Wednesday, 17 February 2016

January 2016 overview

Groundwater levels, January 2016
January was very wet (the 4th wettest January since 1910), with all regions registering above average rainfall.  Over double the average rainfall was recorded in north-eastern areas and along the south coast.

The saturated soils throughout the UK meant groundwater levels responded to recharge in all aquifers. Levels were in the normal range or above, apart from two slowly responding sites in the Chalk of central and eastern England. At fast responding sites, the rapid rise in levels that commenced in December continued into January. 

Levels in many aquifers fell mid-month, but generally rose again by month-end (e.g. in the Chalk of the South Downs, parts of the Cotswolds limestones, most of the Permo-Triassic sandstones and the Carboniferous Limestone of south Wales). At month-end, water levels in the Chalk were notably or exceptionally high (at Wetwang and along the south coast) where levels responded rapidly to the exceptional rainfall, or in the normal range and rising at slowly responding sites. However, groundwater flooding in the south-east of England was localised and minor, with a few flooded cellars and surcharged sewers.
Hydrograph from Chilgrove, showing
groundwater levels in the unconfined Chalk

The hydrograph from Chilgrove (West Sussex) in the unconfined Chalk aquifer of the South Downs shows a groundwater level of about 74 mAOD at the end of January, some 17 m above the average level for that time of year.  The multiple peaks are typical of this observation well: levels rise after periods of prolonged of heavy rainfall but decline during drier periods. This is typical of a responsive part of the Chalk aquifer.

Groundwater level at Newbridge, near Dumfries,
in the Permo-Triassic sandstone
Levels in the Permo-Triassic sandstones were generally in the normal range, with the exception of north-west England and south-west Scotland where they were higher due to the exceptional rainfall over the last three months; a record monthly level was again recorded at Newbridge.

Levels rose in the Magnesian Limestone index boreholes, with a record maximum January level recorded at Brick House Farm.

For more information, see the Hydrological Summary for January 2016.

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