Dune Reserves

PWN, a leading drinking water company in the Netherlands, currently delivers 105 million m3 of water annually to industries and consumers in the province North-Holland. In 1934 the provincial government delegated management of the coastal dune reserve to PWN. Drinking water production and nature conservation in this area have since then been closely interconnected. PWN is innovative, both in advanced purification techniques as well as in management of the nature reserve. The company recharges the dune area with pre-treated surface water taken in from Lake IJssel. The water is then recovered together with some natural dune water and then treated to drinking water standard for distribution to consumers.

Nature reserve and water production

The dune reserve along the North Sea coast is 53 km2. The area is vital for sea defence, water supply, nature conservation and recreation. When regional water supply started only the natural dune water was pumped and treated to drinking water, resulting in lowering of the ground water table and loss of valuable dune vegetation in parts of the area where flora and fauna are very rich.

PWN has been recharging the dune system since 1957. This restores the natural fresh water balance of the area. Currently the use of ground water (made up of natural groundwater and recharged water) totals 45 million m3 per year. Recharge is carried out with the two near-shore open systems Castricum and Kieftenvlak, which consist of parallel recharge basins. Inbetween the basins water is retrieved using parallel series of shallow wells. Besides that, a system with deep well recharge is in operation in the area Watervlak, near Castricum. The original well systems for the abstraction of natural dune water are also still fully functional throughout the dune area. They can be used when water intake is interrupted in case of an accidental pollution spill in Lake IJssel.

Actual operations

PWN has sought to restore the balance between recharge and pumping for decades already. Calculations with the ground water model indicate that unmodified operations in accordance with the old permits leads to a loss of dune slack. PWN appointed Royal HaskoningDHV to lead the study into the optimization of the recharge systems to ensure no harm to the sensitive flora and fauna in the dune slack and to get these new operations permitted.

optimisation of artificial recharge systems in an coastal dune reserve

Nature driven operations

The extent to which extra pumping of each individual well system affects ground water related vegetation was calculated. This exercise led to a new sequence of pumping: first the well systems that do no harm, then the ones that cause minor damage and finally, in the event of high water demand, the systems that affect the dune slack are also pumped.

The innovative nature driven sequence opens the possibility of expansion (compared to current operations) of the production capacity without construction of new wells, mains or recharge basins. Even with an extra production of 6 million m3 per year the valuable dune slack, where nature is groundwater dependent, increases substantially.

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