DIY Floodwall

The concept of "ground water level" is meaningless in times of flood.

Take the wall below earth level and then bank earth up either side of it ( the earth removed from your drainage ditch will form the bank).

This may give some ideas.

They will need scaling down, but should give you some sound ideas.

Del

What caused the 12" rise and will it happen again?

Wood is a poor choice for water exposure. Not too durable and it floats. Well anchored steel plate or prefabbed concrete sections are better choices, if the lake is never drained down for dock and sea wall work.

As Del said, ground water level at the lake is the same as lake level, so a foot down is probably enough.

Does it ever freeze where you are?

Thank you, Lyn. Some in the community here blame it on the 12" drainage culvert that drains the (small, 200 acres) lake, we believe it was plugged with trash for a while. I'm dubious this had much effect, Minnesota had major flooding this June, all over the Minneapolis area, long ways from our little corner.

Happen again? We've had several once-in-100 years weather events in recent years, so who knows. I'd rather be prepared. As to freezing, we get -25 F regularly. Treated wood should last a while, the water exposure was only for 2 weeks or so.

Most building codes will not allow PT wood in contact with the ground and require concrete bases for decks let alone building water barriers. There is a reason. The treated wood will rot in damp ground. It may be that by the time you have another 21 year event, the wood barrier will be useless. Further, the wood can shrink and crack and also render the barrier useless.

Kevinm,

Be careful--there are at least two different concentrations of chemical used in pressure treated lumber. The higher level is fully compliant with code requirements for direct ground contact. It is even described as a material for building foundations.

--John M.

Ha, I send an answer to your concerns but it disappeared when I looked again. I posted this link. The concerns are over the connecting materials and there is an environmental issue with the use of PT material and exposure to water such as a lake. The preservative material will leach out. I am of the opinion that it should not be used but I am living in an area that will not allow PT material for boat houses, rafts, decks, docks, or any structure exposed to surface water. I am also of the opinion that an on site engineer may provide an appropriate solution and take into considerations the permits required. Many if not most jurisdictions require permits to assure that someone is not redirecting water and create another problem for someone else.

That "little corner" wouldn't be the southwest corner would it? We have a little place 31 miles NE of Brookings, SD. About 2-3 miles from the border.

That blocked culvert might do it. There's no shortage of water in Minn. and the weather is getting crazy everywhere.

Maybe the community would find it less expensive to pay someone (or ask the county) to check and keep it clear.

Good luck neighbor!

It sounds like you may have to do a little more design work. Are you eligible for flood insurance? Most insurance companies will want a 100 year flood design. Some homeowners in USA may be eligible for national insurance. I would check with your insurance company (most do not cover flooding) and the local planning board. They may have good information and that could be incorporated in your design and keep insurance companies happy. Twelve inches just sound too close to not be careful. That $14,100 estimate may seem high but if you get caught without adequate coverage and do get flooded that will look like a bargain. Just be careful about your approach to this problem.

It might be cheaper to just raise the house when you take into account the flood insurance cost added to the floodwall, pumps and other assorted costs all for something that's not foolproof....by spending the same amount on raising the house as you did building the berm, you still may realize a substantial yearly savings on flood insurance cost....

http://heusserhousemovers.com/

In terms of size... think of a number and then double it.
Too big isn't a problem... too small and it's a waste of money.
Del

I gave that a GA, as building it also sounds like an excuse for a barbie.

Del

Could you submit a sketch for perusal..?

Great picture! Nice looking wall, perfect for a short term dam.....

The curve is a good idea too, as long as it's the right way round

Del

Good point, though if suitably built, even a straight wall should handle a few days of pressure....though curved (correctly) is still a better move as you said.

If it was me, I would never have bought/built a house anywhere near water (vertically that is! I live on a hill well over 30 ft above the surrounding landscape for hundreds of miles), but assuming I had the same problem as you, then I would build a dam myself!

Digging out foundations at least 3 foot deep and 3 foot wide over the whole length pf the affected area (80ft). Taking the point of the recent highest flood as the place to build. The next flood could be even higher....maybe...

Set in place scaffold poles of around 10 feet long, every few feet, vertically in the earth, almost reaching the top of the final wall. Putting a removable cap on one or two, which will allow you to clean them out and use them to keep a watch on ground water levels with a simple pole.....an old wood auger that just fits inside, welded to a long T-bar, will remove all earth forced in.

