SOIL PREPARATION

linked to the presence of iron compounds. Such compounds may cause blockages of drainpipe inlets and even of the filter material around pipes. In these cases, an agricultural or drainage specialist should be consulted. When outlets are submerged, sediments in the ditch below the outflow must be removed to allow the free flow of water from the outlet pipe. There are certain practices that can be harmful to subsurface drainage systems and those should be avoided. Heavy machinery must not drive along the trench in the first year after installation. At that early stage the soil has not fully settled and may be unable to support heavy loads of vehicular traffic without causing damage to the drain pipes. Other practices to be avoided are the planting of trees close to drain lines since their roots will cause blockages. One should also prevent the direct inflow of surface water into a subsurface drainage system. When such a problem occurs, installation of a sand trap or gravel filled trenches above the drain line can filter out sediments and allow only water to enter the drain.

102 | SOIL DRAINAGE PHOTO: ARC INFRUITEC-NIETVOORBIJ.