Here is interesting information from Clemson Univ. about water depth and turnovers.
https://www.clemson.edu/extension/water/...tion/index.htmlHow do I prevent a turnover?
Proper pond construction is important. The ratio of surface water (epilimnion) to deep water (hypolimnion) is a major determining factor for the frequency and severity of turnovers. Deep ponds with small surface areas often are more prone to severe turnovers because there is a larger volume of deep, low-oxygen water relative to the amount of oxygenated surface water. Broad, shallow ponds have fewer turnovers because less of the pond's volume is tied up in low oxygen deep water. Most stormwater ponds are shallow (6ft deep or less), but some are deeper. It is important to know the topography of the pond's bottom (bathymetry) as well as the average depth of the pond. Over time, the depth of the pond will change as it fills with sediment, so the bottom contours may not be the same as when the pond was constructed originally. (See section on Pond Construction and Sedimentation)
Prevent aquatic weeds from covering more than 20% of the pond surface. Floating and submersed weeds impede circulation and the diffusion of oxygen into the pond. They also remove oxygen from the water as they decay. Controlling aquatic plants will improve circulation and reduce stagnancy.
Reduce nutrients and algae growth. Loading ponds with nutrients from yard fertilizers, exposed sediment, pet waste, and feeding of fish/ducks/turtles will increase algal growth which can further deplete oxygen.
Mechanical circulation can prevent turnovers. The primary purpose of mechanical circulation is not aeration/oxygenation (injecting oxygen into the water). Its purpose is to prevent stratification and bring water to the surface so that it can be exposed to oxygen in the atmosphere. By mixing the water, circulation systems never allow the pond to form layers, thus they do not develop a low oxygen layer on the bottom. In this way a circulation system becomes an insurance investment to prevent a fish kill.
