French drains and cisterns and such

Sounds fine to me, I'd have a good look to see the natural run off chanels and use them if possible. Interfacing the drain to your cistern may be tricky, water has an uncanny knack of flowing everywhere except where you want it to. (there must be a name for this phenomenon).

I take the runoff from the flat roof of my extension into a waterbutt about 3' off the ground...the overflow from this runs down into the garden pond....Took me ages to get this overflow to actually work even with a 3' head over a distance of about 7yards!

Playing with water is fun (discus)

I sympathize, I had a previous post on my last house's flood irrigation system. Still don't understand how or why it worked, but I know you better not mess with it.

Thanks

Emmett

(there must be a name for this phenomenon).

Following the way of the least resistance.

ok....

True...not very funny...but true ...!

(There must be a name for this phenomenon).

It is called the meander effect in free flowing streams. In pipes I do not know that it has a name but it is well known to crush pipes just from flow induced internal strain. The effect arises from a combination of Correalis effect Bernoulli effect or force. Basicly any time you have a straight fluid flow that flow will give rise to a curling flow. The curling flow causes the straight flow to deviate from straight and there can and usually is synergy in the system which causes regular patterns to the meander.

In pipes a high flow rate can generate meander which tends to flatten the pipe at the inside of the bend. This lifting surface then generates enough "lift" to crush the pipe due to highly concentrated Bernoulli effect.

Look to native grasses, shade plants, and increased organic matter in the soil to improve water retention, then maybe engineer something if you still think nature has got it wrong...

If your land is virtually erosion free (hard rock), the idea may work. Otherwise the rain will erode the surface of the land (quite quickly) at the drain. This will lower the land below the lip of the drain. Then, as Del states, the water will happily flow elsewhere.

Your idea is good. (I would just not call it a French drain.)

If I understand you correctly you want to retain as much as possible of the rain that falls and make it available to the trees.

The problem you have is that water standing on the surface will evaporate and disappear.

The way I would go about doing it is to dig a few trenches across your land (on the contour).

fill this trenches with rock and a thin layer of sand above.

This will allow the water to be captured underground and thereby eliminate evaporation.

The trees will have access to the water.

Building up your water table depends on the rock and soil.

Water tanks to catch the runoff from the roof can supply fresh water.

There might be laws against recharging the underground or new storage structures.

We have very nearly understood each other, perhaps I miscommunicated. At the end of the lovely capture system you describe - underground cisterns.

I don't mind pumping the water back up the hill to distribute.

Yes, it "could" work. The main issue is gravity draining. Gravity draining works completely different than pipes flowing full due to to pumps pushing the water. For gravity draining, you need to have a big enough inlet to let the air "burp" out, then once pipe is full and air removed, the line can run full, at much greater capacity than non-vented gravity draining line. Based on flow, density, and slope, you can calculate the required diameter. IF you don't allow the air to burp, line will have water flow capacity of less than 10% of what you might assume.

Previous comment of sand over gravel in trench, you need to place geo-textile between gravel & sand layers, or sand will be washed down into gravel layer, defeating the purpose.

Glenn Black P.Eng.
Process Quality Associates Inc. www.pqa.net

How about building a berm to create a pond to catch that rain water that is running downhill and getting away. I had ten acres in OK. and our pond stayed full from the run off of less than half of our property.

Mr Emmett: I do not know French system. Let us go back to the future and use an old system. Dig a trench along the lowest part of land. Guide the water to a deep well. Lined the well with tar to make it water proof. Hey presto. you have cost effective water supply until next rain.

A helping hand.

Regards

French drains are used to channel water but it is dispersed into the surrounding earth. You might try lining the drains with polly and putting perforated plastic pipe at the bottom then the rock, two inch minus and then sand. feed the pipe into the cistern.

Mediterranean agriculture evolved terassing as a technique for minimizing runoff. Wherever rain is a winter phenomenon and the terrain is sloping, this solution is fairly practical.

Hi, re your freshwater drains.

3 inch bore slotted polly pipe about 15 inches deep under stone (called "2 inch down," for obvious reasons.) filled up to the surface will work perfectly ok. (Done 100's of yards myself.) The trench can be extremely narrow, about 4 inch wide, to use less stone.

The old fashioned way was to lay thin tree branches down in and parallel with the trench. For this the trench had to be wider and deeper (obviously) to accept several thin tree branches, all overlaping each other along the trench.

This does work (otherwise no one would have bothered with it!) and it's "cheap" to do; just a "lot" of labour. The tree branches will last for years. (lifetime)

Hope this is of help. jt.

http://www.fastfreeads.com

The actual name for it is HYDROLOGY. Since you are working with surface flow, your best bet is to capture it into a surface pond. That surface poind should be lines with a plastic that is at least 10 mils thick. The out fall for the pond should then be directed to a cistern. You can calculate the volume of water that is produced by a storm and how much of it will runoff. This will depend on where you live, the amount of vegatation, soil type, etc. This information would allow you to size your basin. Once that is done, since you are watering trees with this water, you need to know what kind and how many of trees (i.e. oak trees don't drink as much as sycamore trees), acres of grass, etc. A calulation could then be made on the demand for the water. This will size your cistren.

