Dredge

What is the dredge?

When there is a lot of dredge in the ditch, not enough water can flow in and out. Every year we check the depth of the ditches in part of our area. Every seven years we check the same area again. People with maintenance obligations in the area in question receive a notice of the dredging inspection at home. They then have one year to check whether there is too much dredging in the ditch and, if necessary, to dredge the ditch. During the dredge inspection, a check is made to see if the ditches in the subarea are deep enough.

What is dregs?

Dredge is a layer of mud at the bottom of ditches. It is created by gradual sedimentation of plant debris (for example, blown-in tree leaves and dead aquatic plants) and clay and sand particles.

What is dredging?

Dredging is the removal of dredge on the bottom of a ditch. This involves removing all dredge down to the natural substrate (the solid hard bottom) of a ditch.

What is the solid ground?

The solid soil is the natural subsoil of the ditch.

How do I dredge (half of) a ditch?

It is important that a ditch be dredged in its entirety. If half of the ditch is dredged, the remaining slack dredge flows back into the dredged ditch half. In many cases, the ditch will still prove to be insufficiently deep. It is therefore important for proper implementation of dredging that the maintainers of a ditch cooperate and jointly dredge the ditch (or have it dredged).

This involves the removal of dredge; the natural subsoil (the solid ground) should never be affected. If the solid soil is too high and therefore the ditch cannot meet the minimum size, only the dredge present should be removed.

We recommend that when carrying out the dredging work, the dredge be removed from the middle of the ditch and stay slightly (about 5% of the ditch width on both sides) away from the shore. This is because of bank stability and natural values present. The removed dredge is best deposited at ground level, more than one meter away from the ditch, to avoid possible backflow of the dredge into the ditch. Culverts can be cleaned with water pressure.

Do I need to dredge a ditch?

There is generally very little dredging in a ditch, but a ditch can land. If you have been notified to dredge a ditch, we actually ask that you excavate and re-profile the ditch properly to prevent landslide.

When should I dredge?

Dredging must be done if a watercourse does not meet the minimum water depth as indicated below for sandy and clay soils. In addition, there must be sufficient dredging for removal, this is indicated in the table below as minimum removable dredging layer. In peatlands, the minimum water depth and therefore the need for dredging is customized. If dredging is required, this includes cleaning culverts in the ditch in question. Culverts can be cleaned with water pressure.

Removing dredge to at least 50 cm water depth where possible, ie:

• Ditches in sandy and clay soils should be dredged at least 20 cm deeper than the minimum water depth. In this way, there is room for accretion of dredge and the ditch will also generally meet the minimum required water depth in future years. The solid bottom should never be affected.
• Ditches in peat soil, never dredge deeper than 10 cm above the solid bottom. To prevent accelerated peat degradation, always leave a layer of dredge in peatland ditches.

How do I measure the dredge layer in the ditch?

You can measure the dredge layer using dipstick, ruler, back of a broom or rake. To determine how much dredge is in the ditch, first measure the depth of the water. This is from the surface of the water to the top of the dredge. You measure this as much as possible in the middle of the ditch. Then, to measure the dredge layer, you push the dipstick/measuring rod through to the solid bottom. The difference between the two measurements is the thickness of the dredge layer.

Am I measuring relative to the summer or winter level?

If there is a summer level and a winter level, the minimum water depth is measured from the summer level.

Road and dike ditches (exception).

Road and dike ditches are stipulated in the legger waters. If a ditch is designated in the legger as a road ditch or dike ditch, the owner of the road parcel or dike parcel must completely dredge the ditch.

Contaminated/polluted dredge

Litter may have ended up in the dredge. The dredge may also be contaminated with heavy metals such as copper, lead, zinc or pesticides. If you suspect that the dredge in the ditch is contaminated, you can have it investigated. If it turns out that the dredge is indeed contaminated, the costs of the sampling and the additional costs related to the removal of the contaminated dredge will be reimbursed by the Water Board.

During which period may I dredge?

The best time to dredge is outside the breeding season. The period for the breeding season is March 15 to July 15. Therefore, the work can be done year-round except between March 15 and July 15. Do legally protected species occur in the ditch? If so, contact an ecological expert to determine an appropriate period for the dredging work.

I have had advance notice.

Before a dredging inspection starts, HHNK sends out a preliminary notice to maintenance parties. In the announcements we indicate when the depth of the ditches will be checked. We also indicate where you can look up which ditches will be checked.

I have received an intention to issue an administrative order.

If the dredging inspection shows that a ditch for which you are liable for maintenance does not meet the minimum depth, you will receive an intention for administrative coercion. In the intention for administrative coercion we request you to dredge the ditch before a specified date. You will be given ample time to do so. After this date we check the ditch again. In the intention to enforce an administrative order it is indicated which ditch it concerns.

I have received an administrative enforcement order.

If, after the date indicated in the letter (intention to enforce an administrative order), the ditch for which you are under an obligation to maintain has not reached the correct depth, you will receive an administrative order. In the administrative coercion order we again request you to dredge the ditch before a specified date. After this date we check the ditch again.

What if the work has not been completed after the date specified in the administrative order?

Should it appear that the ditch is still not at depth after the date mentioned in the administrative order, we will contact the maintainer. Eventually we can perform the work (or have it performed) at the expense of the maintainer. These costs are considerably higher than if the maintainer himself brings the ditch to the correct depth or has it brought to the correct depth. This is because as the water authority we are obliged to have not only dredging but also a sediment survey carried out, whereas private individuals or farmers usually do not. Such a survey costs at least € 1,500. To this we charge an additional € 150 in administrative costs and can impose a fine of between € 100 and € 300.