I think with trout you do not need a warm water refuge. Highly oxygenated water throughout the entire water column during winter ice & snow cover is much more important for trout than keeping water near 39F. Trout survive just fine in streams that form anchor ice during winter. This water ranges from 33F to 32F or less. That is one of the reasons why they call them cold water fish.
From my tests of water temperature during winter aeration under ice and snow cover, mixing of the water column extends a whole lot further than the immediate area surrounding the open hole. Apparently the movement of cold water has a lot less resistance to mixing than the warm water of summer. I don't know how to measure how much less resistance to mixing, but the under ice water movement from a diffuser is impressive. It must be related to the physical properties and density of water as it changes temperature. If you operate one diffuser (1cfm) for 4-6 hrs per day near the bottom at 12-16ft deep, I predict this one diffuser will mix and circulate oxygenated water to 0.7ac to one acre or more of water. Thus 4 single diffusers equidistant in 1/2 of the 8 ac will mix 1/2 of the 'lake' even though each open hole is only 20-50ft dia. If you don't have water deeper than 10 ft then place diffusers along at least 1/2 the length of the belly of the 8 acres. This should provide enough oxygenated refuge to allow trout to survive the winter.
Are you able to go up there during mid winter and make some temperature and DO measurements?
Advanced Reading: Not all ice forms on the water surface. In streams, the turbulent flow can allow the water column to supercool to temperatures below the freezing point (0C-32F), allowing ice to grow in the water column. The first ice to appear is frazil (small disks or spicules of ice suspended in the water column). When turbulence transports frazil to the river bed, the frazil may stick to the bed, forming anchor ice.
Frazil and anchor ice are most likely to form on a cold, clear night when the wind is strong, the humidity of the air is low, and the river is at minimum flow, especially if such a night follows a cold, windy, cloudy day.
Commonly recognized types of stream ice include frazil ice, anchor ice, surface ice, and snow or slush ice. These are distinguishable by their characteristics and origins, and it is common to find all four types present in some combination along any mountain stream. Formation processes of these ice types are strongly interrelated and dependent upon each other.
The accumulation of frazil ice on underwater structures is known as anchor ice. On stream bottoms, it appears as smooth, white pillows. Anchor ice is typically a spongy, flocculent mass of ice crystals that is more porous than ice that forms on the surface. With time, patches of anchor ice may grow horizontally and join to form a continuous carpet of ice on a stream bottom. Maximum anchor ice thickness was about 30 centimeters and average thickness was about 8 centimeters in a Michigan trout stream (Benson, 1955). Anchor ice formation is usually highest during cold, clear nights, when heat loss from the water is greatest. In streams, anchor ice occurs most commonly on gravel and boulders in riffle areas where flow is most turbulent (Benson, 1955). Anchor ice seldom forms on substrates of fine sand, silt, or clay because (1) the anchor ice can lift free before attaining any significant size, or (2) streambed heat flow to the water may be effectively greater in these areas than gravel or rocky areas (Ashton, 1986). Wigle (1970) reported temperatures of 0.4 to 0.5�C at a depth of 10 to 20 centimeters below the bottom of the Niagara River, while temperatures of the water were supercooled, indicating the potential for surface heat transfer to water. Anchor ice may form on stream beds when turbulence is strong enough to transport supercooled water to the bottom, where ice crystals may attach to the bottom and further grow (Ashton, 1986). Anchor ice generally does not form when a surface ice cover is present.
Last edited by Bill Cody; 08/18/17 09:58 PM.
