He said most tile systems are designed to take one-half inch of water off the landscape per day. “The tile lines meter the water, slow it down compared to it running off the landscape.”
The researchers say one thing they still want to determine is what will happen when virtually all farmland has modern drainage systems installed. “The Blue Earth River basin is already close to that,” Schottler said.
He said that when tiling is complete, rivers will eventually widen to a point that will become their new normal width.
“At some point the river flows won’t increase anymore and they won’t widen the rivers more, and there will be a reduction in sediment. We need to find out when that will happen and what the sediment loads will be at that time — will they be the same as before drainage or still higher than before drainage started.”
The study looked at three things that could add to river flow: drainage, changes to the landscape, and changes in the amount of precipitation over time.
Schottler said some increase in precipitation doesn’t nearly account for the added water going into rivers.
He said that while the increased flow from drainage is clear, they do want to more closely study the effect of more soybeans being planted in the state. The amount of farm land in corn has remained virtually unchanged since 1940, but soybeans — which were almost nonexistent before 1940 — have grown dramatically to the point they are now about half of the crop acres.
“Soybeans replaced alfalfa, oats, rye, pasture — all those crops that are green and growing in April are now are gone and have been replaced by soybeans.”
Schottler, one of a team of scientists who has been working on the drainage studies in recent years, said that despite some skeptics, he’s been pleasantly surprised that the basic thesis that drainage sends more water more quickly to the rivers, is being fairly well accepted.