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 December 2011
The rainfall for December 2011 was significantly higher than normal (138% of ten year average) but ends a period of drier than average conditions which started in February 2011. Rainfall for the period January to December 2011 was 72.5% of the ten year average. Flows on the River Trent are currently at or around normal. River Regulation on the Severn from the Clywedog Reservoir in Wales has not been required since October and stores look healthy for the coming summer period. There are no groundwater resources issues. Blithfield Reservoir storage level was at 77% at the end of December. The overall water resources position is robust, however the Company will be keeping a watchful eye on the position over the winter as recharge of Blithfield started unusually late.
Reservoir levels
The Company uses 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 briefly reached top water levels in February 2011 but fell below 60% over the autumn due to the exceptionally dry weather. Levels have risen sharply to 77% following the exceptional rainfall in December and we anticipate recovery above the drought monitoring trigger level. The Company will be continuing to keep a watchful eye on the position over the remaining winter months.
River Severn
Clywedog Reservoir has not been used by the Environment Agency to release water into the River Severn to support river flows since October 2011. Reservoir storage at the end of December was at 87% which is normal for the time of year. Further river regulation is unlikely to be required until Summer 2012.
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 lower than normal. Nevertheless in general the reliable yield of the Company’s groundwater sources is unaffected by groundwater levels, and therefore the Company does not use groundwater levels as a means of assessing the water resources situation.
Rainfall
The rainfall (recorded at the Company’s Seedy Mill treatment works) for December was 138% of the ten year average figure. This comes at the end of a drier than average year .
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