Nat. Hazards Earth Syst. Sci., 20, 197–220, 2020 https://doi.org/10.5194/nhess-20-197-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Sandbag replacement systems – a nonsensical and costly alternative to sandbagging? Lena Lankenau, Christopher Massolle, Bärbel Koppe, and Veronique Krull Institute for Hydraulic and Coastal Engineering, City University of Applied Sciences, 28199 Bremen, Germany Correspondence: Lena Lankenau ([email protected]) Received: 20 May 2019 – Discussion started: 27 May 2019 Revised: 21 November 2019 – Accepted: 27 November 2019 – Published: 17 January 2020 Abstract. In addition to flood defence with sandbags, differ- 1 Introduction ent sandbag replacement systems (SBRSs) have been avail- able for a number of years. The use of sandbags is time- The classic aid in operative flood defence is the sandbag. So- consuming as well as highly intensive in terms of materi- called sandbag replacement systems (SBRSs) have also been als and personnel. In contrast, SBRSs are reusable and re- available for some time now although their use is still very quire lower costs in terms of helpers and logistics, offsetting limited. Figure 1 shows such mobile, location-independent the comparatively higher initial investment costs through re- flood defence systems, which can be subdivided into tube, peated use. So far, SBRSs have rarely been used in Germany basin, flap, trestle, dam or panel systems, and bulk elements. in operational flood protection. The reasons lie in different fi- The systems counteract flooding either by their bulk weight, nancing modalities of investment, operational costs and low which is induced by water, sand or concrete (in container and confidence in the technical performance of SBRSs. These bulk systems), or by their geometry in connection with the problems are addressed by a research programme at the Insti- vertical hydrostatic water pressure (in flap, trestle, dam and tute of Hydraulic Engineering (IWA), City University of Ap- air-filled tube systems – not shown in Fig. 1), with both ap- plied Sciences, Bremen. A series of systematic large-scale proaches resulting in frictional forces on the ground. Panel tests of sandbag systems and SBRSs with a focus on func- systems consist of panels which are held in place by sticks tionality, stability and handling was carried out. The results driven in the ground on alternate sides. But, commonly, showed that the majority of the SBRSs tested are able to pro- location-independent mobile flood protection systems do not vide protection comparable to that of sandbag systems but need additional anchoring to the ground. However, some pro- with a significantly reduced use of materials, simplified lo- ducers offer such a possibility, which introduces a safety sur- gistics and fewer helpers. Nevertheless, it is advisable to de- plus or can be necessary when high-flow velocities or wind velop and perform well-defined certification tests for SBRSs, stress on the non-jet-impounded system are expected. Sand- in order to define clear instructions for and to identify limits bags as well as SBRSs are used in flood disaster manage- to the use of certain SBRSs. For example, not all systems ment, especially in cases when permanent flood protection work equally well on different surfaces. systems like dikes fail or when no permanent flood protec- Supplementary to the practical tests, costs of the procure- tion schemes are available because the endangered area was ment and use of various sandbag systems and SBRSs were thought not to be at risk. Thus, sandbags as well as SBRSs are determined on the basis of realistic scenarios. This provides used in extreme flood events. There has been no regulatory a methodology as well as concrete figures to cost the provi- obligation to demonstrate the functionality of an SBRS so far. sion and use of different protection systems from a holistic In general, however, SBRSs are suitable for flood protection perspective. It turns out that the higher investment costs of and can be equated with sandbagging in terms of function- the SBRSs investigated compared to sandbag systems are al- ality (cf. Pinkard et al., 2007; Niedersaechsischer Landtag, ready offset on the second use of the reusable systems. 2014; Massolle et al., 2018). The effectiveness of the indi- vidual system might differ depending on construction, geom- Published by Copernicus Publications on behalf of the European Geosciences Union. 