Dry feet during construction of tidal culvert

Together with the strengthening of the Lauwersmeer dike, a number of nature projects are being carried out to improve the ecological water quality and nature of the Wadden Sea. One of these is the creation of tidal area Marnewaard, for which a tidal culvert is being constructed right through the Lauwersmeer dike. Henk van Tongeren Water & Techniek ensures dry feet in the construction pit.

Henk van Tongeren Water & Techniek was approached by Combinatie Waddenkwartier in November 2023 to translate the drainage advice into a concrete drainage solution for the construction of the tidal culvert. "The construction pit is about 100 meters long and 13 meters wide, and 6 meters deep," says Jorim Beishuizen, business manager at Henk van Tongeren Water & Techniek. "It's up to us to provide a nice, dry cofferdam so that Combinatie Waddenkwartier can build the tidal culvert 'in the dry'."

Deepwells

Henk van Tongeren Water & Techniek installed a drainage solution consisting of 52 deepwells. "That's pretty decent, considering the size of the tub," Jorim acknowledges. "However, half of them act as buffers, a safety device as risk management. The wells are 15 meters deep; the pumps are suspended about 13 meters below ground level. We have built in 26 submersible pumps, which pump up the groundwater (saltwater, ed.) and discharge it into the sea on the other side of the tub." The capacity for the entire tub is 50 m3 per hour. "The electric pumps are powered by two sets of generators running on HVO 20 fuel, and are equipped with an emergency power supply. The pumps are switched via a pump box that we can read remotely. Indeed, it is even possible to switch the pumps on and off remotely, or adjust the level."

Complex environment

Henk van Tongeren Water & Techniek's drainage solution has been running since last summer vacation and will be in operation for a total of one year, according to Jorim. "The installation of the wells took about five weeks and went entirely according to plan. It did require the necessary coordination with the many stakeholders, because it is quite a complex environment, which is periodically also used by Defense. Planning-wise, it was therefore a challenge to coordinate all the work. But even that succeeded in good consultation with Combinatie Waddenkwartier. Our people are used to this kind of challenges and are enthusiastic about projects where they can fully use their expertise. That is also our strength, thinking along with us from the early stages to find the best possible drainage solution. For us it is now a matter of monitoring the installation and carrying out occasional maintenance so that the combination can build the tidal culvert undisturbed and with dry feet."