Flood Watch IV: Mail from my dad

I just got mail from my dad. I wrote him asking if he thought 9,500 sandbags would be enough to protect the Spolana facility. This is his response. (Note: USACE=US Army Corps of Engineers, RDFW=Rapid Deployment Fortification Wall) :
Hey Doug,
On the average, filled sand bags weigh, an average of 30 pounds per bag.Sand weighs 110 pounds per cubic foot. That gives you 3.66 bags per cubic foot. Sand bag structures must be built in a trapezoidal shape. At ERDC sandbag structures 3 feet high with a 3 ft. wide top and a 9 ft base failed to hold 3 feet of static water and also failed during small wave tests. As water elevation increased, seepage rates increased until the water pressure dislodged the bags and the structure failed. In field testing, the sand bag structure 4 feet high, with a 4 ft. wide top and 12 ft base also failed to hold 4 feet of water and failed. Check USACE ERDC web site under Expedient Flood Fight Structures Program or search RDFW.
Each threat is different. Heights and lengths for sand bag structures differ. To determine sand bag structure trapezoidal volume : Pyramid structures do not work at all.
B1 plus B2 or top width of the structure plus bottom width of structure – Divided by 2, X the height, X the length. That will give you cubic feet. Multiply that by 3.66 and that will tell you how many sand bags you need. Trying to justify 9500 sand bags is odd.
In the US, preparedness is finally taking hold following the Katrina and Rita showings . On the average preparedness costs that are effective are 15% of recovery costs. Or an 85% savings.
In terms of RDFW, each expanded unit holds the equivalent of 35 filled sand bags. We actually had CCC kids fill bags and stack them in a pile and dump them into a single RDFW unit. 7 men crews can build a 100′ long X 4′ ft wide X 4 ft high structure in 1 hour. A sand bag structure of equal strength must be trapezoidal or 4′ top + 12′ base  divided by 2 = 8 X 4 = 32 X 100 = 3200 cubic feet X 3.66 sand bags per C/FT = 11,712 sand bags.
It takes an average of 35 people (in 8 hour shifts) 20 hours to build a 100 ft sand bag wall – 15 filling, 15 daisy chaining, 5 stacking. That is 700 man hours. It takes 7 man hours to build an RDFW 100 ft. long. if we had 35 people we could install 500 lineal feet in one hour or 10,000 feet in 20 hours.

One thought on “Flood Watch IV: Mail from my dad

  1. The 2nd paragraph about sandbag wall failure due to “small wave action” is questionable. I am a professional in this field in the UK of GB (England). I also draw my background experience of ex-forces personnel, that I’ve hired in supervisory & consulting roles for genuine flood & re-enactment situations. I also ensure that my staff get the best available gear for rapid s/bag filling (current the SandHopper from ProEarth Developments – http://www.proearthdev.com), but I am also about to invest in another British s/bag filling funnel system, available from BCB International in Cardiff, Wales.
    However my point from direct experience, could also be the proven fact that Uncle Sam used to insist on using woven polypropylene material for their s/bags. The British & Commonwealth forces (including Canada, Australia, New Zealand & other former colonial nations, such as India) have learnt the harsh lesson of using HESSIAN (Burlap = US-speak) for such s/bag material use. The main reason being that the coarse weave of the material, actually allowed the fibres to “mesh interlocking” with the next course of sandbags laid on top. Then, each course SHOULD be tamped level to had a firmer consistency to that course of s/bags, for the next course to be laid well. Then I have to ask what type of sand was used to fill the s/bags,if the grains where too round, then I can foresee problems with laying courses of s/bags. If the grains where too fine, then I would also see problems with wall construction. When it comes to flood wall construction when threatened with time to allow good wall construction. Then make the foundation base layers, THREE times the width of the width at the top of the wall.

    John Locke.

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