The water rained on the peaks first forms crisp meltwater tributaries, which run into each other and become more powerful as they descend the precipitous pine-covered mountain slopes into the cloud forests.
The only human settlements here are the small knots of workers sent to restore and run the abandoned hydroelectric stations that were discovered dotted around the slopes and waterfalls, as well as their families; after a few decades, some of these stations have expanded to resemble small villages.
The slopes become less steep in the root forests; here, there is little rain, but the forests are still verdant and full of life due to the adaptations of the plants; those that grow near the now less-powerful middle course of the river have roots like mangrove trees, extending far into the river and getting more than enough water from it. These roots grow so tightly that a layer of mossy vegetation sits on top of them, like a forest floor with stilts, undercut by the river.
There are also succulent trees with turgid leaves that store water, and tall trees whose long central roots reach down to the water table. A quirk of the trees here is they're a lot more active than the ones we're used to; their branches sag down or twist up or retract towards the trunk at night, only to perk or spread or unfurl during the day to catch the most sunlight they can. Large and small herbivorous mammals roam between the trees in the wild forest, including deer-like creatures and wild cattle, which are hunted by the human inhabitants further along the river.
Further down the river. as it approaches the floodplains, the forest becomes less wild; swathes of it are used as forest gardens, to grow fruits, berries, roots and medicinal plants that can't be cultivated in the floodplains environment.
The floodplains (they are called this despite the fact that they never really naturally flood) are used primarily by their inhabitants as agricultural land by channelling the slow, meandering river into flooded fields in which are grown grains, leaf and stem vegetables, and edible aquatic plants.
Between the fields the paths are dry and packed for farmers and their vehicles to walk on, though in the water they have to wade or use small paper boats. Creatures live in the flooded fields, some beneficial like shrimps that clean the plants of parasites, but some harmful invaders from the river.
At this point in the course there are four large rivers flowing down the land, crisscrossed by natural and man-made channels, and it's the gaps in between them that are farmed mainly; the far shores of the flanking rivers are occupied by factories and workshops, felling the pine trees that grow rapidly there for timber and strong waterproof paper (which are of a different quality on either side of the floodplains, the 'East' and 'West') and quarrying for rock - it's colder and darker on these shores, more so the further laterally one goes, until eventually unfit for human habitation.
Finally, the rivers meet the coast - the cliffs here are made of smooth, rounded brown rocks that sparkle like compressed sand, and where they slip under the water are covered in a freshwater coral reef that is bursting with life, crabs and shellfish and fish, which like most things in this world is a bounty for humans.
And though the cliffs themselves are lived on by only a few people, this coast is home to the most densely populated human settlement in the world: the Coral City.