Floods and Max Water Height

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Paul_B

Bushcrafter (boy, I've got a lot to say!)
Jul 14, 2008
4,044
454
Lancashire
Do any of you know what water height your vehicle could theoretically cope with?

Following a weekend of driving through floods and turning back at a few in a Vauxhall vivaro I'm curious to know more about driving through floods.

I'm a caution before bravado type who chickens out before it is anywhere close to engine wrecking intakes. Simply not worth the expense. But that doesn't mean I've seen people trying out the floods and succeeding when they really shouldn't have.

I have seen big 4x4s stuck yet rover mini metro / 100 get through something just as deep. Technique plays a part but so does air intake height and no doubt other vehicle related technical specs.

That leads me to ask if you know your air intake height. Anyone know that for a 16 plate vivaro?

Do you know your max water height your vehicle can go through. I've heard from one guy who actually knows that. Guessing there's some brand spec given. Do you?

What are your own rules/ advice on going through or avoiding floods?
 

santaman2000

M.A.B (Mad About Bushcraft)
Jan 15, 2011
16,218
804
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Florida
The general advice is don’t drive into flood waters. Not even “shallow” ones. One problem being you can’t see u deer the surface so you don’t know if that 6” of water over the road is covering a washout (where the roadway underneath has washed away and the true hole is several feet deep) And that doesn’t take into account that relatively shallow water will float most cars.
 

Dogoak

Bushcrafter (boy, I've got a lot to say!)
Jan 24, 2009
2,044
98
Cairngorms
Generally it all depends on the height of your vehicle air intake and axle breather pipes.
There's been many a wannabe 4x4 poser who's fitted a high level air intake and not bothered with the breathers and have found out to their cost after fording!
In theory, for off road driving and deep fording its 2nd gear, low range, and about 10mph so you push a 'bow wave'.
 

Nomad64

Full Member
Nov 21, 2015
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Just out of range
A bit of a random question - FWIW, I have a diesel Defender with no electronics fitted with a sealed snorkel (many aren’t) and axle, engine and gearbox breathers so with the addition of a couple of wading plugs it should in theory be capable if doing this!


Would I do it - no and certainly not in salt water but I have had water over the bonnet on a few occasions.

Here is some more practical advice on wading with a “proper” 4x4


Walking and checking the depth is recommended but not alway practical - applying a risk based approach to decision making to crossing a river in Kenya a few years ago, I took the view that as 99% of a herd of zebra had crossed successfully, I’d assume that the depth of the water was not going to be an issue! ;)

8E7467A1-E0D9-4B94-A4C9-2DE466310395.jpeg

In the UK, the most serious underwater obstacles are likely to be collapsed drains, culverts etc, missing manhole covers and tree trunks or other debris.

The max wading depth of your vehicle should be in the owners manual and is likely to be quite modest - the height of the air intake is one issue (you suck water into your engine and when piston meets incompressible liquid, something has to give and it won’t be the water) but as Dogoak says unless you have breathers for various other components you are likely do do other expensive damage and if water gets into any of the boxes of electrickery that all modern vehicles have dotted around on them, big bills are likely to result.

Unless you are going looking for trouble, if you listen to weather forecasts and traffic warnings, in the UK, there is very little excuse for getting trapped by floodwater in a situation where you can’t turn around and go back the way you came or just wait till the water level drops. If the water is fast flowing then give it a miss.

Discretion is always the better part of valour and the pragmatic (cowardly? ;) ) way of tackling a flooded road is to know your own vehicle’s wading depth and let other vehicles tackle it until you see one that is smaller than yours pass successfully then try your luck.
 
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Broch

Full Member
Jan 18, 2009
2,723
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Mid Wales
I teach off-road and bad weather driving - usually to real 4x4 and what we call soft-roader drivers (4x4 Pandas, Kugas etc.).

Without being able to teach you proper techniques I will just say, unless you really have to, don't.

