When water attacks: blocking floodwaters

As the weather becomes more unpredictable, flooding is expected to increase. So how do you minimise property damage and recover after a flood?

When floods occur, the vast majority of property damage is done not by the flow of water itself, but the pollutants it carries and the damage it does to building materials through after-effects like rot and mould.

Mitigation

Clearly, if you want to minimise expense and cleanup requirements, you need to stop water getting into your home in the first place.

However, stopping water getting into the home actually requires a two-pronged approach. You use a barrier to greatly reduce water flows, and what water gets through (because some inevitably does) has to be removed before it finds its way into the home—usually with a pump of some sort.

The first part of this approach involves building a barrier around the entrances to the home to prevent water ingress. There are a number of ways to do this, but the most common, mainly because it’s the cheapest option, is to use sandbags. There are also other types of flood barriers that we will discuss later.

Sandbags are pretty simple things—they are a relatively strong bag that is filled with sand. They come in a number of different sizes and materials, some more suitable for flood prevention than others (sandbags are also used for other purposes, such as to add weight to lightweight structures for wind stabilisation).

The most common sandbags are simply a robust bag, stitched at one end and open at the other. They are available in several materials:

• Hessian—This natural material is suitable for short term use as it will eventually rot. It will generally last three to six months before failing, and being a porous natural fabric, can easily become mouldy. For short term use (a few days to a week) they can be removed after floodwaters subside, emptied of sand, hosed down and hung up to dry. Never put sandbags away wet, and never put them in your washing machine unless you want to destroy the machine’s rubber seals from the sand.
• Polyethylene—these are similar to hessian bags but are made from woven plastic. They are strong and durable, but vary in UV stability, so check that if buying them for longer term use. Being non-absorbent synthetic material, they don’t absorb contaminants and can be easily hosed clean, dried, and stored for later use.

However, there are several problems with conventional sandbags:

• To fill sandbags, you need sand, and lots of it. Unless you have a big pile of it waiting for the day your area floods, you may not be able to access enough sand or sand-like materials to fill them—they aren’t much use if you can’t fill them.
• Even when filled with dry sand, they are heavy, and filling and moving dozens or hundreds of sandbags can be beyond many people’s physical abilities.
• Some sandbags, especially hessian bags, are made with a very open weave and leak a lot of sand. Avoid these if at all possible, they will be more hassle than they are worth—check quality before buying!

Other options
If sandbags seem like an impossible task for you, what other options are there?

One interesting product is the Floodsax (floodsax.com.au), which consists of a woven nylon sandbag filled with a mixture of water absorbent gel and wood pulp. The bags are initially very light and flat (just 200g in weight), but rapidly swell as they absorb floodwater to form full-sized sandbags, or they can be pre-swelled by dunking them in water for a few minutes. The advantages of these bags are that they are easily handled by almost anyone and require no sand or time consuming filling and so can be implemented immediately.

Their primary disadvantages are that they are very expensive compared to regular sandbags (over $20 each), and that they are designed to be completely disposed of in landfill when used. Because the filling absorbs the water and contaminants, they become toxic waste and must be landfilled. While this is true of the sand in regular sandbags as well, in reality many people simply put the sand on their garden, where contaminants may or may not break down over time (we don’t recommend this as you have no way to know what the sand has absorbed—it could be simply silt, or it could be full of sewage or even toxic pesticides from the farm up the road).

So, are there other options if sandbags seem too wasteful? Well, yes, there are. Portable flood barrier systems have been available for years, but have generally been aimed at the commercial market. However, some are also available for use in domestic properties, so let’s look at what’s available.

Flood barrier panels are all very similar, consisting of interlocking panels of some sort that simply block the water flow. Generally, these sorts of barriers work best on smoother, flat surfaces such as concrete areas—being rigid they are less effective where the land undulates or is covered in loose materials, such as garden beds.

