Busumatako Yangu

Thank you, that's a sincerely appreciated comment. I'm an idealist who has constantly had to learn to seek middle ground

Apologies for the delayed response. It's pruning season and I have had exhausting days of trimming the trees and hauling great quantities to the wood chipper to be recycled back to where they came from, but hopefully composted down, and with the borers and other insect problems substantially reduced. I'll be adding biochar, liquid compost and fungal slurries to these mulch piles. Any idea on how much slurry should be added to an adult mulberry or wax apple tree for example?

Regarding the above answers, thank you all very much and I'm going to post some pictures because I feel that my initial description was somewhat misleading.

Many rivers in Taiwan are monsoonal and are also completely empty during the dry season. During typhoons, they can quickly run 10m higher than usual with tremendous disturbance to both the banks and the river bed. For this reason, many of the rivers have concreted banks and the problem is deferred downstream.

We do have a well being dug on the property, but this is an expensive process and one is probably all we're going to have in the next few years. It's a long way from the vegetable garden and will hopefully be used in the near future to irrigate a lowland orchard. The problem with our ponds is that the soil here just isn't suitable for natural water storage. The soil particles don't bind adequately to create a naturally impermeable surface, so our ponds have liners and are then backfilled with earth to mimic natural conditions more closely. Sadly, this water obviously cannot move through the landscape. They do, however, have a substantial quantity of fish, lotus, water hyacinth and duckweed and are topped up with both rain water and some grey water from surrounding buildings.

I think Redhawk, that your suggestions are very applicable to our situation. Looking at the size and height of our tank, do you think one of the sand filters or tray type filters would be feasible to install on top of the tank? Adding the mineral sulphur to the tank, along with some of our liquid enzyme and beneficial bacteria (we also buy this commercially) would be a great way to fertilize and gradually balance the pH of the field without too much disruption.

I did some research on the perforated plates and believe that they will be very useful in this situation. The catch, often, is trying to purchase these items and get the corresponding fittings here in Taiwan. Rain water isn't collected here anywhere near as much as my home country Australia. I have installed a number of tanks, but try to what local people told me at first, the problem is with the boom and bust nature of the water cycle here. In a heavy rain even the biggest tanks are filled within a day or two. Then, while the rain continues to bucket down for weeks the tanks merely overflow. Once the rain stops, it stops, and then even 20,000L of water gets used up pretty fast. Also, much of the property is flat and thus pumps become a necessity to move this stored water around. Where feasible, I have installed gravity fed systems to passively move water to lower levels.

To be honest, I'm feeling very conflicted about how much we have installed in the way of PVC piping, pond liners, electrical wiring and metal storage tanks. If this infrastructure is done right, then the farm will have a solid basis on which to practice permaculture principles, but it seems very difficult to establish all this without using a lot of petrochemical products and processes. I'm intending to make some amends next year and plant a large section 5 woodlot on the further edges of the farm.

Oh, and about the sentient diet. I believe that there is acknowledgement of the health benefits of alliums, but they are held to have a negative effect on meditative practice. This belief is shared with the local Buddhist version of vegetarianism as well. Mushrooms? Well, that's more of a religious prohibition that is based on fungi growing on decaying matter and thus perceived as not clean.

In conclusion, I'm very happy with the suggestions presented so far. I'm still somewhat unsure how to divert the water through the suggested biological processes and then return it to the storage tanks for pumping. I'll look into Redhawk's suggestion of tray filters and pressure plates. The pond gravity-feed idea is one of the most feasible, but I wasn't aware previously that it is leaking.

Excellent. Some speedy and thoughtful responses. Let me first clarify a few of the questions that F Agricola raised.

In summary, your summary was pretty spot on. However, for now, I'm only looking at our market garden area rather than the whole 20 acre farm.

It's about 60m² of ditch and furrow cultivation. Lots of leafy greens, cabbages, radishes etc on the inner beds and peanuts, pineapples, rosella, corn etc on the outer beds. Thus, looking at the inner intensively irrigated area (40m²) and working on a rough estimate of 6.5L/m² I'm thinking about 250-300L of water per day. This is from Oct-Mar. I'm told that over many years here the dry season keeps getting drier and the wet wetter, and given that it's November and 30°C, these estimates may have to be raised. We are getting a well dug near to the river to take advantage of natural filtration, but it depends on the availability of the excavator driver and he's a very busy man. It's also on the other side of the whole property....

