GROUNDWATER levels in the Surrey hills have reached their highest peaks ever recorded.
Following 21 inches of rain falling on the North Downs in the east of Surrey since the beginning of December, the underground water level is now at its highest level since records began in 1959.
In Mugswell, just a couple of miles from Kingswoood, Chipstead and Coulsdon, detailed observations have been made at a borehole in the grounds of the Well House public house for the last 55 years.
Sutton and East Surrey Water, which takes the measurements, said the average figure for January would show the water at 118ft (36m) below the surface. The latest reading, taken last month, showed the water level to be at 89ft (27m) below the surface. In other words it is almost 30 feet higher than the average.
The repercussions have manifested themselves in the emergence last week of the bourne at Woldingham. A bourne is a river course, much of it underground, which only appears during times of exceedingly high rainfall. The bourne is flowing fast at Woldingham and water is flowing down off the hills towards the Wapses Lodge roundabout, near Caterham, and on to South Croydon by way of Whyteleafe, Kenley and Purley close to the A22 Godstone Road.
More than 100 firefighters have spent the last week trying to stem the flow of water into homes and the Kenley water works, Godstone Road. Playing fields and the Purley underpass near Tesco have been deliberately flooded to save properties from being swamped. Dozens of people have been taken to safety by boat from their homes and have been looked after at a rest centre in Croydon.
Record rainfall fell in Sutton and East Surrey Water's supply area in January. At 232mm (9.15in) recorded at its HQ in London Road, Redhill, the figure was not just more than three times the long-term average for the month of 75mm (2.9in). It was also the wettest month ever recorded since the company began compiling figures in 1910.
The previous wettest January was in 1988 when 180mm (7in) fell. The previous wettest month was September 1968 when 225mm (8.8in) was recorded.
Rainfall in December was 193mm (7.6in) – 233% of the long term average of 83mm (3.2in). It was the second highest December rainfall recorded, the highest being December 1914.
"This level of rainfall is unprecedented and is causing serious problems locally and nationally, said Richard Rap, Sutton and East Surrey Water's Operations Manager (Production), speaking earlier this month.
Andrew McKenzie, from the British Geological Survey, said last week that the Survey had records of the Well House borehole going back to 1942.
He said: "I just looked at the data I have, which isn't the most up to date, only to the 5th of February, when levels were reported as 105.24 metres above sea level - the average value at this time of year would normally be around 95 metres above sea level. It looks as if at that point levels were still rising.
"In 2001 it maxed out at 104.48 metres, so this is a metre higher than previous records in a series going back to the 1940s."
The British Geological Survey said that two Well House boreholes measure the water levels in the North Downs Chalk. Rainwater penetrates the Newhaven and Seaford Chalk Formation, the Lewes Nodular Chalk Formation and the New Pit Chalk Formation, it said.
"This is a dug well, which is 50.6 metres deep and was constructed before 1877 in the garden of the Well House Inn pub. Monitoring has been carried out here since 1942.
"A purpose-built observation borehole was constructed 50 metres away in 1999, but this original well is still used for long-term monitoring, and it is this data that is held on the archive."
Weather expert Ian Currie, of Rickman Hill, Coulsdon, said this week that the winter of 2013-14 had been the wettest of any in at least two centuries. By February 18, he had recorded more than 550mm (21 inches) of rain since December 1 and most of this had fallen since the middle of December.
"I expect the flooding situation to get worse in places as all this rain percolates through the chalk levels in the North Downs and works its way down to the valleys. It takes a long time to filter down through the chalk."
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