An example of flood barrier panels is the Boxwall mobile flood barrier system made by Swedish company NOAQ (noaq.com) and available through Bluemont (bluemont.com.au), which consists of right-angle injection-moulded polypropylene plastic barrier panels that lock together to form a wall. They come in 52cm and 100cm high versions, both of which are around a metre wide (corner sections are also available), and weigh 6kg and 15kg respectively, so are easily handled by two people.

However, Boxwall panels work by forming a seal with a smooth, flat surface. They have a rubber seal under the front edge of the base part of the panel and drainage channels to drain any seepage out the back. This causes a pressure differential between the front and back of the panel which presses the panel onto the ground, making them stable until waters recede.

Bluemont also have a similar system that uses fold-out panels called the AquaFence, which is available in heights up to 2.1 metres, so can handle even extreme flooding.

Another type of barrier is the tubular barrier system, which is usually ‘inflated’ with water to form a massive, heavy barrier. Examples include the NOAQ Tubewall (which is not available here that we could find) and similar tubular systems such as the NoFloods barriers from Bluemont. Tubular systems can be implemented in just a few minutes and can be used to protect larger areas, so while they are generally designed for commercial purposes, if you have the need, you can completely surround a property with a flood barrier in just a few minutes—provided you have the means to fill the barrier with water rapidly. Tubular systems can work better on uneven surfaces than panels due to their flexibility and the attached anchoring skirt on the bottom of the tube (if used).

Panel and tubular (and similar) flood barrier systems have one massive advantage over sandbags—they are indefinitely reusable, requiring a simple hosing off once flood waters recede, saving large quantities of material from landfill (and saving you the appropriate landfill dumpage costs).

Another alternative is to not use flood barriers at all, but instead use watertight door seals on all external doors. While this means the home is floodproof all the time (assuming the doors are closed!), seals are prone to wear over time, so they need to be checked and maintained. Of course, the rest of the house has to be designed to withstand immersing water without damage, so outer walls must be water tight. This also means that you have no way to enter and exit the house unless there is an entry point above the flood water level.

There are quite a few flood barrier systems on the market, some designed to be left in place and others designed for rapid implementation. What you choose depends on your situation, budget and likelihood of a flood (for example, a flood-prone property should have a rapid deployment system of some sort).

How to use sandbags
Okay, so your property rarely suffers from flooding but it is a possibility, and you have decided to stick with sandbags as they are cheap and fairly effective. While sandbags might seem simple—the filled sandbags are stacked to form a barrier—there are a few things to remember when using sandbags that will determine how successful your barrier is in keeping the floodwaters out:

• Plan ahead. Trying to fill dozens or hundreds of sandbags at the last minute and getting them into place is one of the main reasons sandbag barriers fail—sandbags are useless if they aren’t ready to go and in place before the flood waters rise
• Fill the bags to around 2/3 full—too full and you won’t be able to close them properly and they may be too heavy to move
• Don’t tie the bag top as this changes the shape, making them harder to stack with minimal gaps. Some bags have a drawstring, but for flood use it’s best not to use it.
• Once filled with sand, fold over the top opening, folding it under the bag once it has been laid, to prevent sand spillage
• Stagger bags when stacking, like laying bricks. This makes for a more solid, more watertight barrier
• Use heavy duty plastic sheeting in front of the sandbag wall to make it more watertight. Start by laying the plastic down, with the first layer of bags holding it in place
• Start with a relatively flat surface, cleared of debris if possible
• You don’t need to sandbag the whole perimeter, just openings—doorways, roller doors and brickwork vents
• Leave at least one doorway able to be accessed—build a wall away from the door to give enough space to open the door.

Second stage—water extraction
No matter how good your barrier, there is a good chance that you will get some water seeping through it. Small volumes should seep into the ground, but remember that during flood conditions, stormwater drainage isn’t likely to be working, so water may build up between the barrier and the house. This needs to be removed, and the simplest option is a pump of some sort.

What you need is a high volume, low pressure pump. Fortunately, these are cheap and readily available from hardware stores, and are usually called dirty water pumps. Even a cheap dirty water pump can move upwards of 15,000 litres per hour.

