Predicting river aquatic productivity and dissolved oxygen before and after dam removal

The potential changes to dissolved oxygen concentrations caused by combined sewer overflows (CSOs) are an important consideration before and after dam removal in many urban rivers. An old 2-m-high dam was recently (autumn 2012) removed in Columbus, Ohio, USA, from the fourth-order urban Lower Olentangy River, which has several major CSOs. Two simulation models were developed using STELLA® 9.1.4 to investigate the interactions of hydrology, water quality, and CSOs in the Olentangy River reservoir before removal of the Fifth Avenue Dam. The first simulation model, focusing on daily dissolved oxygen (DO), was created to predict DO changes in the pollution found in CSOs before and then 120 h after dam removal. Field DO data in 2009, 2011, and 2012 were used to calibrate and validate the model. The second simulation model, a weekly water quality model, was created to simulate one-year streamflow, gross primary productivity (GPP), and DO changes before dam removal, and to predict long-term water quality changes 2 years after dam removal. Field streamflow and water quality data from 2004 and 2009 were used to calibrate that model. Results from both field data analysis and model simulations suggest that there are great differences in water quality between base flow and flooding periods and that DO concentrations will continue to be significantly impacted by CSO discharges even after dam removal.