Hölscher Group – Project Elzmündung, Kappel Grafenhausen (Southwestern Germany)
The Hölscher Group is a medium-sized globally operating company with numerous international subsidiaries. They offer a comprehensive range of services in the fields of dewatering, well drilling, water treatment and groundwater management. These include construction measures in infrastructure or industrial construction, energy and environmental technology or services such as operation, maintenance, and repairs. The Hölscher Group has companies based in Canada, United Kingdom, Denmark, Poland, Romania, The Netherlands, Qatar and Germany.
This project complexity resulting from numerous changes to engineering design and still remaining within programme deadlines and because of large dimension of vertical filter well design uncommon in normal well construction, but required to extract adequate quantities of water in order to achieve specified dewatering levels within polder area. Engineering design is definitely a template for best practice in future for similar projects.
General Situation
This year there have been flooding disasters in several areas of Germany due to heavy rainfall and the resulting overflowing of rivers. Many lost all their belongings and unfortunately some people even lost their lives. This highlights the importance of proactive flood protection.
Extensive renaturation work is currently being carried out along the upper Rhine as part of the “Integrated Rhine Programme” (IRP) to create 13 flood protection polders acting as near-natural floodplains. If the polders become waterlogged in the event of high-water levels in the Rhine, the groundwater levels in many villages surrounding the polders rise to such an extent that damage to buildings and infrastructure becomes inevitable.
To counteract this, extraction wells have been created, that automatically start up when a critical groundwater level has been reached in order to regulate groundwater levels. As a result of this, future flooding disasters can be prevented.
Project Specification
The IRP was agreed between France and Germany in 1982 with construction starting in 2008 and completion planned by 2020. The polder areas are 469 hectares in size and the maximum retention volume is about 5,300,000 m³. The total investment by the authorities for the Elzmündung flood retention area is about 77,000,000.00 €. Hölscher Wasserbau GmbH started with construction of the extraction wells in October 2017 with an overall commissioned project volume amounting to 6,549,950.00 €.
Challenges
There were a number of technical challenges with this project, which needed to be overcome by Hölscher Wasserbau GmbH. On a technical side, numerous details of or changes to the engineering design required in-depth discussion with clients, suppliers and subcontractors. The engineering design of some of the concrete structures enhousing the extraction wells were altered numerous times and as a result intense coordination between all parties involved was required.
Technical implementation
Hölscher Wasserbau GmbH acted as general contractor for the project, and all services associated with construction of the extraction wells were coordinated by ourselves. At the onset of the project, eight exploratory boreholes were constructed and a total of 13,000 m² of temporary groundwork areas and construction roads were built and decommissioned again at the end of the project. Afterwards in total 89 wells DN 300 were drilled for dewatering purposes along the pipe routes and structures. Our Instrumentation and control engineering department installed and operated a state-of-the-art groundwater measuring network during the entire lifespan of the project.
In total, about 850 m of underground pipeline with diameters ranging from DN 100 to DN 900 were constructed. In addition, two watertight building pits with driven sheet pile walls were built and numerous prefabricated concrete elements were set. Among these were well head chambers weighing approximately 30 tonnes each, drainage shafts, pipe supports as well as a concrete outlet structure into the Rhine. A pre-set neutralisation plant ensured for the harmless and pH-neutral discharge of the water.
Furthermore, 1,900 m of cable and 3,200 m of cable pipe were laid beneath ground, in part also beneath the river “Elz”. Hölscher Wasserbau GmbH was also responsible for all hydraulic engineering measures in the surroundings of the outlet structure into the receiving water.
At a later date, eight more vertical filter wells DN 1200 were constructed, with a drilling diameter of 2,000 mm to a depth of 26 m. The filter sections were made from stainless steel wire wrapped screens in different gap widths and depth-differentiated gravel pack depending on the grain distribution of the natural
sediment.
The development of the wells was conducted by our in-house high-performance desanding method and well performance was evaluated by means of geophysical logging and pumping tests. After completion of the project, Hölscher Wasserbau GmbH ensured for flawless restoration of the original ground conditions. Agricultural pathways were partially resurfaced with asphalt for this purpose.
Conclusion
The specifications and quality criteria of the client were met to the fullest extent and Hölscher Wasserbau GmbH was able to make an important and sustainable contribution to flood protection in the upper Rhine region. As a result, people can be protected from future flooding events and the natural environment remains preserved in future.
Water has been their passion for more than 60 years. They are the market leading specialists in Site Dewatering, Well Drilling, Water Treatment and Groundwater Management.
Innovative solutions, sustainable technologies and their dedicated employees, make every project happen – all over the world. They prove this, on a daily basis, on more than 1,000 projects a year.
