Hot Springs Tunisia.
Whilst driving along the route beside the Sahara desert we came across a hot spring and cooling tower. Water was being extracted from the spring but needed to be cooled as the water came out of the ground in excess of 50 degrees centigrade.
How to cool boiling water in the middle of the desert?
The cooling tower was made of concrete approximately 100 feet tall and the water pumped to the top of it where it was released to cascade down what looked like a washing board but on a greater scale. There were vents in the layers all the way down which allowed air to pass through. This helped cool the water which then came out at the bottom. It was possible to put your hands in the water here but not for too long as it was still quite hot. The use of the cooling towers can help the water temperature to drop by approximately 10 Degrees Centigrade it is then cooled further through a series of concrete canals.
The water passed along a concrete channel to reach a small pyramid type structure where the water rose to the top then cascaded down the side channels cooling it further. The water was then carried away along a complex of concrete water channels and then used for irrigation purposes for crops in the nearby fields. The water is then stored in giant ponds.
Approximately 5% of water is lost through evaporation but by the end of this cooling method the temperature can drop as low as 35-37C. The water is then transported away to the oases where it is used to irrigate giant green houses and fields of fruit and vegetables. Because of the rapid drops in temperature at night some of the heated water can be pumped around the giant green houses to maintain the temperature to optimise fruit growth. The types of fruit grown in the greenhouses include different kinds of melon and tomatoes. It is also useful for watering the camels and apparently they prefer warm water to cold water. Not only this the water is slightly salty so it encourages the camels to eat as well.
It is interesting to think that there are 100s of bore holes that have been drilled to source water. In the summer the temperature in the desert can reach 70C but it can also drop below zero to around -10 in December. Some of the geothermal water is used to heat houses, swimming pools and to provide heat for the hammams.
The water is used for various things in the following percentages.
Washing and camels 0.3%
Tourism and swimming pools 0.8%