What are these large land channels in Iraq?

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There are many of these in the area. They sometimes start and stop periodically. They do not appear to be for transportation or carrying water, just curious what they are.

These are water channels  en.wikipedia.org/wiki/Channel_(geography)

Yes, they are for water, you can see the erosion channels in their sides.



Why were they made ? They do not transport water, they are for water storage and access.

You can see the natural water courses  are either skipped by the cut, or the water course is diverted into the cut, and after the cut, its dry again.. the water is lost to the cut.


Maybe  deep enough to get to the water table ? 
Anyway,the river floods, and when the flood is clear, the cut  is filled with water still.

Or if it rains locally and no flood, the cut collects the rain water,


All that said, it might not be effective.  Seems novel. "I have brilliant idea , cut river channel from here to there, and then the river  water is kept !". .. 
As I point out, the water goes down into the sediments,and flows   ( ... who needs an above ground  irrigation channel when you can just tap the sand bed water..  its refreshed by the floods each year.. thats why civilisation was early to the this area . )  and the dry air above the water takes off a lot of water too.