Wednesday, 24 June 2015

May 2015 overview

Recessions in groundwater levels continued during May, despite the wet conditions over much of the UK. Soil moisture deficits (SMDs) have become established in south-eastern areas, meaning rainfall is taken up by the soil rather than recharging aquifers. 
Groundwater levels, May 2015

Across most Chalk aquifers, levels remained normal although they declined at a slightly faster rate than is typical. In Yorkshire, Wetwang and Dalton Holme were notably low. Compared to April, more of the Wessex and Hampshire Chalk was below normal; notably low levels were recorded at Ashton Farm and Tilshead, which recorded its sixth lowest May level in 47 years. Only two Chalk boreholes (Therfield Rectory and Little Bucket Farm) recorded above normal levels – these boreholes continued to be influenced by the wet conditions of 2013/14. 

Elsewhere the situation was mixed. In south-west England and south Wales, levels remained normal. Levels in the Jurassic limestone were below normal in southern areas and nearer normal further north. Swan House, in the Magnesian Limestone, was an exception, recording below normal levels due to limited recharge this winter. 

Several Permo-Triassic boreholes remained at exceptionally high levels, the legacy of exceptional recharge in 2013/14, whilst others were close to their seasonal norms. An exception was Llanfair D.C. in north Wales, where levels were slightly below normal. 

Any moderation of recessions in the Chalk from a wet May was yet to show at month-end. Low levels in Wessex and Hampshire may persist through the summer or decline further, though still well above the minima of 2011/12.

For more information, see the Hydrological Summary for May 2015 [PDF].

Tuesday, 16 June 2015

Hydrological Outlook from June 2015

The latest Hydrological Outlook is available.

In the Chalk, May groundwater levels were mainly normal in the south-east, but levels were below normal (and notably low in some boreholes) in parts of southern England and Yorkshire. 

Levels were mixed in other aquifers, with exceptionally high levels persisting in parts of the Permo-Triassic sandstone. 

The one month outlook suggests a similar situation will continue in June, although levels in the Permo-Triassic are likely to be notably high rather than exceptional. 

The groundwater situation is unlikely to change significantly through the summer; the three month outlook suggests normal levels will dominate, but with below-normal levels persisting in parts of north-east and southern England (although there is a possibility that levels in some parts of Wessex may return to normal).

For further information see the full Hydrological Outlook for June.

Wednesday, 20 May 2015

April 2015 overview

Groundwater levels, April 2015
With little rainfall and some very warm weather, soil moisture deficits (SMDs) climbed steeply through April and, by month end, were substantially above average across the main aquifer areas (SMDs were double the typical end-of-April magnitude across the Chalk outcrop).

Consequently, levels fell at index wells throughout the country, with a few exceptions: the slowly-responding Chalk at Therfield Rectory and Dial Farm in eastern England, the Permo-Triassic sandstones at Nuttalls Farm and the Carboniferous Limestone at Alstonfield in the Midlands.

In the Chalk, levels were generally still within the normal range but below average for the time of year in Yorkshire, Northern Ireland and Dorset-Wiltshire, whilst they remained above average in the eastern part of the North Downs and upper Lee valley of Hertfordshire. However, compared with the exceptionally high groundwater levels in the Chalk in April 2014, when groundwater flooding was still present in some areas, they are now up to 4 m lower across southern England (and over 6 m and 12 m lower at Therfield Rectory and Stonor Park, respectively).
Groundwater level hydrograph, Stonor Park (unconfined  Berkshire Downs Chalk)
In the fast responding Jurassic and Magnesian limestones, levels remained average or below and in the slow responding Permo-Triassic sandstones they were average or above (still exceptionally high at Newbridge, an area receiving above‑average autumn and winter rainfall, and Nuttalls Farm). Groundwater levels in the Lower Greensand of south-east England remained above average. With the modest rise in level at Alstonfield, Carboniferous Limestone levels were in the normal range in both Derbyshire and south Wales.

As little recharge is anticipated from now until the autumn, the current picture is likely to persist unless substantial late spring or summer rainfall is received.

For more information, see the Hydrological Summary for April 2015 [PDF].

Hydrological Outlook from May 2015

The latest Hydrological Outlook is available!

