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Useful Methods of Keeping Yourself and Others Dry in a Flood. Click on title to see section ...

1. Hints for Personnel Involved in Flood Emergencies
2. Pre-flood Precautions
3. Sandbagging
4. Priority of Work
5. Alternative Methods of Quickly  Adding to the Height of a Bank
6. Minor Breaks in the Bank
7. Boils-Spongy Spots or Areas in, on,  or Near the Bank
8. Interference with Stopbanks In and After Floods
 

1. Hints for Personnel Involved in Flood Emergencies
New Zealand towns are invariably built on or near a river crossing, a stream or waterway and danger from flooding is common. Stopbanks constructed to keep out floodwaters often have a design standard that can be beaten during above design or unusual storm events. Some of the following simple means of adding to the protection from a bank can be employed in emergencies and will ensure that the many enthusiastic helpers always available at those times can be gainfully employed.

2. Pre-flood Precautions
a. Regular patrols of urban stopbanks are needed to check for damage.
b. Tracks, both stock and walking tracks, should be inspected.   Low spots caused by, say, children crossing the bank, should be filled to a height above the surrounding bank crest.
c. Carefully fill in all areas where holes from stock camping or tramping are evident.
d. Check for holes dug by kids for "huts" or adults for garden sheds, dog kennels, etc.
e. Rabbit holes, although not so prevalent these days, have been the cause of many old and spectacular bank failures.   Do not just block the entrance – dig the hole right out and backfill with compacted soil.
f. Fill and ram all old fence postholes in a bank.
g. A stopbank with good even grass cover will survive overtopping for considerable periods without damage but bare patches on the back slope are the first to scour out.
h. Check all pipes and floodgates under the bank for blockage, damage or breakage and see that all floodgates are shutting.   Regular checks are required.
i. It is much easier to ensure a floodgate is undamaged and operating on a sunny day when the river is low, than at night in a flood with three metres of water over it.
j. Look for gates with broken hinges or doors pulled back and sometimes tied up by people hoping to get better drainage and meaning to get back to close them before the river rises.
k. Check for trees fallen against the bank or where a build-up of debris in the floodway will jet water between it and the bank.   (The Cattle Flat stopbank was once holed by an 200mm square strainer lying on the berm pointing diagonally at the toe of the bank).
l. Report any instances of gravel stock piles left by contractors or Local Bodies in the floodway (it is not much use providing a 100% clear floodway if overtopping or scour of the protection works occurs through a blockage of part of it by gravel heaps. This is a constant problem which needs prompt action).

3. Sandbagging
This is the most common means of adding that little bit to the height of the stopbank. The following notes describe steps involved in sandbagging operations. It is important to note that these procedures can be supplemented by the use of polythene (see FEMA notes).

Consultation
Unless there are prior arrangements, consult with Environment Southland before raising stopbanks In some cases stopbanks are designed to overtop at certain levels. Sandbagging on these banks, indeed any stopbanks, can make flooding worse for some people while protecting others.

Sandbags
Every organisation involved in this work should have a ready supply, source, or stock of bags, preferably tied in bundles and strategically placed for quick use. The sandbags referred to in this manual are woven polyethylene bags commonly used for fertiliser, seed etc.

Fill Materials
Knowing where to get material to fill the bags is helpful in emergencies and strategically spaced spoil heaps or sources of sand (e.g. concrete manufacturers,) should be organised. Sandbag fill can be crusher dust, sand, gravel or earth. Permeability is important but less so if polythene is used with the sandbags.

Sandbag Filling
Filling the bags is where lots of people go wrong. Never put more than five shovels full in a bag as they cannot be properly placed, carried or built upon if filled to the top. Bags can be filled with elevators or concrete trucks to speed up filling, but make sure they are not overfilled. As a general rule: half full is plenty.

Sandbag Placing
Always lie the bags flat, never vertical, and place the bag on the flap of the previously laid one.
A badly laid bottom layer may cause an eventual three layer heap to fall over or collapse.
Place the first layer as close to the riverside of the top of the bank as possible – you may wish to walk on the landward side of the bags or carry more sandbags along the crest. Walking with one foot on top of the bank and the other halfway down the landward batter with a sandbag over your shoulder is bad for your bank and your back.
Keep foot traffic and or vehicular traffic on the stopbank to an absolute minimum.   The vibration from such traffic on saturated stopbanks can lead to liquefaction and subsequent bank failure.   If a bank shows signs of liquefaction, it is better to construct a new bank behind the old one if it is safe to do so.

4. Priority of Work
a. Always bag the most sensitive areas first, such as where overtopping would allow water to run onto holes, stock scrapings or bare patches on the back of the bank.
A good grassed bank can stand considerable overtopping but it will fail rapidly at stock crossings, children’s tracks and "huts" etc.
b. If there are two or more spots at risk of overtopping, sandbag the highest bank first.   A break on a high bank is likely to cause more damage than a break in a low bank.
c. Always secure your retreat in case a bank breaks.
d. Do not dig dirt from the landward side of the bank to fill sandbags to lift the top. This weakens the foundations, leaves an area vulnerable to backscour when overtopping occurs and leaves an area vulnerable to stock damage and bad drainage after the flood.
e. Do not allow any machinery on top of stopbanks, they will endanger the stability.

