Natural swimming pond in Thailand

[xye]

Hi all,

I'm new to this forum, but I've begun to build a home on a ~1.5 acre (0.6 hectare) plot of land on the outskirts of Bangkok, Thailand. I have very little experience in building ponds, but a ridiculous amount of engineering resources around to rely on. So...

My wife and I hired a team of local construction workers and are directing them ourselves. Along the way, we are designing and building our own water circulation systems based on the locally ubiquitous "long tail boat" propellers and other equipment.

There are all kinds of little questions that come up along the way from things like "what is the minimum water turnover rate before bad things start to happen?" to "are there any rules of thumb for drilling the holes in the water pipe that goes under the regeneration zone?"

Is this a good place to post such questions? If not, does anyone have any suggestions of forums better suited to it?

If anyone is interested, here is my blog about the pond building:
http://mibproj.blogspot.com/search/label/Pond

 

[MitchM]

Welcome.
You may find more relevant information at www.pondboss.com

 

[Meyer Jordan]

Good luck! Although swim ponds have been constructed for years in Europe and S.E. Asia, I have seen NO documented scientific proof that they are as safe as conventional swimming pools. And no one that constructs these professionally can or will present such proof. Entirely too many water borne pathogens (Bacterial, Viral and Parasitic) exist to gamble with the health, and maybe life, of a loved one or anyone else, for that matter.

 

[Timothy]

Welcome to the forums!
I was in Bangkok in '66 and went to Lampang from there for 14 months. Thailand is a beautiful country, and I found the people to be very genteel. Sawadee!
I haven't any background in your type of pool, but a neighbor has relatives in Italy and their pool is half plants and half swimming area. He has told me their pool is crystal clear and they use no chemicals at all. As you glean information on this method, please share your findings. I think it is an interesting concept and not unlike any natural lake.

 

[xye]

Welcome.
You may find more relevant information at www.pondboss.com

Thank you very much for the link. I will definitely take a look.

 

[xye]

Although swim ponds have been constructed for years in Europe and S.E. Asia, I have seen NO documented scientific proof that they are as safe as conventional swimming pools.

I agree with you about this. Most of the literature I have read on the subject, even the stuff written by big NSP proponents, seems to suggest that NSP's don't have the level of sterility that a chlorine sterilized swimming pool would achieve. I think the goal is less ambitious, though. It is to achieve something more like the level of natural balance that a natural pond or lake achieves without complete sterilization. Even swimming at the beach is less safe than a swimming pool.

In my case, chlorination isn't really an option since I have about a 2000 square meter pond/pool that is primarily a landscaping feature with water plants, etc, and is meant to be a swimming pool second. The water circulation and filtration of an NSP seemed like a much better option compared to just leaving a large stagnant body of water around.

I'm not planning on taking too much risk, though. I plan on getting professional water quality measurements done once the filtration circulation system is operational. I'll share the results once I do in case anyone else is interested. I'm curious to compare the natural filtered pond water to the tap water here in Thailand. ;-)

I have seen scholarly work done on this kind of slow sand filtration. I'll see if I can dig up any links.

 

[Nepen]

Welcome! I'm originally from Thailand my dad has land in Chachongsao province and is building a small one room house at the edge of the fish farm. Your plans are much more sophisticated though I've swam in many natural pond growing up (my aunts and uncle have many fish farm) but I don't think it's very hygienic

I think that if you have water turn over at least once an hour your then your water will not be stagnant. For my pond, the water is turning twice in an hour and I think that seems to be common here.

 

[xye]

Welcome! I'm originally from Thailand my dad has land in Chachongsao province and is building a small one room house at the edge of the fish farm.

<snip>

I think that if you have water turn over at least once an hour your then your water will not be stagnant. For my pond, the water is turning twice in an hour and I think that seems to be common here.

I've been to Chachongsao once or twice.

My wife grew up swimming in the canals around Ayutthaya, but even they are much dirtier now.

Can you confirm the turnover rate of twice an hour? That sounds extreme to me. My pond is about 2000 square metres, with an average depth of about 2 metres for a total of about 4000 cubic metres. At twice an hour turnover, that is 8000 cubic meters per hour or 8,000,000 liters per hour. For reference, that is over 2000 liters per second.

