD. The alternatives considered will have negligible impact on phytoplankton production.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1981
- Accession Number
- ADA098271