Depth isn't the real issue (a standard Defender is only 500mm BTW) - it's flow i.e. speed of water that causes real problems. The pressure on a body by a flow of fluid is "density x speed squared/2" so the force exerted is that times the square area being push. Normal cars, being lower to the ground, don't allow much water to flow underneath so get a high force pushing them. Add that to the fact they are lighter and it's not a very high depth/speed combination to sweep a standard car away.

Even rugged 4x4s are full of electronics so a fan belt and fan spinning around throws water everywhere and can quickly result in the engine stopping.
 

Broch

Full Member
Jan 18, 2009
2,723
1,939
Mid Wales
Generally it all depends on the height of your vehicle air intake and axle breather pipes.
There's been many a wannabe 4x4 poser who's fitted a high level air intake and not bothered with the breathers and have found out to their cost after fording!
In theory, for off road driving and deep fording its 2nd gear, low range, and about 10mph so you push a 'bow wave'.
We're no longer supposed to teach 'push a bow wave' because it causes bank erosion on rivers :) - however, in flood waters it's still the best techniques unless there's a vehicle coming the other way - in which case you flood them!
 

Tengu

Full Member
Jan 10, 2006
10,613
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Wiltshire
Ouch. I learned about driving in floods the hard way.

But, I am forever daring, and I love fords.

Plenty in Cornwall, often of very varying water levels, and not all have a measure...

The worse was the one I thought was a big puddle; turns out it was a DEEP big puddle.

I was lucky and I wont go that way again if its been raining.

If Im in a very sensible mood I will wade first to check depths and holes.

And yes, some of those fords have nasty holes.
 

Paul_B

Bushcrafter (boy, I've got a lot to say!)
Jul 14, 2008
4,044
454
Lancashire
Oh don't worry I am a flood coward. Round here most storms, certainly the names ones, result in flooding. Mostly, wait for your turn and claim the centre. You occasionally get idiots in SUVs or 4x4s who won't wait their turn to go the other way, cue water over the bonnet.

Usually I'm turning around if I can't see the ground through the water or if there's a strong flow to the water. Yesterday a few spots had a real flow to them but were low. A few had the water actually flowing from one side across the road but also bubbling up through the road surface. Limestone area just there and a lot of high water table springs around.

My vehicle is a Vauxhall vivaro swb van, new shape. I know the pre 1991 vivaros had very low intakes for the class but 1991 redesign it got raised a little. Still don't know if the van would have a higher water level than most normal cars, non SUVs. Higher clearance should mean it does.

As for defenders, I know just what they can cope with courtesy of days visiting road building sites with my civil engineer dad. One weekend site visit when nobody was around we took a detour to check out a cutting. My dad, who has had land rover off road driving courses, took it up a very steep slope up the side of the cutting. The issue was heavy rain, very steep slope, lots of mud and vertical manmade cutting cliff above and below our track. Let's just say the mud and water was flowing over the bonnet but the landy coped with it.

No idea how it was equipped. Don't even recall a snorkel but it would have been capable. He drove them where heavy earth moving kit went. Iirc 6 wheel drive, articulated bulk carriers with rear tractor sized tyres for example. Impressive driving anyway
 

Laurentius

Native
Aug 13, 2009
1,830
142
Knowhere
I teach off-road and bad weather driving - usually to real 4x4 and what we call soft-roader drivers (4x4 Pandas, Kugas etc.).

Without being able to teach you proper techniques I will just say, unless you really have to, don't.

Depth isn't the real issue (a standard Defender is only 500mm BTW) - it's flow i.e. speed of water that causes real problems. The pressure on a body by a flow of fluid is "density x speed squared/2" so the force exerted is that times the square area being push. Normal cars, being lower to the ground, don't allow much water to flow underneath so get a high force pushing them. Add that to the fact they are lighter and it's not a very high depth/speed combination to sweep a standard car away.

Even rugged 4x4s are full of electronics so a fan belt and fan spinning around throws water everywhere and can quickly result in the engine stopping.
Pretty good summary, not depth but the flow. I can remember years ago getting stuck in a flood the water being above the bottom of the door, and the electrics having conked out. I was pushed out by a Toyota Hilux diesel which romped through the same depth of water. A local sport in Kenilworth during times such as this is watching cars attempt to go through the ford at Abbey Fields. I have seen well equiped 4x4s with snorkels think better of it and turn back.
 

