Natural solutions for water purification
Water purification is crucial to ensure the availability of clean water and combat environmental pollution. A major challenge is the improvement of our water quality. This is why the European Water Framework Directive 2000/60/EC (WFD) came into force in 2000. The European Union (EU) member states agreed to have clean and ecologically healthy ground and surface water by 2027. Although water quality is slowly improving, the report on most Flemish watercourses is poor or inadequate.
The Ringbeek success story
Clean water for tomorrow
The water quality of the Ringbeek, between Wingene and Oostkamp, which flows into the Hertsbergebeek, is an example of such a watercourse that scores insufficiently. Nitrogen and phosphorus concentrations are too high, especially in summer. Excessive levels of nitrogen and phosphorus often lead to algal blooms, which in turn cause the water to become turbid and low in oxygen. This causes other plants to wither, and various small aquatic creatures and fish to die. The exceedance of nitrogen and phosphorus levels in the Ringbeek is due, on the one hand, to agricultural activities in the area and, on the other, to domestic wastewater flowing into the stream via a rain shower after a dry period. This is partly the result of the fragmentation of our public space. Everything and everyone are trying to find a place in a very limited number of square kilometres. Fields, nature, and houses are scattered around, which leads to frequent standard violations. The challenges are complex, and the solutions are innovative.
Better water quality thanks to helophyte filters
This innovative solution partly lies in the installation of an iron sand and reed bed filter, also known as a helophyte filter. The water of the Ringbeek is naturally and sustainably purified before it flows into the Hertsbergebeek. Helophyte filters have already been successfully applied in the Netherlands, but in Flanders, they are still relatively unknown and perhaps unloved… Yet their operation is simple because nature does nearly all the work: the wetland plants create an ideal habitat for bacteria that live around the roots of these plants. These bacteria thrive on the waste materials in the dirty water, convert it into nutrients, and consume it, resulting in pure water.
Louis Deforche, Senior Project Leader Waterways: “For us, the forest, farmer, and local residents do not have to clash. Working together towards a sustainable future where clean water is central is our ultimate goal.”
The path to clear water. The Ringbeek as an example
For the Ringbeek, we specifically chose a horizontally flowing reed bed filter shaped like a folded, wide canal to remove nitrogen from the water and solve the nitrate and nitrite problem. The reeds are planted with sods from the area, which makes our work very local. In addition to reeds, we will experiment with other plant species in a deeper zone. We are specifically considering cattails because, in addition to purification, they can also be used as bio-based building material. After nitrogen purification, we direct the water to an iron sand filter to remove the phosphate. Thanks to intelligent, automatically adjustable inlet and outlet structures, the entire system can also be easily operated. This way, we direct the polluted water after a dry period — when the concentration of contaminants is highest — to both filters. The amount of water that will be directed to the filters and how long the polluted mass will remain there will be continuously measured and monitored. Based on this data, we will further refine the purification capacity, determine the optimal residence time, and study various substrates, with the ultimate aim of obtaining the cleanest possible water. The helophyte filter covers a total surface of approximately 4,400 m². The iron sand filter is about 400 m² in size.
Since we cannot place pumps or heavy installations in the agricultural area, the entire process is gravity-driven. To create a gradient, the water level is raised using fish ladders. The fish passages divide the total gradient into manageable sections, allowing perch, stone loach, and gobby to swim upstream and migrate freely at a crossing point. When designing the fish passages, we take into account landscape, technical, and hydraulic aspects.
Landscape and nature in balance
With the helophyte filter, we not only ensure that the water of the Ringbeek is purified in an environmentally friendly way but also that the landscape becomes more varied. We consciously choose to plant new shrubs and preserve existing old pollard willows because they are very important for bats, which use them as nesting and orientation points on their flight routes. The tree is also indispensable as a shelter or nesting place for many birds and insects. Moreover, the pollard willow, due to its historical and cultural value, is undeniably part of the Flemish landscape.
Lowie Bouvijn, Hydraulic Infrastructure Engineer: “Our practical experience in the design, permitting, and construction of helophyte filters is reinforced by our collaboration with UGent. By obtaining precise measurement results in the field, we can continuously refine our knowledge and methods.”
Collaboration and coordination: the key to success
Finally, we place strong emphasis on coordination to achieve a high-quality and broadly supported design for the entire area and the various stakeholders. Through participation, we bring together different partners, such as local residents, farmers, Natuurpunt, the Agentschap Natuur en Bos (Agency for Nature and Forests), Departement Landbouw en Zeevisserij (Agency for Agriculture and Fisheries), the province of West Flanders, and the Flanders Environment Agency (VMM), to discuss a constructive step-by-step plan. We believe that the forest, farmer and local residents do not need to clash. To the contrary, we align them with each other. Working together towards a sustainable future where clean water is central is our ultimate goal. The entire project consists of seven phases: preliminary study, participation process, topographical survey, preliminary design, preparation of estimate/list of measurements, preparation of environmental permit application and tender dossier
With this inspiring story of the Ringbeek, we show that innovative and natural solutions are the key to effective water purification. By using helophyte filters and intelligent infrastructure, we not only ensure clean water but also a richer and healthier landscape. The collaboration between different stakeholders, from farmers to nature conservationists, illustrates that sustainable water management is possible when we come together with a shared vision.
This study is part of the Interreg Flanders-Netherlands project Aquatuur. It was carried out with the expertise of our project partners Ghent University, Zeeland University, and the Flemish Environment Agency (VMM).
