STORM SURGE BARRIER IN NIEUWPOORT
Utility and need
In order to protect the coast and the hinterland from severe storm surges, the Flemish Government approved the Masterplan for Coastal Safety in 2011. Storm surges are one of the most important natural threats in the North Sea region. Today, the coastal ports are most threatened with a risk of flooding in the event of severe storms. Nieuwpoort and its hinterland are also unprepared for the high water levels associated with heavy storms.
To protect Nieuwpoort and its surroundings, the Masterplan highlights the need for the construction of a storm surge barrier at the mouth of the Yser as a priority. After thorough studies and an architectural design, a horizontal sector gate with a passage of 38 metres was chosen.
Protection from the storm surge barrier is already necessary in the event of storm surges that have a chance of occurring once every 10 years. However, the storm surge barrier will also provide protection against a 1000-year storm. This takes account of the rise in the sea level up to 2100.
The movable steel barrier is a construction that rotates around a horizontal axis. The barrier is sited in a parked position in a concrete threshold at the bottom of the Yser. The steel barrier rotates between two cast steel shafts that are anchored in a concrete abutment. These two abutments are connected to the banks of the Yser.
If a storm surge is predicted or in the event of a test closure, the barrier is rotated 90 degrees to the retaining position. For maintenance purposes, the barrier can be rotated to the maintenance position of 180 degrees. In the three positions (parked, turning and maintenance), the storm surge barrier can be locked and unlocked with the help of a remote control.
On both sides, the storm surge barrier is equipped with a movement mechanism so that it can be rotated in one continuous movement from its parked position to a rotation position or maintenance position. The capacity of this mechanism is sufficiently large that, even if only one of the two mechanisms is operating, the barrier will still rotate to the retaining position at any possible level of water.
The closing level is set at +6m TAW. This means that if the water level rises above this level, the flood defences will be closed.
One test closure will take place on an annual basis. The barrier will then be rotated to the turning position during a full tide. A test closure will be done every two weeks. These test closures will be shorter in duration.
The operation will be carried out from the control building and this will be built on the head of the barrier on the right bank.
The closure of the storm surge barrier also takes into account adverse effects on the water management of the hinterland. The barrier is closed at low waters. In addition, the barrier will be opened in the interim between two storm peaks.
During the studies, the Coastal Division also devoted a great deal of attention to the impact that the construction of a storm surge barrier would have on pleasure cruising. After its construction, there will be a passage width of 38 metres. A flow rate of more than 3 knots (with a maximum of 3.7 knots) occurs during 0.7% of the recreational shipping season (or 2.1% after expansion of the marina).
In response to the concerns expressed during the study phase, Minister Weyts decided to invest 8 million euro in a package of additional measures that meet the local concerns.
More precisely, in the abutments of the existing design, additional side tubes (so-called bypass sewers) will be built. This will allow the flow rate at spring tide to be no longer above 3 knots. This approach also has a positive effect on the sailing traffic capacity. The additional measures will be carried out at the latest within the current works, so that extra nuisance for the environment and impact on the protection program of Nieuwpoort remains limited.