Thursday, 15 October 2015

September 2015 overview

Groundwater levels, September 2015
September was a dry month, with less than half of the long-term average rainfall.  The west of Scotland was particularly dry, but only south eastern England had close to or slightly above average rainfall.

Soil moisture deficits remained similar to those at the end of August for most regions in England and Wales, but were closer to average. Consequently, the majority of the index boreholes continued their seasonal recessions in September.

In the Chalk, levels were average or below, except at Ashton Farm where they were notably high following an increase in September. Increases were also observed at West Woodyates Manor, Compton House and Chilgrove House (all in Dorset or the western South Downs). 

Levels in the Jurassic limestones were similar to, or below, those recorded recorded at the end of August. In the Magnesian Limestone, levels fell but remained in the normal range. 

Groundwater levels at Alstonefield (Carboniferous Limestone)
In the slower responding Permo Triassic sandstones, levels fell at all of the index boreholes. With the exceptions of Llanfair DC and Skirwith, levels were normal or above.  A new period of record month-end maximum level was recorded at Newbridge (for the fourth consecutive month) and levels remained notably high at Nuttalls Farm. 

In the fast responding Carboniferous Limestone, levels fell and remained in the normal range at Alstonefield. In south Wales, levels rose at Greenfield Garage and fell at Pant y Lladron, but levels remained above normal in both boreholes.

For more information, see the Hydrological Summary for September 2015.

Hydrological Outlook from October 2015

The latest Hydrological Outlook is available.
Hydrological Outlook from October 2015

Following a dry September, the probability that UK precipitation for October-November-December will fall into the driest of five equal categories is 15% and the probability that it will fall into the wettest of five equal categories is 35%.

Across the chalk aquifer, levels in September were below normal in central southern England and in much of eastern England, and normal elsewhere. 

Levels in other aquifers were mixed, mostly normal to below except for above normal levels in parts of the Permo-Triassic sandstone and Carboniferous limestone. 

Groundwater levels are expected to be normal to below normal over the next month, but with above normal levels occurring in parts of the southern Chalk, mainly in response to the August rainfall. Over the next three months, normal levels predominate, but the outlook is much more uncertain as this is the period where winter recharge typically starts; entering the recharge season with broadly normal groundwater levels, the outlook is highly sensitive to late autumn rainfall.

For further information see the full Hydrological Outlook for October.