This would be a modern age Quarter made of two new buildings. I’m recommending that they be Ageless for the addition of later ages.
Locks: May only be placed on a River or Navigable River. If placed on a River, allows that river tile to be traveled through by Naval units at a speed of 1 tile per turn. Additionally, generates +X gold and +Y influence each time a foreign Merchant passes through the Lock.
Dam: May only be placed on a River or Navigable River. Generates +X Production for all river tiles of this River’s name that are developed by this settlement (definitely need to improve the wording here). Additionally, increases the Fresh Water reach of tiles adjacent, and upstream from the dam, to the river by 1.
Locks and Dam - Quarter - a Universal quarter that may be built by any civilization, the Locks and Dam doubles Production and Gold of all tiles on this river. Only one such quarter may be placed on an individual river.