The fate of legacy sediments and its impact on dissolved oxygen in urban stream during storms

Abstract:

Bubbly Creek is a tributary of the South Branch of the Chicago River in the Chicago Area Waterway System (CAWS). The approximated 2-km tributary with a mean depth of 2 m and width of 45 m contains abundant contaminated organic muck and waste in its benthic sediments. In the 19^th century, Bubbly Creek was used as a drainage channel for the stockyard waste. Back in 1936, Racine Avenue Pumping Station, which is located at the upstream-end of Bubbly Creek, went into operation. The combined sewer overflows (CSO) from RAPS bring plentiful nutrients and urban sediments to the channel during storm events. Therefore, the entrainment and transport of sediments from Bubbly Creek and their impact on water quality, especially dissolved oxygen (DO), in CAWS have been of interests for a long time. In this study, the 3D numerical model, Environmental Fluid Dynamics Code (EFDC), was applied to study cohesive sediment transport of benthic sediments as well as potential entrainment, transport and fate of legacy sediments from Bubbly Creek to CAWS. Furthermore, the eutrophication water quality model will be applied to investigate the exchange of nutrients and DO between water column and benthic sediments via the sediment diagenesis model. The sediment diagenesis model in EFDC enables dynamic flux exchange of nutrients and oxygen, which is known as sediment oxygen demand (SOD), based on the chemicals in water and sediment. The present work focuses on modeling the impact of CSO and legacy sediments on the dynamics of SOD and DO variation during storm events in the urban waterway system, CAWS. The resuspended sediments and nutrients carried by CSO should increase SOD and drop DO significantly due to the release of organic compounds and nutrients during storm events.