Operativer Hochwasserschutz-Eignung, Einsatz und Leistungsfähigkeit von Sandsackersatzsystemen in praxisorientierten Versuchsreihen

authored by: Christopher Massolle
supervised by: Torsten Schlurmann
Abstract: Operational Flood Protection - Suitability, use and Performance of Sandbag Replacement Systems in Practice-Oriented Test Series Extreme flood events such as the 2013 flooding in Central Europe and 2017 flooding in southern Lower Saxony demonstrate that an enormous amount of material and personnel is required for the deployment of sandbag systems to defend dyke lines at risk of breaching and to protect low-lying habitats and objects against flooding. Their construction also requires time, which is available in limited supply during a flood scenario. Therefore, despite all efforts, flood damage amounting to millions of Euros occurs over and over because the necessary protective measures cannot be sufficiently deployed on site in a timely manner. Due to the expected increased frequency of extreme weather events resulting from climate change, it can be assumed that this problem will worsen in the future. In addition to sandbag systems, so-called sandbag replacement systems (SBRS) can also be used in operational flood protection, whereby the latter can be installed and dismantled many times faster and with less strain on personnel and resources. Consequently SBRS enable the protection of a greater distance in a shorter time. However, the use of many available systems such as water-filled hose systems or simple folding systems is considered debatable, and they are mostly not used in Germany due to a lack of confidence in the designs or a lack of certification programmes. In Germany, there is no certification programme for SBRS so far, although two certification programmes for SRBS exist at the international level, whereby the latter only include a realistic test implementation and test evaluation to a limited extent. For example, the international certification tests are generally carried out on a smooth and cleaned concrete substrate, whereas systems in operational flood protection are used on a wide variety of substrates such as grass, gravel and cobblestones, and possibly with terrain variations in the form of pavements, etc. Furthermore, testing for the international certification requires meeting a decisive and very strict evaluation criterion for water permeability of the system. This means that the sandbag dam, which has proven itself in operational flood protection, would not receive certification as a mobile flood protection system under either international certification scheme.In order to test the suitability, use and functional capability of SBRS for the defence of dyke sections at risk of breaching and for the protection of low-lying areas under practical boundary conditions, a test facility specially designed for this purpose was set up in cooperation with the training centre of the Technisches Hilfswerk (THW) in Hoya. The facility consists of a 15 m long and 3 m high homogeneously constructed dyke equipped with sensor technology, and a water impoundment area in which flood events can be simulated as often as desired. At the test facility, dyke defence systems installed on the inner or outer slope of the dyke can be loaded with different water levels, and the resulting seepage line locations within the dyke body as well as the seepage volumes can be measured. At the test facility, it is also possible to test fully mobile linear flood protection systems set up on a grass subsoil, with regard to the parameters of assembly and dismantling time, stability and water permeability. A total of 14 SBRS and four sandbag constructions were tested as reference systems at the test facility for suitability, use and functional capability in operational flood protection. The tests showed that all SBRS could be erected and dismantled in a significantly shorter time and with less labour than the sandbag constructions. Of the three tested dyke defence measures, it was found that installation of tarpaulin sheeting on the wet side of the dyke embankment does not have a positive effect on the reduction of the seepage line position and is therefore not recommended for practical use. On the other hand, the two alternative dyke defence measures showed very positive results and a recommendation is made for the practical adoption of these SBRS as an effective and resource-saving application. According to the strict evaluation criteria of the two international certification programmes, sandbag dam protection is not certifiable because water permeability limits are exceeded, despite being operationally usable. Similarly, testing of the linear defence systems showed that, depending on the certification, four or eight SBRS would not have received certification because water permeability limits are exceeded. However it is considered that the exceeded water permeability volumes were practically controllable and the systems sufficiently stable. In addition, findings were obtained regarding the stability of SBRS on a soft subsoil. In contrast to their use on solid ground such as concrete, systems supported at points were deficient on soft, soaking wet subsoil, showing instability, despite system manufacturer's specifications indicating these systems would be stable. Taking into account the test results, the majority of the tested SBRS are deemed to have a good usability, but it is debatable whether the two international certification programmes available so far are practically suitable.
Organisation(s): Ludwig-Franzius-Institute of Hydraulics, Estuarine and Coastal Engineering
Type: Doctoral thesis
No. of pages: 226
Publication date: 2023
Publication status: Published
Sustainable Development Goals: SDG 13 - Climate Action
Electronic version(s): https://doi.org/10.15488/14745 (Access: Open)