Fill mines below the biomes watertable || sealevel with water.
Possible mechanism:
[ ] for every 20 blocks of air below the watertable 1(!) sourceblock of brackish-water is spawned at the lowest level of the mine/cave
[ ] for every 10 blocks of air below sealevel 1(!) sourceblock of brackish-water is spawned at the lowest level of the mine/cave
[ ] once the lowest level is full of sourceblocks, the second level gets 1(!) block for every additional 30 blocks of air below watertable OR every 20 below sealevel
[ ] below-ground blocks within 10 blocks range of a waterblock will get a 'damp-caves' condition, fuelsources have shorter burntimes due to wetness (same for torches, obv)
[ ] a block keeps knowledge if it belongs to a cavesystem, and thus keeps track of all the sourceblocks and airblocks in the system(?)
Could also work with exposed blockfaces instead of air
Fill mines below the biomes watertable || sealevel with water.
Possible mechanism:
Could also work with exposed blockfaces instead of air