Using local materials for pond lining
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| I was wondering if any of you have experience with lining surface runoff harvesting ponds, using local available materials as clay, bentonite or gley or cement/clay mixtures or that sort of stuff? Plastic liners are all good of course, but perhaps some local materials will also do the job if you allow some small seepage?
For instance, imagine I have a hole in the ground of 50 to 70 meter cubic somewhere at a small farm in Uganda where a farmer would like to grow tomatoes during the dry season using the runoff from her compound. Would properly puddled clay do the job or will it just crack up when empty and be useless the next year?
| Hi M,
Here are some ideas we use in Western Australia.
|SearNet conducted some on-farm trials of pond sealing materials and had very interesting results. We tried out engaging pottery experts to line the sides of the ponds using clay. the result is that depending on moisture/dry conditions, the layer expanded/contracted, and eventually they failed. My take is that runoff ponds seal themselves gradually. During Y1, the sealing is optimal but progressively become effective with time.
This FAO document, Controlling Water Losses in Ponds, has some good ideas for sealing ponds.
Manual puddling may be combined with the overflow of a runoff infiltration pit (i.e. attempt to separate the fine clay particles from the heavier sand/silt) could work and doesn't involve transporting a lot of clay.
Moving pigs into a ditch that fills with water after rains and having them puddle & compact and somewhat "glei" it is also a traditional way to reduce soil infiltration, but it takes a while to work.
However you are right, longish dry-out periods will likely affect the pond seal.
|CONTROLLING WATER LOSSES IN PONDS|
|Thanks B, |
I suppose this is a returning problem when using clay, you mean the ponds stop sealing themselves after year 1 already? I suppose also, if this is in really arid lands the long dry spell will make it more difficult...
|Does anyone have an example of ponds that have already worked for say 5 years in a development context? |
Apart from focussing on the pond I would also suggest storing water where the crops grow by putting the right biology into the soil: soil bacteria secrete a sticky substance that glues soil particles together and gives the soil structure, greatly enhancing its water-and-oxygen-holding capacity. The fungi grow filaments of great lengths, functioning like extended roots and bringing nutrients to the plants from deep down and far away. The way to get these microorganisms is by creating a good compost pile (takes about one month) and from that making 'compost tea' (easy!) and then just spray it on soil and crops.
Concerning sealing the pond, yes pigs could work well, and cattle, because of their weight, even better...
Hope you are still interested in this theme of sealing ponds. Clay alone will create problems if the pond level changes regularly with the clay being exposed to sun too long. In Peru, since ancient times clay was mixed with cactus juice. they would let it sit for a couple of weeks to 'cure' just like cement, and then apply it to line the canals. They lasted only 500+ years! Would do wonders for pond lining. Of course you have to experiment with the type of clay and cactus you have to figure out right proportions.
|Glad to hear that many are quite interested on the theme of pond lining. I gave a brief treatment on the issue in my book but unfortunately it is not in English yet. Will try to make amends below. The main issue in pond lining is economics; we don't find any material that are 100% impermeable, cheap, cheaper to repair and lasting over 20 yrs. So, let's analyze the issue in each case to see how much water you could afford to let seep-out.
In the case of irrigation water, if you are not using extremely expensive drip irrigation, your water losses during distribution will amount to over 30%. And since most irrigation water comes with a high concentration of fine silt/sand/clay, over time, seepage from your unlined pond will be less than even 10%. So, instead of trying cut down seepage with costly lining, you'd better spend your resources on improving the efficiency of distribution. On the other hand, if you can afford good drip irrigation, you may not worry too much about the kind of low cost treatments we talk about, but keep reading.
In the case of potable water, very few would keep treated water in an open pond, since you can´t afford to lose that quality. If you keep untreated drinkable water in an open pond, better figure out the losses you can cut down within the treatment process and compare that to the cost of lining your pond. Now that you know how much you can afford to spend on your pond lining, it is easier to make a decision on the materials to choose from.
Clay pond liners came into being as social pressure built up to prevent leakage from waste dumps. It is cheap if the pond is quite large and the liner thickness is over 20cm, so that mechanical compaction is viable. It is not really clay, but clayey silt or silty clay (in engineering terms). For water ponds, such a material, well compacted, would hold the seepage to less than 10%, even if water level goes up and down, exposing it to drying. For smaller ponds, animal compaction (with buffaloes, like in Sri Lanka) may work, but you need more clay, with the risk of fissures developing upon drying.
