Effect of selective water intake on the oxygen regime of a stratified reservoir

Abstract

1. A mathematical model of the oxygen regime of a stratified reservoir, which makes it possible to calculate this regime for a selective water intake with allowance for variation of the balance between the production, expiration, and destruction of phytoplankton with varying depth of this intake, and also with consideration given to photosynthetic aeration of the epilimnion and hypolimnion, is developed. 2. Results of this calculation indicate that the oxygen content near the bottom of the reservoir increases with increasing depth of selective water intake, and reaches a maximum when water is drawn off only from the hypolimnion. On the whole, these results suggest that selective water intake can be used as a rather effective nature-conserving measure to improve the oxygen regime of a reservoir in its near-bottom layers and to prevent the development of starvation phenomena here. 3. With the reservoir in service, this goal can be achieved by drawing off water from the hypolimnion using a bottom water outlet, which can be activated during the summer when the oxygen content near the bottom drops to a critical level (below 4 mg/liter), or by increasing the drawdown of water during this period through the turbines of the hydroelectric plant (with water drawn off from the zone of the thermocline). Under these conditions, however, the intake of water from the surface layer (epilimnion), for example, by drawing it down through a spillway dam, as computational results have shown, may lead only to degradation of the reservoir's oxygen regime.