Gravity-fed Pond/Tank Drip Irrigation With or Without Electronic Control.

Whenever designing a drip system the first thing you need to decide on is the drippers. Whether it’s do it yourself or commercial I’d first find out the drip tube or dripping system technical information for pressure rating, drip spacing, and flow rate. Pressure is especially important for gravity-fed systems.

To begin with you need to decide if you want Pressure Compensation (PC) drippers to account for elevation change. For every 1 meter of elevation change there is a 9.8 kPa  pressure change with it. That 1 meter is 10% of the 100 kPa (1 bar) minimum recommended for most commercial drip tubes. A 10 meter change in elevation may see the highest drippers simply not drip and others just end up blocking because of the low pressure. Assuming sufficient flow rate, drip lines higher in the landscape will see less pressure the higher they are relative to the bottom drip lines where gravity wants the water to naturally run to. Without a high enough flow rate, there may not be enough water to pressurise the top drippers. The length of piping an drip tubes and whether they’re made into a loop also matters as pipes have friction losses and pressure equalisation to take into account.

Most commercial drip tubes should work fine with about 1 bar (14.7 psi, 100 kPa, 10.2 meter head) if they actually get 1 bar. For example this PC drip tube only needs 50 kPa (0.5 Bar) for pressure compensation but recommends 100 kPa (1 bar) minimum. In general, the higher the pressure, the less likely the drippers are to block, but it depends on the dripper and water. Some drippers are designed to oscillate to clear blockages but need pressure to do so, and pressure is often short in supply in gravity-fed systems not designed well.

For extremely low pressure systems or low drip flow rates that resist blockages, you’re better off looking at wick siphon irrigation, which I will cover that at a later date.

Sizing your piping and connectors for flow rate based upon how many drippers you use and their flow rate matters a lot in any irrigation system, but especially gravity-fed where the pressure is generally lower. You must also account for the pipe & connector friction losses mentioned in gravity-fed systems in order to deliver the pressure needed at the dripper.
You can find pressure drop calculators to help you there. Remember that the longer the pipe, the more pressure drop. So if you have to run a long pipe to your garden, it’s always best to go large for gravity-fed. That includes the internal size of the connectors and any fittings. As one simple flow restriction upstream could ruin your plants day.

Now that you know the size of pipe you need to supply the water to the drippers, you have to get that water from somewhere, and here I’m covering a gravity-fed pond system.

A submerged pipe and pond inlet that is floated just below the surface and moved with the water level but prevented from landing on the bottom is one way to then feed a sediment filter without sucking in lots of debris. This can then be fed to a filtration system such that your drippers don’t block. Another way is to use a pond siphon where the piping runs higher than the water level in order to help prevent debris entering.

Many people think using a mesh filter on the inlet is a good idea, however they can be problematic if not well designed. If you do use a plain mesh inlet filter, I’d make the mesh area large and make the mesh the lowest point of the inlet so that when you weren’t watering, anything large sucked against the mesh would drop away. A cone mesh filter with the peak pointing down for example. Cones have larger surface areas!

I can’t help you with pond filter sediment experience, however there are a lot of commercial and homemade designs out there. Ideally you add a pressure gauge before and after whatever filter you use. That way you’ll know if it’s performing as expected, or the pipe leading to it is blocked(likely the inlet). Add a valve before the filter too for maintenance. Personally I’d probably want a large high flow biological filter I never had to clean. I’d make mine a submersible cylinder mesh with multiple cylindrical layers of filter medium, with the inlet in the middle of it. Let the microbes live on the filter medium and clean the water naturally I say. Might be a bit of a bastard getting it into the middle of a large pond though. 🙂

However if that level of filtration or water treatment isn’t enough there are large commercial systems by Puricare that treat water by oxidation to help prevent irrigation blockage. It uses an ozone generator, a UV light and hydrogen peroxide to produce hydroxyl radicals. In India rather than filter or treat they use simple non-pressure compensating button drippers because of high hardness bore (calcium and magnesium) water blocking most drippers, they can be unplugged cleared and plugged back in. There’s also evidence Magnetically treated water can help reduce the build up of these divalent elements in hard water.

Once you have your water, filter, treatment, piping and drippers all worked out, you may want to automatically control their operation. Electronic soil moisture or timer controllers are one option, there are lots of those around and it’s what most people use. Tropf Blumat is a passive system for home gardens and doesn’t need electronics, but I don’t believe they have a commercial version. Evapotranspiration as used in Aqualone and Measured Irrigation are other options.

If you’re really keen on understanding watering check out The Scientist’s Garden.

Know of other automated irrigation systems that don’t require electronics? Please comment.

Others I know of include siphon watering timers where water is dripped into a siphon container and once the water level reaches the siphon outlet it over flows, siphoning water to plants, empties, and then starts the drip timer process again.

Personally I like evapotranspiration controllers like Aqualone. Before I knew about theirs I made one of my own design that’s more redundant, but I’m trying to simplify it to come up with a good design that doesn’t require magnets, or like mine; pressure valves. Ideally I want one that anyone could make that will hold mains (500 kPa) pressure and be easily made by anyone anywhere.