"Una" wrote in message ...
MNRebecca wrote:
But would there
have been ditches WITHOUT such bridges in the first place?

Quite likely. In most of the world where ditch irrigation is used no
pump is involved. Methods of getting water from the ditch to the field
generally require the ditch water level to be higher than the bottoms
of the furrows in the field. To get water across the ditch bank there
are siphon tubes, removable barriers as simple as a plank, etc.


or, if they used a pump initially at ground level, it would be less
efficient since it had to do a lot of "sucking". With the bridge in place,
they could easily put the pump in the water, driven by a shaft from the
motor on the bridge.

I concur that the bridge was probably reused from some other purpose.