Flood prevention

Sometimes low tech is the best answer.

Dikes and windmills are proven technology that have been used in places like The Netherlands for literally centuries.

Hi. I have also seen a similar situation and I pass on some words of wisdom from a hydrologist friend of mine who has since passed away. A couple of Quotes of his. If possible. 1/Drain water, never contain. (Reason:- Nature will break down everything Dikes, Levees etc.given the opportunity.) 2/ Use water to create its own barriers. (Reason:- Water flowing upon itself will not destroy water.) He had shown photos of a location in India where he had used diversion channels in an isosole triangle splitting the water from upstream and either side of the township to create a lineal flow of 'rolling back on its self' water on the river which flowed either side of the town during flood times. By using a simple ditch with a almost vertical rock pitched face on the town side of the ditches to channel the water along the channel but with sufficient cross current toward the township side to create a 'roll back wave' about a metre or so higher than the water would normally be without the channel and rock wall. The effect was the water flowed much faster along the channels and out to sea such that it increased the water volume by more than 30%. I thought he was ingenious to say the least. What ever you do, seek good guidance from a recognised Hydrologist and as a previous respondant suggested, it is many times the simplist methods that work best. Best of luck in your endeavours.

Hello tecmate,

That arrangement in India sounds interetsing. I am busy now but am sending this in to 'mark' the thread to read later. Can you tell me where the Towns are you mention please?

Take care..............

Alas, I only know that it was in the early 1960s when Singhi was assisting with flood mitigation works near my home town here in Australia. He had many photos of flood prone lands in his home area of India near the south west coast. As I do not have reference to his township and I could not pronounce it anyway, he said it was a common practice. We did a lot of armour rock protection works along the Herbert River and also along the sea front around my home town. I used his philosophies to create groynes to re-create and reclaim eroded sands from the sea shore line and also to create wave breakup surfaces to dissipate wave actions on the foreshores. In the river sections of the protection works, it created a wave height in places higher than 8 ft, to the best estimates we had, without breaking fully over the river banks. Singhi also showed me how to build a highway over boggy marsh and mangrove swamp lands using the simplist methods of explosives in rainwater down pipes buried vertically in a pattern and the carriageway filled with 20 metres of sand. When the explosives were activated, the mud was pushed sideways out from under the sand burden and the sand sank to replace the mud. The highway built on top has not required rectification works since 1962. It is a pity that all these innovative and simple methods have not been collated into a library for the younger generation to look back on.

Hello tecmate,

I thank you for the reply post, you are very kind, thank you.

Your friend certainly sounds like he had talent! Building a road like that is pretty clever. And it is quicker and, does not disturb the boggy land too much, as would be the case with heavy tractors etc. It would enable the subterranean vegetation to bond and knit webs as they normally do. Ok so they way it was done was violent but, the basic construction of the bog and it's interweaving flora channels were mostly allowed to stay together.......just, shifted over a few yards that's all?

I am fascinated by the way such people look at an area and think "that is do-able"! And then get stuck in 'on the job' as it were, to build whatever the project is. Using explosive in that way, when the ground is going to be disturbed anyway, is worth a try and that word-of-mouth way of doing things which are known to work and be successful, you often find in the 'back-woods' where things have to be done and if say the explosive works, then fine. If it doesn't, then you would not be recounting it to me, so it has to be worth trying. And of course it would save a whole lot of money and time?

I saw a flood prevention that you would not recognise as such. It was in a little town I went to in North Spain. The place had a small range of mountains on one side and the sea on the other. The Town was about 4 miles, 6.4 Km from the start of the rise of these mountains. What looked like a road was built from the flood plain to the sea with walls several metres thick. When the weather was nice the channel which was only three Metres below parts of the Town, in other areas it was level with the terrain. In the summer it was used as a road only by the locals.. And a layer of heavy aggregate and sand was used to keep up the places it wwhich washed away by the floods. It had simple walk ways over it and maybe two places cars and light trucks could cross.

It appeared more like a 'lane' in the 'English' sense with the walls as the 'banks' or as in Cornwall the banks would be in stone. It was made from local stone and, because it was not huge, being just large enough to take the water from the mountains, and was build from the surrounding natural rock and shale it was not an eyesore as a concrete gully would be.

I was there just two weeks and they had been using part of it as a temp' car park, but when the rain came the locals moved their cars and truck onto normal roads, the water came flooding down and was allowed to flow across the beach. It was good design because it blended in, and being used as a local road and often times a car park, it was used year round.

I will see if I can recall the name and get some pictures.

Take care and thanks once again for the reply post...........

Love that explosive solution. Very innovative.

Not having hardly any information to go on I can only make some suggestions. If you fight mother nature you will only win most of the time. The trick is to use it to your advantage.

Given the rivers will flood. When it does the town is in the way. Raise the town, move the town, dam the rivers to move the flooding up stream (if possible)

What is frequency of the floods, hight, topography, etc. Some cultures live with flooding for a good portion of the year. Their water is slow in flood stage.

It is past my bed time so (un)til then

Brad

Hi!

I am sorry to note the damage caused by floods due to High Tides in the water bodies surrounding your town.

It is the geographic situation of the town and its topography that must be causing recurring flooding. This kind of a situation calls for a thorough technical study in a hydraulically simulated model of the Town, its surroundings and the proximity of the sea. I think it is the Municipal Administration of the Town that should initiate permanent steps in this direction since it concerns the safety of all the Town's inhabitants and their properties. Solutions can be found by carrying out Engineering Model Studies - 2-Dimensional Numerical Studies or 3-Dimensional Physical Hydraulic Scale Model Studies in reputed Hydraulic Laboratories located world-wide, notably in Holland, Denmark, England and the United States of America.

