Reaeration at Low-Head Hydraulic Structures

1. Presently, one of the mos~cited water quality parameters in the freshwater hydrosphere (rivers, lakes, and reservoirs) is dissolved oxygen (DO). The oxygen concentration in surface waters is a prime indicator of the quality of that water for human use as well as use by the aquatic biota. Many naturally occurring biological and chemical processes use oxygen, thereby diminishing the DO concentration in the water. The physical process of oxygen transfer or oxygen absorption from the atmosphere or air bubbles acts to replenish the used oxygen. This process is termed reaeration. 2. Low-head hydraulic structures within the US Army Corps of Engineers are generally associated with navigation projects. These structures are usually "run-of-the-river" and are used to maintain a constant upstream pool elevation. The oxygen transfer in these deeper, slower pools is lower than that of the open river. Biological and chemical oxygen demands may accumulate and concentrate in the impoundment and thereby degrade the DO concentration in the stored water because of the excess demand compared to reaeration potential. Without sufficient reaeration, release of