note: one is transporting water.not cars.

 

if water absorbed through dirt all the better.

 

so as long as there is a hole that isn't blocking the path.

 

only that much structural integrity is required.

 

so the length of the tunnel can be cost-effective.

 

use the very earth that is being dugged out,

 

to hold the structural integrity.

 

and re-route the water to destination.

 

 

 

 it can also further be reinforced by support beams,

 

within the tunnel. as, nothing is being transported but water.

 

so as it holds its structural integrity,

 

it will do its job.