To farm fish, you need a completely reliable supply of clean water; if the water supply fails, a life’s work can be destroyed in minutes.
The fish farm was situated in a flat area, near sea-level, with roadside ditches like small rivers running all year. The farmer’s home was a converted watermill; a fine Georgian fronted building with outhouses and a large millpond. The fish were high quality trout, bred for fishing lakes, farmed in a series of cascaded ponds which were fed by a spring. These beautiful fish, although moving fast and with great agility, gave me a deep feeling of calm. The farmer also sensed this strongly, and it was clear that he loved his work and his fish. However, running this farm involved one terrible worry: if the water supply (and hence the fishes’ oxygen) is cut off for more than 20 minutes, the fish die. Tragically, this actually had happened in the past, and it took him four years to rebuild his stock. He had called me in because in a dry year – and they were becoming more frequent – the flow rate from the spring was dropping from a hundred thousand litres a day to fifteen thousand. This was forcing him to recirculate the fishery water, which meant relying on pumps, aerator sprays and a constant supply of electricity.
Having looked round the fishery ponds we walked upstream, over the weir (which had a V-cut) and up to the supply pond. The V-cut in a weir is a convenient way to measure flow rates; it’s done by recording the depth of water flowing through the V. The flow rate can be found using standard look-up tables.
The water contained carbon dioxide, proving that it had flowed through Sussex downland chalk. There was a millstream, about 100 metres long; this was needed to allow the carbon dioxide to diminish to a level at which the fish would not suffer from the ‘bends’.
So the requirement was for another source of water to supplement the existing spring, with flows of at least fifty thousand litres a day. Ideally, the new source would be ‘artesian’, meaning that the water pressure in the borehole would be sufficient to push the water up to the surface without the need for any pumps.
Using my heavy copper outdoor L-rods, I scanned the two fields either side of the stream and found that the eastern field above the fisheries had the best possibilities. There, I located two good sources. One with two streams crossing had the highest yield, but the second, with a smaller output was, I predicted, artesian. I marked both locations with flags. The position was ideal for running a pipe above the weir; this meant it could supplement the supply for the whole fishery.
We went back to the upper pond at the mill, and I dowsed for possible underground spring flows into the feeder pond. I detected two major potential flows from the north, but also a second source at the eastern end of the pond. The mechanical diggers that are now available can scoop earth down to a depth of more than four metres, and so I dowsed to find out what quantities would flow out from a hole four metres deep. I found that the two areas together would yield around 800 cubic metres per day. This is a very large quantity and I was a bit worried about the accuracy of my findings, as dowsing to find the quantity is not easy.
Some time later, I received an email from the farmer, saying that he had spent three days digging with an excavator. He was delighted to report that, “Today’s flow rate is 596.38 cubic metres per day! This is the highest I have recorded since the flooding in and around Chichester, back in the nineties.”
He had found water where I predicted; his V-cut flow meter was now recording 600 cubic metres per day. To express it another way, that is six hundred tonnes of water per day, or enough to fill an Olympic-size swimming-pool every four days. Downstream, the ancient stream has re-established itself, supplying village ponds and irrigating fields.
There was more good news: the well did prove to be artesian, so the farmer no longer has to rely on pumps and electricity or diesel. So he is a very happy customer: he has a reliable, energy-efficient water supply and his fish farm is safe.
He is also one step further towards realising his dream: he hopes one day to get the water mill running again, not to grind corn but to generate electricity.