5. Alternative Methods of Quickly Adding to the Height of a Bank

a. Driving steel or wooden stakes into the crest and fixing a plank to them.   Placing the plank on bags helps to seal out the water.   Shovels of earth on the back and front will help as does digging in timber or hitting it down before nailing to the wooden stakes.
b. Lay concrete posts along the top of the bank with a slight overlap and sealed with a shovel of earth.
c. Hay bales on top of the bank skewered to the bank with steel standards or placed in front of wooden stakes can also be used.
d. Perhaps you can think of other methods.   There is plenty of room for the application of ingenuity using the resources and materials on hand.   If possible however, seek engineering advice to ensure that your intentions do not backfire.

6. Minor Breaks in the Bank
a. Do not attempt to seal up at the break but move away from it where the velocity drops as the spilled water fans out.
b. Drive a line of steel standards in a circle around the break.   Lay netting wire between these on the upstream side and feed shredded hay bales into the floodwater in the break.   This will catch on the netting, stilling water enough to allow sand bags to be built in the lee of the netting. Several rows of netting each causing a drop of water is possible.
Trees anchored in the break or floated into them also prevent some water leaving the river.
c. The edge of the break will widen if not protected and this can be done with rock, rubble, and old machinery where these can be transported to the break. Temporary repairs can be made with netting draped over the scouring face and weighted by one or more concrete posts; haybales wet and weighted with posts; or even netting sausages full of shredded hay once again weighted by concrete posts.

7. Boils – Spongy Spots or Areas in, on, or Near the Bank
When stopbanks, particularly those constructed prior to proper compaction techniques, come under load during a flood, boils or spongy spots can develop on the bank slopes.   These boils can also develop behind well-constructed banks on poor foundations e.g. where a silt blanket overlies gravel or other porous ground.   Breaking of the boil can cause an outlet of water which can result in piping or scouring out of the bank.

Be particularly concerned if dirty water is coming out of such an area as this could mean scouring is taking place in the bank.
The preferred solution is:
a. To encircle the area with a sandbag wall empounding the water coming out of the boil until it is at a height sufficient to exert a back pressure on the outside floodwaters.

Alternative solutions are:
a. Lay hay over the boil, overlay with netting and pin the netting with sandbags. This is less effective in stopping seepage but prevents a burst in the turf layer and loss of soil.
b. Allow the area to flood by dozing up a subsidiary bank back from the main bank.
In all cases, keep kids off the area as they cannot resist the temptation to jump on the boils and burst them.

After all this should the bank show signs of liquefying, do not tamper with it – if it is not possible to ring bag the area off on the dry side of the bank, immediately warn those in the path of any likely break and take steps, long quick ones, to move to safety.

8. Interference with Stopbanks In and After Floods
Do not decide to cut a hole in a bank during a flood for any reason whatsoever without getting Environment Southland advice and buying yourself some hefty indemnity insurance. You could cause death or injury, loss of stock or property damage and possibly be prosecuted for it. Civil Defence may make a decision to do this work themselves but this would only be done in consultation with Environment Southland. In any case, they have the Indemnity Insurance behind them if things go wrong.

The resulting scour hole may develop at a point where it could eat back into the river causing tremendous damage and yet be at a site where it is impossible to get machinery to block it off.
The site may be such that a subsequent tide can spill salty water over pasture if it cannot be blocked quickly.
Any hole cut to let water out should not be permanently filled without consulting Environment Southland as the proper compaction methods and materials need to be employed.
If you know of other hints, let us know, and additions to this booklet can be made.

Information Supplied by
Environment Southland
AUGUST 2000

AFTER A FLOOD

It may take time to get everything back to normal after an emergency.

	Contact your doctor if you are unwell.
	Let your local Council know of any conditions that could be dangerous or could encourage the spread of diseases.

Floodwaters can carry bugs that cause disease from the ground surface, septic tanks and sewerage systems.  These can contaminate food.

Wash cooking, eating, and other kitchen utensils in hot soapy water if they have been covered by floodwater.  Rinse thoroughly in safe water, then disinfect by immersing for one minute in a solution of 500 ml (about two cups) of household bleach in 10 litres of water.  Rinse again in safe water.  Alternatively boil all utensils for three minutes.

Destroy all unpackaged food and food items packed in paper, cardboard or non-waterproof material that have been exposed directly to the floodwater.

Get rid of all foods needing refrigeration when they have been unrefrigerated for more than two hours.

If the power has been off to the freezer for more than two days, get rid of all thawed food.

