LIFE NARMENA - Winterbeek
Background and description of the area
The Winterbeek, a tributary of the Demer, meanders over a course of 32km from Beringen to Scherpenheuvel-Zichem. Throughout its trajectory, the Winterbeek bears different names: Kleine Beek, Winterbeek, Zwart Water and finally La Hulpe, before flowing into the Demer. In NARMENA we will mainly focus on the area of the Kloosterbeemden and Demerbroeken.
Due to the alternation of dry and wet conditions and the transition from nutrient-poor to nutrient-rich environments, the Winterbeek valley is home to a wide variety of biotopes, each with their typical fauna and flora. The valley is therefore of exceptional importance for nature conservation and biodiversity in Flanders. Large parts of the valley have been designated as a nature reserve and are protected at the European level, as a Habitats Directive. It is therefore not surprising that this authentic streamscape attracts many hikers and nature enthusiasts. Areas dedicated to agriculture and residences are limited in the valley. Local farmers have largely adapted their farming activities to the wet properties of the area.
In addition to the important nature function of the area, the valley also acts as a flooding area. The storage capacity of the natural floodplains in this valley has a regulating effect on high discharges. The conservation of these zones is essential to prevent the risk of flooding increases further downstream.
The structural quality of the Winterbeek is very valuable. There are few 'human' interventions. For example, the stream has practically no artificial bank protection and a still natural course with many meanders.
Research from the past years has shown that the Winterbeek is strongly polluted over a 17 km section, mainly by heavy metals and chlorides. The contamination is largely the result of earlier waste water discharges from industries and households. These substances are carried along by the current and have accumulated in the sediments of the river. In addition, the floodplains area and the banks of this watercourse are also contaminated by flooding and by placing clearance sludge on the banks.
Today, the discharges of the pollutants have stopped. However, the historical contamination in the sediment threatens, if it is not already present in, the flood areas.
LIFE NARMENA focuses specifically on techniques to remediate the heavy metals, particularly cadmium and arsenic.
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Remediation and planning
Since this subarea is of natural value, impactful remediation techniques, such as excavating soil and sediment are to be avoided. A nature-based remediation is planned here within the framework of LIFE NARMENA. It is important that the upstream sections of the river are first tackled before measures can be taken in the latter subarea. In this sense, the planning of the pilot project depends on the timing of the remediation works in the upstream areas. To prevent extra influx of contamination, sludge traps are constructed at the start of the remediation works of the first subareas.
Free surface water flow constructed wetland
In the sphere of influence of the Winterbeek, near the Kloosterbeemden and Demerbroeken, an artificial wetland is planned that will provide a damping of the stream. Works are planned to raise the groundwater to the level of the Grote Leigracht, almost permanently inundating the area. This will lead to reduction processes in the subsoil, as a result of which sulphides will be formed that bind to cadmium and other heavy metals. This greatly reduces mobility and bioavailability, leading to immobilization of the contamination and reduced uptake by organisms. A possible side effect of this technique is the unwanted mobilization of some other chemical elements, such as phosphorus, in anaerobic conditions. This will be closely monitored in the early years of the construction of the wetland.
This type of wetland is a natural local phenomenon in the region, from which many typical habitats will develop. It will therefore promote nature conservation and biodiversity in this area.
Conventional remediation works in sub-area three are currently ongoing. The descriptive soil survey (BBO) has been completed and the baseline monitoring is in the pipeline as input for the soil remediation project (BSP). We are currently still defining the specific contour of the area to be inundated and we determine, based on hydrodynamic modelling, the influence on the entire water system. Since groundwater is currently much lower than surface level, some interventions will be required to retain the water. The implementation of the works is planned for early 2021.
- An area of 34.4 hectares with improved flood resistance (being the total of the three pilot areas).
- A volume of 26,700,000 m³ improved water quality (being the total of the three pilot areas).
- An increase of 165,000 m³ of water storage capacity (being the total of the three pilot areas).
- A possible decrease of cadmium, arsenic and radium concentrations in the surface water (This cannot be quantified at the current stage of the project).
- Reduction in CO2 emissions.
- Increased protection and improvement of biodiversity.