Gravity Fed Drip Irrigation - large setup

13 years ago

I'm in the middle of installing community garden.

The next step is to put in place a gravity-fed irrigation system.

The garden is about 30,000 sq ft with about 19,000 sq feet of it for gardening. The rest is landscaped for group activities and social. We've installed 800' of deer fencing and varmint fencing, rototilled several hundred yards of garden beds, and will start putting in plants in about a week.

For the irrigation side - I have on-site a 4,500 gallon plastic cistern and a 3,000 gallon plastic cistern.

The current plan is to harvest rainwater in the 3,000 gallon cistern off of a building roof that's about 500' away and periodically transfer the water to the 4,500 gallon reservioir cistern using hose and a pump. The local fire company will give us our first fill-up for the reservoir cistern.

I can pull about 1,000 gallons per inch of rain, more if I need to (by connecting into more of the building's downspouts)

The reservoir cistern is sited at the high point of the garden outside of the fence. It's about a four foot drop to garden beds which start 45-50' away. The garden itself has about a seven foot drop from the uphill fence to the downhill side of the fence across a distance of about 200'

The reservoir cistern is empty - I can put cribbing underneath it if I need to raise it to drive the gravity-fed irrigation . There's no electrity for the near future.

There are five distinct zones to the garden - colorscaped beds for community activies, communal vegetable rows for tomatoes, peppers, and such, private plot vegetables, youth gradening, and strawberry/ raspberry rows.

I have trades people involved who can drill holes in largish cisterns and put in the piping. They just need to know what to do.

If anybody can share some experiences with gravity fed irrigation what to do or what to avoid or can recommend a company to help with it, I'd deeply appreciate you sharing your thoughts.

Thanks,

Todd

ps. I've learned two things going through this proces -

1) rent a Dingo with rototiller and auger attachments at the start of the project, not midway through it.

2) take an ibuprofen before setting out to work on the garden

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Comments (5)

lehua49
13 years ago
Todd,

Man you are doing the hard stuff. Two ibuprofen is better. Here is the hydraulics. Approximately 0.5 psi for every foot of elevation the water level is from the garden surface. For example if the height difference is 10 feet you will experience 5 psi at the garden outlet pipe. The pressure will decrease as the height of the water level decreases. In low pressure water distribution pipe sizes need to be bigger because your flow velocity will be low. See what flow your system will deliver by filling a 5 gallon bucket up and timing the fill. Do it several times and average the gallons per minute. You will now know how long it will take to deliver a certain amount of water to a zone. At least you won't need pressure regulators but probably a filter screen if your going with drip or soaker hoses. Think about pvc with holes drilled into it at what ever spacing you need(I can help you with this). You need to calculate the usage flow rate of the drip tubing or soaker hose to plan correctly for even distribution. Who will coordinate the water regime for the garden? Talk to a local landscaper to help you and you will advertise his name in the garden. Trial and error is a way of learning life. Aloha
thmcintyre
Original Author
13 years ago
Thanks for the insights - I like the idea of drilled PVC pipes rather than going with drip or soaker hoses.