I was hoping for turnover rate of about 4-6 hours. Does this sound problematic to anyone? If so, how do you get the massive flow rates?

 

[Nepen]

My pond, sadly, is only about 1500 gallon now that I re-calculate the volume (planned 2500 but something went wrong in the digging and measuring process!!!). Plus water in bog and stream, I have about 2300 gallon. I'm using 2 pumps - 4200 and 2900 GPH. The rating for my pumps make it about 3 turn over an hour but I dont think I get that much.

I grow up near the beach, so I'm more of a beach girl. I only swim in the pond of my family's. My grandmother has a house on the river and I went in there once or twice but I got freak out if I couldnt see my legs

 

[Meyer Jordan]

I've been to Chachongsao once or twice.

My wife grew up swimming in the canals around Ayutthaya, but even they are much dirtier now.

Can you confirm the turnover rate of twice an hour? That sounds extreme to me. My pond is about 2000 square metres, with an average depth of about 2 metres for a total of about 4000 cubic metres. At twice an hour turnover, that is 8000 cubic meters per hour or 8,000,000 liters per hour. For reference, that is over 2000 liters per second.

I was hoping for turnover rate of about 4-6 hours. Does this sound problematic to anyone? If so, how do you get the massive flow rates?

Turnover rates can be confusing. In a pond populated with fish, a turnover rate of 1.5 - 2 times per hour is recommended. This is because most decorative pond fish are notorious as waste producers and also because most garden ponds usually have a high fish biomass. The 4 - 6 hour turnover rate that you mention is what is usually recommended in a conventional swimming pool where the goal is maintaining the circulation of disinfectants. In a 'natural' swim pond, the turnover rate should be based on the bio-conversion rate of the regeneration zone, bather load and ratio of regeneration zone to overall pond surface area. Sufficient time (resident time) must be allowed for the bacteria in the 'regen' zone to efficiently oxidize any organic waste.

 

[xye]

I've been reading up a lot on turnover rates. I was actually inspired by the info from Nepen above. Her pond is about 5.7 cubic meters, which made me realize that the project I've undertaken is probably quite unusually large. (I have a tendency to bite of more than I can chew. This pond is somewhere in the range of 4000 cubic meters.) That led me to look for reference info about NSP's, but there really isn't very much.

I found a number of pages that refer vaguely to NSP's normally having 1-2 day turnover rates, but these seemed to be observations and not explanations or objectives. On this site, I found a post on the subject of NSP flow rates, and one of the messages also refers to 1-2 days turnover rates being mentioned in the book "Natural Swimming Pools" (Michael Littlewood). I have this book and searched through it, and found no mention. I'm wondering if I have the wrong volume or something.

So I read up a bit on lake retention times (turnover rates) and found that most lakes seem to be on the order of years. Of course, most lakes are several orders of magnitude larger than my pond, but it made me realize that turnover rates aren't actually required for clean water, and in larger bodies of water, other biological activities must be going on to keep the water clean.

Meyer Jordan's informative post above appears to support this idea. In particular, the idea that the swimming pool turnover rates are needed mostly to circulate disinfectants means that it really doesn't apply to my pond.

Not having found very precise info about turnover rates in NSP's, I began a different direction for my research. I'm now fairly convinced that the theory behind how an NSP functions as an effective filter is very similar to "slow sand filtration". The theory of operation, and the requirements of operation are both nearly identical. And I realized that the numbers for flow rates are surprisingly similar. This can't be a coincidence.

The slower flow rate numbers will particularly make my goal of having the circulation pumps entirely solar powered much easier.

So now I am working under the assumption that I am building a giant "slow sand filter" and doing my calculations using those principles accordingly.

For anyone that wants to see some updated pictures of the status of the pond building, or a bit more details about slow sand filters and how it affects my calculations for the circulation pumps, here is my blog post from today:
http://mibproj.blogspot.com/2015/07/pond-update-laying-out-pipes-in.html

The retaining walls for the sand area are done (2 out of 3) and the PVC pipes for circulating the water around are finished laying down. Now we really have to get down to business and wash the gravel and sand for the substrate. I estimate that we need about 600 cubic meters of the stuff, and we've probably only processed about 20 cubic meters so far. (Mostly we've been testing out different techniques.)

