Next to a river the best way to tell where to plant is to dig and see how deep the in the ground is the moister...MJ will grow it's roots accordingly.Plant so the roots can reach the wet ground but not submerged,just plant it so the roots are an inch or 2 above the wet earth and water as needed until the roots reach the moister in the earth.Then the plant will monitor it's own watering cycle.
Hope that helps.
If you can run a hose or PVC pipe down a hill to your plants,you wont have to be near a river and it can be more low key.make sure the hose or PVC is burried so know one can follow it to yuor crop.

I think you had your no water theory confused with an automatic watering system...no? :thumbsup: