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.]

Tuesday, 19 August 2014

July 2014 overview

Groundwater levels, July 2014
July was a pleasant summer month over most of the UK.  The rainfall total was slightly below average, but the distribution varied significantly.  Thunderstorms brought downpours to areas of the Midlands, the south-east and East Anglia.  Wales and parts of England were notably dry.

Groundwater levels in the very responsive Carboniferous Limestone aquifer of south Wales fell as a result of the low rainfall there.  This is the only site with below normal groundwater levels on our map this month.

Across the rest of the UK, groundwater levels are in the normal or above normal range for the time of year.  Levels are falling at the moment as we are in the recession phase of the annual cycle of groundwater fluctuations.

Below is the hydrograph for Wetwang, a 46 m deep borehole used to measure groundwater level in the Chalk aquifer in Yorkshire.  The dashed line shows the average groundwater level by month.  The observed level (solid black line) indicates the low levels at the start of the year, followed by a rapid recovery during the wet months of January and February.  The steepest section of the recovery shows almost 10 m rise in water level in a little over a month.  The recession, which started in late February, was initially steep, followed by a period of rather stable level during May and June.  During July the groundwater level at Wetwang has closely followed the monthly average line.  Groundwater levels are expected to continue to fall until the autumn.

Groundwater levels at Wetwang, unconfined Chalk

Friday, 18 July 2014

Groundwater outlook - from July 2014

Hydrological Outlook from July 2014
At this time of year, significant groundwater recharge is unlikely and groundwater levels are not strongly influenced by variations in rainfall.  Levels are expected to fall during the next three months along a similar trajectory to recent months.  There is unlikely to be any significant change to the groundwater situation until October, when water use by plants reduces and rainfall will begin to dictate the groundwater outlook.

View or download the most recent Hydrological Outlook from the Hydrological Outlook UK website.

Wednesday, 16 July 2014

June 2014 overview

Groundwater levels, June 2014
Groundwater levels normally fall in the summer months.  Recharge is limited as most of the rain that falls is captured by dry soils and used by growing plants. Groundwater drains naturally from aquifers towards rivers
and the sea.  During these months, there is more water leaving the aquifers than replenishing them, so we see water levels fall.  This falling section of a groundwater hydrograph is called the recession.

Hydrographs in most wells are showing the summer recession.  For example, in the Chalk aquifer at Little Bucket Farm, and in the Permo-Triassic Sandstones at Bussels No. 7a.
Falling groundwater levels in the Chalk at Little Bucket Farm (Kent)

Heavy rainfall in some areas in May was enough to interrupt the recession, so we see the hydrograph curving upwards, e.g. in the Lincolnshire Limestone at New Red Lion.
Interrupted recession in the Lincolnshire Limestone
at New Red Lion (east of Grantham, Lincolnshire)

Levels in some areas remain exceptionally high for the time of year, due to the exceptional spring rainfall, even though they are falling.  This is the case in the Permo-Triassic Sandstone aquifers of the north west (e.g. Skirwith) and the south west (e.g. Bussels No. 7a).

For more information, see the Hydrological Summary for June 2014 [PDF].

Wednesday, 2 July 2014

May 2014 overview

Groundwater levels, May 2014
The weather in May was changeable, and the total rainfall varied significantly across the UK.  We saw heavy rainfall at the end of May, which caused unusually low soil moisture deficits in most areas. Despite the generally high rainfall, groundwater levels mostly continued to fall.

Chalk water levels generally fell during May but remained within the normal range or above, with exceptionally high levels at Stonor Park (Chilterns). However, in Yorkshire levels remained below average, even though the monthly rainfall total over the chalk of Yorkshire was mostly >175% of the average for May.  Local rises in levels were recorded in parts of Lincolnshire and Suffolk.

In the Permo-Triassic sandstones, despite falls, water  levels remained above previous monthly maxima in the north-west (for the fifth consecutive month) and were also very high in the south-west. Levels elsewhere were above average and rose in north Wales.

In the Upper Greensand of south-west England, at Lime Kiln Way, levels fell slightly 
but remained above the previous monthly maximum for the fourth consecutive month. 

In the Magnesian Limestone, water levels in the indicator boreholes were notably high in the north. In the other limestone aquifers, levels returned to the normal range, except at Pant y Lladron where they were exceptionally high with a rise of 5m recorded across the 24th-25th May in response to rainfall