Hydraulic design of winter lake aeration system

Shallow, eutrophic lakes in the upper Midwest of the United States are subject to fish mortality due to oxygen depletion under ice (winterkill). Current practices employed to prevent this phenomenon typically create an area of open water, which poses a hazard to winter lake users. An aeration system has been designed and hydraulically modeled that: (1) Will maintain oxygen concentrations adequate for fish survival while minimizing oxygen consumption; and (2) will not destroy or weaken the ice cover. This system consists of back-to-back manifolds, each incorporating a flow diffuser, that withdraw water from a layer within the naturally occurring winter thermocline and return it after aeration to this same layer. This is done at very low velocity with a minimum of vertical entrainment or mixing. Between withdrawal and reinsertion, the water is aerated by conventional means, e.g., free overfall or cascading aeration. Since a stable density stratification is maintained, warm water from the bottom is prevented from moving to the surface where ice melting would occur, and oxygenated water is separated from the sediment where most of the winter oxygen demand resides.