| Sub-drains |
| The primary purpose of a sub-drain is to intercept subsurface water. A sub-drain consists of a perforated pipe backfilled with gravel and wrapped in filter fabric. Sub-drain are commonly used to prevent water from entering a basement or crawl space. They are also used to control groundwater in slopes to maintain slope stability. Sub-drains can also be used to minimize soil expansion near foundations. |
| Surface Drains |
| The purpose of a surface drain is to collect surface water. Surface drains can be anything from a 2-imch diameter patio drain to a 3-foot square drop inlet in a parking lot. Though surface drains collect water, they have a very different function than a sub-drain. |
