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Designing for flooding

 
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I'm trying to get some ideas down on a base map for our 1 acre homestead. We're bordered on our southern boundary by a river that floods periodically, with run off from farmland further up river, as it rushes to its final destination - the Atlantic about 2 miles away.

Its mainly just grass at the moment, relatively level, slightly acidic with some very sandy banks and willows here and there. For context:



IMG_20180903_174540.jpg
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Our driveway, far side from the river in September
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River levels in 'normal' weather
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Flood impression this winter, just on the river bank where a pond seems to want to be.
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More flooding this winter, this I am told is about average levels, but has been higher.
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River levels at higher water
 
Mj Lacey
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The 100 year event, has caused the house (on the right side of the bank / flood defence in the first image) to be under 4 ft of water in 1999. The defences were increased after this and in theory shouldn't breach now unless there is some sort of apocalyptic event (...).

But beyond this, a few inches of water after high rain events is normal during the winter. We share a piece of land with our neighbour who has an annual raised bed circa 1.5ft high - this hasn't ever been near to breached (wasn't there in 99), so I'm confident of we're shouldn't be inundated by more than this.

I'm struggling for ideas or resources however that would help with these small surges of energy that come onto the site just a couple of times a year. I can't possibly expect to contain a river surging past my property - it is just too much water, but I am keen to try and give any earthworks or planting here the best chance of success.

I cannot find here or elsewhere online anyone dealing with my situation surprisingly. I know there was a video of Geoff Lawton at a property on a riverbank in I think Mississippi, but it no longer seems to exist online. Some locally have talked about chinampas, this is an interesting idea but I'm worried I'll do more harm than good with this sort of earthworks and have no idea how to estimate the level of elevation change on the landscape necessary to make the system resilient. Designing for the 100 year event would mean digging some significant trenches!

I can see a forest garden, perennial system here, rather than an annual one but wondering if the hive mind has any view on how to manage these few but not insignificant pulses annually, along with ensuring that any earthworks are useful and worth doing.

Thanks all!


 
Mj Lacey
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Bumping in case anyone has a view, although maybe I've posted in the wrong sub?
 
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Here's that video:  https://vimeo.com/168769028

I wanted it to have a lot more detail about the structures they built to deflect and slow the floodwater.  It looks like they are very strong constructions of wood and/or wire and stone.
 
Mj Lacey
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Tyler Ludens wrote:Here's that video:  https://vimeo.com/168769028

I wanted it to have a lot more detail about the structures they built to deflect and slow the floodwater.  It looks like they are very strong constructions of wood and/or wire and stone.



Thats great to see - thanks Tyler! My flooding is probably not quite so severe, but some ideas to ponder for sure.
 
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From my experience, I question the practicality of keeping such a small block from flooding without tons of earthworks.
Why buy a block that floods and then try to harness nature/
I get flooding at part of my farm, and its annoying if it goes higher than I have allowed for, but to stop that would be impractical.
I work around the flood area, but I have 20 acres, so its possible.
Can you just enjoy the block for what it is, put good gravel on the roads, berms to deflect running water from your house or shed and let nature deal with the rest.
Your neighbours works may in fact impact on your place by pushing flood waters to you.
Banks, flood waters and neighbours can be an explosive misx
 
Tyler Ludens
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I don't think the idea is to keep it from flooding.  I think the idea is to try to prevent the flooding from causing damage to structures and gardens.

 
John C Daley
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OK, I am interested to see a solution. That video of the flat farm in a flood plain was good
 
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If your neighbours have similar problems perhaps you could club together and have the river dredged? It sounds to me like it could well be topsoil runoff from higher up that is causing your problem so hauling up the rich silt from the riverbed and using it to raise the level of your land could prove a win/win.
Also I would be curious to hear what your waterside plantings look like. Willows are indeed great for situations like these and as you do some research there are probably other trees that would grow practically in the water if given a chance. Because while a sudden flood is dangerous it seems to me your deeper problem is damp ground which is never healthy for humans. Eucalyptus is a terrible invader here in our dry country but I have heard that parts of Australia would be uninhabitable without it.
 
John C Daley
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Dredging rivers has been shown to be the worst method of dealing with floods. The video is very good, it explains that by using berms or walls to divert the
flowing water away from where it can do damage, and letting still water just hang around, the destructive elements of floods can be addressed.
Rushing water has a lot of power, still water has little.
Sure having things inundated even if the water is  still, is not helpful.
Willows etc will hold the bank  against erosion up to a point, but flooding itself is often made worse by those upstream dredging etc to get the water away quicker.
By holding water back and letting it slowly resede is the natural and safest way to deal with floods.
 
Mj Lacey
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Natasha Abrahams wrote:If your neighbours have similar problems perhaps you could club together and have the river dredged? It sounds to me like it could well be topsoil runoff from higher up that is causing your problem so hauling up the rich silt from the riverbed and using it to raise the level of your land could prove a win/win.
Also I would be curious to hear what your waterside plantings look like. Willows are indeed great for situations like these and as you do some research there are probably other trees that would grow practically in the water if given a chance. Because while a sudden flood is dangerous it seems to me your deeper problem is damp ground which is never healthy for humans. Eucalyptus is a terrible invader here in our dry country but I have heard that parts of Australia would be uninhabitable without it.



Unfortunately our boundary is the river bank, so we have no rights to do anything in the river itself. In truth, my situation is unlikely to get anywhere near as severe as that depicted in the video, but the principles stand nonetheless.

I get the sense that some sort of 'on current' shallow swales could be a viable answer - albeit an intensive one given the volume of organic matter that would be necessary to make meaningful impact. By on current I mean creating channels that run parallel to the river, which is obviously going to be roughly on contour too. Planting options then would be increased and indeed anything planted at the top of these swales may have longer to establish, so long as a major flood event doesn't scupper that.
 
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