Logan Dunn
Assistant Resource Manager
N ow and then, a visitor might have wandered in one of the parks and discovered a small hole in the ground, or even a massive great hole, big enough for a car to fall into (if the car was ever allowed off-trail, that is). And those holes are almost inevitably connected with drainage tiles. The ‘big hole’ is likely the result of what we call a ‘blowout,’ which is when a main-line tile is damaged and exposed because of erosion from leaking water.
Much of the land that forms the 29,000-plus acres of Metro Parks was used for agriculture in the past. So when Metro Parks engages in wetland construction, one of the first tasks is to remove drainage tile from the site. Tiles are artificial drainage devices that are made to capture rainwater or surface flows below the ground, in order to dry a field for conventional agriculture. You see, when a farmer attempts to grow his or her crops, standing water can be very detrimental to the overall success of their crop, often drowning the plants and leading to a reduction in yield.
To install field tile, and drain substantially wet areas that retain water, one must first dig a trench, sometimes up to 5 feet deep. Drain tile is primarily used today in the form of black corrugated plastic, but historically tile was made of clay and came in several different shapes and sizes. Furthermore, the tile “system” is a system of tiles that work together to drain a particular area, usually involving a “main” or main-line tile. A “main” is a larger tile, typically 12 to 18 inches in diameter. It is the heart of the tile system. Lateral tile, generally 3 to 8 inches in diameter, feeds water directly to the “main” tile and the “main” tile deflects the water to alternative drainage spots like a ditch, creek or river (think of a root system in this case).
Now, why is field tile so detrimental to wetland restoration projects? Well, I am glad you asked! When restoring wetland ecosystems, typically, we want the water to stay on site and not shed off to a nearby ditch, creek, or river (at least not immediately). Field tiles drain our wetlands and diminish the quality of our aquatic ecosystems, therefore disrupting this artificial system is a must! Disrupting tile systems usually involves some sort of heavy machinery like an excavator, or a loader with an arm and a bucket, to dig deep and remove the field tile. By removing the field tile, water will not be so quick to liquidate an area, but rather stay on site, including surface flow water that drains from higher topographic elevations. Once the pools fill with run-off and precipitation, natural wetland ecosystems filter out all of the contaminants prior to overflowing and shedding off into the nearby ditch, creek or river. These wetland ecosystems also provide critical habitat for various amphibian, avian, mammalian and insect species.
Reforestation projects can also be hindered by artificial drainage. Trees need water to grow and thrive, just like anything else. When we begin conversations regarding floodplain habitat, most of the areas lie wet or contain hydric soils that allow for much longer inundation periods. Artificial tile can ultimately drain these floodplain habitats, discouraging the natural progression of critical floodplain habitat that alters species composition and fecundity.
In the end, drainage can be detrimental to restoration projects across the board, so restoring the natural hydrology of a site is one of our first considerations. Although, it is important to remember that not every scenario is the same and some artificial drainage can remain intact for the purpose of protection of nearby facilities, utilities or agreements with neighboring farmers and soil and water conservation districts.
