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December rains and desalination boosts reservoirs

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HEAVY rain in December combined with three weeks of processing seawater to top up the Island’s depleted drinking-water supplies means reservoir levels are almost three-quarters full.

Helier Smith, Jersey Water chief executive

By the end of November, after months of very low rainfall, reservoir levels had fallen to 46 per cent, leading Jersey Water to turn on the desalination plant at La Rosière between La Moye Prison and Corbière, for the first time in seven years.

Then it started raining – and continued to do so. The company turned off the plant in the week before Christmas when supplies had risen 62 per cent. More rain over the holidays resulted in the final reading of 2018 standing at a healthy 69.7 per cent full – and rising.

‘At the moment we are 72 per cent full as we have gained a few per cent since the end of the year,’ Jersey Water chief executive Helier Smith told the JEP on Wednesday.

‘Val de la Mare is 85 per cent full but Queen’s Valley is 55 per cent full overall so we are filling it up with water from Grands Vaux.

‘However, the top part of Queen’s Valley is actually 100 per cent full but the lower part of the reservoir is at 50 per cent.’

On New Year’s Day last year, reservoir levels were 98.7 per cent full. This year’s figure of 69.7 per cent was 16 per cent down on the five-year average of 83 per cent.

Even though only 0.2 mm of rain has fallen so far this month – and the company’s long-range forecast is for dry weather conditions up to the end of February – Mr Smith says there are no plans to bring the desalination plant back into service at the present time.

It costs £5,000 a day to run the plant, which uses a reverse osmosis process to remove salt from seawater and pump it to Val de la Mare for further dilution before being pumped to the other reservoirs It can produce 10.8 million litres a day and the Island’s average daily consumption in winter is 18 million litres.

However, as the company likes to be at full capacity by 1 April, Mr Smith says they may have to resort to running the desalination plant again in late winter or early spring.

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