i can feel what your saying bout the river feel. Unfortunately i'm more of a visual person, ideas come to me with pictures lol. Maybe i'll try to draw something up regarding your river theme, might be a good idea as i have never tried grades before.
[attachment=599:name]Here is an older pic of my 92 G corner bow, open the one on the next post it's much easier to see. It has filled in alot up front since this. No grades or hills or anything, but the most important theing to keep in mind is having tall, hardy stuff in the back to hide the mechanicals as that is the only place for it to come in and out. Corner tanks are great, smaller footprint, better viewability (if that's a word, I guess it is now.....) Lighting is difficult to spread evenly, but it can be done. Flow and distribution can also be a challenge, play around with it, you'll probably want a powerhead in addition to the filter outflow. I point my outflow down and at the BACK of the tank to get to the back plants, the powerhead point straight forward and centered for the front stuff. Seems to work fairly well. Good luck and enjoy, corner tanks are very cool!!
Here is my wild low-tech 92 G corner tank. It has been growing for about 7 years. I have a piece of wood in the back to hide the filter inlet. As you can see I also have an internal filter (which is now hidden further in the back). There is also a power head with a sponge filter attached. My spray bar is along the right side of the tank along with the internal filter and power head. The tank is unheated and besides the plants it contains loaches, garra, danios, and barbs.
Corner tanks are terrific in rooms lacking wall space. Best of all my wife thinks it looks great in the living room.
Have a great time designing your new tank!
I have been thinking a bit and maybe thinking about doing drifwoot in the middle and back, then building the tank up on the back end with lots of ferns and Nana, really look like a cliff almost, i dunno we will see when the time comes too