Knowledge Bank

The Lower Olentangy River in Columbus, Ohio has a sharp change in slope and width near the crossing of the Henderson Rd. bridge. This sudden change in morphology had not been directly addressed, but previous studies suggest that these changes are results of the low-head dam near North Broadway, three kilometers downstream. The water surface elevation (WSE) is modeled by solving a gradually varied flow equation with input data collected by 16 stream gages in 2014, a nearby USGS gage station, and bathymetry data collected with a depth sounder in 2015. Two WSE profiles are computed, one using observed water elevation at the dam as a boundary condition, and the second using a boundary condition representing water elevation without the dam. The simulations using observed and lowered boundary conditions converge 2.2 and 1.7 km upstream at low and high flow. The effect of the dam does not extend to the sharp change in slope. At low flow, widths increase 15.5% in the influence of the dam, but at high flow width decreases by 1.65%. Bathymetry data show a 22.9% decrease in bed slope downstream of Henderson Rd., which contributes to the decreasing slope and increasing width.