We have had the water tested and it's pretty good as far as heavy metals go. There are some infrequent fish die offs and it's definitely very turgid with a lot of algae.
The soil content is likewise low in heay metals, but also low in fertility with a pH around 7.5 - we are adding organic compost and animal manure at the time of planting.  
I'll go with defining organic in our context rather than speaking about Taiwan in general. It's a meditation and yoga retreat with an emphasis on sentient/yoga diets (no garlic,onion,egg,meat,mushrooms) and we have more than 10 people who live on the property, many volunteers who stay here and also many guests. It's not so realistic in this rural and agricultural environment to be overly demanding about organic purity. I want to do the best I practically can. We generate A LOT of food scraps and make hot compost, we use farm-grown mulch regularly - but it breaks down fast, we use farm-made enyzmes and liquid compost along with commercial organic fertilizers.
I absolutely agree about planting trees and shrubs around the perimeter of the garden.

As to S Bengi's suggestions. We already collect duck weed from the river and our ponds. Algae - not a bad idea, but also a lot of work. Sediment - I worry there would be more concentrated pollution in the silt. I'm not sure how many people wanting to keep their veggie plots clean would appreciate the free herbicides that the local mango farmers contribute, but I'll try to be grateful The pump is specially designed for river use, so it doesn't clog 'easily' but it certainly does clog. Regularly and at the bottom of a 10m ladder climb down a typhoon wall. I also agree on the ponds - it could be an option to pump into our pond and from there into the water tank. I will use a feeder tank for liquid compost and probably a weekly flood of the ditches would be very helpful. No need for swales on this section as it's very flat and, to be honest, we have a whole season where getting rid of excess water quickly is critical.

So, in conclusion, my thoughts for now...
1. Adding a foam sheet around the river pump will help prevent contamination, but will be a nightmare to regularly access and clean.
2. I'm looking at in-line filters, but they also have to be easy to screw in and out and cope with high pressure
3. A slow sand filter appeals to me, but I'm concerned it's not practical with a 20,000L tank to top up and the pump costing quite a lot to run if I reduce the incoming pressure into the tank and thus take much longer to fill it. Ideas?
4. Gravity feeding water down into the 20,000L tank from our lotus pond. Easier to access and filter. Might need to install a float valve
5. I'll certainly accept a better solution rather than an extremely expensive/perfect solution. I'd be very grateful to hear from anyone with any experience filtering river water into holding tanks for irrigation water. I'm also really pleased with the responses I have so far. Thanks for the suggestions

Hi everyone,

Long time lurker, first time poster here. I manage a 25 year old organic farm in the south of Taiwan and we have roughly 20 acres of land planted out with mango, lychee, curry trees, guavas, bananas and many speciality fruit trees. There are three large ponds, a market garden and we use/have experimented with liquid composts, natural farming techniques, permaculture design, local pruning techniques, aquaponics, grey water systems, green manures, crop rotation etc.

Currently, we have a pressing issue with our irrigation system and I would appreciate any help or advice. We have a powerful (5bar or roughly 70psi) electric pump in a nearby river which was previously used to irrigate the market gardens. Unfortunately, the river is full of sediment, algae and all the neighbours spray their mango trees rather freely. There is a 20,000L (5,000G) rainwater tank (not refilled for many months of the year due to the dry season) which I am considering using as a settlement/filtration tank. The tank input could have an in-line filter attached. This would then have a submersible pump floating on the surface of the water in the tank which would, in turn, pump to the sprinkler system.

My questions - would a clay/sand/charcoal filter work adequately in only one tank which would fill under high pressure? How long would the water have to stay in the tank before pumping out again? Does anyone have any suggestions for a low-tech and effective solution for filtering out muddy and potentially chemically affected water that would be suitable for our situation?

Thanks in advance and I'm happy to share feedback on our progress