Needless to say, there have to be sincere and committed efforts to first of all formulate the problem in a mathematical manner, pose it to a rigorous mathematical modelling as stated above and analyse the results thereof, formulate permanent protective measures together with the costing thereof and implement the same in all seriousness well before the occurrence of the next floods...

I suppose I could provide some leads...?

You could be describing New Orleans; or maybe a place like Bangladesh (except for the loss amount). This sounds like a problem for "exactly" engineers. But just out of curiosity, what is the approximate location? East coast or West? Was this flooding in conjunction with a weather event? Such as cyclone? Perhaps a bit of river diversion could be the best solution...even if not a perfect or permanent solution. In a situation and locality like you describe, the only viable way might be to provide a lower area of very large area to impound water that would otherwise flood your town long enough for the water level to subside to the sea. .

The simplest, low tech solutions are likely to be the best.

1. Deepen and widen the river channel as much as possible.

2. Straighten the flow path past the town as much as you can.

3. Levee banks around the town with self closing valves on the drains provide for the occasions when you have too much water to handle and it would otherwise flood.

Don't skimp on the base width of your levee banks as this makes them more prone to failure.

If you are in a high rainfall area, provide plenty of drainage through your banks to avoid local flooding from retained rain.

You mention that the last flooding was the worst ever.

Check upstream conditions. Substantial land clearing will increase the rate of runoff into your river and increase peak flood level.

Works upstream that straighten the river will have a similar effect.

If it is feasible, arrange an area near the town where excess water can temporarily store. This can reduce your flood peak.

Reasonable estimates can be made of the effect of all of these measures.

Depending on your local situation, much of the above may not be applicable, but hopefully some of it will help.

Good luck

New Orleans was formerly a impressive example of low cost natural levee construction and management. A century or so before the current debacle was designed and built the intrinsic problems with this delta town were obvious to the residents.

Designs were called for. Although it was a hot battle a innovative design using woven reed mats to stabilize dredging materials was chosen for implementation. The construction went quickly and well. The project was completed under budget.

The flow capacity through the channels had been artfully designed so that the natural flow was sufficient to keep the channels clear without dredging.

The system lasted so long with little or no maintenance that most residents were unaware that there was a system in place when progress in the art of river boat building and barge traffic mandated that a new system with deeper channels be developed.

That system used concrete and failed miserably within a short period of time leading to the construction of the system that just failed recently.

If you are looking for a natural system that self-maintains and lasts consider the historic one originally developed for New Orleans. In comparison to its successors it was a marvel of hydraulic engineering.

I could not find a description of this historic natural materials engineering project online. I think that I read about it in American Heritage magazine, although it may have been in Scientific American.

Sincerely,

Mr. Gee

Woven materials: what a fascinating idea. Given the weaving and basket making traditions in Fiji, it should be possible to find expert knowledge of the most suitable local materials.

In Europe, red alder Alnus glutinosa has been used in flood prone areas because it has the property of not decaying when under water: Venice for example, is built on alder pilings. Something with similar qualities may be present in the local flora.

On raising the town you could place it on long piers say 10 foot high, 10 to 20 foot apart running under the town so the flood waters pass underneath. Your needs are unique so here is a link on how high the piers raise the water.

http://www.utexas.edu/research/ctr/pdf_reports/1805_S.pdf

Just an Idea

Brad

GA UV,

Hard to know exactly what he's dealing with but that's a good readable report even for a bonehead like me.

Hi , I am geologist and geotechnition , I found your question very interesting , First I want to know location of your town , I think it must be in India and more precisely in southern India , where the rivers are having shorter runoff and having large catchment area with heavy rains during monsoon . I hope your effort for the noble cause will yield great result .

thank you all for the most valuable comments.

my town is located in the South Pacific nation of Fiji. given our status as a developing nation, as i said before, we only have the leisure of low cost tech. the floods were a result of two low pressure systems that passed over Fiji within a space of few days. we had never seen nor expected such behavior from mother nature.

i hope to write to the local council using your comments and some research in the hope that it may better our defenses against such devastation in future.

RAM

Thank you Ram44, for the information.

What you need is a low cost, simple solution in execution. One that can be implemented constantly.

What gets me is I missed the news of this happening in Fiji.

Sounds like you had your hundred year flood. That has been happening a lot in the world lately.

Brad

Very sorry to hear of this also.

I lived in Suva many years ago. We used to take our horses bareback and swim with them in the sea. It was very flat in that area, shallow for a horse a good way out before it would be deep enough for them to swim.

A very different place was Matai-Suva. We went body surfing there. It was deep very near the shore and there was a strong undertow. It seemed that the river flow had hollowed out a deep channel.

Thinking about your problems, I couldn't help thinking how different these two places are in terms of hydrodynamics. I hope there is something practical that can be done for your situation that will not be too costly. Best of luck.

Hey Ram44,

Get a copy of "Rising Tide: The Great Mississippi Flood of 1927 and How It Changed America", by John M. Barry. It's a great read about the history of flood control and the great flood. You'll be more informed and ready to spring into specific issues after taking in the book. It's a great read.

I'm curious about the "head cut" phenomonon. It's when a river starts to dig a deep channel and erode steep banks. I think it's a result of dredging and levys, and I want to find how to "fix" it.