How to...move safely in shallow flood water

Published:  01 September, 2008

The most commonly seen risk-taking activity is untrained responders moving around in what they perceive to be low-risk water. This is often because they are simply not aware of the hazards lurking beneath the surface and in the water itself.

Before we even consider the physical hazards of flood water; the hazards to health from contaminants in the water should be highlighted. In rural flooding, this will include fertilisers, pesticides, slurry, and manure. In urban flooding, everything that runs through the sewers will be mixed in with the flood water, as will fuels, oils, and industrial chemicals. It is evident why a full drysuit with integral socks is essential for responders.

 The different types of bacteria and viruses present in flood water are innumerable and thorough decontamination of personnel and equipment is essential. Even to the untrained eye, fast-flowing water poses a hazard. Here is often quoted research from the Ohio Department of Natural Resources (1980);

Current Velocity Force on Legs Force on Body
3mph / 4.8 kph 75 Newtons 149 Newtons
6mph / 9.7 kph 299 Newtons 596 Newtons
9mph / 14.5 kph 672 Newtons 1343 Newtons
12 mph / 19.3 kph 1196 Newtons 2393 Newtons

So in a 3mph current, there is a horizontal force pressing on the back of the legs which is approx equivalent to a weight of 7.5 kg. This may not seem much, but with unstable terrain underfoot it is enough to make wading challenging, if not impossible.

It is very easy to see that water, only a few inches deep, flowing quickly down a tarmac street is more than capable of washing an adult off their feet. Typically in this (second) stage of the flood, where the water is travelling rapidly, the risks are highest and only expert teams should be deployed into the water.

It is normally during the third stage of the flood, where the water speed has reduced, that wading starts to be an option. To the untrained eye the flood water now looks much safer.

A second critical factor when assessing a site is the depth of the water. Knee depth is manageable for most responders, with mid-thigh approaching the maximum; although that is going to vary depending on the size of the responder. Suffice to say, a shorter, lighter person is going to get washed off their feet in much less water than a taller, heavier person. This is because more of the responder’s body is in the water, making them more buoyant, and therefore the force exerted on the ground is reduced.

The third factor that needs to be considered before wading across somewhere is the makeup of the ground underneath. The traction that you will have on a smooth tarmac surface is going to be much more than a soft sandy bottom, likewise if the surface is rocky there is an increased likelihood of lower limb injuries, and the possibility of an entrapment. Difficult terrain will require more time, effort, and energy to cross.

Before looking at wading techniques, let’s examine the physical hazards that the initial phase of the flooding will have caused; there could be debris that has been carried and deposited; drain-covers may have been blown off by back-pressure; and normal road-furniture will now be covered with murky flood water.

The risk of missing covers cannot be over-emphasised. Once the water levels start to drop, and the sewerage systems start to flow normally, these become siphons, and if a responder accidentally steps into the void there is a very real danger to their life. Where missing covers are likely, wading poles are essential lifesaving equipment. The surface indications of powerful siphons can be very subtle and difficult to detect. An everyday example of this is letting the plug out in a deep bath – the suction is strong given the small size of the opening, but the water is quite shallow before the whirlpool appears.

Body position

The most effective position for wading is to face upstream (looking for incoming hazards), with your knees bent so that they are slightly in front of your toes. As the water speed increases, you will need to lean further forward to maintain effective grip. A wider stance will give additional stability. Move just one contact point at a time, and being sure that you are secure and stable on one foot before moving the other.

Wading poles

A very simple and cost-effective way to vastly increase the safety of wading in floods is to provide the wader with a pole. This may be a specifically-designed wading pole, it could be a raft paddle (held with the blade in the hand, the T-grip on the ground), or a fire-beater, or a broom handle. This can be used for support when wading, but is far more effective if used as a feeler, or probe, to feel the ground for hazards before placing your feet. Sweeping the ground that you are about to step into is most effective method – similar to how people who are visually-impaired use a white stick.

It should be noted, that it is preferable not to use the pole as a “crutch” and put any weight onto it. The pole may not take your weight, and suddenly break. Secondly, you would then be distributing your weight between three points of contact, instead of just two – reducing the grip that you have with your feet.

Line astern

It would be very unusual for any responder to be operating singly, and so moving as a team often provides a lot more stability, safety, and security. The simplest technique is known as “line astern”, where multiple responders stand in a line, facing upstream, and hold onto each other’s buoyancy aids. Ideally, the buoyancy aids will be held with one hand at the shoulder strap and one hand at the waist. This then provides maximum leverage to force them down should the person be washed off their feet.

The most effective line will position the largest responder at the head of the line, using the wading pole. The responders behind will then tuck into his eddy as tightly as possible. As with all wading formations, the closer together people are, the more efficient the manoeuvre will be. If the line becomes any longer than four people, it starts to become unwieldy, and there is a risk of snaking. It’s usually better to split down into multiple smaller lines.

When evacuating casualties with this method, it is best to place them in the middle – with very strict instructions that if they are washed off their feet then they are to let go of the responder in front of them. It is the responsibility of the responder behind to remain hands-on with the casualty, and if washed away then to swim to safety with them. Not forgetting the mantra of “self, team, victim”. If the responder’s life is endangered, then the casualty should be released – they will, of course, be wearing at least a buoyancy aid and helmet and so will remain on the surface.

The wedge
With casualties that require a little more protection, or if we have a larger group that we are unwilling to split, the wedge is a very effective technique. The responders arrange themselves like a rack of ten-pin bowling pins. The largest at the front, facing upstream, with the wading pole, two behind him, three behind them, four behind them and so on.
Again, a very tight profile is important. With the wedge formation, a vulnerable casualty can wade in the centre of the wedge, very well protected from the force of the water, and also surrounded by responders. A stretcher could also be floated in this formation. Good communication and co-ordination are important for the shape to remain effective and pointing directly upstream.

Line abreast

With long distances of low-speed water to cross, moving sideways in the Line Astern or Wedge formation quickly becomes tedious and tiring. In an urban environment, where you are reasonably confident of the ground under foot, line abreast is a viable technique; although it should be emphasised, it is not very effective in higher energy waters, and can put a strain on knees.

Instead of facing upstream, the responders now face the direction that they wish to travel. They hold a wading pole at approximately waist height, in order to support their fellow responders should one stumble or fall. There is a risk that the team could all walk into the same obstacle at once (for example, a kerbstone) and all fall together – it may be wise to have a few members of the group with extra wading poles probe ahead.
Anybody considering using these techniques should seek professional training in swiftwater and flood rescue. Additional wading techniques that increase the safety of responders (such as the use of tethers) are beyond the scope of this article.

  • Operation Florian

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