You've got a 12 inch and 15 inch pipe carrying water, sounds big enough. Can't imagine it was cheap, but the Last picture looks 100% better than the 1st picture!

That 1st picture is nothing more than a Miserable weed factory with it's own irrigation system!!

Probably a silly question,, but is there any reason you couldn't put in a pump at the outlet end and recycle the water back to the top of the field ??

I know one guy who has such a sub problem with Bureau of Rec. Canal, he dug a deep trench just off the Bureau's easement, laid in perferated line then dug another ditch to a lower field dropped in solid pipe, and irrigates the Lower field with FREE water !!