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://bgs.ac.uk/data/waterwatch.html) are made in several thousand wells by the Environment Agency, 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 wells shown in this timeline are a small subset of the total network, chosen as representative of important aquifers, and located in areas not significantly affected by pumping. They form a baseline for assessing changes in aquifer storage from month to month.

This timeline

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 ‘2^nd 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.