Navigating the map
To pan: left-click on the map and drag.
To zoom: Drag the vertical slider on the left of the map, use the mouse wheel or
hold down the Shift key and drag a rectangle.
Using the time slider
Drag the time tab or use the Play, Pause, Next and Previous buttons to navigate
along the time slider.
View groundwater levels
Left-click on a well to return details of the groundwater level at the currently
displayed time, as well as how this value compares to the monthly average.
About groundwater levels
Groundwater levels are a measure of how much water is stored in an aquifer,
recording the depth to the water table (expressed as metres above sea level)
below which the rocks are saturated. They generally rise during the winter
months as recharge from rainfall enters the aquifer,
and fall during the summer as water is discharged into rivers or pumped from wells.
Groundwater level can be affected by the position of the well with respect to rivers
and springs. However in a given well the pattern of rise and fall is primarily controlled
by variations in climate.
Measuring groundwater levels
Measurements in the UK (http://www.bgs.ac.uk/research/groundwater/datainfo/levels/home.html
) are made in several thousand wells by the Environment Agency (England), Natural Resources Wales, Scottish Environmental Protection Agency and the Department of Environment (Northern Ireland), to allow aquifers to be managed sustainably. Measurements in some wells are still made by manually lowering in measuring tapes, but increasingly automatic instruments are used, and some send data daily using radio or phone links.
The colours on the map are a reflection of the level in a given month, compared
to the level expected from long term averages. A similar map is published each month
in the NERC Hydrological summary (http://www.ceh.ac.uk/data/nrfa/nhmp/monthly_hs.html
), although this map
uses a different way of calculating the relative levels. The published Hydrological
Summaries rank a month relative to the full period of observation, so we might say
that a month is the ‘2nd
driest in 60 years of record’. This map only
looks at data from 1970 onwards, and uses a slightly different method of calculation,
so the timeline and the summary may not match exactly. The timeline also shows
actual locations for wells – in the Hydrological Summaries the locations of some
wells are adjusted to enhance clarity on the printed page. Not all wells have data
from 1970, so the number of wells shown changes with time.