Of course, you need to be able to power that pump. Mains power pumps may be useless if the power goes out and you don’t have a backup. A backup can be as simple as a small generator (genset), but remember, during flood conditions, fuel can rapidly become unobtainable and/or become contaminated. If your genset doesn’t have a good supply of fuel then your pump isn’t going to be much use if the power is out.

A more reliable option is a backup power system like a Bluetti or Ecoflow Delta series portable power station, but it must have enough capacity to run your pump for the entire likely flood period. If your barrier is very leaky, the pump may need to run continuously, but if your barrier is doing its job then only intermittent use should be required. Many of these portable power systems are designed to be used with solar panels to extend runtime, so it’s worth considering including solar panels in your backup system.

You can bypass electricity completely and use a petrol powered pump. These move a lot of water but need regular refuelling, and they are designed to move a lot of water continuously, so are less suitable for moving smaller quantities of seepage water and may be damaged if allowed to run dry.

A simple pump option that requires no mains power is a high flow marine bilge pump connected to a 12V battery. However, bilge pumps are not rated for silty water (which is odd, because seawater mixed with bilge debris is hardly clean) and will fail sooner or later, at least according to the manufacturers.

In many situations, there simply may not be an option to remove water if a suitable pump and/or power source is unavailable.

Dangers of floodwater
Aside from the danger to property and possessions, floodwater can harbour other dangers:

Contaminants and bacteria can cause life-threatening infections—don’t enter floodwater if you can help it, and particularly if you have open wounds that will contact the water

Debris hazards include hidden objects, especially sharp objects, and you can also suffer injury from impact from moving debris in fast-flowing currents

Fast moving currents themselves are also a hazard as they can make it difficult to maintain a footing—losing your footing in a fast-flowing flood can be very dangerous

Depending on where you live, animals—such as crocodiles, snakes, insects and spiders—can be a hidden hazard. This is especially the case up north, where saltwater crocs regularly move inland during flooding

Hidden stormwater drains can produce massive suction and you may not even know one is there until you feel yourself being pulled in. If you must move through floodwaters, a small boat (the common tinny or even a kayak) is vastly safer than wading through unknown water

Sewage is a serious problem in flooding as sewers back up, contaminating floodwaters with bacteria and disease-causing microbes of all sorts. This is another reason to avoid moving through flood waters if possible. And don’t forget, water backing up can come up through drains and toilets in the house, so put plugs in the sinks and block the toilet with a heavy ball of fabric or even something as simple as an inflated balloon. The Toilet Stopper from Floodshield (floodshield.com) in the UK (they ship globally) is designed for exactly this purpose.

If you must wade through flood waters because there are no other options, then wear appropriate clothing. Wear waders if you have them, otherwise solid clothing like jeans, and solid footwear, although you will need to change out of the wet clothes immediately after you exit the water. While wearing shorts seems like a better option, bare legs have zero protection against anything that may be in the floodwater, including all of the nasties mentioned previously.

Preventing flooding
Of course, it would be nice to not have to deal with floods, but as the climate warms and flood events become more common and more severe, then you have to plan to minimise the damage if possible.

If your property generally sees just minor flooding, you may be able to use adequate drainage and landscaping (e.g. swales) to reduce or prevent low level flooding. Earth berms around the home, integrated into the garden for stability, can also do a good job of keeping out flood waters

If building on a flood plain or flood-prone land, build to suit the site, with a raised house and a lower level that is flood resistant. We covered this subject in detail in the article “Preparing homes and towns for floods” in Renew 168.

Be prepared!
If you must live in a flood-prone location, then ensure you have the basics to protect yourself, your family and your home, ready to go. A small boat of some sort is invaluable and there are very cheap options—anything that keeps you out of the water is good. Have a set of waders for each person in the house, and if you intend to stay and protect the home, then keep your chosen flood barrier system maintained and ready to go—increasingly unstable weather can create a flood with only a few days’ or even hours’ notice.

Also, make sure that important things like family albums, records etc are protected, either placed up on high shelving or in waterproof boxes or bags. And don’t forget your pets or other animals—don’t just leave them to fend for themselves, they trust you to take care of them, so ensure you do.