What you are attempting may not be legal. Why not put in a small
pond with a waterfall or some kind of fountain to make the noise you
seek?

Interesting thought.

Do they have inexpensive self-priming pond pumps that would pull water
from the ditch 30 feet away, and up into, for example, a large fountain
bird bath? It could be rigged up with a float switch to only turn on when
the birds knocked the water level down.

Sure they do, or a sump pump..... though.... in my county (desert
w/irrigation) you'd need a permit, or it would be consider water stealing.
Yikes! ~ jan
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(Do you know where your water quality is?)
Also ponding troll free at:
http://groups.google.com/group/The-Freshwater-Aquarium