The maintenance of the drainage system starts with a regular check-up of the drain and, if necessary, with cleaning and repairing the outlet. Whether major maintenance is necessary depends on the results of the check-up.

During a rainy period, the outlets can be checked whether there is actual outflow. Water can be collected from several drains and the volume can be measured. This can be converted to the number of millimetres per hectare. This requires the number of seconds which are needed to collect 1 litter of water. Then the following formula can be used:
86,400 / (length of drain X distance between the drains X seconds) = volume of drained water in millimetres per day. This should amount at least to 7 millimetres.

Field drain
A number of drill holes can be made to find the cause of a badly flowing drain. No water from these drill holes should flow over the surface of the land. A more precise measurement can be obtained by installing vertically several perforated drainage pipes, each with a length of 1,20 meter high. These pipes should be covered with a filter sock. The water level can be regularly read in these pipes. By placing them right next to the field drains and in between the field drains, the effect of the drainage will become visible. By placing one or more at differing distances to the outlet, these will also give an impression of the hydraulic fall as well as the presence of air locks or a negative fall. The water level can be checked approximately 24 hours after installing these pipes or after drilling the holes.

Outlets must be able to carry large volumes of water. By carrying out a brief check regularly and a proper inspection every spring and autumn, problems in the drainage system can be detected. The problems can be caused by vegetation or by cattle but also by the mechanical cleaning of the ditches. Outlets damaged by frost or floating ice should be repaired swiftly. When the drainage water is rich in iron, the outlets must be cleaned a couple of times a year. This takes little time. Iron can build up especially in the first few meters of the field drains. This is easily removed using a hose with a length of 2 or 3 meters.

Field drains
Sediment can gather, especially in the period just after the drains are laid. The soil around the pipes has at that time, not yet settled. This happens in particular on sandy soils with little lutum. The soil particles are easily washed away with the running water in and around the pipes and can cause sediment to gather in the field drains, in the perforations and also in the casing material. The higher the level of ground water when the drainage system is being installed, the greater the risk of blockage. Iron can be the cause of a lot of trouble for drainage. Iron can severely disrupt the transport of water both temporarily and permanently, when seepage water is involved.

If it is detected that the system is draining an insufficient volume of water related to the ground water level, then at random a number of field drains should be flushed. If there are no complaints about the de-watering of the plot after drainage and the system appears to be working well, there is no reason to flush the drains. Unnecessary flushing of the drains can loosen soil particles such that these will form a deposit inside the drain after the flushing, even to the extent that more sediment will gather than there was before the flushing. 

The timing of the flushing is important as the transport of the loosened soil particles is made easier when the field drains are transporting water. The volume of water used is in most cases only meant for loosening the dirt in the drain. The excess of ground water which is drained by the system is also used for removal of the dirt from the drain. Therefore, it is advised against flushing during the summer period when the ground water level is low. The best time is between November and March. During this period the drains transport a large volume of water because there is more precipitation than evaporation. When the flushing is done during the autumn, this will result in a better functioning system in the spring.

Vereniging Nederlandse Drainagebedrijven

Norgervaart 26
9336 TE  Huis ter Heide (Dr)