198 L. Lankenau et al.: Sandbag replacement systems etry and filling. Nevertheless, decision makers need to have are not subject to the direct influence of high hydrostatic reliable information about the general functionality of an in- pressures or the dynamic impact caused by waves and flot- dividual SBRS. This information is not always available, es- sam. They are therefore less endangered in terms of their pecially not from an independent source. functionality. Sandbagging is time-consuming as well as highly inten- In Germany, operational flood defence is regulated as part sive with respect to materials and personnel. SBRSs have the of hazard prevention or disaster control at the federal state potential to be much more efficient flood defences as their level. Direct responsibility lies at the municipal level and thus use entails significantly lower material, personnel and time with the local districts and cities. This includes the responsi- requirements than conventional sandbagging. For example, bility of providing the necessary material for the protection 16 500 sandbags and 250 t of sand are required to build up of the general public, and sandbags – which are the signifi- a 100 m long and 1.0 m high sandbag dam (cf. THW, 2017). cantly cheaper option – are as a rule preferred over SBRSs. Without considering additional efforts, such as the logistics In the case of a disaster event, assistance can be requested of supplying materials and personnel, 60 helpers would take from the federal state or the federal government although about 10 h to fill the sandbags and set up the dam (cf. THW, the financing of such assistance will still remain initially 2017). However, the advantage of using sandbags lies in the with the affected administrative districts or cities. Ultimately, possibilities for flexible deployment and many years of prac- the costs of major damage events, such as those caused by tical experience. Figure 2 shows firefighters raising a dike by the Elbe floods of 2002, 2006 and 2013, will be borne pre- setting up a temporary sandbag dam. dominantly by the federal state and the federal government. SBRSs either do not need a filling at all or the filling is Once such an event occurs, however, no time can be lost in put in place with technical assistance such as pumps (water procuring SBRSs if they are not already standing by. Thus, filling), wheel loaders (sand filling) or cranes (bulk elements the cost of procuring and stocking SBRSs, in addition to a made of concrete). Thus, the systems can be set up and dis- lack of confidence in or knowledge about their functionality, mantled with considerably less time and fewer people (cf. presents a major hurdle to their use. Massolle et al., 2018). Logistical efforts are minimised if no Therefore, in Germany during the Elbe flood in 2013, filling is needed or if water, which can usually be obtained SBRSs were only used in isolated cases (AQUARIWA, 2019; locally, is used. In contrast to sandbags, SBRSs are reusable Mobildeich, 2019) despite the fact that the use of sandbag- and do not have to be disposed of at high cost after a flood ging for operational flood defence is very time-, material- event. From these points of view, SBRSs can also be suit- and labour-intensive. Figure 4 shows two SBRSs after the able for scheduled flood protection measures in areas where Elbe flood in 2013. The two systems were successfully used no permanent flood protection schemes can be applied. The to prevent the hinterland from flooding (Niedersaechsischer main disadvantage of SBRSs is the higher cost of acquisi- Landtag, 2014). tion. However, the lower expenditure on helpers, logistics In order to increase the confidence of decision makers and disposal of material means that these higher investment in SBRSs and to promote the availability of only well- costs can be offset through reuse. Furthermore, there is lim- functioning SBRSs, it is desirable to carry out systematic ited confidence in and a lack of knowledge of the function- tests on functionality, stability and handling and to develop ality of SBRSs. Besides the low confidence in the general relevant certification procedures. In addition to the function- functionality of an SBRS, possible vandalism or mechani- ality of SBRSs, their costs and efficiency in terms of person- cal influences, e.g. the impact of flotsam or vehicles as well nel, time and logistics compared to sandbagging should be as the collective failure (causing a domino effect) of SBRSs, investigated to likewise support decision makers. are of great concern. In general, the functionality of sandbag At the international level, corresponding certification al- dams can also be endangered by vandalism or mechanical ready exists. It can be awarded by the globally active test- influences but rather less by a collective failure, unless the ing and certification service, FM Approvals (FM Approvals, sandbag dam heavily overflows with the flow travelling over 2019), based on the American National Standard for Flood long distances. Abatement Equipment (ANSI and FM Approvals, 2014), and Temporary flood dams made out of sandbags or linear by the British Standards Institution (BSI, 2019a) based on SBRSs are set up in order to protect the hinterland from in- the Publicly Available Specification (PAS) for flood pro- undation. Beyond that, sandbags are also used on inner em- tection products (specification type 2, temporary and de- bankments, securing saturated dikes either on selected points mountable flood protection products; BSI, 2014).