Lake Gatun in the center of the Panama provides the fresh water that powers the locks in the canal. My question is this: is more of this fresh water lost to the sea if you have one big “Panamax” ship down go through the locks to the ocean, or is more lost when you fill up the lock with a lot of little pleasure yachts going down instead?
The locks operate by allowing water to flow from the upper lock to the lower one, waiting until the levels are equalized, and then opening the gate to allow the boat(s) to pass. When the boat or boats pass to the lower lock, they displace some of the fresh water in the lower lock so that it moves back into the upper lock again. Then, the water is released from the lower lock into the canal so that the level is equalized with the canal, and the boats can float out again. This is the water that is “lost”. Question is, how much is lost and which causes more loss?
One of the problems these days is that there is so much traffic in the canal that there is not enough fresh water to replace all the water that flows out of the lakes via the canal. So, the panama canal commission is trying to figure out how to minimize the amount of water lost, and one idea was to reduce the number of lock-fuls of small yachts that are allowed to pass through the canals each month. However, I’m not sure that will reduce the water loss.
Another problem is the amount of salt water that makes its way into the lake while boats are going up the locks. Yes, the water generally flows down, but while the lock doors are open, some mixing can occur and a little salt gets in to the wrong place, and from there a little gets into the upper lock, and from there into the lake.