Water resources
Summary of supply sources
We obtain our water resources from three sources: Blithfield Reservoir, the River Severn and groundwater from 25 sites across our supply area. Approximately 40% of the total water available to us is taken from groundwater sources and the remaining 60% from the two surface water sources.
Groundwater is abstracted from over 60 boreholes (2-3 per source), all of which allow water to be pumped from the Triassic Sandstone aquifer. This aquifer is very porous (like a sponge) which means that it can hold large quantities of water in between the sand grains and in cracks in the rock. As the sandstone can hold large volumes of water the water levels within the sandstone do not fall very far in dry periods. This makes the groundwater sources a very reliable supply of water.
Blithfield Reservoir is an impoundment reservoir with a capacity of approximately 18.224 billion litres of water. It was formed in 1953 by the construction of a dam across the River Blithe. The raw water is taken out of the reservoir by pipeline to the treatment works at Seedy Mill near Lichfield before going into the distribution network. (For further information on Blithfield reservoir, its construction and history, visit our Blithfield Website.)
The River Severn is a regulated river i.e. flows in the river are augmented by inputs from both groundwater and reservoirs at its head at times of low flows. The regulation of the River Severn is controlled and operated by the Environment Agency who monitor and report on the situation regularly. We take water from the River Severn at Hampton Loade where it is stored in Chelmarsh Reservoir before being treated and distributed.
Current water resources position at the end of July 2010
The rainfall for July 2010 was low, at 65% of the ten year average, and this follows three months of below average rainfall. Flows on the River Severn and Trent are currently below average and River Regulation is underway on the Severn. There are no groundwater resources issues. Blithfield Reservoir storage level was at 65% at the end of July. The overall water resources position is healthy, however we will be keeping an eye on the position over the next month as Blithfield storage is slightly below average for the time of year.
Reservoir levels
We use the level in Blithfield Reservoir as the main indicator of resource availability. Regular analyses of refill scenarios for Blithfield Reservoir are routinely undertaken during the refill season and the levels are monitored continuously. Blithfield reservoir was at 65% at the end of July, which is slightly below average for the time of year, and just below the drought monitoring trigger level. This trigger level is typically crossed once every 5 years, so is not a particularly unusual position, however, we will watch the position over the next month, and take action to conserve reservoir storage.
River Severn
Clywedog Reservoir is being used by the Environment Agency to release water into the River Severn to support river flows, which occurs most summers. Clywedog Reservoir storage at the end of July was at 85%. The Shropshire Groundwater Scheme was also used by the Environment Agency in July. Further river regulation is likely to continue as required for the next few weeks.
Groundwater
Groundwater levels in the Sherwood Sandstone aquifer do not tend to react rapidly to short periods of high or low rainfall. Current groundwater levels are within the normal range. In general the reliable yield of our groundwater sources is unaffected by groundwater levels, and therefore we do not use groundwater levels as a means of assessing the water resources situation.
Rainfall
The rainfall (recorded at the Seedy Mill treatment works) for July was 65% of the ten year average figure. This follows a dry spring.
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