So I'm looking for some advice on earthworks, swales and irrigation for our community supported agriculture (CSA) project because we don't have a mains water supply. We were originally planning to have a borehole dug and use water for that for irrigation and what not. Unfortunately, though even going as far as 90 metres (original plan was to only go 45m) into the ground the borehole digging company didn't find water and gave up. There's been a few theories of why this is but we have as good as abandoned that approach and have been looking into other solutions for getting water. At the moment we are thinking to build a 10m x 10m pond/small reservoir which would be fed from the roof of our polytunnel which we're modifying to accept guttering. We then plan to pump the water out up to a header tank for drip irrigation or directly to a sprinkler.
Our land is really pretty flat and is a fairly free draining sandy loam which has about 2 feet of soil before you hit limestone. There's no slope on it and no hills. We mainly growing vegetables.
So my question is, is there any earthworks that we could do on such land that could directly irrigate two polytunnels of about 30m x 7m as well as the land (2 acres) in times when needed which could eliminate the need for a pump? Also, does anyone have any experience of making ponds without a pond liner? How much clay content needs to be in the soil etc and if water is drained out of a clay lined pond would it crack and lose water?
Any help, advice or points in the right direction are greatly appreciated!