Looking good, Jack. You certainly have some red clay soil there. Our clay is more of an orange color. I see we use the same tunnel construction method.
May I offer a suggestion on your waterfall? If you could stack up a series of flatter rocks, slightly stagger back, for the water to run down it would give it a bit more visual interest. Just be careful of it not splashing outside your liner area. Also, mixing in smaller sizes of river rock will blend in the larger rock to the landscape. I am current finishing up a similar project for a client and will grab a few pics today.
-Brian