Modeling Framework for Organic Sediment Resuspension and Oxygen Demand: Case of Bubbly Creek in Chicago

Abstract

A modeling framework that combines both two-dimensional (2D) and one-dimensional (1D) numerical models for the evaluation of organic-matter transport across the bed-water interface is presented. Emphasis is placed on capturing oxygen demand in the water column associated with the resuspension of organic sediments from the bottom. The proposed numerical approach solves the hydrodynamics coupled with sediment transport and water quality dynamics and represents a substantial improvement to the state of the art of water quality modeling methodologies available in the literature. A biochemical oxygen demand (BOD)–dissolved oxygen (DO) water quality module is incorporated into the 2D depth-averaged numerical model STREMR-HySedWq. The model is applied to the South Fork of the South Branch of the Chicago River, known as Bubbly Creek, with the goal of modeling combined sewer overflow (CSO) events and their impact on DO levels in the short-term (hours or days). Given the intermittent nature of this kind of events, STREMR-HySedWq was used for modeling the overflow phase, while the period following a given CSO event, when water is essentially quiescent in the creek, was modeled with a simpler 1D, area-averaged, dispersion-reaction BOD-DO model. The proposed conceptual and numerical approach is capable of capturing the key processes, thus providing both useful preliminary results as well as important guidance to assess potential water quality improvement and sediment management solutions in Bubbly Creek, Illinois.