In the past, the Grote Nete was surrounded by a levee in the entire valley. This is now causing local flooding. The removal of the levee and some outlet structures in certain places means that the tributaries are reconnected with the Grote Nete. This will prevent flooding and allow fish to move freely again.
In some rivers, we build barriers to raise groundwater levels. This allows wet river nature to flourish even in dry periods. These barriers do not increase the flood risk. They only affect the river when the water is low. When the water is high, the river is above the barriers anyway.
Carrs occur in very wet places, which usually flood in winter and may only dry out superficially in summer. They are almost impassable and show a lot of variation. Tree trunks, stumps, large grass and sedge pollen and deadwood form small islands here, which act as somewhat drier havens for animals and plants.
Depoldering means giving land back to the river. First, we construct a new levee inland. Then we make openings in the old levee, creating additional room between the old and the new levee where the river can (over)flow. This reduces the power of the water and the water level of the river while limiting the risk of flooding in the region. The tides are given free rein again, which results in the resurgence of valuable tidal nature.
When we dredge, we deepen a fairway by removing excess sediment from the bottom of the river.
Flood areas can naturally absorb water, so water managers often use them for this purpose.
A flood control area is an area of flat land alongside a river that buffers water under extreme weather conditions. The water flows across an overflow levee and onto the area. A ring levee always protects the hinterland to prevent any residential areas from being flooded as well.
A flood control area with reduced tides has the same structure as an ordinary flood control area but its overflow levee also has a smart sluice system. At high tide, a high inlet sluice allows a limited amount of water in, just enough to trigger the development of tidal mudflats and marshes. At low tide, the water slowly flows back through a low outlet sluice and towards the river Scheldt. The area therefore ensures water safety while fostering the development of a tidal natural environment.
We are raising the current average groundwater level to turn Polder of Lier into wetlands. This means the water level is slightly higher, especially in summer. There is plenty of room for this, as the surrounding residential areas are almost 3 metres higher than the flood area. The flexible sluice system allows us to adjust the water level in the flood area. This also guarantees that the local residents will stay safe and dry at all times.
A GRUP is a regional spatial implementation plan (gewestelijk ruimtelijk uitvoeringsplan). The authorities in Flanders use spatial implementation plans to define what is and isn't permitted on all plots in a given area. This type of plan can be prepared by a municipality, a province or – in the case of a GRUP – the Flemish region.
Tidal marshes are infiltrated with gullies and creeks that fill with water flows at high tide and drain again at low tide.
At high tide, a high inlet sluice lets a limited quantity of water onto the flood control area with reduced tides. At low tide, the water slowly flows back to the Scheldt through an outlet sluice.
A MER is a Flemish environmental impact report (milieueffectenrapport). It gives a detailed overview of the potential environmental consequences of certain activities or interventions in an area. An environmental impact report is prepared before the implementation of a project or plan in the Flemish region. It ensures that adverse environmental effects can be caught at an early stage
Nesting islands are breeding grounds for birds. They can arise naturally or be created. If they are in a tidal area, they include a nutrient-rich layer of silt. This is an impassable obstacle for predators.
An overflow levee allows water to flow onto a flood area when the water level is extremely high.
A polder is a relatively low-lying piece of land that people have drained permanently. The polder water level is artificially controlled.
As early as 1883, engineers noticed that parts of the quay wall in Antwerp were subsiding towards the Scheldt. We are now stabilising the quay wall once and for all with sustainable and innovative techniques.
We are reconnecting around 30 meanders to the Demer. Meanders are natural curves of a river. They make the river more dynamic and natural and attract more life to the water. During heavy rainfall, they can also act as an extra water buffer. Because the meanders are less deep than the Demer, they also help to push the water up. This stops the area from getting too dry in summer.
A ring levee is built on the outer edge of a flood area to protect the hinterland. Such a levee is strong enough to hold back water during a flood, even during storm tides. There is usually a towpath on top of the ring levee. The towpath allows cyclists and walkers to enjoy the tidal natural environment.
The authorities in Flanders use spatial implementation plans (ruimtelijke uitvoeringsplannen) to define what is and isn't permitted on all plots in a given area. This type of plan can be prepared by a municipality, a province or the Flemish region.
An artificial sand martin wall consists of concrete elements placed next to each other. Each element has a number of holes that sand martins can use as nesting sites.
Ebb and flow occur twice a day. Twice a month, the high tide is higher, and the low tide is lower. A lunar month is the time it takes the moon to pass through all its phases. When the gravitational forces of the sun and moon work together, a spring tide occurs. That is when the water reaches its highest level. If this coincides with a powerful westerly to northwesterly storm, the water can rise by another 3 metres. The combination of a spring tide with such a heavy storm is called a storm tide.
TAW is the benchmark used for height measurements in Belgium. A TAW height of 0 metres is equivalent to the average sea level at low tide in Ostend.
Tweede Algemene Waterpassing (TAW) translates as second general water benchmark. It is the benchmark for height measurements in Belgium. A TAW height of 0 metres is equivalent to the average sea level at low tide in Ostend.
Tidal marshes are higher parts of the riverbank that only flood at strong high tides. Saline tidal marshes are mainly home to herbs and grasses that can withstand quite a lot of salt, such as sea lavender and glassworts. Brackish tidal marshes welcome a mixture of salt and fresh water and attract reeds and sea asters. Freshwater marshes form further upstream. They form a changeable landscape with shrubbery, reed beds and tidal willow forests.
Tidal nature arises in tidal areas. These areas are largely dry at low tide and get flooded again at high tide. There is constant movement of sand and silt with the tides. This creates a magnificent tidal natural environment that includes tidal mudflats and marshes.
Tidal willow forests are forests of high-growing willows in the natural flood zones of large rivers.
In the past, horses or human pullers used towpaths to tow boats. Now they are primarily used to provide maintenance services to the canals, banks, bridges and so on. They are often also public paths for walkers, cyclists, roller skaters and even anglers. Businesses and residents can obtain permits to access the towpath with motorised vehicles. Speed pedelecs are also allowed to ride on some stretches of towpath, provided that they stick to the 30km/h speed limit.
A water barrier is an object or structure that is used to hold back water. Some water barriers are fixed. They can't be moved. Examples of this are levees, slopes, buildings or even street furniture. Other water barriers are mobile. They can be moved and are only activated when there is a risk of flooding.
A water barrier wall is an artificial elevation in the landscape in the shape of a wall created to protect the area behind it from flooding
In the context of the Sigma Plan, wetlands are marshy areas that are unaffected by the tides. The groundwater there is high in winter and drops in summer. The landscape can range from open water and reed beds to alluvial forests and wet grasslands.
The winter riverbed is the area a river takes up in winter. There is more precipitation in winter than in summer, which causes the river to expand outside its narrower summer riverbed. The water will remain in the winter riverbed until it flows back to the river naturally, soaks into the ground or evaporates. If we restore the winter riverbed in certain places, we give the river more room to flood safely. The natural relief or local levees protect the hinterland.