Tidal Effects on Mine Water Temperature

[Chris Wolkersdorfer]

Dear Forum Member,

recently I measured the water temperature at a mine water discharge near the ocean. The mine water temperature shows an oscillation which is clearly influenced by tidal effects, but not by the air temperature. The temperature increase at the end of the curve is induced by a heavy rainfall event.

Does anybody have an explanation for that observation?

Air and water temperature at a near shore mine water discharge.

HSO.jpg (23.08 KiB) Viewed 14239 times

Chris

[CJ@RESPEC]

Very interesting! How is the temperature being measured (appears to be on an logger) and where? If the temperature was being measured in a location where it is being impacted by earth tides, you may be able to see subtle temperature ups and downs because fluid being forced "in" our "out" near the gauge could have different temps because of geothermal gradient. For example, I have observed in well bores (with temperature sensor is in casing) that increases in pressure can cause increases in pressure and conversely pressure drops cause temperature drops. This is because increasing pressure "pushes" warmer fluid past the gauge and when the pressure drops it "pulls" cooler fluid past the gauge. I wonder if a similar situation could occur in your example. However my gut reaction is that the swings you are observing are too large (0.1 degrees C). Assuming is deep enough to be in geothermal regime and know gradient, one could back calculate what difference in depth would be required to get this result and could rule out my explanation.

Cheers,
CJ

[Chris Wolkersdorfer]

The temperature is measured in a discharge pipe (Q around 1000 l/min) with a temperature, electrical conductivity and pressure transducer (Van Essen CTD Diver) every 10 minutes. The discharge pipe is connected to an underground mine at an unknown location and the mine dips under the ocean. I think you are correct, the tides push up water from the depth and consequently causes the oscillation. We measured up to 17 deg C in deeper parts of the mine and therefore, the 0.1 difference might bepossible. Yet, I agree, I have to calculate if it is possible. Thanks.

Kind regards

Chris