In the vacation resort of Carolinensiel-Harlesiel, a dyke is being raised and reinforced to protect against tides in the harbour area. The construction project is divided into two construction phases, the first of which was successfully completed in 2024.
Where water and land meets
In Lower Saxony, a considerable part of the state is protected from flooding from the North Sea by a 610-kilometre-long dyke system. Here, too, the consequences of climate change are becoming increasingly noticeable - sea levels are rising, storm surges are increasing and coastal protection is facing major challenges. Regular monitoring of design water levels and wave run-ups is therefore necessary.
Deich- und Sielacht Harlingerland is responsible for maintaining and renewing the approximately 28 kilometre-long section of the dyke between Dornumergrode and Harlesiel. Past calculations have shown that the dyke in Harlesiel is around 1.50 metres too low and needs to be extended in order to meet current safety requirements. In addition, numerous roads need to be adapted to the adjusted dyke height.
These reassessments are based on various parameters: the local conditions of the mean high tide, the highest water level measured to date and the swell conditions. In addition, a safety margin is added to take account of future sea level rise. The settlement and subsidence of the dyke body are also calculated.
History of the dyke remodelling
The conversion work in Harlesiel began back in 2016 with preparatory demolition work, including for catering establishments. This was followed by earthworks and roadworks as well as the laying of new drinking water pipes.
The first construction phase was realised from April to October 2024. During this period, the dyke body was raised from +7.50 to +9.00 m NHN (metres above mean sea level). The second construction phase follows the same principle: between April and October 2025, the 4.3-kilometre-long dyke is to be raised from +6.30 to +8.20 metres above sea level.
Building materials from the region - sustainable and efficient
Proven materials are used for the construction of the sea dyke: sandy soil for the dyke core and clay for the covering. Loam, a cohesive soil consisting of loam, silt, sand and organic components, is characterised by its high density and low water permeability and is therefore ideal for dyke construction.
The required clover soil is extracted directly on site as part of a salt marsh renaturalisation project in the Harlesiel dyke foreland. This significantly reduces the number of earth transports required and emphasises the sustainable nature of the overall project.
Special solution: crown wall with efficient reinforcement management
Normally, sea dykes are constructed with a three metre wide crown and gently sloping embankments - 1:6 on the outside and 1:3 on the inside - with a grass cover to control wave overflows. The dense development and numerous road crossings in Harlesiel make a standard construction method for the dyke impossible and require a technically customised special solution. By building a crown wall with a stone revetment, the required protection height can be reliably achieved even with a restricted embankment width.
The around 380 STUDIX® Headed Connectors from Peikko, which are integrated into the structure, play a central role in the efficient reinforcement routing. The ETA-approved connection system not only guarantees an economical and safe design, but also maintains structural flexibility - especially with regard to possible future extensions or adjustments. The solution is ideal for reinforced concrete consoles and has also proven itself in highly stressed, dynamic applications such as dyke construction - a significant contribution to long-term coastal protection in the Harlesiel region.
