A blind inlet, similar to a French drain, is a structure that replaces a tile riser.
The blind inlet is placed in the lowest point of farmed depressions or potholes to reduce the amount of sediment, nutrients, and other contaminants that would otherwise be transported to receiving ditches or streams.
A blind inlet is located at the lowest elevation point of farmed depressions or potholes, where tile risers would normally be located.
Compared to a tile riser, a blind inlet acts as a water treatment system. Blind inlets reduce the export of nutrients, pesticides, and sediment compared to tile risers.
Blind inlets remove field obstructions (risers) and improve drainage in depressions where no tile riser exists.
- As a sediment control structure, the blind inlet has an estimated lifetime of 10 years.
- 100% No-till management is encouraged for this practice to fully succeed.
- There is no further maintenance required after installation is completed.
- Unlike tile risers, blind inlets do not impede farm machinery. Blind inlets can support heavy machinery.
- A blind inlet will not “fix” a poorly functioning outlet. Properly functioning downstream drainage is required.
- Studies in the pothole region of NE Indiana show that blind inlets reduce sediment loads in water moving through them when compared to a tile riser by 79% and total phosphorous by 78%.
- Accumulated sediment over the lifetime of 12 years did not appreciably decrease flow rates or cause maintenance issues. Monitoring over 12 years indicated reduced soluble reactive phosphorus and sediment loading. Soluble reactive phosphorus removal is partly a function of the choice of gravel media, for example, steel slag will significantly improve removal compared to traditional limestone gravel.
- Estimated cost of the blind inlet depends on the size of the inlet and raw materials availability
- NE Indiana contractors are estimating costs between $1500 and $3000 for complete installation.
- NRCS Blind Inlet for Water Quality Funding Codes: EQUIP, MRBI, GLRI Nearshore Health, National Water Quality Initiative, Edge of Field Water Quality Monitoring Initiative, RCPP-WLEB, WLEB.
Similar to a French drain, a blind inlet consists of coarse material (gravel) backfilled around perforated pipe, which are installed 2” above the bottom of the excavation. This coarse material acts as a storage zone for water infiltrating laterally through the soil and vertically through a 12” layer of sandy material (pit run).
Pit run filter media and soil sidewalls of the excavation are separated from the coarse gravel material by a geotextile to limit clogging of the storage media that envelope the perforated drain pipes.
Runoff water from the closed depression infiltrates through the filter material, slowing its journey to the tile and depositing sediment, nutrients, and pesticides in the filter material and on the soil surface surrounding the blind inlet.
- Once constructed, the blind inlet requires no routine maintenance.
- Care is required to avoid tearing the geotextile during deep tillage operations.
- If significant surface disturbance is required, protect the blind inlet from siltation.
Jessica D’Ambrosio, The Nature Conservancy (firstname.lastname@example.org)
Dr. Chad Penn, USDA-ARS, West Lafayette, IN (email@example.com)
Stan Livingston, USDA-ARS, West Lafayette, IN (firstname.lastname@example.org)
Douglas Smith, USDA-ARS, Temple, TX (email@example.com)
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- Consult your SWCD, NRCS or a drainage contractor, as proper sizing and construction are critical.
- Alternative media may be used as long as flow rates are not compromised
- Try to install during dry or frozen conditions to minimize soil compaction of the zone around inlet.
- A 100% no-till management system is recommended for this practice to fully succeed.
- This practice will not improve drainage efficiency; a working downstream drainage network is required.
- System is designed to withstand farm machinery