
Originally Posted by
Robert Tulip
We are looking at a tidal powered system to pump 250 KL per day, or 125 KL per tide. At one square metre per kilolitre, a circular lower bag (B) fixed to the ocean floor would require diameter about fourteen metres. The lower surface of this bellows bag does not move as it is fixed to the ocean floor. It could rest on sand, with the two chamber bag affixed to a single mooring point, and so aligned down-current from the anchor. This is at about 200m below the surface.
The upper bag (A) has fixed volume of water of brackicity calculated to rest on the lower bag at constant depth from the surface, with depth tuned by addition of salt or water to bag A. The fabric barrier between bags A and B is a single layer, so the rise of bag A on a rising tide expands the volume of bag B just like a bellows and the fall of bag A produces strong gravitational pressure on bag B, giving strong pumping pressure. If bag A has diameter 14 metres and height say 10 metres, it will produce large suction for an inlet pipe to bag B, and strong pressure for the outlet pipe, which could go to the ocean surface.
The inlet pipe to bag B could be reinforced fabric about one metre in diameter, either resting on the ocean floor or with some fresh water buoyancy sacks to keep it at constant depth, going down to the thermocline at about 500 metres depth to access nutrient-rich water.
This tidal pump arrangement is also suitable to pump fresh water from waterbags into a shore based reticulation system. For example, bags at the bottom of Moreton Bay or Sydney Harbour, if suitable locations exist, could pump imported or recycled fresh water to existing water pumping stations.