Plenty of rebar along its length.

Also Rebar to be left sticking out of the foundations between the scaffold poles (depending upon bricks to be used) to key the wall to the concrete base. Place bricks at each level at 90° to the wall to hold inner and outer layers to each other firmly...

Plenty of rebar and steel nets need to be used (expensive!) to make sure that there would be as good as no cracking and keeping the concrete foundations wet for weeks to promote proper setting at maximum strength. If very dry weather, then covering with plastic to stop drying out may be needed.... Really slow curing gives best structural strength.

When that is complete, build a wall, of at least two brick thickness around that rebar, make it as attractive as possible to please the ladies!!! Also at least 3 foot high. If higher, make it 3 bricks thick and key in bricks at 90° to the run of the wall....maybe with pockets for certain types of plants that like dry mountain sides! For the times when the water is NOT high!! Rebar in wall, or nets cut to fit unseen in the mortar levels....every level....

I know tend to "over" engineer such building and up to now, everything I have made has done its job and has never needs repairing....but do not under estimate the water pressures the wall may get...doing it once and right!!

As to type of brick, I would myself use attractive house bricks, ones probably NOT designed to be part of a permanent dam, but I would assume that they would hold out the water for a day or two at least, but look far better......but the bricks used must be "fired" ones to make sure they do not soften under water....

Adding certain water based glues to the mortar, can reduce water ingress. Whether this will be needed, only you can judge....

Adding a sump to the dry side to allow easy pumping out of any water that spills over may also be an option....assuming its say wind driven waves and not a serious "waterfall" only....

Doing the work properly, planning in advance and talking to your house insurers FIRST! may in fact reduce your insurance costs...and save a bit....

I know that I over do building strength, thats just me.....but knowing certain people here on CR4, they will "jump" on that as being WRONG!

Of course it will be the ones that have never built anything unusual themselves and had little or no experience......wait up!!

Though I have never built such a dam either, but thats about how I would do it if needed....

Just a comment on two things
1. Insurance companies and...

2. The concept of a hundred year flood design.

Both are F'ing useless.
1. Insurance companies will just run out on you (look at the flood along the East coast in the New York area... claims still not honoured I believe...(That's the beauty of capitalism... if you have enough you can can just screw the other guy)
2. Statistically, the once in 100 years is just as likely to be tomorrow as any other day in the next century.

Del
(call me an old cynic if you like)

Your "2. Statistically..." while correct is misleading. It is simply a basis for design, there is no expectation that it will actually occur in the lifetime of the project, or if it does occur, that it will only occur once during that lifetime.

All bets are off if the thousand year storm moves in!

It's only a sensible basis for a design if you take the height of the 100year storm and double it!

I'm glad you agree on #1

Del

Or, keep the drain/overflow pipe clear. ;>)

Thanks to whoever for the GA's earlier.

On the "one in a hundred" issue, in Aus, the Geo grid is broken into small areas (around 1km square I believe) and each and every square has nominated attirbutes for rainfall, temperature, evaporation, wind speed and so on. The media reports "A one in a hundred" event if any one of those squares exceeds that situation.

Thus almost each year we hear of one in a hundred floods, one in a hundred dry spells, one in a hundred hot weather events and so on. I suppose they have to make the news somehow.

It always interested me to some extent because the old family farm was made up of 24 of those sections, plus we had permit to occupy another 12, so a one in a hundred event happened almost every 3 years somewhere on our property.

" ... so a one in a hundred event happened almost every 3 years somewhere on our property."
Statistics, politicians and accountants, don't we just love 'em eh?Del

http://www.aquadam.net/RefMaterials/AquaDam%20Applications.pdf

You have a few options available to you.

I would recommend a cut-off wall, either consisting of a slurry Bentonite Clay or a thin concrete wall.

With either type cut-off wall, you should extend it down to the Frost Depth of your area for several reasons: (1) To prevent frost heave of the wall, and (2) To minimize hydraulic "piping" of the elevated lake water from flowing under the wall and your intended dry area and house behind the wall. If you have sandy soils in your vicinity, coupled with frequent -25F degree temperatures, the frost depth may reach down in excess of 5 or 6 or 7 feet or more below grade. Check with your local Code Enforcement Officer (or the water dept.) to see what the typical frost penetration depth is for your area.

