For rivers...

You might look into some type of polystyrene tube/channel if you want it to retain water... think like evestroughing, but wider. And you could use a surplus (Princess Auto) pond pump to route the water from one end to the other if you even want it to flow. I know some places have vinyl hosing (roll-out downspout tube, or pool backwash tube) but ya might want a larger diameter. Just slit one side, and open up, presto, tube becomes channel. Just bond the ends to a reservoir at either end, one for the pump to pull from, other to catch the water from the pump.

For roads... you can use walkway paving stones... check locally if there is a maker, and see how much they ask for damaged ones. Place pattern-down, and dust the concrete with sand. Then ya only have to use weed-killer at the joints. Another way is if you have aneighbor with a rototiller (powered soil-chewer for tilling garden in the spring, etc) you can 'cut' a path for the road... then weed-kill it/paving-stone it, whatever.

And then there is the other tankers in the area... " If you build it, they will come... " [>:]

WhiteWolf