Hi Herbie,

Thanks for the added details. The new 24 at .17 grade will do 700 acres and the existing 20 will do 430 acres. I would say they chose the most practical solution, perhaps not the perfect solution. Adding the new 24 should greatly increase what life is left on the old 20 since it will reduce pressures on it. To step up to a 30 would likely be lots more dollars. There are many contractors around who can trench in up to 24  in. Bigger usually involves a track hoe -- slower and more labor.

The 18 should easily handle the 230 acres.

Your solution is even better if not all the acres are pattern tiled.

No doubt those who are pattern tiling will get the biggest benefit, but the other landowners in the district will now have a main in place that they can hook onto.  Our dad's and probably granddads benefited from the original tile and it just turns out that it is this generation which has to step up to the plate to update the old systems to handle modern drainage needs.

Good luck with your project.