Velocity field measurements at an overfall

The velocities and circulation patterns were measured and characterized for flows in the vicinity of an aerated straight drop overfall. The velocity v ectors were determined for multiple tailwater levels at a constant flow rat e and for multiple flow rates at a constant tailwater level. An acoustic Do ppler velocimeter (ADV) was used to acquire three-dimensional component flo w velocities along the channel centerline. The ADV probe performed well in areas of relatively low flow velocity and low air entrainment, but the prob e did not perform well in areas with high flow velocity and high air entrai nment. The velocity measurements are presented and the near boundary flow v elocities agreed well with previously, measured boundary stresses. The velo cities near the vertical wall and horizontal floor were observed to be simi lar in magnitude for a range of tailwater elevations and discharges. These velocity field measurements provide fundamental information about the veloc ities and circulation patterns in the vicinity of an overfall. This informa tion enhances our understanding of the forces that cause headcut erosion.