The Relationship Between High River Stage, Water Velocity and Scour, and Its Impact on the Hydraulic Conductivity of the Riverbed at the Bolton Well Field along Great Miami River, Southwest Ohio

Understanding dynamic interactions between a riverbed and aquifer is crucial for assessing the ability of river bank filtration (RBF) systems to help provide good quality drinking-water. One of the biggest concerns with RBF is that high river stage and water velocity can scour the biologically active riverbed colmotation layer, considered essential to the attenuation of contaminants as surface water infiltrates into the aquifer, and subsequently flows to production wells.  The location for this study is a site of municipal water production and induced infiltration in southwest Ohio.  The study goals are 1) to measure riverbed scour during storm events and to relate scour to the river stage and water velocity and 2) to measure the impact of storm events and scour on the hydraulic conductivity of the riverbed.  Direct monitoring of scour is being conducted using four Roctest^® vibrating-wire total-pressure load cells, which measure total pressure induced by the sediment, water and atmosphere. Pressure transducers installed in the river provide water and atmospheric pressures which are subtracted from the total pressure to infer the sediment height. River velocity is measured directly above the load cells using a SonTec^® aquatic Doppler velocity sensor.

Changes in riverbed hydraulic conductivity during storm events are estimated through calibration of VS2DH simulations of heat transport throughout the system.  Model calibration is performed using temperature hydraulic-head data collected in nine shallow wells placed in the riverbed in close proximity to the load cells.  Similar data are also collected in three deeper monitoring wells on the riverbank between the river and the production well.  We expect that high river stages and velocities will result in increases of riverbed hydraulic conductivity as a consequence of riverbed scour. This research will increase our capacity to predict the movement of water and contaminants through riverbank filtration systems.