SCOMAN

Full Member
Dec 31, 2005
2,023
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Perthshire
I was previously a Flood Rescue Team member and Water Incident Commander. In short don't drive in flood water in a vehicle that has not been 'marinised' and you know it's limitations and through water you have not checked. Whilst the water may appear to be a few inches deep you don't know what's happening below the road surface. This could be undermined by water flow or in fact have already sunk or been washed away. There is no way of knowing without wading. You can only safely wade with a properly trained team with the right equipment.
Look up 'Road gives way after flooding' on YouTube there's hundreds of videos of examples. I can't emphasise enough the hazards of entering flood water on foot or in a car even a boat if you've not been trained to operate in that environment. It is not something trained teams do lightly. Anyone nipping through because it doesn't look that deep will put a number of people at risk if they have to come and rescue you.
The other downside of flood water, as anyone who has been flooded will know, this is not fresh drinkable river or rain water. It carries significant health hazards. In short an appeal; Stay away from seafronts when there's big storm waves and stay away from flood water if at all possible.
 

Paul_B

Bushcrafter (boy, I've got a lot to say!)
Jul 14, 2008
4,044
454
Lancashire
As a kayakers I know the power of even shallow water. I don't drive through floods without having confidence it's safe. Never if I can't see the road condition below. Usually it's in areas I've known to safely flood before. We get a lot of it round here so we're used to what's safe because we've experienced it before.

Road condition isn't guaranteed right enough but I learnt about floods and roads from a civil engineer involved in new builds and repairs. I learnt about geology from him and at university. We are not in an area known for sinkholes in the roads. The geology is stable and flooding is common without damage.

Nothing is guaranteed but an educated guess with good safety margins and common sense is as good as you can get. That and finding another way or preferably never being out in it in the first place.
 

santaman2000

M.A.B (Mad About Bushcraft)
Jan 15, 2011
16,218
804
63
Florida
Be advised: sinkholes are not the same as washouts. Floods rarely occur with sinkholes: and sinkholes never need floods or occur. Your house can disappear into a sinkhole during a dry period as the underground aquifer dries up and the ground collapses into it
 

Woody girl

Full Member
Mar 31, 2018
2,461
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Exmoor
Sinkholes are possible with flooding or just heavy rain. I can't find it now but after the last storm one swallowed half a garden somewhere or other.
We are on flood alert and it could flood all the way to Tiverton!
Could get cut off this weekend as we are bordered by two rivers. The barle and the exe.
I shan't be going out at all, as even the buses can get caught out. Twice I've been on a bus attempting to navigate floods and come to a halt . Those doors don't keep out the water at all!
Safest to stay at home. Plenty of things to do and lots of projects to get done . Ideal time to get on with them.
One thing I was taught about going through flood water is not to throttle off as it can suck water into the engine via the exhaust pipe. And try to stay on the high point of the road ie in the middle. Not always easy on most roads,
 
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Nomad64

Full Member
Nov 21, 2015
1,073
573
Just out of range
I think that these cars and vans were washed out of a carpark rather than failed attempts to ford the Wye but this is about ten miles from me but it gives a clear idea of what happens to vehicles in swiftly moving water.

https://www.theguardian.com/uk-news/video/2020/feb/17/storm-dennis-cars-swept-away-by-flooding-in-wales-video

Sadly, this lady was in a car that got stuck in floods and was swept away and drowned when she got out.

https://www.bbc.co.uk/news/uk-england-hereford-worcester-51539199

All a bit Biblical at the moment.
 

Insel Affen

Settler
Aug 27, 2014
525
83
York, N Yorks
Are people still taught to walk the route first? Not a great idea when it comes to rivers, but not unachievable either. It used to be a technique taught in the Army and was certainly taught for 'puddles' off road.
 
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