Hi Legate,
oops sorry regarding the 'borrowing'. I think what I had in mind
was some sort of subtle crossover between the two stories, like your party comes across mysterious hobbit tracks in the snow, finds items lost by the other party or has an encounter with enemies defeated by the 'Downers' party etc. I like this sort of thing because it gives an impression that oher people are also around in the area on their own business. In a way a bit like the mentions of Gondolin in The Hobbit, which give glimpses of other stories. On the other hand it looks as if your timeframe doesn't match so probably this wouldn't work.
So, hoomm, what happens after the floods have subsided? You've already had the Tharbad refugees, and it seems likely that a great natural disaster would force migration of both people and animals. I'd also guess that by autumn many people would be getting desperate for food after just making it through the Fell Winter then perhaps having their crops destroyed by flooding.
Meanwhile the after-effects of the flood will still be felt, bridges and roads washed away, landslides still not cleared up. That's a point, who would clear up landslides etc? I guess you could come across a Dwarven waggon train stuck on the road and having to improvise a bridge, meanwhile trying to keeping the trolls at bay. Could be a chance for a bit of problem-solving how to get the road repaired and a rescue mission to find any travellers who have mysteriously disappeared in the night, folowing the muddy troll or wolf-prints.
On a darker note, perhaps alongside one of the fast flowing streams of the moors flash-flooding has uncovered Something Which Was Better Left Undisturbed
(tombs, mewlips, nameless things which gnaw the world below etc).
By the way I like the website (even though I don't know any Czech) and its both cool and weird to see the maps in another language!
Cheers