The biggest problem I have with my last version (malabor-6.png) is that the rivers on the eastern side of the Gulf don't run through the thin strip of mainland shown on the map; instead, they all originate in the low hills about 100 miles inland. I was hoping for more of a sense that there's a huge continent off to the east of the map we see, so we might get something like a Mississippi running through the hills and into the Gulf of Malabor. This turns out to be harder than I'd like. I've spent the last five days on this, and haven't really been able to get the kind of effect I like.

First, I'm going to separate the "hills" I'm looking for on the northern arm of the mainland from the "mountains" I want to get in the south. The only way to do this is to specify the general course of the mountains in my original sketch:
sketch.png
This gives a lot more heterogeneity in the heights, which looks much better.

I've also settled on simulating the continent to the east by generating a random terrain, running rivers through it, and recording the sizes of these rivers at the edges of the terrain. I then use these rivers as "seeds" for the rivers on the map itself. This gives us something like
malabor-7.png
I'm still not entirely happy with this. With only a week to go in the Challenge, though, I'm going to have to move on to other things, like the (required) forests and settlements, along with labels and the like.

I'd still like to revisit the rivers at some time in the future, but it might be with the next Challenge, or as a general WIP.