It is essentially an optical illusion. What they have done is build an ad hoc da of sorts across the Helmand River. It is more like a gate of sorts, built of earthern and wood materials which cause the water to "stack up" behind the constriction and raise the level of the water. This allows them to push water into canal inlets that wouldnormally only receive water during the months when the river is high.
The Helmand is one of the few rivers in the world that simply dissipate into the desert.
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