What Water Flow Rate Is Required & Rainwater Harvesting

[VincentBali]

What Water Flow Rate Is Required & Rainwater Harvesting

I live in Bali but am hanging out in BKK while my wife attends hospital. Greatly enjoying reading the Farming in Thailand Forum as I have bought 1.2 hectare (7.5 rai) of sloping hillside land out in rural east Bali to build a house next year. I’m not thinking of farming but already we have planted many fruit trees, vegetables etc for our own consumption and for our workers to sell any excess.

When we get back in January we are going to have a bore hole dug to establish a water supply.

Below us are rice fields with plenty of water but my land is on a steep ridge 60/80m above. Also we are on the foothills of Bali’s largest volcano so we expect to encounter plenty of rock when we dig.

No other foreigners live in the area so no track record of wells/bore holes being dug. The locals go down to the river in the rice fields to wash, collect water, sustain their livestock etc.

Two questions, if you don’t mind;

1. what water flow rate (cubic metres a day) do we need to see to irrigate 7.5 rai of domestic garden, a bit of lawn, vegetable gardens, fruit trees etc?

2. has anyone tried rainwater harvesting i.e. collecting and storing rain during the rainy season to be used during the dry? We have plenty of land for this so we could create a reservoir at the bottom (possibly lined with geo-membrane) and pump up to the house and gardens

Any thoughts would be appreciated.

We have talked to a number of bore drillers and their bore depth estimates range from 30m to 100m. BTW, in Bali the cost per metre of drilling is much higher than in Thailand so count yourself lucky.

Thanks

[chownah]

Irrigation needs depends on the weather and soil type and crop. A general rule of thumb for hot weather and no rain fall is that you will need to apply the equivalent of between 5 and 10 cm in depth of water to cover the entire area to be irrigated and this is done every two weeks. You want to irrigate 1.2 hectare which is 12,000 square metres so you will need 12,000 x 0.10 = 1,200 cubic metres every two weeks so 1,200 / 14 = about 85 cubic metres per day.......but this would be for a water intensive crop and in extremely hot and dry weather so consider that you only apply 5 cm every two weeks and your numbers are all cut in half so you would need 600 cubic metres every two weeks or about 42 cubic metres per day.

The figures above are for farming type irrigation systems where water is dispersed somewhat evenly over the surface of the area being irrigated and reduced water consumption can be achieved by more careful distribution with the ultimate in water savings being realized with a drip irrigation system......I suspect that another poster here called Maizefarmer is hot on my heals and will vet what I have posted for accuracy and reasonableness and will fill you in on alot of good information on drip irrigation systems; something he has alot of experience with.

Chownah

P.S. Another way to save water is to apply a mulch to the surface to reduce evaporation from the soil surface.

Chownah

[VincentBali]

Thanks Chownah

That’s a great help. I will investigate drip irrigation - if anyone has any knowledge or views on this I would be pleased to hear.

Hopefully, I can cut back on the 42 cubic metres per day you estimate as that is 29 litres a minute every minute of every day – enough to deplete most aquifers, I would have thought.

I read on this forum that Isaan is getting drier and drier each year – is rain harvesting (i.e. storing rainwater in tanks or reservoirs for use in the dry season) practiced at all in Thailand?

[RamdomChances]

I've split this from the borehole thread, you might get a bit more info.

[chownah]

that is 29 litres a minute every minute of every day

Actually this is only what you would have to pump in the dry periods. If your soil has good water holding capacity and the root zone is deep enough you wouldn't have to water established plants until about two weeks after the last good heavy rainfall.

Also in rereading your origial post I see that you have fruit trees. Some fruit trees do not require irrigation at all in some climates. Trees often have very deep root systems and thus can extract water from depths that other crops can not reach.

In evaluating your water needs you need to find out about the rainfall; both the amount and distribution throughout the year and evaluate the area you expect to have in what types of crops. For instance, I grow sunn hemp (a legume and not related to regular hemp) as a green manure crop and if it is planted in wet soil then it will grow for 45 days without further rainfall at which time it is plowed into the soil to increase soil fertility, organic matter content, and soil permeability.....so that crop might not have to be irrigated at all or at most only once at planting...it might benefit from more water but I don't know as I'm just starting to work it into my rotation. For seed production it only needs to be planted to wetness (or irrigated once after planting) and then irrigated once more when flowering begins....this is enough to develop a seed crop...this seed crop actually benefits from dryness to dry the seeds when mature.....so this crop only needs to be irrigated twice in a four month period...again it might give a better crop if irrigated more but I'm learning about this too so I don't know yet. What I'm trying to point out is that there are many variables that determing how much water you will need and you might not need as much as you think if you plan things properly around the rainfall patterns at your location. You are smart to be thinking seriously about water for your gardens and trees. Water is probably the most important input for farming and gardening and I don't want to give the impression that you should develop your water source minimally...on the contrary I would recommend developing your water resource to the fullest extent.....my examples of crops that require less water are offered as encouragement that once you get as much water as you can then there are many ways to make it do even more than you might have thought initially.

Chownah