Here's a 5-z waterfall that I played for a while. Two biomes, a warm moist tropical broadleaf forest on limestone, and a single square of hot mountains. Both are basic wilderness. All civilizations are still alive (I only use 100 years of history), and you've got plentiful iron, coal, and flux in the first few levels. I actually got bored because with a couple of steel-plated squads it seemed too easy, but it's a nice spot to learn about waterfalls. If anyone figures out how to tweak the values to e.g. make the region haunted, please share!
Just use the finder to search for a 3x3 site with flux, no aquifer, and a brook. That puts you in the right square. Then use ukmh to shift the 3x3 box move down and right, so you're up against the right edge of the local map, and the river is running through the middle of the 3x3 box. This places the waterfall in the middle of the embark site.
If you want to find it manually, then on the world map it's in the leftmost column, 3rd row from the bottom, and on the regional map it's 6th column from the left, 8th row from the bottom. The local map has a river coming in from the top and leaving from the right. Enjoy
[WORLD_GEN]
[TITLE:Waterfall]
[SEED:827491688]
[HISTORY_SEED:1140864096]
[NAME_SEED:2501696768]
[CREATURE_SEED:1864836784]
[DIM:65:65]
[EMBARK_POINTS:1274]
[END_YEAR:100]
[BEAST_END_YEAR:2:80]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:0]
[ELEVATION:50:400:202:202]
[RAINFALL:0:100:101:101]
[TEMPERATURE:50:80:101:101]
[DRAINAGE:0:100:101:101]
[VOLCANISM:0:100:101:101]
[SAVAGERY:0:100:101:101]
[ELEVATION_FREQUENCY:1:1:2:3:2:1]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[TITAN_NUMBER:3]
[TITAN_ATTACK_TRIGGER:80:0:100000]
[DEMON_NUMBER:22]
[GOOD_SQ_COUNTS:6:63:127]
[EVIL_SQ_COUNTS:6:63:127]
[PEAK_NUMBER_MIN:3]
[PARTIAL_OCEAN_EDGE_MIN:1]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:1]
[REGION_COUNTS:SWAMP:66:0:0]
[REGION_COUNTS:DESERT:66:0:0]
[REGION_COUNTS:FOREST:264:0:0]
[REGION_COUNTS:MOUNTAINS:528:0:0]
[REGION_COUNTS:OCEAN:528:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:528:0:0]
[REGION_COUNTS:HILLS:528:0:0]
[EROSION_CYCLE_COUNT:250]
[RIVER_MINS:25:25]
[PERIODICALLY_ERODE_EXTREMES:1]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:2750]
[CAVERN_LAYER_COUNT:3]
[CAVERN_LAYER_OPENNESS_MIN:0]
[CAVERN_LAYER_OPENNESS_MAX:100]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:100]
[CAVERN_LAYER_WATER_MIN:0]
[CAVERN_LAYER_WATER_MAX:100]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:15]
[LEVELS_ABOVE_LAYER_1:5]
[LEVELS_ABOVE_LAYER_2:1]
[LEVELS_ABOVE_LAYER_3:1]
[LEVELS_ABOVE_LAYER_4:1]
[LEVELS_ABOVE_LAYER_5:2]
[LEVELS_AT_BOTTOM:1]
[CAVE_MIN_SIZE:5]
[CAVE_MIN_SIZE:5]
[CAVE_MAX_SIZE:25]
[MOUNTAIN_CAVE_MIN:6]
[NON_MOUNTAIN_CAVE_MIN:12]
[ALL_CAVES_VISIBLE:0]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:10]
[TOTAL_CIV_POPULATION:20000]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:528:1056:528]
[RAIN_RANGES:264:528:264]
[DRAINAGE_RANGES:264:528:264]
[SAVAGERY_RANGES:264:528:264]
[VOLCANISM_RANGES:264:528:264]