Observation on Tile Drainage Performance

In arid and semi-arid climates, tile must maintain the plant rootzone as a low-salt environment. Through evapotranspiration, the rootzone serves to concentrate salts in the soil water, and the tile system provides egress for the saline water below that rootzone. Envelopes are material placed around tile to improve water movement from the soil into the tile. Filters are envelopes having the additional function of excluding loose soil particles that might enter and clog the tile. The need for filters is demonstrated only in alluvial soils. Periodic flushing out of tile appears to be an alternative to using filters. Materials clogging tile lines have been in the D₅₀ size range of 0.06 mm to 0.12 mm. Satisfactory filter design criteria are based on the standard deviation of normally distributed particle sizes in a large sample, and the well established filter to aquifer ratio. For the size materials that have been found to clog tile lines, filters with D₅₀ = 1.0 mm and σ ≥ 1.0 mm are desirable. A technique to protect tile lines during subbing-in and to lessen envelope requirements is discussed.