venetian well - any suggestions ?

Hello Permies !

I have been chewing on this idea for some time, I thought I could bounce it off the Community...

I need to set up a rainwater collection & storage system that can ensure water supply all year round, the storage part being the more troublesome one.

I have considered above-ground tanks - not a good idea in an area with winter temperatures as low as minus 25 Centigrade - as well as underground tanks - the issue with these being that there is potential for structural damage / collapse due to the pressure of heaving clay soil in wet weather... so I have discarded these options.

Then I started thinking about creating a Venetian well (or Venetian cistern), and it seems this could be THE solution as long as I can iron out some details.

The general concept of the Venetian cistern is explained here: http://www.venipedia.org/wiki/index.php?title=Wellhead or here: http://blog.davidboucher.com/2009/04/venetian-wells.html

My plan & related queries :

- The cistern (the funnel under the ground) will be dug into clay soil. For easier design & building, I thought I could make it an inverted pyramid (a square when seen from above) rather than an inverted cone (a circle when seen from above). The well head & shaft would be built of pre-cast concrete rings of c. 1m / 3 feet in diameter. The cistern will collect rainwater from the building roofs (house, sheds), French drain around the house, and the rain falling on the area itself.

- I intend to dig only as deep as 2m (6 feet) - I'm concerned that digging further I might hit the water table (my neighbour found water at 3m / 10 feet). You may ask why I'm not digging a well instead - the answer is (a) I will be digging a well as well; (b) local water is extremely hard, so I'd like to avoid using well water except in emergencies.

- The outer perimeter of the funnel will be 4x4 metres (that's 12x12 feet). The bottom perimeter will depend on the slope that turns out to be best (see below).

- I have found no info on the optimal slope. I would guess that some slope would be beneficial (a) for more stability; (b) to ensure that water captured on the surface goes through the sand filter rather than around it along vertical walls; (c) probably easier to dig and apply the lining. But then the steeper the wall slope the less the cistern's volume

- I am considering the following options for lining: (a) concrete (am I right to assume that given the stability of the sloped walls, I will not need to build a very sturdy structure? And that a relatively thin concrete layer will suffice?) - concrete would be probably ideal as it would neutralise rainwater acidity, but then it does seem to involve more work & cost; (b) pond liner - lacks the neutalising chemical action of concrete; (c) the clay subsoil itself / no lining

- The most difficult bit (for me at least) is to calculate the amount of water that can be stored in the interstitial spaces of sand / gravel inside the cistern's funnel. The volume of the funnel and shaft is easy to calculate, but that does not equal volume of water... So I don't know how much water the cistern can store, beyond the volume stored in the shaft ... Any ideas?

- Last but not least: Instead of filling the funnel around the shaft only with sand, I have been thinking of piling rocks on the bottom 2ft of the cistern, then coarse gravel, and then sand for the top 1m (3ft) or so... in the hope that this will increase the storage capacity outside the shaft. Do you think this could help...?

Any thoughts or advice would be greatly appreciated !

Best
Levente

Hi Levente:

Interesting question (and I love venetian wells - beautiful).

Caveat - I have no practical experience with venetian wells. That being said - I would love to know your location. If you get down to -25 C, you would probably experience heaving due to frost in the soils and the clay lining of the well which would crack - that would be my main concern.

There may be other approaches that would work to give you multiple yields from a single element. I'm just "spit-balling" an idea here, so here it goes.....

What if you constructed a large ferro cement above ground cistern - because of the way they are made, I believe they can withstand heaving - or they may require a cement pad base. They are very robust and with enough volume, probably wouldn't freeze, especially if you insulated it well. You could insulate it either with something like straw bales built around it - or it could be part of a sun-facing glasshouse attached to a home or other structure. The heat gain created by the glass house would probably be enough to keep the water liquid.

Another thought is adding a RMH to the construction of the ferro cement cistern. With a little stick fuel, you could keep the cistern warm enough not to freeze (it seems). The cistern would also then have it's own microclimate depending on where it was placed that would be essentially warmer in the winter and cooler in the summer - perhaps a niche for starting early seedlings or extending a harvest into the cold season?

In my extremely limited understanding of venetian wells - the sand acts as a fine filter. Gravel wouldn't perform that same purpose, necessarily. In fact, "decomposed gravel" is still decomposing and will make your rainwater harder. What is your roof made of? That will dictate how "potable" your rainwater is and what steps you need to take. There are "first flush" systems designed to divert the initial flush of rain that contains the most debris away from the cistern.

