Monitoring and Regulating Tidal Influenced Groundwater Heads During Reconstruction Works of a Hydraulic Barrier Structure at the Eider Estuary in Germany

Abstract

The “Eidersperrwerk” is the largest coastal protection construction in Germany located at the estuary of the River Eider into the North-Sea. The “Eidersperrwerk” consists out of five chambers with a length of 40 m and a width of 35 m. In the chambers the water level usually fluctuates between 3 and 5 m due to the tidal movement. At the bottom of each chamber there’s a reinforced concrete slab with a thickness of 0.8 m founded on piles which are driven into bearing sands. This sand aquifer is hydraulically connected to the tidal influenced North-Sea. Hence, the groundwater heads are corresponding with the water levels of the North-Sea. Recently, an overhaul of the construction was necessary. Over the last five years one chamber after the other was completely emptied over a period of several months. Due to the missing water load the stability of the concrete slab against uplift was only guaranteed at a certain hydraulic head in the sands. In this context a groundwater monitoring system was established to observe the groundwater heads as well as the deflection of the slab. Also, a pressure relief system was installed to regulate the groundwater heads if necessary. This system is taking advantage of the existing hydrogeological boundary conditions. The supervision and the control of the monitoring system as well as the visualization of the measured data were realized over a webserver with an intuitive graphical interface. Operating this system it was possible to carry out the overhaul without any disturbance due to stability problems caused by hydraulic conditions.