 

[tbendl]

Following. I looked at NSP's when I built my pond, I'll be very curious how this turns out.

 

[Nepen]

interesting My family fish farm has ponds which are about that size and they dont seem to be using any filter, just large pump taking the water and just dump it right back. Or just the floating water wheels to give oxygen. But tons of plants.

 

[Meyer Jordan]

I am more interested in exactly what you are putting in place for pathogen control. In this area turn-over rates and sand filtration would have no impact. I would think that this would be the number one priority considering this s to be used for human immersion.

 

[xye]

I am more interested in exactly what you are putting in place for pathogen control. In this area turn-over rates and sand filtration would have no impact. I would think that this would be the number one priority considering this s to be used for human immersion.

With regards to whether sand filtration helps with pathogen control, I found this quote from Wikipedia quite interesting:
Slow sand filters differ from all other filters used to treat drinking water in that they work by using a complex biological film that grows naturally on the surface of the sand. The sand itself does not perform any filtration function but simply acts as a substrate, unlike its counterparts for UV and pressurized treatments.

I was also intrigued by this quote on the same page:
Although they are often the preferred technology in many developing countries because of their low energy requirements and robust performance, they are also used to treat water in some of the most developed countries, such as the UK, where they are used to treat water supplied to London. Slow sand filters now are also being tested for pathogen control of nutrient solutions in hydroponic systems.

Slow sand filtration is described as an extremely effective and proven form of pathogen control for processing dirty drinking water in various reputable places including the CDC and the WHO.

The following is from a page on the CDC website:
Slow sand filter lab effectiveness studies with a mature biolayer have shown 99.98% protozoan, 90-99% bacterial, and variable viral reduction. Field effectiveness studies have documented E. coli removal rates of 80-98%.

The WHO seems to say pretty much the same thing:
Under suitable circumstances, slow sand filtration may be not only the cheapest and simplest but also the most efficient method of water treatment. Its advantages have been proved in practice over a long period, and it is still the chosen method of water purification in certain highly industrialized cities as well as in rural areas mid small communities.

On the biosandfilter.org website I found this:
With raw water, a filtrate quality is possible that has less than 1 NTU, 95% removal of coliforms, 99% removal of Cryptosporidium and Giardia cysts, 75% removal of colour, 10% removal of Total Organic Content (WEDC, 1999 [ref_02]). As a single process, slow sand filtration was ranked second most effective of all treatment processes, given a range of pathogenic, chemical and aesthetic factors.

Most of the literature on NSP's is so aesthetic and "natural must be better" oriented that it took me quite a while to associate it with the above data. I'm not sure if anyone else finds this stuff interesting, but in case they do... maybe they'll benefit from some of these links gathered in one place.

Slow sand filtration seems to be one of the top choices for pathogen removal. I'm certainly no expert on this subject, but I've definitely found the research on the subject to be quite compelling. And if I'm right that NSP's use exactly the same principals, then it isn't "fringe science" at all.

The other thing I've begun to wonder about is whether chlorine itself is really all that safe. It is clearly antiseptic, but that is because it is a common poison. The CDC has a web page on all the toxic effects of chlorine:
http://www.bt.cdc.gov/agent/chlorine/basics/facts.asp

It is quite scary reading.

Presumably this is in much higher doses than goes into a swimming pool. But if you can forgive me a ridiculous oversimplification: one process is used to make dirty drinking water potable all around the world, the other one was used as a poison gas chemical weapon in WWI (and Syria now)... which one would you rather swim in? (I know, I know, the levels of chlorine are probably a million times different. And in case anyone thinks I'm actually serious, I'm just joking here. But it still makes one pause and think a bit, doesn't it?)

We don't have children, so I'm not sure if this would have changed my calculus at all. (With kids, I imagine you might not want to take even the tiniest fraction of a risk, but with only adults I'm willing to at least try.) And I'm still planning on doing the lab tests to the water once the system is operational. I'll try to remember to post the results.

Please wish me luck! (I still need it.)