Save foods in waterproof, airtight containers (eg tins) that have been in floodwater, but make sure they are thoroughly cleaned before opening by:

washing and scrubbing in warm water which contains soap or detergent, then rinsing in clean water.

soaking for at least one minute in a solution of 500 ml (two cups) of household bleach mixed with 10 litres of water; then rinsing in clean water from a safe supply.

Write on the contents of tins if labels are damaged so you know what is inside them.

Wash and disinfect your can opener before using.

Throw out the contents of bottles with crown tops and crimped or screw caps if water rose above the neck of the bottle.  It is safer to get rid of all home preserves, as these are a higher risk than commercial items.

DO NOT use packaged or canned food if it is has been punctured or is bulging or leaking or the top has popped up.  Throw out any canned foods dented on the side or along the top or bottom seams.

Cook all food thoroughly and eat immediately.  Cook only enough for each meal.  DO NOT save leftovers.

IF IN DOUBT THROW IT OUT!

If your water tank is affected by floodwater get rid of the water (it may be polluted), clean the tank out and disinfect it.

Boil water before drinking.   If you use bore water, pump the bore to waste for 24 hours.  If the bore is under water do not pump.

Report any rubbish contaminated by hazardous substances to Civil Defence.

Tell your insurance company about any condemned item of property before getting rid of it. If you are not insured make a list of any items being dumped.  Have it checked and signed by a responsible person in case you are eligible for a relief grant.  Take photos (or video) if necessary to record what you are getting rid of.

Get your septic tank pumped out to remove all silt and sludge if it has been covered by flood water.

Note: Septic tanks may not work properly until the level of the water underground has gone down.

Before you come back to your house:

Contact an electrician or the electrical supply authority before switching power on again if water has reached underfloor wiring or wall sockets or the structure has been damaged by an earthquake.

Contact gas supply authorities if the gas meter has been affected by water.

Restoring a house after flood damage
Soon after heavy rains have stopped and waters have drained off the ground surface, sewers will generally return to normal function.  It is important to clean up, drain and dry out the house as quickly as possible.

Take photos (or video) of the damage before starting the clean-up.  Take out everything that is wet and that can be moved - floor coverings, furniture, bedding, clothing, etc and put them outside to dry when the weather is fine.

IF INSURED CONSULT AN INSURANCE ASSESSOR.
Get rid of mattresses and other large items that have been soaked with floodwater.  Foam rubber mattress or pillows may be able to be washed, disinfected and dried in the open air.

Get rid of contaminated clothing, carpets, upholstered furniture, toys and bedding unless they can be cleaned and disinfected.

Checked for trapped water and mud in wall cavities, as well as under shower trays, baths, benches and bottom shelves.  You may have to chisel out some bricks at the bottom of brick veneer walls.

Remove skirting, if necessary, and cut out softened plasterboard in damaged areas.  (Consult an expert such as an insurance assessor or builder).

Use heaters (eg hot air blowers for underfloor space), but open all doors and windows.

Replace wall linings, floor coverings etc only after things have dried out. Contact a Building Inspector at your local Council if you are unsure whether the materials are dry enough.

Leave redecorating for at least three months after finishing the repairs to prevent risk of mould, blistering and peeling.

DO NOT light fires in brick fireplaces for at least two weeks, and then use only small fires until the firebricks have dried out.

Consult an engineer if there are signs that the house has moved on its foundations, eg buckled floors, new cracks in walls, out of shape door frames.

Cleaning out a basement after flooding

	Check all floor drains in the basement to see that they are clear of debris and drain away water under the house.  Try to increase the airflow to speed drying.
	Drain any surface pools by pumping or bailing.   Wash or flush down walls, shelves and floors with clear water and sweep to remove contaminated water and sediment. Use a solution of one litre of household bleach in 10 litres of water to rinse down walls, floors and other equipment.   Leave on for 30 minutes before rinsing with clear water.   Keep windows open during this treatment.
	Use plenty of hot water and soap or dishwashing detergent for the final clean-up of walls, floors, cupboards etc
	Ventilate area by opening all windows or use fans, if power is available.
	Use a commercial deodoriser, if necessary, to remove any remaining smells.

Make sure all those helping with the clean-up wear rubber gloves and wash their hands thoroughly before eating, drinking or smoking.

Disinfect any cuts and cover with a waterproof dressing.

Keep small children away during the clean-up phase.

Take precautions against insect bites by using repellents and wearing trousers and long-sleeved tops.

Wash any clothing, bedding and other contaminated materials, such as curtains, using detergent.   Rinse in clean water with added household bleach to kill any bacteria.

Get rid of contaminated clothing so that people do not find it and put it on.

Go back to normal showering, bathing and clothes washing as soon as there is spare clean water.

 DO NOT move explosives that have been wet.   Contact Civil Defence.

DO NOT go near or handle drums or containers of chemicals you find without having protective clothing and equipment.   Report them to your local Council.

Wear rubber boots and rubber gloves during clean-up procedures so your skin is not exposed to any contamination.

For further help, contact your local Council see the white pages of your telephone book.

Information kindly supplied by
Southland District Council
March 2000