A gravity flow system is used to release water into the Panama Canal locks, i.e. there are no electrical pumps utilized in the process. Huge culverts, each "large enough to drive a train through", fill each lock chamber with 101,000 cubic meters of water in about 8 minutes.
As can be seen in the picture below, ships leaving Gatun Lake must go down to enter the Caribbean Sea. The Gatun Locks are used for this part of the transit.
Panama Canal Picture (c) Linda Garrison
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