What is it:
A blind inlet, also known as a French drain, is a structure that is placed in the lowest point of farmed depressions or pot-holes to minimize the amount of sediment, and potentially other contaminants, that would be transported to receiving ditches or streams.
How does it help:
The most common practice that is used to drain farmed depressions is a tile riser, which is essentially a pipe that acts as a direct conduit for water from the field to the receiving ditch or stream. This can result in excessive loading of sediment and other contaminants to surface water from fields that are often several miles from the ditch or stream. This means that the runoff water quality from these fields that are relatively far from the stream can greatly impact the water quality, because there is no filtering or other type of processing that occurs during drainage of the excess water.
A blind inlet or French drain is used in place of the tile riser to filter at least sediment from the water that is drained from the field. The blind inlet should be able to remove at least 90% of the sediments from the drainage water. According to research done by scientists with USDA-ARS, phosphorus loads in samples channeled through blind inlets were 78% lower than those samples channeled through tile risers. Other sorption materials can be added in the blind inlet to remove additional contaminants.
This practice is applicable to any landscape where surface drainage patterns result in isolated depressional areas (aka pot-holes), and the climate is sufficiently humid to result in reduced trafficability or the loss of crops due to excessive amounts of water in the depressional area. The size of the blind inlet should be determined by the acreage of the depressional area and local precipitation patterns. An engineer should be consulted in designing a blind inlet, to ensure adequate ability to remove excess runoff water.
The cost of operating and maintaining this practice should be minimal. Producers can till directly over the blind inlet to ensure sedimentation does not inhibit infiltration. No-till producers may use gypsum at 1 to 2 ton/ac to improve infiltration after sedimentation.