Reservoir levels plummet

Tuesday 06 November 2018

Guernsey's reservoir stocks have reached the lowest levels recorded in a decade, at just 73.9% capacity.

This is thanks to the minimal rainfall the island has seen so far this autumn, with only 72mm being recorded in October.

This is more rain in October than Guernsey has received over the last few years, with just 55mm being recorded for the same month in 2017, but the Guernsey Met Office's annual report for 2017 spoke of a run of dry Octobers for some years.

Over the last 10 years, the amount of rain was still 13% less than the average for this time of year, which is 83.2mm. 

So now, while the reservoir sits at nearly 74% capacity, it is usually closer to 90%, indicating a substantial decline. In just the last four weeks, there has been a 3% decline, according to Guernsey Water. In 2016, the utility issued a warning about the water levels in St Saviours when it dropped to just below 78%.

"Winter is coming. Rainfaill has been steadily increasing, this month saw 72mm and the reservoir is currently at 73% capacity, however these levels are some of the lowest over the last decade," it said in a post on social media. 

"So with an uncertain forecast of substantial rainfall, we encourage you to use water wisely." 

The annual weather summary for 2017 from the Guernsey Met Office Annual Report. 

Jon Holt, Guernsey Water's Operation Manager: "We would always advise our customers to use water wisely. To help, we have handy advice sheets on our website with tips on how to be more efficient with water usage at home, work and school.

"With the storage levels 73.91% full the water supply perspective continues to be in a reasonably healthy position for the remainder of the year and into early 2019. However as the levels are close to being the lowest (for October month end) over the last ten year period, together with uncertain forecast of substantial rainfall in the short and medium term, efforts are being made to maximise water collection where possible.

"Following six months of low or very low rainfall, which has been only 54% of the climatic mean, the situation is being carefully monitored and will continue to be done so until levels return to normal."

Despite the warning, the reservoir is not about to dry up.

It still holds 3,241 megalitres of water in total, and collected 240 more megalitres just last month from streams flowing into the site. 

Rainfall has previously always picked up in November and December as well, with the Met Office report showing in 2017 rain levels rose from that 55mm mark in October, to to 77mm in November and 125mm in December. 

Pictured top: St Saviour's reservoir.