The reservoir temperature controls · AT 136214 · 1934
A reservoir holds more than one temperature.
A dam chooses which part of a lake becomes a river. Schauberger proposed drawing from different depths, blending the releases, and letting a temperature-responsive float govern the gate. The reservoir becomes a source of thermal choices.
RESERVOIR CROSS-SECTIONSummer stratification
Summer separates a warm surface from a colder deep layer. Lowering the intake through the thermocline brings cooler water into the blend.
2 m · upper water28 m · deep water
The second intake stays at 2 m.
Upper intake onlySelected depth only
Share of the total release. Total flow stays constant.
0.5°C24°C
Upper intake · 2 m23.5°C50% of release
Selected depth6.0°C50% of release
Mixed release14.8°C0.8°C above target
Illustrative 30 m reservoir · ideal two-stream mixing · selected example temperatures, not measurements or operating targets. The diagram explores intake selection; it does not reproduce the full patented dam.
How the temperature readout is calculated
The model holds the reservoir profile and total discharge fixed. It treats water density and heat capacity as equal in both streams, with complete mixing and no heat exchange before the outlet. If f is the fraction supplied by the adjustable intake:
Tout = (1 − f) × Tupper + f × Tdepth
The summer profile decreases from 24°C at the surface to 22°C at 8 m, then to 6°C at 18 m. Winter increases from 0.5°C to 4°C by 15 m. Mixed water is 10°C throughout. Real intakes draw from a layer of finite thickness; inflows, wind, drawdown and heat exchange change the profile over time. The target button finds the nearest available blend, rounded to one percentage point. A blend can only fall between the temperatures available at its two intakes.
01 / Schauberger's proposal
The atmosphere moves the gate.
In patent AT 136214, filed in 1930 and published in 1934, Schauberger describes a gate coupled to a floating, bell-shaped chamber. Air trapped inside the bell responds to external temperature. Its changing volume alters buoyancy and moves the connected sluice gate.
The gate admits deeper water into riser pipes. Diverter pipes can deliver that water to different levels on the downstream face, while upper water passes over a separate spillway. The flows meet below the dam. A curved structure at the foot encourages their mixing.
His purpose was to adjust the temperature of the released water to surrounding conditions, then influence its behaviour along the downstream channel. The mechanism joins an environmental input, a movable gate and a mixed-water output—an early proposal for automatic thermal regulation.
In this text, "heavy" and "light" water refer to density differences associated with temperature. They do not mean deuterium-rich heavy water.
Summer and winter reverse the choice.
For a summer-stratified reservoir, a deeper intake commonly accesses colder water. Beneath winter ice, water near 4°C can lie below colder surface water, so a deeper release can be warmer. When the water column is mixed, changing depth offers little thermal choice.
The report attributed to Forchheimer in The Water Wizard compares winter, summer-day and summer-night operation. It also discusses routing bottom water over the dam's outer face. That wall-wetting arrangement is a separate part of the historical design from selecting the downstream release temperature.
02 / The modern counterpart
Selective withdrawal.
At Cougar Dam in Oregon, a sliding intake gate allows release temperatures to follow the river's seasonal pattern more closely. A low outlet had previously released cold water in summer and retained surface heat for release later in the year, shifting the timing experienced by fish. [3]
Shasta's temperature-control device and Folsom's temperature shutters likewise make reservoir depth part of downstream temperature management. Reclamation uses reservoir–river models to support those operating decisions. [4]
03 / What to observe
Manage a season, not one number.
The useful target depends on the river, season and organisms downstream. Releasing the coldest available water all the time is not the goal. The relevant question is how a release fits the river's thermal pattern and how much cold water remains for later.
Read temperature profiles alongside reservoir level, discharge and dissolved oxygen. Track the release downstream as weather, tributaries and travel time change it. The depth selector is one control within that larger system.
Try winter, then increase the adjustable intake share. The outlet warms. Try mixed water: the same control no longer changes temperature.
The source record
The Water Wizard, translated and edited by Callum Coats, 1997: reservoir mixing and floating caisson, printed pp. 120–121 / PDF pp. 125–126, Figure 23; "Expert Opinion of Professor Philipp Forchheimer," printed pp. 131–134 / PDF pp. 136–139, Figure 30. These page references refer to the 220-page PDF edition.
AT 136214, filed 23 April 1930, published 10 January 1934. Original patent record ↗. English specification reproduced in The Water Wizard, printed pp. 208–211 / PDF pp. 213–216.
U.S. Geological Survey, Temperature and Water ↗: seasonal stratification, ecological effects and the Cougar Dam intake example.