SOIL PREPARATION

SUMMARY TYPES OF DRAINAGE SYSTEMS

• The causes of drainage problems are many, but typically are over- irrigation, leaking earthen dams and canals, blocked natural wa- terways and soil layers with a slow permeability. • Surface drainage refers to the removal of water that collects and ponds on the soil surface. This can be avoided by ridging, levelling of vineyard soils, and surface inlets to subsurface drains or shallow ditches. Surface water must be removed at a flow rate that will not cause erosion. • Subsurface drainage is normally not done when soils are shallower than 800 mm. The maximum depth of the drainage system will be determined by the height of the water level in the river or other waterways where the drainage water is discharged. • Cut-off drains are installed when water moves laterally on imper- meable subsoil down-slope. These drains can be installed outside the vineyard, perpendicular to the direction of water flow. Cut-off

drains must be installed at least 300 mm deep into the imperme- able layer. • Open ditches are a simple and cheap method of drainage but are an obstacle to traffic. Stone drains can be constructed by placing a layer of stone at the bottom of an open ditch and then filling the ditch in with soil. It works best in clayey soil which will not block the openings between stones as easily as sand and silt. Stone drains are less prone to blocking than pipe drains. • Various kinds of material are used for pipe drains. High density poly- ethylene piping that is corrugated, lightweight and flexible and suited for both manual and mechanical installation is popular for drainage today. Drain pipes must preferably be installed at depths of 1.5-2.0 m; the minimum recommended depth is one meter. Drainage filters or en- velopes of mineral, organic or syn- thetic origin must be placed around drain pipes to prevent clogging of drain pipes and improve water flow into the pipes.

96 | SOIL DRAINAGE