What is this bridge for, exactly? Here it is, from both sides:

http://personal.morris.umn.edu/~webb...ndeBridge1.jpg
http://personal.morris.umn.edu/~webb...ndeBridge2.jpg

Some info:
1. It's old (obviously). Boards (for walking across) seem too rotted
to hold much weight.
2. I don't think it's wide enough for a tractor to drive across, but
it's obviously not just for human foot traffic, right?
3. The ditch of water beneath it is maybe 10-15 feet wide. I think
it's a man-made tributary from the Chippewa River. It seems to run
neatly along the boundaries of farm quarter sections in the area. The
bridge seems to connect two farms across the water.

Was the water used for irrigation, do you think? What role did the
bridge play? Thanks if you can help (or direct me to another source).