For small ponds, a better choice will be a 'soil cement' liner, but not the version USBR promoted. I myself experimented in Ecuador with fine silty soil (ancient volcanic ash), well dried and sieved, and mixed with about 5% cement. We applied a 7cm thick liner, manually compacted, to an irrigation canal with a medium fast flow, and it held well for over a year (till the municipality donated 1000 bags of cement to the canal owners!). As a pond liner it may allow 2-3% seepage (not measured, but I estimate that based on the density). The beauty of it is that anybody can repair whatever fissure appears, bloody cheap and in no time. Now, Andean volcanic soil has a variety of minerals that may work well with cement to hold the particles together. You should experiment with the soil you have and you may try a bit of lime too. Cheaper pozzolanic cement may come in handy too.
On the use of cactus sap with clayey soil, I haven't had the opportunity to try it myself, but many friends of mine have and I got their testimonies. They generally use it as mortar between blocks of rock in canal lining and I am sure it was used in many ancient water reservoirs too, especially to cement the dikes. Following my prior reasoning, I doubt they went to the extent of lining the pond floor, as preventing that seepage was not worth the trouble. As far as the proportions and the types of clay used, I will consult with my friends, but you have to bear with me for a couple of months when I will return from my next trip to Peru. Internet is as alien to them as geomembranes!
Hope this helps. I value your comments. If you give details of the materials you have in the area, together we can come up with a decent solution.
With reference to the interest shown in reducing seepage in ponds and earth dams, kindly note that I have received good results applying the methods described as follows:
Seepage in earth dams can be much reduced by compacting the floor using either a farm tractor or a herd of livestock driven back and forth over the floor. A thin layer of waterproof material, such as Black Cotton Soil, animal dung or lime, will also seal a dam reservoir.
Source: ‘Household Dams for Maasai Women’ 2014. An unpublished manual by Erik Nissen-Petersen, ASAL Consultants Ltd., Kenya.
|Guess since we are not all civil engineers, a clarification is necessary with respect to pond lining.
My previous explanation applies especially to lining the bottom and the sides of a hole excavated in firm land. I would extend such arguments to a pond built up by constructing a dike across the lower edge of a natural depression, only if the depth of retained water is less than a couple of meters. Seepage through a dam / dike is a totally different beast compared to seepage through the floor of a reservoir / pond. My rationale behind comparing the cost of preventing seepage through pond lining and the cost of reducing water distribution losses does not apply in the case of seepage through a dam, because such seepage will compromise the safety of the reservoir itself and the people living below it.
Again, you can't prevent seepage through a dam 100%, but you should attempt to control it to a level where you can collect the seeping water without damaging the dam structure and then drain it safely using a system that works 24 hours a day. The 2000 yr old reservoirs in Sri Lanka had a very elaborate water control system (see link to the right) to prevent high pressure water seeping through the sluice gates, which is still intact today. They of course had elephants to compact those earth dams. If you do not have access to such resources, the best bet is to have a series of small reservoirs (less than a couple of meters of water depth) in cascade, along the same river (see the same article).
|ANCESTRAL WATER NURTURING TECHNOLOGIES|
J W K,
Thanks for your invitation to share some experience on small scale water project by presenting an abstract. Kindly find my abstract below.
Low-cost satellite survey of water sources
The Google Earth programme is being used by this company successfully to identify suitable stretches of sandy ephemeral water courses, also called dry riverbeds, by zooming in on water-indicating trees on riverbanks, waterholes in riverbeds and geological formations to indicate water storage in sandy riverbeds suitable for exploited by hand-dug wells or river-intakes.
Satellite images are used to calculate the approximately volume of annual runoff that passes over a specific place by combing the size, gradient and ground cover of the watershed with the mean annual rainfall.
Google Earth images are also used to assess the extractability of water from the sand of riverbeds as agricultural land produces fine textured sand with tiny voids from where less than 5% of water can be extracted while rocky and stony hills produce coarse sand with larger voids from where up to 35% of water can be extracted.
Satellite images are used as well for a first-hand evaluation of existing surface water reservoirs, such as sand dams and earth dams.
It is an economical advantage to use satellite images as expensive working time and transport are reduced to specific site visits for thruthing of the satellite images and for investigation of identified sections of riverbeds for drawing plans and profiles from where the volume of extractable water can be calculated for a specific project.
An illustrated manual of 32 pages has been produced on this technique which is awaiting support for publication.