Management and organization

Mowing maintenance

Vegetation on the banks and in the water provides habitat for many species of plants and animals and increases biodiversity. It also provides structure and prevents erosion of the banks. Through management and maintenance, we ensure that this vegetation remains in good condition and that it does not interfere with water supply and drainage. We believe it is important that species are affected as little as possible by maintenance and are able to recover as well as possible. Together with our contractors, we are working on methods and techniques that contribute to this, such as cutting water plants above the bottom, allowing small aquatic animals to escape, or warning fish. How often we carry out maintenance is tailored to each watercourse and each bank. We record this in management plans. For example, we mow nature-friendly banks (NFBs) less often. In addition, we leave 10% of the vegetation along the banks and more where possible. We ask those responsible for maintenance to carry out ditch maintenance in this way too.

Dredging

The waterbed is important for water quality. Most of the waterbeds in our area that were polluted with chemicals in the past have now been cleaned up. We are also tackling the remaining polluted waterbeds. This means that these waterbeds are no longer a source of chemical pollution. However, over time, a layer of silt consisting of dead plant remains mixed with soil and sludge particles forms on the waterbed. To keep the ditch at the correct depth, we remove this silt on a regular basis. In some places, we dredge extra specifically to improve water quality. We call this quality dredging and do it for a number of reasons:

  • removing the waterbed as a source of nitrogen and phosphate in surface water;
  • prevention of oxygen deficiency in surface water due to the decomposition of plant debris in the waterbed;
  • ensuring good soil structure for the rooting of aquatic plants;
  • reducing the turbidity of surface water caused by suspended sludge particles.

To ensure that this high-quality dredging has a lasting positive effect, it is important that the source of the dredging is also addressed.

Interior design

The layout of the water and the banks has a major impact on water quality. Factors such as the substrate, water depth, and steepness of the embankment help determine which species can occur. Variation in these factors creates different habitats. For example, fish like to spawn in shallow water but need deep spots to overwinter.

Nature-friendly banksmake an important contribution because they increase biodiversity, both on land and in the water. These banks have a gentle slope (gradual transition from land to water) and offer a variety of wet and dry conditions. This makes them a pleasant habitat for all kinds of plants and animals.

By 2021, we will have constructed approximately 275 kilometre nature-friendly banks. Between 2022 and 2027, we plan to kilometre at least another 75 kilometre in collaboration with the province, municipalities, and land managers. We are also focusing on the management and maintenance, or in some cases refurbishment, of existing nature-friendly banks, including reed banks.

Level management

Water levels in our area are largely unnatural, with many places having a fixed water level or, conversely, a low water level in winter and a higher water level in summer. In winter, we drain off excess precipitation to prevent flooding, and in summer we replenish shortages and flush where necessary for irrigation and to prevent desiccation, salinization, or algae blooms. This is because much of the area lies below sea level.

In terms of water level management, water quality benefits from retaining local water, with high water levels in winter and low water levels in summer. Many areas are not equipped for this, so adjusting water level management not only causes economic damage but also has major consequences for the risk of flooding, water availability, and land subsidence. In the coming years, we will therefore only adjust the water level in (sub)areas where there is room for this in the water system. Where new opportunities arise in the future for adapting land use and layout, we will investigate whether it is possible to adjust the water level and improve water quality.