You may want to extend the top of the cut-off wall 12" or 24" above the finish floor elevation of your house (basement of First Floor?) in the event that the lake level rises again for whatever reason...it is quite possible to receive precipitation greater than a 100-year event. that should give you enough "Freeboard", just in case of future flooding.

The beauty of having a clay cut-off wall is that once it become wet it swells and seals up any drying cracks in it's mass, effectively holding back the elevated water level. Naturally, you're going to have to berm up the soil along the length of the cut-off wall to achieve the desired top of wall elevation. Do not use a clay-rich soil, because it will not do a proper job of retaining the water.....useless. I wouldn't use anything less than a 6-inch thick clay wall.

You could install a concrete cut-off wall, but that will involve installing reinforcement steel (rebar) horizontally and vertically to minimize concrete shrinkage cracking. I would suggest at least a 4-inch thick wall as a minimum. Any cracks, which tend to grow and open up with concrete age) in the wall negate it's effectiveness and will allow flood water to migrate through the wall. The main problem with a reinforced concrete wall is the principal cost, and future repairs and maintenance.

Another alternative is to install a corrugated fiberglass or other UV stabilized plastic (if exposed to sunlight). Depth and top elevation being the same as described above. Make sure the edges of each sheet are overlapped and screwed together w/ SS deck screws. To make the joints waterproof I would suggest using a Polysulfide sealant (available in chalking tubes or cans) between the sheets, or use ribbons of SYNKO-FLEX® WATERSTOP between the sheet at the overlaps. This may be the most economical and easiest to construct method available to you.

As a measure of last resort, you may have to "jackup" the house to the required elevation to satisfy your insurance carrier or the National Flood Insurance guidelines.

I would not use brick or concrete block walls, as they can be porous and flood waters can migrate through them or their joints.

If you do install a cut-off wall of any sort, make sure you have adequate positive drainage of the area between the wall and the house if eliminate localized flooding due to storms and snow melt. BUT, under no circumstances pass a drainage pipe originating from that drainage impoundment area THROUGH the cut-off wall, otherwise the flood waters will find it's way back into the area you wish to keep dry.

Another option following on from captain Moosies idea is to use steel sheet piles which come interlocking connections. connections can be seal with liquid bitumen, pitch or something similar. Can be expensive but that will be dependant on the length and thickness of the piles.

A sump will be required to pump out rainwater etc which fall behind it or depending on levels an outfall through the piles with a NRV valve on it..

Easily clad the structure too with stone or brick. I saw a lovely job done where the piles were clad with stone and backfilled with clay and used as a raised flower bed

Steel and Aluminum sheet piling is extremely expensive.

Hopefully, the soil isn't bony with cobbles or there's shallow bedrock/Ledgerock.

The problem I see with installing any barrier without knowing the site specifics of soils and bedrock, is that the piezometric surface will be the level of the lake. If the water is higher than the land during periods of flooding and the soil is loaded with hydraulic connections with sand or fractures in the bedrock, the water will find the level by flowing through such conduits. If the soil is sandy or the bedrock is shallow and highly weathered a dam may be an exercise in futility in many circumstances. I would also warn that in many jurisdictions including where I live, a permit is required to install these water "dams". These permits will require some knowledge of the conditions and assure that the barrier simply does not redirect water from one property to the next. An engineered solution is best approach even if the costs seem higher. Putting a dollar value on the solution that is BAT is difficult but may be priceless.

As usual you provide good food for thought and I enjoy your responses.

Hi Captain- thank you for the reasonable-sounding suggestions. Winter is here, and I'm talking to landscape contractors for construction next spring. They seem willing, but not all that knowledgeable ("what is bentonite clay?").

Can you possibly direct me towards more info on cut-off walls? (C E Rickard's chapter 9 was quite helpful). Thank you htesto

Here's some information regarding Bentonite clay. I hope this answers your questions.

You could simply Google Search "cut-off walls". But I think you'd be better served by talking to a local Professional Engineer (Civil Engineer) for advice. The reason being that there are many types of cutoff walls that can be constructed to hold back flood waters.

http://sturgismaterials.com/products-view/sodium-bentonite/

Also, please remember that your neighbours properties could become the bypass around the ends of your walls!!

Need to protect from what could flow around the ends of whatever you choose to do.