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 September 2009
May, June and July were very wet months, which were followed by two very dry months in August and September. Flows on the River Severn are currently below average and River Regulation (releases from Clywedog Reservoir) were initiated by the Environment Agency at the end of September. There are no groundwater resources issues. Blithfield Reservoir storage level was at 67% at the end of September. This is not uncommon for this time of year, however it is at the threshold of the first reservoir trigger level (the drought monitoring curve). No further action is proposed at this stage. We will continue to review this position.
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 67% at the end of September, this is slightly below average for the time of year.
River Severn
The surface water reservoirs used to support flows in the River Severn were in a healthy position at the end of September (Clywedog 87% and Vyrnwy 90%) and therefore there are no concerns over availability of resources for river support.
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 our Seedy Mill treatment works) for September was significantly lower than the ten year average at 31%. This is the second very dry month in a row (rainfall in August was 59% of the 10 year average). However the previous three months were very wet May (110%), June (152%) and July (166%).
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