Wow! That's awesome. Very nice work, and what a great piece of information. Its looks like a lot of thought and preparation went into it.
Ok, as far as comments, I agree with Hans' list and would add the following:
1. Placename labels are running parallel to latitude (?), but I don't see the lines. Otherwise, make them straight.
2. Topography is quite nice. Snow and ice elevations seem to be more opaque than mid elevations, to my eye.
Also, maybe shade out watershed with white opacity and let a revised watershed boundary do more work. This would give more 'eye-pull' to the colorful spill travel time line.
3. Watch for covering placenames with callouts. If you can't avoid conflict, then removed placename. IMHO
4. On Alaska / watershed locator map, can you add the wateshed?
5. On the river mouth, there is a disconnect between the travel-time model layer and the surface hydrology - I see blue lines at the mouth with separate yellow lines next to them.
Why were they not included in the model? Did you use a water polygon layer to account for river mouth hydrology? Also, at the river mouth, left of Kushtaka Lake, is that water flowing
uphill (to the east)? Somethings to look at / tidy up.
6. Possibly move the center of the background ocean radial-fill into the watershed so you give a pseudo-bathymetric effect: lighter blue near coast and contours around coast.
7. In the 'about the map' box, possibly use Sentence case and include (I would like to know) what time of year the river flow data represent (spring, summer, fall). You mentioned 1949-2004
data spread, but limited to fast flowing criteria - so it sounds like a fast-moving threshold was used - do tell. Also, any space to include a small reference to ESRI travel-time analysis function(s) used?
8. Last one! I like the color ramp of the travel-time line, though it might be more informative to use a two or three color ramp, where early, mid, later travel-time phases can be easily identified.
Was tidal influence at the mouth accounted for in the travel time model? I guess so if you were using river gages, etc.
Above are suggestions. I think you have done an excellent job. Thanks for sharing!!