Okay, I really love band music. This is really good.
The moving parts at m. 48 I think need to be rebeamed in triplets, but otherwise your score is solid.
This piece is very idiomatic for band as it is. I think it might be a bit of a cliché to add a fast section, and I think it might take from the organic nature of the music you've so far acheived. I was going to criticize that the piece seemed a little too "through-composed" for my liking, but a second listening revealed to me that I actually like the flow of your material, but what I want more of is organic orchestration. The first half of the score is better, but I think starting around page 10, it seems like you lose the balance between your theoretical idea and your ensemble, because the texture starts to get choppy. What I mean is eg. on page 14 the saxes/dbl reeds do something, then they stop and the high brass does something, then they stop and the low brass does something and this is more or less the pattern for the rest of the piece. I don't think this is "wrong" or anything, but if this is a competition piece, I think orchestrating this a little more elegantly will elevate the piece more than a fast section would. This is a water piece, and water doesn't behave discretely, I think you could let instruments' parts spill over and conflict with what interrupts it. I don't even think it would be that difficult for you with this piece; there is even an opportunity to elevate your 3 over 4 idea by letting an idea in 3 "spill over" into where your next idea is in 4 is one idea.
The cool thing about bands is they are ravenous for new music - so when writing for band is the perfect time to get creative with doubling and textures.
Thanks for sharing.