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Are there any recognized studies on the effectiveness of sand-bags in protecting property in some disaster or flood? Many times on the major news they talk about how sand-bags are used in a flood , how many people 'pull' together and make a great effort to save various properties. The thing is in many such instances the News people do not follow up on whether the sand-bags held. There has been a few mentions of it being successful but they do not mention much if or when the sand bags actually fail. So have there been any official studies in the effectiveness of sand bags?

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    $\begingroup$ dx.doi.org/10.1016/j.geotexmem.2010.11.010 Not sure I'd call this a recognized ref, though. $\endgroup$ – Deer Hunter Jan 8 '15 at 9:17
  • $\begingroup$ Is anyone working on an alternative to sand-bags? I heard some group is working on bigger portable 'blocks' that fit together like big 'jig-saw' pieces forming a kind of portable wall. $\endgroup$ – 201044 Jan 9 '15 at 0:01
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    $\begingroup$ Sandbags definitely work. How well the work will be very dependant on lots of factors - how they are stacked, how big they are, what pressure head they are holding back against, what they are made of etc. Of course, none are going to work perfectly, so it also depends on the severity and duration of the flood, as well as the ability to pump water out. $\endgroup$ – naught101 Jan 9 '15 at 3:47
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    $\begingroup$ Whenever all of the relevant conditions are not right? Maybe your question is too broad? Maybe something like "What are the most common causes of sandbag failure?" would be more answerable? But then, a common, small failure might be less relevant than an uncommon catastrophic failure. $\endgroup$ – naught101 Jan 9 '15 at 4:01
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    $\begingroup$ I haven't read this article, but it looks like a good place to start. $\endgroup$ – naught101 Jan 9 '15 at 4:05
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There have been a few studies related to the effectiveness of sandbags in flood events, these are usually based on observations performed after flood events. Overall, studies have shown that sandbags only have modest protection in its use as a domestic (1).

A major factor the research shows is that the maximum effectiveness occurs to about 1 metre depth (1), they can, on occasion, hold out in higher flood levels, but as Reeve and Badr (2) determined, leakage between the bags increases rapidly with increasing flood water levels. However, due to the unique nature of each flood conditions, there is still a large degree of uncertainty as to what effectiveness actually means in terms of sandbags (1). However, the major degree of effectiveness is highly dependent on the number of rows of sandbags and the duration of the flood (2).

Asides from floodwater height and duration, and height of sandbags, other factors that affect their effectiveness include:

  • Waves on the flood waters increase instability of sandbag walls/dikes, especially as floodwater depth increases (5).

  • Ambient conditions - temperature mainly, if low enough - ice could form between the bags decreasing their effectiveness (5).

  • Speed of flood waters - having eyewitnessing (and being caught in) a flash flood (3), fast moving water itself (and the debris it invariably contains) can severely degrade the effectiveness of sandbags.

  • The time taken to build the sandbag wall, as well as build up the height of the wall should the flood levels rise.

In reference to the comment about alternatives, one major alternative is preventative action, even though it is impossible to fully protect against floods, particularly large-scale and flash-flooding. After the 2002 floods of the Elbe River in Germany, it was found that household preventative measures lessen the damage from a large scale flood (4). Related, flood minimalisation techniques are explored including soil bioengineering (6).

References

(1) Botzen et al. 2008 Willingness of Homeowners to Mitigate Climate Risk through Insurance

(2) Reeve and Badr, 2003 Performance of sandbags for domestic flood defence, Proceedings of the ICE - Water and Maritime Engineering, Volume 156, Issue 4, 01

(3) Worst Queensland Floods In 35 Years 11/01/11 YouTube news clip

(4) Kreibich et al. 2005 Flood loss reduction of private households due to building precautionary measures -- lessons learned from the Elbe flood in August 2002 Natural Hazards and Earth System Science

(5) Raymond, 2009, Wave action and the effects of the environment on sandbag dike performance Thesis - University of Manitoba

(6) Dhital and Tang, 2015 Soil bioengineering application for flood hazard minimization in the foothills of Siwaliks, Nepal Ecological Engineering

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  • $\begingroup$ Why does ice decrease the effectiveness? I would have thought that it would block up holes, and decrease the porosity of the sand? $\endgroup$ – naught101 Jan 9 '15 at 7:46
  • $\begingroup$ The authors suggest it could make a sliding surface. $\endgroup$ – user889 Jan 9 '15 at 8:06
  • $\begingroup$ Leakage between the bags can be reduced by plastic sheeting on the outside of the bags and pumps behind the dyke may be able to keep up with slower leakage. Of course as the height increases you need to increase the base thickness to support the dyke. $\endgroup$ – haresfur Jan 10 '15 at 3:45
  • $\begingroup$ I saw in a National Film Board documentary they were using sandbags in the 1950's I think..Talk about a lack of progress.. $\endgroup$ – 201044 Jul 22 '15 at 3:01
  • $\begingroup$ User 889 gave very useful information. Reading it I don't see why sandbags are still the preferred method now and for the last 50 years. Talk about lack of progress.... $\endgroup$ – 201044 Aug 15 '15 at 11:36

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