Ferro cement cisterns can be very artistic and beautiful - you could even build them into a structure such as a patio or glass house.

OK - those are just my initial thoughts.

I don't have answers for you, but I have a few more issues you may wish to consider.

I am assuming that you plan to use this water for household use rather than garden use. Based upon this......
1- have you calculated how much water your household uses daily?
2- do you plan use the water for ALL household use or do you plan to use hard water for some functions and rainwater for others?
3- does your area receive year around rainfall or only in a certain season?
4- will you have a back up water source?
4x4x6 meters isn't very large considering much of the volume will be taken up by sand.

As a benchmark.....I live in an area that gets on average 60 inches of rain per year. Thus we have access to enough natural rainfall. Our original catchment tank was a 10x 6 foot cylinder. It proved to be too small. We added a 16x6 foot cylindrical tank, which now sufficesfor a family of two.

Jennifer Wadsworth wrote:Hi Levente:

Interesting question (and I love venetian wells - beautiful).

Caveat - I have no practical experience with venetian wells. That being said - I would love to know your location. If you get down to -25 C, you would probably experience heaving due to frost in the soils and the clay lining of the well which would crack - that would be my main concern.

There may be other approaches that would work to give you multiple yields from a single element. I'm just "spit-balling" an idea here, so here it goes.....

What if you constructed a large ferro cement above ground cistern - because of the way they are made, I believe they can withstand heaving - or they may require a cement pad base. They are very robust and with enough volume, probably wouldn't freeze, especially if you insulated it well. You could insulate it either with something like straw bales built around it - or it could be part of a sun-facing glasshouse attached to a home or other structure. The heat gain created by the glass house would probably be enough to keep the water liquid.

Another thought is adding a RMH to the construction of the ferro cement cistern. With a little stick fuel, you could keep the cistern warm enough not to freeze (it seems). The cistern would also then have it's own microclimate depending on where it was placed that would be essentially warmer in the winter and cooler in the summer - perhaps a niche for starting early seedlings or extending a harvest into the cold season?

In my extremely limited understanding of venetian wells - the sand acts as a fine filter. Gravel wouldn't perform that same purpose, necessarily. In fact, "decomposed gravel" is still decomposing and will make your rainwater harder. What is your roof made of? That will dictate how "potable" your rainwater is and what steps you need to take. There are "first flush" systems designed to divert the initial flush of rain that contains the most debris away from the cistern.

Ferro cement cisterns can be very artistic and beautiful - you could even build them into a structure such as a patio or glass house.

OK - those are just my initial thoughts.

Hello Jennifer,

Thanks for sharing your ideas.

I believe you mean decomposed *granite*. I'm not sure about the type of gravel I will be using - maybe granite - but regardless of that, it would go under a layer of at least 3ft of fine sand. Would that thickness be sufficient for a filter layer?

Rainwater getting harder is hopefully not an issue, as rainwater is rather acid to start with, so if any "hardening" factors are present, such as concrete, they would neutralise the acidity.

Roof will be tiles, no contamination issues there aside from bird droppings. I don't think I will worry about first flush, as I'm counting on the sand filter. I may even use a layer of permeable soil on top of the sand (with herbaceous plants growing in it), for additional purification of ground run-off through soil bacteria

There are other issues with above ground containers, including ferrocement ones, in addition to risk of freezing: (a) I haven't got enough space above ground where the best spot would be for an above-ground tank; (b) I want to collect ground level run-off as well, in addition to roof water, all in the same sand-filter cistern

Best
L_

Su Ba wrote:I don't have answers for you, but I have a few more issues you may wish to consider.

I am assuming that you plan to use this water for household use rather than garden use. Based upon this......
1- have you calculated how much water your household uses daily?
2- do you plan use the water for ALL household use or do you plan to use hard water for some functions and rainwater for others?
3- does your area receive year around rainfall or only in a certain season?
4- will you have a back up water source?
4x4x6 meters isn't very large considering much of the volume will be taken up by sand.

As a benchmark.....I live in an area that gets on average 60 inches of rain per year. Thus we have access to enough natural rainfall. Our original catchment tank was a 10x 6 foot cylinder. It proved to be too small. We added a 16x6 foot cylindrical tank, which now sufficesfor a family of two.

