Variation within the plot
Within the same parcel, there can be quite a lot of variation in ditch level, soil type, stratification, and/or permeability. This should be taken into account when constructing drains, for example by placing the local drains higher or lower, closer together or further apart. Sometimes drainage is not necessary on certain parts of a plot. In another case drainage on a part is pointless.
Lot pattern
The plot pattern and the plot shape present within the plot usually indicates in which direction the drains will be located. It can also influence the choice of which parcels are drained first and in what order this takes place over several years. It is also an important part of the total plan for grassland improvement and parcel layout. The plot size and the construction of a possible plot path can also play a role. This is shown in figure 14. Figure 15 shows how the drain pipe can run on a plot that is enclosed on two sides.
Attenuations
When constructing a drainage system, some ditches can sometimes be filled. These damping influence the chosen drain direction. The drain pipe should preferably not cross damped ditches. Ditches that have been filled in, in the past should also be avoided as much as possible. Lastly, it is important to determine whether ditches will be filled in the future. This is important for several reasons. In the first place, the drain cannot end in such future damping. The water discharge from the ditch to which the drains that need to be constructed should not be disrupted by future damping. When crossing a cushioning cannot be avoided, the following points should be taken into account.
The ditch that needs to be filled must carefully be cleaned before the filling is carried out. This means free from dredge.
The material used to fill the ditch must, as far as possible, consist of material comparable to the immediate surroundings and the soil of the adjacent parcels. This will prevent a permanent height or low difference due to sagging. There is also less chance of flooding or additional drying out at the location of the damping.
Provisions must be made to support the drain where it intersects the damping. This can be done, for example, by applying a quantity of sand at the location of the intersection. So-called bridges can also be installed or a perforated smooth tube can be slid around the drain. When installing a bridge or smooth tube, a slot is of course required at the location of the damping.
The material that is being used for the damping should preferably be settled or pressed before the drainage is applied.
Ditch distance
The presence of a different ditch level, a parcel path, or a public road sometimes makes it impossible to fill ditches. And the question of whether a permit is granted by the competent authority for filling in a ditch or changing a plot pattern remains. In addition to the height of the ditch level, the existing ditch distance is an important factor for the drainage status of a plot. After all, even if the desired drain distance is calculated scientifically and reliably based on observations in the field, the ditch distance must be divisible by the calculated drain distance. If this calculation is incorrect, then a narrower or wider drain distance must be chosen.