cutting ditches to move water around a ranch ("stock pond" refills) on a mega-site

When cutting an irrigation stream on contour, what have you found works the best for cutting the stream (passive water flow to the 1st stock pond then across a field to where it's needed, think your favorite gold mining operation water pond)? I have the funds and about 1acre foot to irrigate land from a stream with. What would you recommend using to cut the irrigation trenches?

When I get operating at full capacity there will need to be at least 2 Olympic swimming pools flowing through the channels per day (It's a megasite).

I've already ruled out a trencher, and  bulldozer.

Rather than valves I plan to use a sluce gate system.

I use a pointed hoe for digging ditches.

Digging during a rainstorm really helps.

Have you done the calculations about the cross sectional area of the channel needed to carry that volume?
Then made an allowance for the gradient of that channel to get the volume of water through in the time scale you speak of?

That comes out to around 1000 gallons per minute if these ditches are running 24/7.

If I was putting in a bunch of ditches for that sort of flow, I would buy or have made a v-bucket for an excavator. A bit of googling suggests around an 18" flat bottom, and then slope the sides at 45*. Make it as big as your excacator can easily handle, no need to go full depth but the flexibility is good. Google thinks 1.2 feet deep is a minimum ditches depth for a shallow slope ditch to handle this flow..

I've done a ditch that handles maybe 2-3x this much water in storms with a 50" cleanup bucket on a 150 size excavator, from the side, eyeballing for slope; it works fine, but the ditch shape is not as good as a v-bucket would give you, and it takes more care to achieve an acceptable shape. You can also just dig an overly wide square-sided ditch and let the sides slump; again the v-bucket will do a better job.

In my soil the 150 was a great size for this, a 120 would have been plenty good, and my 3.3 ton mini can do the same job, slowly. If our heavy clay hardpan was close enough to the surface to hit while ditching, the 150 would be frustratingly slow and the mini absolutely futile. If I had to ditch in the hardpan I would consider a 200 to be absolute minimum.. so, consider your ground before investing in that bucket.