I'll have more detailed plans tomorrow once I finish the sod-busting/rototilling and can take some accurate measurements.
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bg, Perfectly fine. I use adjustable emitters. Just see what the system does and adjust. The plants need less when young(small root system) and more as they mature(large root system). You could actually put emitters on both side of the plant to get coverage faster. All depends on how long you run your irrigation. Trial and error is the best method. Aloha
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1) The pond is about 12 feet wide and the st on the surface and 25 feet long at the longest the surface. It is 5 feet deep at the deepest point but the width is considerabaly smaller at the bootom than at the top 2) The pond surface is at about the same level as some of the lower beds but it will not be used directly for the irrigation system. 3) The beds are already built and are terraced. 4) short answer no. However at any given time we will try to group plants with simmilar watering needs 5) No, However there is only so much water avaliable for the wole garden. We can't use up all the pon water or our fish will be very sad and our modest sized rainroof collection system might have a hard time filling the barrels. 6) I messured the beds today and they are about 8 ft X 5 ft for the most part. There are 8 beds that size and 1 bes that is 3 X 8. 7) the emmiters are non pressure compensating 1/2 GPH at 30 PSI 8) The drums will be linked and were planning on getting between 4- 6 (depends on how cheap we can find them for and how much water we can capture) 9) Average annual precipitation is 45 - 50 inchesdistributed as follows Jan 3.3 Feb 3 Mar 3.9 (APR 4 May 4.5 June 3.7 July 4 Aug 4 Sep 3.9 OCT 3.5) Nov 3.8 Dec 3.5 () growing season Currently the pond collects runoff from a 10 X 25 tarp plus its surface area. However, the roof with gutters for collecting rain will be over top of part of the tarp (approx 56 sq feet) Yes. Our club meets every week once a week nobody is at the garden to turn water n and off at other times. I found a 0 PSI timer and automatic rainshutoff. I think you misunderstood. It is not a community garden. Rather it is a college Club. (Organic Gardening Club) We hope that with the irrigation system we will be able to donate a box of produce a week to a local shelter plus have some extra for the members of the club. We want to do this from the 8 8 X 6 beds. We do have a few extra beds that I didn't include becuase we don't plan to irrigate them. Right now with hand watering once a week we get good production in the fall and froma few specific crops in the summer but many crops fail do to lack of moisture. Thanks for any help you can give.
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Mr. Aloha, Why yes, I will provide more substance. My water well provides 8 gpm, my well pump is 1/2 hp. I want to use a generator to pump the water into the cistern. This will be above ground and be a 200 gallon capacity. The cistern is at the top of our property and I'd like to have 2-4 different drip zones coming off of it. My raw land is in the Rocky Mountains in the subalpine zone. I'm going to plant a line of 10 northwest poplar 9 yards apart and 5 yards away an adjacent line of 15 golden willow 3 yards apart. I'm planting clusters of blue spruce and douglas fir. I will plant groves of saskatoon bushes, wild roses and pin cherries. Each grouping or line will require a different amount of water. I'd like to have a timer system with 2-4 lines. My questions include what would the pressure be coming out of a cistern with a 200 gallon capacity? Is it logical to assume 200 gallons would be large enough to water a line of 10 poplar, 15 willows in one zone, etc assuming a daily watering of 1 hour? Can I add other zones? Thanks for your insight. Doc
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I use gravity feed for my garden. If you want to lay drip lines and all of those other fancy attachments for shop bought irrigation you need to find out the litres per minute where your garden tap is. Get a 9 litre bucket, run the tap on full and when it is running fast fill the bucket and time it to see how long it takes to fill then work out the litres per minute. Here is the formula Litres per minute = 9 litre bucket x 60 seconds -------------------------------------- Time to fill the bucket So for the first line 9 x 60 = 540 Time to fill bucket say 10 seconds Divide 540 by 10 seconds which means that you have 54 litres per minute. Now if a sprinkler uses 2 litres per minute you can have 27 of them. If a dripper uses 1 litre you can have 54 of them. Or you can mix and match, using what you want to as long as the total does not go over the maximum of your litres per minute. (If you use gallons or pints change litres to what you use. The fittings from a shop should tell you how many pints? of water are used a minute) Now having said all of that, I don't use the shop bought attachments! Instead I run alkathene (low pressure irrigation pipe) under the mulch and with a fine drill bit, I have drilled holes where I want the water to come out, effectivly drip feeding each individual plant. If you do this, make sure that the holes are on the side of the hose and not the bottom so that the little holes do not get clogged up when the hose is turned off and there is a back suction. Also I do not have any lines that have an end, instead they all join up to form a grid - this also helps to keep the presure equalised. Those lines that run around my garden are flat - there is not any slope there. One other thing to get the pressure as high as possible, I use 25mm main line to my garden tap - it is not until the hose on the tap that the line reduces to 15mm which helps with the pressure. I used to reduce the 25mm line feeding the tap connection to 15mm just before the connection, but when I changed it to 25mm going into the tap connection the pressure from the garden hose increased :D If your garden tap is not right next to your garden, extend the line and put one in - as the longer you have water running through large pipes, the better the pressure at the other end. Gravity feed is brilliant and works well. It is easy to add in lines and make changes and it is such a great feeling when it works as you want it to. My tanks are ony about 100m away from the garden. Good luck!
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lehua49
13 years ago
Mc,

Less likely to clog over the long term. Aloha
jsnyd23
13 years ago
Not sure I agree with the idea of drilled holes in PVC. I think the best way to go would be using T-Tape. It works great at low pressures (like those found in a gravity fed system) and won't clog like you may experience with open holes in PVC. Lehua's approximation with .5psi per foot was very accurate, however for exact measurements it is 1 pound of pressure for every 2.3 feet of elevation. If you have a drawing of the garden you can submit it to Dripworks and they will design the system for free (no obligation to purchase). I think they even offer a 10% discount to community gardens.

Here is a link that might be useful: Free Drip Irrigation Design
lehua49
13 years ago
Js,

I am with you except drip lines with pressure compensated emitters have a history of clogging because of the torture track path the water has to travel through before exiting the emitter and not pristine municipal water. Otherwise the holes would be similar to drilled holes in PVC. The size of the holes is the key factor. The hole size should relate to the slope of the tube. This can be achieved by the trial and error method or calculated. Drip is already figured for you but you need the flow rates, pressure and slope to complete the design. One step at a time when gardeners are beginning to size up the situation. Whatever you feel comfortable with and gets the job done. I learned by trial and error and experimenting. Good Link but you might not want to give all the contact info required by the site to get the info. It is not hard to get the info other places. There are past thread experiments discussing these very systems. Aloha

Gravity Fed Drip Irrigation - large setup

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Gravity Fed Drip Irrigation - large setup

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thmcintyreOriginal Author

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