Improving River Aeration at an Underflow Dam

The aeration occurring in flow through dams can be a significant contribution to the dissolved oxygen resources of a river receiving the oxygen consuming organic material of waste waters. Changes in physical or operational characteristics of a dam can affect the rate of aeration. The aeration rate at Lock and Dam No. 2 on the Mississippi River near Hastings, Minnesota, had been reduced by a factor of three by an increase in tailwater elevation resulting from the construction of another dam downstream. Conversion of the underflow gate structure to an overflow condition by the installation of bulkheads and increasing downstream turbulence almost restored the lost aeration capacity. This study demonstrates that aeration at dams can be improved through changes in operation and indicates that the contribution of dams to river-dissolved oxygen resources should be included in the consideration of dam design and operation.