Filter envelopes aid tile drainage in Sacramento—San Joaquin Delta tests

Enveloping perforated bituminized fiber and plastic subsurface tile drain in a safflower straw sandwich gave excellent performance in maintaining field drainage in Sacramento-San Joaquin Delta tests. A 1-inch glass fiber mat also gave good performance, but tile drains tested without a protecting filter envelope were not successful. The drain failure resulted from sealing by the muck soil, which reduced water movement into the tile—probably a major reason for disappointing experiences with tile in the Delta.