Retaining Wall along small creek

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Old 06-26-10, 09:04 AM
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Retaining Wall along small creek

I want to put a retaining wall along my small creek, it's about 3 feet from top of ground to bottom of creek along bank, creek runs about a 4" pipe worth of freeflow unless we have a large rain, then it picks up. It's maybe 8 ft across.

I'd like to put in these 8 x 18 x 12 interlocking blocks. I tried this before with a crush stone base, but it looks like the water was able to wash the stone when it flooded, and walls started to fall.

Can I not do it again, with a concrete base, putting in 12" of crushed stone behind the block with a drainage pipe behind it. If i stack 4 stones high (32"), do i pour like a 4" deep foundation 12" wide, will this do the trick?....thanks for any help.....Dan
 
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Old 06-26-10, 10:03 AM
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I'm not an expert on this, but you may need to put rip rap of some kind at the base of the wall to prevent that scouring. I can imagine that high velocity flows would still be able to undermine that concrete base.

This could be helpful: http://rds.yahoo.com/_ylt=A0geulaIJS...lood_walls.pdf
 
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Old 06-26-10, 12:52 PM
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I would probably put rocks below the concrete to would make it more difficult for scouring.
 
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Old 06-26-10, 04:42 PM
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Hi Dan,

The main issue you need to address is horizontal hydrostatic pressure on the wall during periods of heavy rain. The conditions of the creek you mention indicates substantial water draining towards the creek, and this wall of water coming from your property may produce enormous pressure which could cause the wall to buckle or collapse. When the creek swells from a 4” flow to an 8’ spread, its not clear how much water is coming from upstream sources vs. how much water is coming from direction of your land behind the wall . . . that’s a judgment call, but if you have a steeply sloped property, there is going to be substantial weight from water that is out of sight but trying to move underground to the creek. Another issue is how fast the water is moving down this creek during heavy storm events as that could cause erosion and undermine your footing.

Your wall is not very tall so the hydrostatic pressure is far less than what it would be if it were substantially taller. The interlocking brick will likely act to impede flow whereas large boulders would allow the water to be released quicker. Here in S. FL we have many retaining walls of all types that range from sea walls to lake retaining walls, both of which use construction methods that can go far beyond what you need. In our naturalized areas with short embankments, the preferred technique is placing several layers of large boulders on a sloped bank (a layer of erosion cloth first laid down) allowing the water to percolate through the boulders.

The drainage pipe you refer to needs to be carefully considered. If installed correctly, it could help relieve some of the hydrostatic pressure . . . installed incorrectly, it may not be effective. For example, the number of drain pipes will help to equalize the pressure across the wall if roughly dispersing it equally . . . one pipe at one end of wall may do little to relieve pressure at opposite end (probably an exaggeration relative to what you’re planning but trying to make a point). The other issue is whether the drainage system may have discharge pipes say at half-height of wall with others at bottom . . . if the storm water must permeate all the way though soil to reach a bottom drain pipe(s), then the peak hydrostatic pressure on the wall will not be relieved until the water moving toward this creek begins to recede and given time to percolate through soil. Lastly, draining to front side vs. back side of wall will make a tremendous difference.

In terms of what to do . . . if the retaining wall was say only 15 ft. long and involved a few hundred $ of investment, then I would wing-it but still be thoughtful about how I constructed it. If it was 100 ft., and representing 1,000’s of $ of investment, I might spring a hundred or so bucks to have a seasoned pro consult me about proper way to brace/support wall. I would also scout out that creek, or something comparable to it, to see if I could find a retaining wall similar to what I was planning to build . . . I would be looking for something obviously standing for awhile, and trying to see how it was constructed . . . I wouldn’t hesitate to talk w/ owner to see if that discussion might be helpful. Lastly, identify mfg. of your interlocking blocks to see if you can talk w/ a technical specialist . . . doubtful that person will go out far on a limb w/o knowing site conditions, especially if terrain is steeply sloped . . . but should be able to advise the type of load the block is engineered to handle, and possible methods to use to beef-up its capability.

These links may be helpful in generating ideas YouTube - Retaining Wall Failure Caused by Water {there are numerous other videos by this retaining wall specialist}; Retaining wall - Wikipedia, the free encyclopedia.
 
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Old 03-28-11, 07:31 PM
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Creek erosion, seeking solutions

Hi Folks,
Just joined up and am seeking solutions/input to a pretty serious erosion problem along a creek at the bottom of my small property in Costa Rica. I have a vertical bank approx 12 ft high alongside a creek that changes from a knee high stream in the dry season to a raging river when the heavy tropical rains start. The eroding bank is only about 8 feet from a large cement patio which is in danger of collapsing should this erosion continue. The area in question is at the apex of an s-bend or oxbow in the creek. At the peak of last years rains the creek rose as much as 8 or 9 feet, yikes! I am proposing building a cement and river rock retaining wall with extemsive rebar for structural support. This wall needs to be at least 6 ft tall, maybe 8 feet to really protect the vulnerable area. Am also considering planting bamboo behind the retaining wall. As well as damage from the rising creek the entire property slopes down towards the creek and the vertical wall produces alot of water.
Any suggestions, recommendations etc most welcome! Muchas Gracias
 
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Old 03-29-11, 08:50 PM
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someguy052, Autumn,

WHOA!!!

