Hoogheemraadschap van Delfland
Institution profile Delfland region Water quality and waste water management Delfland in numbers Contact person at Delfland
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Institution profile
Delfland is one of the Netherlands’ twenty-six water boards. The area in which Delfland operates is bordered by the North Sea, the Nieuwe Waterweg and the Berkel en Rodenrijs line, Zoetermeer and Wassenaar. In an area of 41,000 hectares/410 km², some 1.4 million people live and work, and approximately 40,000 businesses are established in the region.
Delfland has three key tasks:
- maintenance of flood defences
- water level control
- water quality control.
Proper execution of the key tasks, including cooperation and consideration for nature, are the directives of Delfland's policy. The water board does not limit itself to the struggle against water.
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Polder-boezem system of the Delfland region
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Figure 1: Delfland map |
The Delfland region, as well as a large portion of the Netherlands, is located far below the Amsterdam Ordnance Datum Level (NAP). NAP is 'Normaal Amsterdams Peil', the Dutch reference for height and depth measurements. Normal Null is used similarly in Germany and is equal to NAP. The lowest point in the Delfland region is approximately 6.5 meters below NAP. Should a dune or dike collapse, the land behind it would flood. The consequences of a failure in the flood defences in the Delfland region would be felt as far way as the Utrechtse Heuvelrug. The result would be inundation by seawater of about 50% of the Netherlands. To limit the danger, Delfland maintains the sea and river flood defence structures and quays. This primary maintenance of dikes and dams in Delfland is to a level that ensures that these flood defences should be able to withstand a wind-force and water level which, on average, does not occur more than once every 10,000 years.
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Figure 2: Polder-boezem system |
The areas behind the dunes and dikes mainly consist of low-lying water storage areas (polders) and slightly higher located drainage canals (boezems). Rainfall in the area would naturally flow into the lower polders. A number of (polder) pumping stations transport the water into the water system of the boezem. Delfland maintains a water level in the boezem at 42 centimeters below NAP. When a rise in the water level of the boezem occurs or is anticipated, superfluous water is pumped through the intermediate storage area and drainage canal system, using Delfland’s six large (boezem) pumping stations. The water is then pumped into either the North Sea or the Nieuwe Waterweg.
Water management involves the regulation of water levels in streams, lakes, ditches and canals. This is vital for constructions, agriculture, shipping, nature and recreation. The height at which the water level of an area is set depends on the functional use of a given area. Should the weather forecaster predict heavy rainfall, Delfland will then lower the water levels as a preventive measure. This diminishes the risk of flooding the streams, and canals and any possible inconvenience caused to inhabitants and businesses. Another option is to store water in the designated (intermediate) storage areas.
During dry summers, the Delfland region may experience a water shortage. Originally, the pumping station in Leidschendam transported fresh water from the Rijnland region, just north of Delfland, into the region. These days, most of the water is transported into the region through a four kilometres long pipeline at a speed of 4,000 litres of water per second. This pipeline was built in 1988 to deliver fresh water from a lake north of Brielle (Brielse Meer) to Hoek van Holland. If low water-levels occur in dry periods the pumping stations distribute the water.
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Water quality and waste water management
Another one of Delfland’s key tasks is ensuring that the surface water in the Delfland management region is of a high quality. This entails the treatment of waste water and limiting discharges onto surface water as much as possible. After all, clean and fresh water is important to humans as well as all plant and animal life. Delfland therefore works on creating conditions that lead to an optimal habitat for all. This can be realised by constructing nature-friendly banks, or through ecological maintenance of waters and quays.
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Figure 3: Delfland coast |
Delfland treats the waste water from homes and businesses in the region. The water board has four large waste water treatment plants in The Hague, Den Hoorn, Hoek van Holland en Vlaardingen. Waste water from homes and businesses in the region is transported from the municipal sewage system by pumping stations into the pressurised pipelines towards the waste water treatment plants. The treatment plants then treat the waste water. Yearly about 125 million cubic meters of waste water is processed and then emitted into the North Sea or onto the Nieuwe Waterweg.
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Delfland in numbers
• 4,500 km ditches and canals
• 420 km boezem quays
• 240 km polder quays
• 150 polder pumping stations
• 6 boezem pumping stations
• 32 sewage pumping stations
• 160 km pressurised sewage pipeline
• 4 waste water treatment plants
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Contact person at Delfland
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Erwin Meijboom
Mr. Erwin Meijboom has been employed with Delfland for the last three years and is responsible for the emission management of the Delfland Water Board.
He has been involved in drawing up the policy for ecological water management. Erwin Meijboom has been engaged in multi-disciplinary working groups to create and carry out project proposals in the field of water management, innovation and climate adaptation. His background is in the environmental sciences, water quality management and public administration.