Hello Su Ba,

1. Indeed the water is for household use, hence the need for filtration and neutralisation of acidity. Yes I have calculated the amount of water that the household will need. If I manage to calculate the volume of *water* that the cistern can hold, then I would be able to know whether those needs will be met (or not) by the stored water. Unfortunately I have no way of calculating that. I can only say that, if the well saft fills with water, I would have about 1.5 cubic metres (1500 litres) in the shaft, plus an unknown amount (say another 3 cubic metres? a wild guess) in the interstitial spaces of the sand / gravel / stones

2. Haven't got a clear plan in this respect yet. Hard water would be used only in emergency

3. The area is zone 5 temperate continental (Transylvania, Romania). Precipitation is year-round, but some months can be wetter / drier than others. Droughts lasting 3 months or more are not unusual nowadays

4. The well (hard water) will be the back up. Oh and there is a village mains system, which I may hook up to, but in dry periods there is water shortage (water flows through pipes for only a few hours a day - and that's also hard water!) so that's the main reason I'm thinking of becoming self-sufficient

Indeed the volume is small, and I may be able to expand the cistern's dimension laterally about 3ft in width & length (not depth), but not much more than that as it starts getting too close to the house foundations.

Many thanks !
L_

Levente:

Thanks for your response. Indeed I did mean decomposed "granite"! Good catch. (typing faster than thinking - apparently)

A few more thoughts:
--how much rain do you get where you are?
--is there a particular reason (health, clogging up pipes) that you don't want to use hard water from your potential well in the house? Just curious. I understand the desire for redundant and alternative systems.
--regarding above ground cisterns, as the daughter of a civil engineer who has designed water systems on three continents (N. America, Africa, Asia), I can personally say that I have seen what is essentially a ferrocement cistern being "charged" by two bull elephants in the Tsavo game reserve in Kenya to get at the water. My dad managed to design an "elephant-proof" tank back in the late 70s (no mean feat - there were many unsuccessful versions!) that still stands today. So you can engineer them to be very sturdy is my point. However I hear you about the space limitations. You can do "dry install" cisterns (water flows into the top of the cistern) - usually these need to be in close proximity to the water source (i.e. your roof). There are also "wet install" cisterns that can be at a significant distance from the water source and are fed through an underground pipe - this gives you more flexibility in placement. I've been involved in several of these around the Phoenix Arizona area here in the US.
--Brad Lancaster, author of "Rainwater Harvesting for Drylands and Beyond, Vol 1-2" has a rainwater calculator to help you determine the size of your water harvesting feature(s) and is applicable even if you don't live in a "dryland". As always, an overflow plan is critical. Downhill swales if you have slope or infiltration basins if your land is pretty flat...
--Art Ludwig's books are also extremely helpful. (I saw Art on this forum a few days back - you might PM him).
--How will you get the water from the venetian well to the house? Hand pump? Solar/wind pump? Animal powered? One of the benefits of an above ground system is that you can design in head pressure and not need a pump.
--As for figuring out how much water the well will hold with the sand/other materials in it. I would get a smaller container (5 gallon bucket for instance) - fill it with the approximate mixture of materials you plan to use for the filter (measuring the amounts of each as you put them in). Then add water from a measured source (1 gallon/2 litre contain, say) and see how much it takes. You can then extrapolate that percentage to the volume of your larger system. X% sand +Y% gravel in volume Z can hold W % water.

Keep us posted on your thought process. It's an interesting project.

Jennifer,

Great idea for estimating the volume of water ! Thanks - I'll try it.

To be honest, I don't think I've seen above-ground cisterns - ferrocement or other material - used here locally or elsewhere in climates analogue to mine. But that may be just my ignorance, so I'll keep an open mind and keep researching. Thanks for your suggestions in this respect as well

I have bought Art Ludwig's books - water storage and grey water. Noted that underground cisterns are dealth with in only a couple of paragraphs ... hmm !

Best
L_

I can hardly wait for Brad Lancaster's Vol 3 (due out sometime next year, I believe) - he deals with water storage that's NOT in the soil. (Vol 1 was an intro to water harvesting and Vol 2 was about earthworks and storing water in the soil for rehydration of landscapes and watersheds).

If you have drawings/plans to share, I know I'd be interested to see them.

Best, Jen