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.

Una