Pond Erosion

[cloudhopper]

We have 2 ponds of about 3/4 rai each in size and 1.5m deep. Unfortunately they were excavated long before I learned about pond construction and most of the sides sloped 1:1 are suffering noticeable cave-ins after 5 years. At first I thought this might reach some equilibrium as a talus slope formed but not so far.

Any suggestions for a cure? Unfortunately re-sloping is not an option. I thought about pounding a line of bamboo poles in along the edge to break up the wave action; naturally I'd like to avoid concrete, sangkasee etc.

[ozzydom]

cloudhopper, do you have overflow pipes to maintain a set level or do your ponds levels rise and fall with precipitation?

The slopes below water level should by now have a longer slope ,so maybe lowering your max level will help, otherwise your suggestion of a bamboo retaining wall will help.

Our ponds were constructed with 4:1 camber but still got a bit of cave in when big rains overwhelmed our 4 inch over flows,upgrading to 8 inch overflows helped the situation.

[cloudhopper]

Thanks Oz. The first pond was dug out of a marshy area and is spring fed (water table) and never overflows. The second is continuously fed from an irrigation canal and constantly overflows back into another klong. Anyway, neither changes level much...

[slapout]

cloud; I used the bamboo stakes , about 3 inch across to do what you need. They worked good and erosion was controlled. We used bamboo ties from the row of stakes back to the dike about every 8 foot to give additional strength.

[jaideeguy]

Another suggestion CH, would be to plant this grass that i call 'the King's grass' that I used to keep the banks of a small stream we had as a border on some land we once had here from eroding. It did help some, but unfortunately the big rains and flooding came before it got fully established.

The reason I call it 'the King's grass'is that we got it free from the King's Royal Project 'Mae hong Krai' [sp] off hiway 118, just out of CM on the way to CR. If your water levels remain constant, then I think it would get established easily....especially with the rainy season comming.

Then there are other aquatic plants that you could plant in the water.....

Edited May 15, 2009 by jaideeguy

[cloudhopper]

Yeah that would be "ya fek" and we can get it free up here too, but it's past the point where that will help so I'm going with "mai pai" (the bamboo poles).

[allcladrad]

Just a suggestion, if you get the erosion controlled with the bamboo, then might be a good time to plant the vetiver. The bamboo will fail in a few years.

[cloudhopper]

Hi I don't know if that's the same as ya fek but others have concurred with this advice. I wouldn't have thought it could stop a vertical wall from peeling but the roots are supposed to go down several meters. Time will tell...

[Maizefarmer]

Crazy slope ratio – it is surface water (movement) causing the corrosion and subsequent collapse (i.e. the cause is established is it)? The point I’m making is that, wave action is not always the cause of dam boundary collapse. Another big cause is seasonal fluctuation in the water line – the repeated wetting/drying of the bank edge between the upper and lower level results in weakening, and then collapse.

These dams/ponds are not too big, one other feasible solution (meaning affordable) is to cut a 55degree – 75degree wedge into the dam wall, with the bottom of the wedge no more than about 10degree – 20degree off the existing slope angle perpendicular line(any more than this and the soil volume between the wedge bottom edge and the slope in the dam wall will be too thin, have insufficient volume and start to loose any of whatever natural stability it may have).

The wedge is then filled with coarse sized loose gravel - 2”–3” average diameter should be fine.

This is very effective at putting a stop to water line erosion and bank collapse - but a number of practical “construction” points should be adhered to:

1. Make sure you have a fairly accurate idea of the seasonal upper & lower water line fluctuation, and allow for a wedge/water face of 5” plus above & below the mean water line.

2. The narrower the wedge angle, the deeper the wedge will recede into the slope for a given wedge/water face width.

3. Conversely, the wider the wedge angle, the shallower it will recede into the slope for a given wedge/water face width.

4. The more loose the natural soil type, the more you should err on a wider chosen wedge angle, and the less the wedge should be dug off the slope angle perpendicular i.e. the closer the bottom edge of the wedge should be to 10degree off the slope perpendicular (and should in any event never exceed anything greater than around 20degree)

5. Give a good 5” plus wedge face above/below the mean water line (i.e. wedge “mouth” on/with the slope).

6. Planting a grass or legume with a shallow spread out root structure (as opposed to tapping down) in the bank soil above the top edge of the wedge will go a long way to binding the soil.

Why all the math and detail?

Well, get the angles/dimensions right and this will prove to be a very effective, cheap and long lasting solution, get it wrong and the structure won’t last long.

[Chayakon]

Had the same problems but with a new pond, the soil is very sandy here, planted 40,000 'ya fek' last year and 70% has done its job, still got problems but would have been a lot worse.

The grass is free, stick it in and try the bamboo option as well, I might try it myself on the worst parts.

Good luck

[Smithson]

With it's long roots I think the Ya Fek can have the additional benefit of lowering nitrate levels in your pond.

[wagner54]

when you plant Ya Fek are you using seeds or roots? Also does any one know where to get some near Ubon Ratchatoni?

[Pond Life]

As far as I know Ya Fek is always propagated using root stock.

I think it does not produce seeds, which is why it doesnt get out of control.