The project with the sonic name "Long-term securing of the allowance in Iffezheim", or LSG for short, was already started in March 2014. Tractebel Hydroprojekt GmbH was commissioned by the then Waterways and Shipping Office Freiburg to design a conveyor system that would be able to supply approximately 8,600 tons of gravel per day from a storage area on German territory via the rest of the Rhine to a berth on French territory about 1 km away.
There, the gravel should be able to be loaded onto ships using suitable loading technology, which then sail downhill on the Rhine side canal (Grand Canal D'Alsace) to Iffezheim. The overall objective of the project is to take over gravel from the newly emerging Weil-Breisach flood retention area, transport it 140 km by ship to a lake near the Iffezheim dam and store it sub-aquatically in a lake for a long time. This gravel should be available for the addition of bedload in the future. The addition of the slide is intended to counteract the erosion of the Rhine sole in order to prevent or contain the associated drop in the water level in the area below the Iffezheim dam.
The constant addition of the bedload results from a state-treaty obligation of Germany towards France. Appropriate measures must be taken by the Federal Republic of Germany to this end. Since the gravel is now scarce as an additive in the immediate vicinity around Iffezheim, the required quantity must now be obtained in this way. The containment room from which the gravel for the realization of the LSG project originates is part of the Integrated Rhine Programme (IRP) of the state of Baden-Württemberg. The gravel material already produced there is mined, loaded and transported to the storage area by the state of Baden-Württemberg (represented by the Freiburg Regional Council). The planning basis is based on approximately 10 million tonnes of gravel over a seven-year period.
We were commissioned by the Waterways and Shipping Office Oberrhein to develop the performance phases 3 to 5 according to HOAI, based on a preliminary planning by the engineering community Fichtner-KED. However, it quickly became apparent that this preliminary planning could not be implemented in many places, so that we were subsequently commissioned in parts with the repetition of the performance phase 2 as well as with several feasibility studies. At the beginning of the planning, we faced numerous challenges. First of all, it had to be ensured that more than 230 truckloads of gravel could be unloaded in the storage area every day. With a predetermined daily working time of eight hours, this means that, in theory, a truck with 37 tons of gravel reaches the storage site every two minutes. In order to solve this logistical task, only several fully automatic truck unloading stations were considered. Since it was stipulated as a planning boundary condition that the ship loading must not be hindered by a delivery failure of the trucks of up to two days, a solution had to be found, how the gravel can first be stored on a dump. This stockpile must be able to store almost 18,000 tonnes and deliver them continuously as needed. Various loading technologies were developed and compared in a comprehensive preliminary planning. In the end, the choice was also made for a fully automatic system consisting of a heap belt and a drain tunnel with dosing belts located at the foot of the dump. This "buffer heap" occupies an area of 7,500 m² and has a height of 15 m. The gravel is transported to this height via a heap belt conveyor and dropped over the heap via a so-called belt grinding trolley, which can be moved along the dump. In the ceiling of the extraction tunnel there are eight extractors, which, according to a sophisticated system, abandon the gravel from the dump to a second belt conveyor according to demand. From there, the onward transport takes place via several intermediate stations, via the Restrhein and the Rhine Island, to the French side in the direction of ship loading.
The ship loader with a total weight of 540 tons and a height of almost 30 m was another big challenge. On the one hand, it must be able to fully reach the elongated shape of a transport vessel by means of a simultaneous pivoting and translational movement of its loading boom from the specified fixed location, which means that the loading boom is telescopic during the loading phase. On the other hand, it is necessary to throw the gravel as low as possible, low in dust and noise, but above all in a targeted manner. Due to the large discharge, the drop height is at least 18 meters. Last but not least, the loading has to take place in an extremely tight time window of just 90 minutes per ship unit, since the lying times of the ships must follow a fragile ship circulation plan, so that the entire transport logistics does not come to a standstill.
All the problems that had to be solved cannot be listed here. At the end of the planning, however, a fully automatic loading system was created, which is then operated with just two people. The system is optimally designed from the point of view of process safety, environmental impact and occupational safety. The total construction costs amount to 23.8 million euros. The planning documents are currently in the court of the German and French approval authorities. We do not expect serious objections, as the authorities have been continuously involved in the run-up to and throughout the planning process. However, it is still unclear when the plant will be tendered.
Torsten Fraaß – Magdeburg