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 should be located at a field’s lowest elevation point, where drainage patterns result in reduced trafficability or crop losses occur due to frequent saturated soils. A blind inlet can be installed any place where a tile riser is recommended, or where drainage in depressional areas is causing a problem.
Water that flows through a blind inlet filters first through soil and rock before
entering the tile system, compared to a tile riser where water goes through
the tile system without being filtered. Compared to tile risers, blind inlets
reduce plugging from debris and reduce the export of nutrients, pesticides,
Installations of blind inlets remove field obstructions (risers) that need to be
farmed around. Installations improve drainage in depressions where no tile
Blind inlets remove field obstructions (risers) and improve drainage in depressions where no tile riser exists.
• As a sediment-control structure, a blind inlet has an estimated lifetime of 10 years. One hundred percent no-till management is encouraged for this
practice to minimize soil disturbance and maximize its lifespan.
• Once constructed, a blind inlet requires no routine maintenance; however, care is required to avoid tearing the geotextile during deeptillage operations.
• If significant disturbance to the field surface is required, protect the blind inlet using silt fences or other soil-erosion protection.
• Try to install the inlet during dry or frozen conditions to minimize soil compaction of the zone around the inlet.
• Unlike tile risers, blind inlets do not impede farm machinery. Blind inlets can support heavy machinery traffic.
• A blind inlet will not “fix” a poorly functioning tile 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 and NW Ohio 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