---- Updated to 1.19 ----
To update, simply replace the datapack in the datapack folder of your world at the same time you update your Minecraft version.


This datapack adds underground rivers and canyons to Minecraft. In the vanilla generation the saddle valleys between high mountains split up rivers. With this datapack the rivers continue through these areas - either underground or forming canyons. The humidity is increased in the canyons and underground rivers so that lush caves generate there more frequently.

This datapack works by modifying the new density functions available since 1.18.2.

If you create a new world with this datapack use the "Datapack" button during world creation to make sure the datapack is active during initial world generation.
If you add the datapack to an existing world (create a backup first), close and reload the world after adding the datapack to your world folder (/reload does not work) - Chunk borders would exist but be limited to the canyons and underground rivers themselves.