Speaking of the weather, the wet spring has intensified an already heated debate:
“How much flooding here in America is created by tile lines? The grass waterways and field timber finger ditches are gone and replaced with more tile lines. The earth doesn’t get a chance to absorb moisture anymore once the rain stops. Has greed started to make us not be concerned with mankind downstream? I live along the Mississippi River and a lot of the backwaters I got to fish as a child are just silted full now.”
That’s from Todd Lammers in Guttenberg, Iowa. Thanks for the question. To be clear, we are talking about subsurface drainage that outlets to local creeks or drainage ditches. The answer is complicated. Full disclosure: we have been installing tile systems on our farm as fast as we can pay for it, so I clearly have a bias. Here are some of the factors.
The soil types, structure and topography. The heavier the soil and the flatter the land increases the value tile drainage to farmers. Does it contribute to flooding downstream on our Wabash watershed? In one sense yes. Without tile this would still be uncultivated swamp like it was in 1880, and nothing mitigates flooding like square miles of swamp. But there is also the sponge effect: by providing an exit for excess water in the upper 30” or so of our land when it is not raining, our fields can absorb far more rainfall before surface runoff begins. To be sure about the same amount of water ends up in the Wabash, but not nearly as rapidly. This year, after the wettest twelve-month period in recorded history, we noticed no gullies from surface runoff, while neighboring fields experienced serious washing regardless of tillage system.
On our soils, given our topography, in our watershed, drainage tile does not appear to increase flooding issues downstream, and may well mitigate heavy rainfall events. Here is the real problem: more frequent and larger rain events, and a steady increase in annual precipitation as shown in these graphics. Parts of eastern Iowa have added 5” annual rainfall per century. The problem with flooding is that extra water has to be somewhere. Levees, dams and drainage can help control the flow, but the precipitation trend means we’re all going to be affected.