Normal groundwater levels were widespread across the Chalk in April, but with below-normal levels in north-east England and Wessex contrasting with above-normal levels at a few boreholes in the south-east. Groundwater levels were variable in other aquifers, with above-normal levels in parts of the Permo-Triassic sandstone. 

With evapotranspiration increasing and seasonal recessions generally well established, the outlook for both one and three months is for a broadly similar situation to persist. Levels in most aquifers are likely to be normal or below, with above-normal levels largely confined to some central and northern parts of the Permo-Triassic sandstone aquifer. Below normal levels are likely over the next three months in western and north-east England, with the possibility of notably low levels in some localities. 

For further information see the full Hydrological Outlook for May.

Wednesday, 22 April 2015

March 2015 overview

Groundwater levels, March 2015

With dry conditions prevailing across southern and eastern England during March, soil moisture deficits (SMDs) began to develop across the Chalk outcrop. Groundwater levels in index boreholes generally fell in March and, with a few exceptions, were in the normal range or just below for the time of year.

Levels in the Chalk receded in most areas and were below average for the time of year in the Yorkshire Wolds and at Tilshead in Wiltshire. However, modest rises (less than 1 m) were recorded in parts of the Chilterns (Stonor Park and Therfield Rectory), Norfolk (Washpit Farm) and Lincolnshire (Aylesby). In the North Downs, Well House Inn has risen but remains normal, whereas Little Bucket Farm remains notably high despite a fall in water level. Levels in the South Downs were slightly above normal, reflecting higher late-winter rainfall in the far south-east of England.

Groundwater level at Wetwang, Chalk of Yorkshire
In the faster responding Jurassic and Magnesian limestones of central England, levels fell and were average or below. In the Permo-Triassic sandstones, levels were relatively stable, remaining exceptionally high at Nuttalls Farm in the Midlands and at Newbridge in south-west Scotland. Levels at Lime Kiln Way in the Upper Greensand of south-west England fell and remain in the normal range, while in the Lower Greensand of south-east England, levels remain high despite falling. In the flashy Carboniferous Limestone, levels fell and are normal in south Wales and below normal at Alstonfield (Derbyshire).

As SMDs increase throughout the spring and summer, significant recharge is unlikely unless exceptional rainfall is received, with levels likely to continue their normal seasonal recessions from now until the autumn.

For more information, see the Hydrological Summary for March 2015 [PDF].

Thursday, 16 April 2015

Hydrological Outlook from April 2015

Hydrological outlook map The latest Hydrological Outlook is available!

In March, normal groundwater levels were widespread across the Chalk, but with below-normal levels in north-east England and above-normal levels in the far south-east. Levels were variable in other aquifers, with both above- and below-normal levels in the Permo-Triassic of central England. 

With recessions established in most aquifers, groundwater levels over one to three months are relatively insensitive to  rainfall, with significant recharge unlikely unless rainfall is exceptional. 

The one month outlook suggests significant areas of the Chalk aquifer will see below normal levels and, except in the far south-east, the three month outlook suggests a predominance of below normal levels, with an increased probability of some notably low levels by mid-summer. Levels in the Permo-Triassic of northern England and southern Scotland are likely to remain normal or above.

For further information see the full Hydrological Outlook for August.

Wednesday, 20 August 2014

Hydrological Outlook from August 2014

The latest Hydrological Outlook states that the groundwater levels in August will generally be unaffected by the amount of rainfall we have.  This is because large soil moisture deficits have built up over the summer and rainfall will not reach the water table while these deficits exist.

Looking further ahead, the prediction for precipitation over the next 3 months is not a clear "wet" or "dry" scenario:  "The probability that UK precipitation for August-September-October will fall into the driest of five categories is around 20% and the probability that it will fall into the wettest category is 25-30%".  The timing of the soil moisture deficit being overcome by rainfall (and the reduced efforts of sunshine and plants in evaporation and transpiration), and thus the groundwater recharge season starting, will depend upon when the rain falls, and how persistent it is.

The general outlook is for groundwater levels to be in the near-normal range across the majority of aquifers.

For further information see the full Hydrological Outlook for August.

[Apologies for not posting this sooner.]