A retaining wall is one thing. Adding the creek to the mix changes EVERYTHING!!!

In either case, it needs to be engineered. That will include testing of the soil involved as well as just how much water flow is involved AT THE HIGH WATER MARK. You don't care what the flow is when there is none or very little. You want the wall to deal with it when the creek is flowing at its MAX.

Your issues are beyond DIY, and your questions are WAY beyond the scope of a DIY forum.
 
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Old 03-30-11, 03:53 AM
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I agree with Mike. And woe be unto you if you are planning this on footwaters of any National Forest. Drainage from headwaters are controlled by your state EPD. You can't come within 25' of a stream and 50' from a stream with trout in it, so check your local, state and Federal regulations regarding the creek. Where we live, we need permission from the government (never get it) or from the TVA to modify land around waterways.
 
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Old 03-30-11, 07:00 AM
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Hola Autumn. Where is your place in CR? Do you have any pictures you can post? How much of the property along the creek do you own or can modify? I'm asking because controlling a creek in some regions of CR is a totally different problem than many people in the US understand. I spend most of my time in Guanacaste province and around the north end of Lake Arenal. The rainfall, terrain & soil can vary dramatically between locations just a few miles apart. It sounds like you are in a difficult location. The outer edge of an oxbow receives the highest velocity flow and a lot of erosion.

Without seeing your location I'm thinking large rocks in the outer rim of the oxbow to slow the flow and try to force the current more to the center and away from your property. I've seen a lot of retaining walls fail in CR when the creek undermines the foundation or the soil behind the wall becomes saturated and just pushes the wall over (land slide). The rainfall in some areas of CR are off the chart compared to the US. We may get the hurricane volume heavy rains once in a while but not as a regular occurrence that keeps the soil saturated. The rainy season late last year in CR was really bad. There were more washed out roads and failed retaining walls than I can count.
 
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Old 04-01-11, 09:44 AM
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Hola Dane,
Thanks for your response. Things in CR are DEFINITELY different than North America. I just wrote a lengthy reply to your post and it got swallowed up when I tried to upload some pix. Will keep this one shorter. I am in the San Vito area near the Panama border. We get ALOT of rain here. Last years rains did substantial damage to the area in question. I have control of approx 100 meters of one side of the creek. The pix will show you what I had installed last year - sandbags held by rebar and large bamboo poles, backfilled with rock. This held just fine but everything around it got washed away. The creek rose at least a meter above this construction. Am currently proposing installing a substantial rock and cement wall to further diffuse and redirect the flow. The creek rose at least another meter above last years construction. Am also considering installing a trench drain above the seeping wall with perforated pipe and gravel to redirect some of the runoff coming from the land above. Will attempt a second photo upload. One pic is of the patio area under threat. Currently it is only about 8 feet from the edge. Yikes! Was just in the Arenal area last week. Stayed in Il Castillo, enjoyed the hotsprings (Tico style, across the road from $$Tabacon, lovely!)Okay, computer not allowing photo upload, can I email photos to you directly? Totally appreciative of your input. Gracias! Autumn
 
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Old 04-01-11, 11:23 AM
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I have a friend from NC that moved to Golfito last year to sell real estate. He's been wanting me to come look at some property around San Vito. Small world.

It sounds like you have a pretty good handle on what's going on and the scale of work it will take to keep the Costa Rican creeks in check. I'm just afraid whatever you build the creek will eat away at the edges until it behind your wall, but you just need enough to protect your property and hopefully there won't be many more bad rainy seasons.
 
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Old 04-04-11, 07:26 AM
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Creek erosion continued. . .

Thanks everybody for the input.
I have taken all the advice into consideration and hired a contractor with extensive experience to design and implement the project.
Right now there are 4 guys working in the creek, moving rocks to redirect the flow.
Then we begin constructing a rock and cement wall in front of the threatened area to protect it from further erosion. Will try and post photos as the project progresses if anybody is interested. These Costa Rican guys sure know how to work!
 
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Old 06-24-11, 09:17 AM
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HELP Please, with erosion on a small lake

I rent a house on a small lake. The small dock is falling apart and the yard is going into the lake. The chain link fence is almost horizontal. There are 12 houses around the lake. Some have seawalls some don't. I can deduct cost and labor from my rent if only I knew what to do.
 
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Old 06-24-11, 10:03 AM
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First I would post some pictures so we can see what kind of problem you are having.
 
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Old 06-24-11, 03:33 PM
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http://www.doityourself.com/forum/el...your-post.html. That way we can see what you see. Also, although you say you can do it, make sure you have all this in writing and determine the boundaries you are allowed to modify.
 
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Old 06-25-11, 08:13 AM
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And check thoroughly with local authorities before doing ANYTHING! Working near a body of water (still or moving) usually involves a rather lengthy set of restrictions.
 
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