Minipolder in the Haarlemmermeer

One of the core tasks of the Water Board is to ensure that we all keep our feet dry. This requires constant adjustments to the water system. For example, the Rijnland Water Board is currently constructing a so-called peak storage facility in the southwestern tip of the Haarlemmermeerpolder. If the storage basin of Rijnland (including the Ringvaart of the Haarlemmermeer) threatens to overflow, it can temporarily buffer more than a million cubic meters of water and thus prevent worse. The peak storage will be constructed by Combinatie Leeghwater, consisting of KWS (GWW) and Van Hattum en Blankevoort (civil works). 

Jörg Dreyer is Environmental Manager for the Leeghwater Combination and explains what this peak storage is for. "During a heavy rainfall, especially in the summer, there is a chance that the pumping stations will no longer be able to get rid of the water and that due to the high water levels, quays of, for example, the Ringvaart of the Haarlemmermeer will overflow and possibly even collapse. Then the polder will flood. This plays out especially in the area around the Kagerplassen, because here you are furthest away from the four Rhineland inlet pumping stations (Gouda, Halfweg, Spaarndam, Katwijk; ed.). As a result, it takes the most time before the storage basin level can be controlled here. As a solution, the peak storage facility was designed, an interim storage facility with a storage capacity of over a million cubic meters of water. It is expected that this facility will be needed on average once every fifteen years."

The peak storage area, in effect a polder within a polder, consists concretely of a 3.8-kilometer-long dike with maintenance paths covering an area of 67 hectares between Lisserdijk, the A44 and a new dike on the northeast side. An inlet structure has been built at the southern tip where excess water from the Ringvaart canal is discharged inward. Further included in the dike body are two culvert structures that are open under normal conditions, and an outlet structure and outlet channel where the water is drained again after a peak load. The civil works consist of the aforementioned structures, the outlet channel, a road bridge over the canal and five bridges for agricultural traffic. The earth, road and water works include the 3.8 km of dikes and 7 km of ditch construction.

Berry Borgstein, Van Hattum en Blankevoort's Chief Executioner and Technical Manager Realization, zooms in further on how the peak storage works. "Think of it as a basin of water of over a million cubic meters that we gradually fill up from the Ringvaart canal. To this end, we first close inlet 1, inlet 2 and the outlet construction. Then, at the inlet structure, the dry bulkheads are removed and the four inlet valves are gradually tilted so that the water flows from the Ringvaart canal at fifteen cubic meters per second into a voiding bowl. This is an elongated pond twenty meters wide, where the flowing water is regulated before it reaches the filling ditch. This fill ditch runs all the way around and fills with water in four hours. Time that the two farmers in the area have to leave the polder with their cows. When the fill ditch is full, the water eventually flows into the peak storage area." 

At the time, Combinatie Leeghwater won the contract by scoring maximum on the points of ground balance, sustainability and environmental management in addition to its ingenious design. Dreyer: "Our plan has a closed soil balance. That meant coming up with a logistical plan on the front end and making it feasible for all the clay, sand and soil in the area. In the end, the dike was made with the released soil from the waterways to the left and right of the dike, with clay as the water-sealing layer and a bit of topsoil as the top layer for the grasses. The soil flow plan avoided the supply and removal of materials, and with all kinds of intermediate depots, we were able to minimize soil movements."

Under the sustainability section, Combinatie Leeghwater scored in part by using electric equipment. Borgstein: "The five agricultural bridges in the middle of the peak storage and the culvert structures were built using battery packs as much as possible. These were used, for example, for the vibrators, construction lamps, construction saws and butterfly machines. Furthermore, we used wood-wrapped EPS blocks for the formwork of the concrete bridges poured on site. The wood went to a sheltered workshop after use, EPS went to a recycling company."

For environmental management, an arrangement was made by mutual agreement with the intended tenants of the grassland in the peak storage area. Furthermore, a sounding board group was established for local residents and stakeholders. During the construction of the peak storage, the wishes of the surrounding area were extensively taken into account by limiting nuisance and by keeping the mini-polder available for agriculture and cattle breeding almost continuously. Moreover, the structures, such as the inlet construction, hardly stand out in the landscape. Even the small concrete bridge embankments are finished with masonry to blend better into the landscape. Some of the piling was done with soil-formed piles, due to the proximity of a listed building.

In the winter of 2024/2025, this peak storage will be subjected to testing. Says Borgstein, "We'll be ready much earlier, but we can't test until the quays are overgrown, so that requires a grass season. Then let the water come."