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dealing with annual flooding  RSS feed

 
paul wheaton
master steward
Posts: 22493
Location: missoula, montana (zone 4)
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It seems that for the last year I have seen a lot of properties with some serious flooding every year.  It seems challenging to even think about what to plant - what perennials survive that sort of thing. 

And then as I look around at these properties, I see that the real problem with the flooding is how it shifts the soil.  Sometimes taking the soil away from trees.

So I thought ....  it would be good if the soil were higher.  And ...  it seems that sometimes the water takes soil away and sometimes it leaves more soil behind. 

I tried to think about encouraging the water to leave soil behind.  After all, as the years pass, wouldn't there be more and more soil until the whole property would be higher?  And then the soil would be deeper.  And then floods would be nearly a non concern. 

So I thought about the idea of late in the fall, digging a sort of backwards ditch.  Leaving a short berm all the way around the property, except for, say, the driveway.  The important thing would be to have only one point that water could come in.  As long as there is not flow, then the water would come in and slowly leave later.  Because the soil leaves slowly, it should leave behind a lot of soil.


 
              
Posts: 133
Location: West Iowa
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Depends how big of area we are talking about.  If I had an area with water  sitting around for prolonged time period, I would just build a pond and be merry.  Cattails love moist areas and supposedly they are very useful.  Anything such as berms are a good idea to stop the rushing water and the momentum will be lost and the soil settles down.  Ponds after many years typically start filling in the shallow areas because of all the soil it stopped. 
 
Leah Sattler
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Flood plains can be awesome for growing things because of the deep rich soil that is deposited. sometimes your stuff will be wiped out though which is why flood plains are often used to grow annual crops. you might want to consult an engineer in the field. you don't want to end up creating flash flood problems by narrowing the access the water has to the property.
 
Susan Monroe
Posts: 1093
Location: Western WA
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That's why swales are so valuable.  Even terraced swales, if that's what they're called, narrower ones.

The higher soil is washed off to the lower levels, as things stand now, and then washed into the rivers (causing silt buildup), and the lighter humus is washed out to sea.

Anything that can slow the water down is good: rows of rocks, logs pinned down across the slopes, gabions to slow the water and collect debris, sowing ground cover plants with deep roots, like clover.

One of the problems is the nature of much of the soil around here.  I'm lucky, and live in a level, elevated area of sandy/rocky loam.  Much of western WA is clay, and that's the devil to work with, due to its propensity to flow when liquified.  But if you can prevent it from starting to move, that may be enough.

About twenty years ago, I read a small article about annual flooding in a residential yard.  The owner thought about it and decided what he needed was drainage.  So he bought a few pounds of earthworms and scattered them at dusk at the edge of his flooded area.  The next year, water didn't accumulate there.  It's the only time I've seen that suggestion.  Improving the soil would increase the earthworm population, which might improve drainage.  An idea, anyway.

And don't build in the flood plains.  Too late now, eh?

Sue
 
Steve Nicolini
Posts: 224
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Did he still have a healthy supply of earthworms the following year?

Wal Mart put up a store on the floodplains of the Upper Iowa river, just north of Decorah (my friends home town) and last year guess what happened.  Everyone went to Wal Mart to buy products that would get rid of all the damn water in their houses.  Thanks Wal Mart and Decorah city council.

Paul, you said let water in in one place.  Say you are on some land with no structures yet, just bought.  Would you set up gravity fed water ways and this berm ditch thing before building anything?

I think it would be cool to use that one inlet and branch off from it, maybe having waterways feeding storing tanks or ponds on the property.
 
Matt Ferrall
Posts: 555
Location: Western WA,usda zone 6/7,80inches of rain,250feet elevation
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Since I have lived on flood plains all my life,flood dynamics have always intrested me.My property gets added to on flood years while others get taken from.Someday Ill get taken from too but in the mean time,the land is cheap and fertile.Instead of leveling the land,I raised the high spots to build on and lowered the low spots to increase water storage capacity during a flood.All the farmers in my area who leveled their land to work it with a tractor,experience complete innundation while I am far above the water.Flood plain soils develop over time.As the water spreads out and slows down,the particulates settle out and raise the soil level.I dont want to create pinch points where flow is increased too much,nor do I want to block the waters ability to flow down its natural channels.My main goal is to slow the flow and get those particulates to settle out.As I clear plants I dont want from the forest,I pile them up in the old channels.Then I drop a tree or two of something I dont care for on top of the whole mess to lock it into place.When it floods,the water is still free to move but is slowed down.As an added benefit,all the twigs and branches that would have moved with the water get trapped in the brush pile sustaining it and adding to my biomass.
 
Devon Olsen
Posts: 1066
Location: SE Wyoming -zone 4
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interesting thread, a family member recently bought a property that happens to be part of a large draw, in this case, most if not all of the water shed that feeds the draw narrows out on his land before forming the main draw

after looking at the land i think that it is definately possible to make something wonderful with this property if i can manage to slow, spread and sink all of the water that comes through his land and build soil so that it actually retains water, as it stands now, it rained all night the day before i went to the property and the dirt was dry as bones when i got there so obvious retention issues there

the one concern that i have is that being right above a draw, that house placement may not work where i was thinking because of the big floods, so the question is, where might i be able to find a floodplain map for antelope hills, wy?
 
John Elliott
pollinator
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That might be a difficult search, Devon. You may have to settle for a good topographic map and a little analysis of where the natural catchments are.

Is there a lot of sand in the soil composition? Is that why it drains so quickly? If so, amending the soil with some clay might help. I had a magnolia tree that was just barely hanging in on some sandy soil. After I took to emptying the cat box in the mulch around it and upped the clay content of the soil, it really took off.
 
Devon Olsen
Posts: 1066
Location: SE Wyoming -zone 4
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yes i believe there may not be a whole lot of clay on the land, i have yet to do a soil compostion test though, ill do that the next time i have an afternoon and a couple of empty mason jars so i can test a few of the key locations that i want to play with

but that cat litter bit is definitely interesting that it only takes a bit of cat litter to make the difference
there is a clay company around here that i dont know much about but i like their sign so i may contact them if i need a large amount of clay...
 
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