This is probably the best approach, but since evaporation is a major concern, the evaporation from surface of the pond should be minimized. This can be accomplished by covering it with ping-pong balls or other means to block the evaporation without interfering with water motion.

"I was thinking of French drains as viable and far more aesthetic."

Your plan then is to dig much larger holes, fill them with med/large rocks and store water in the spaces or voids between the rocks?

I think that it would be far better to dig a cistern, line it with rocks & mortar to make a water tight cistern to HOLD water for future use.

The so called 'French' drain is not water tight. Its purpose is to allow the water to leach away into the soil quite rapidly for disposal. The construction effort will have been wasted.

I think we have a consensus that a large, underground cistern at the bottom of the property would be viable.

The exact method for channelling water there seems to fall into two categories; a covered or uncovered trench.

An uncovered trench has the advantage of being obvious and simple.

A covered trench has the advantage of being less conspicuous.

Either approach is going to depend on the soil quality I find when I move in. If too porous, a membrane lined trench either filled with gravel or perforated pipe covered with gravel is probably the way to go. If there is any surface run at all.

Much will be learned when I splash around in the first rainstorm observing water flow and absorption. I have often been the idiot who didn't come in from the rain! Perhaps the only capturable runoff will be from the roofs.

Thanks for all the great advice, suggestions, and historical details! Now I know why tree branch doesn't go in the compost pile! Bonus.

Emmett

you can use your "french drain" idea except that you would need to line your drain ditches w/ betonite(used for waterproofing the bottoms of landfills etc) which will give you a good reliable and non erosive channel bottom. you will also need to oversize them a little to allow for the "100 year rain" effect. it will also be necessary to map out your property to get reliable elevations in order to route your channels. the cistern can be done from cinder blocks and hyrd cement for grout and you can use a down pipe baffel overflow from one to the next. the deeper you go w/ the cistern depth the more stable the water temp will be due to earth cooling/ insulation... .would bee a lot of work but when done worth the effort

Given the unusual rainfall they are apparently having at my new home, 100 year planning would have been appropriate!

And proper elevations! Hot dog! An opportunity to add another toy to the collection.

Taught myself celestial navigation while reading the Master and Commander series, got to teach a group of new engineers how to use slide rules recently ( wanted to know what they were missing), and now surveying basics!

Anyone (heh like there is any doubt in my mind) know a good book on practical surveying? (Why do I duck when I ask these questions?)

Emmett

Whether you use ditches or french drains to collect the water, you might want to add a pond to settle any fines. This will protect your cistern from filling with mud and your pump from wearing out prematurely.

A French Drain is a type of covered ditch. make sure you size the filter material so that it will handle the required runoff and not blind off. If this happens, the water will just run over the top of it.

Data on rainfall is available from NOAA.

Neat idea!

The concept is well established in the East for stormwater management. It makes use of subsurface retention chambers of several types, crushed stone surrounded by filter fabric being one of them, and these subsurface chambers absorb the storm runoff and allow it to enter the ground water table.

Hi edignan,

"Non, mon ami. You're all wet if you think French drains have anything whatsoever to do with France. In fact, they were invented in Concord by Henry French, father of sculptor Daniel Chester French, whom we must flood with congratulations for their effectiveness."

John

Ahhh...but where did he get his name? (or was he just a good kisser?)

A few points:-

The water will bring a lot of sediment into the cistern, make sure that you can clean this out in some manner from time to time.

If entering the cistern physically for cleaning (or any other reason!), make sure that a strong fan is used to purge any unwanted gases before entering. run it continually. Better is to have some sort of air quality test system (please do not use a Canary!!), before entering. A naked flame is also not recommended!!

Do not go alone to clean the cistern, make sure that you have a rope around you so that your assistant will not be stupid enough to go in after you if you collapse in there....he can hopefully pull you out, a pulley system will help dramatically!! Make sure that he fully understands that and any other risks....have a telephone handy at all times....

There is a book called "Water for Every Farm" by a bloke called Yoemans, that could really help you. I have a copy somewhere at home but can't easily lay my hands on it right now to quote the ISBN.

The title will be plenty, thanks.

And to the previous poster: officially written up in an accident investigation was a Navy chief inspecting the fuel crews work on an A-6. They had been in the wing plugging leaks with all proper equipment. He used a Zippo to see better. They had to scrape him off the "overhead" as they were down in the hangar deck of a carrier at the time.

So lessee...thats 40 feet straight up, carry the one; with enough velocity to turn him into a greasy spot, so add a factor of ten - yup. Adds up to a really bad idea!

Emmett

Andy's post is so right, the amount of multiple fatalities from confined space incidents is mind blowing. I remember one on the great Barrier Reef a couple of years ago where several people died trying to rescue the fallen in a pontoon of a floatin mooring.

Prefabricated geocomposite drains may wrok also in this project. It may be easy to carry and install if you do not have local gravel.

http://geosynthetic.blogspot.com/search/label/findrain