River Severn Regulation

River Severn Regulation System Designed and constructed in the 1960’s. Major component - Llyn Clywedog. Lake Vyrnwy and Shropshire Groundwater Scheme - phases 1-4 at present. Operation is governed by a control point 200km downstream of Llyn Clywedog, at Bewdley. Clywedog - Utilises high rainfall during the winter months in the Welsh Mountains (yearly rainfall of 2000mm). Was built solely for River Severn Regulation as a result of an act of parliament in 1963. SGWS - In 1970’s it was realised the combined output from C an V alone would not be sufficient to support the R.Severn in dry weather. This was because of increased demands for water use for the R. Severn and the svere drought of 1976.

Beneficiaries of River Regulation Abstractors and Water Companies Fisheries Tidal Environments Navigation Hydro-electric Power Recreation Fisheries - long periods of reduced flows can have effect on river wildlife - release to keep these habitats maintained. Estuary has second highest tidal range in the world. Saline/sediment intrusion can be combatted by large releases from Clywedog. HEP - C can generate electricity via HEP to power the release values. If additional electricity is made, it can be sold onto the National Grid. Recreation - widely used by anglrs/ramblers, canoeists and other boat users. For these users it is important that the amenity value of the river is preserved.

River Severn Regulation System Statutory duty to ensure flows are maintained. 5-day mean flow at Bewdley - 850Ml/d. Daily mean flow - 650Ml/d at Bewdley. Additional releases from any regulation source to ensure flows at Bewdley are maintained. By maintaining Bewdley Flows there is sufficent water for Lower Severn - abstractors - Upton/Mythe and Glous. & Sharpness Canal and nature and wetland reserves

Shropshire Ground Water Scheme Lake Vyrnwy Liverpool Shropshire Ground Water Scheme Lake Vyrnwy Montford Walcot Buildwas Shelton Wolverhampton & South Staffs. Llyn Clywedog Ironbridge PS Hampton Lode Birmingham Dolwen Trimpley Res Bewdley Frankley Elan Valley Reservoirs Mythe Gloucester Input flow readings/abstractions into Spreadsheet to forecast the next few days and maintain the level at Bewdley Gauging Station

How do we Regulate? Monitor Flows at strategic points downstream towards Bewdley. Follow operating rules - make necessary releases from both reservoirs and groundwater based on current drawdown levels from Llyn Clywedog reservoir. Monitor abstraction sources upstream of Bewdley - Shelton, Ironbridge, Trimpley and Hampton Loade

How do we Regulate? (2) Use a spreadsheet tool to calculate predicted recessions at Bewdley. Lag times from reservoirs/ Met Office rainfall forecasts to calculate Bewdley Flows. Daily liaison with Hampton Loade operators to discuss predicted and actual abstractions. Receive daily STW Trimpley abstractions via e-mail. MO - have to coincide releases with lulls in the weather. Frequent minor flood events can allow significant reductions in regulation releases - resource saving. Timing is crucial however. Have to have daily liaison with the Met Office verbally.

Release Options Routine releases of 18.2 Ml/d from Llyn Clywedog, maximum 500Ml/d 45 Ml/d from Lake Vyrnwy depending on local inflows, max 450Mld. Shropshire Groundwater – maximum 185Ml/d

Top part - yesterday’s daily abstraction Future anticipated abstractions Chelmarsh reservoir level Problems with abstractions (i.e. pollution) Maintenance issues

Hampton Loade (2) Ideally ….. We want Hampton Loade to stick to their projected abstraction over the week (hence greyed out boxes for first three days on the fax). Try to get them to fill Chelmarsh reservoir (bankside storage) so they can use this water during pollution incidents.

How Hampton Loade Help us Can map the 850Ml/d at Bewdley by altering their intake of water by observing the flow at Bewdley using telemetry. Can use Chelmarsh as secondary regulation. So if flow at Bewdley is close to 850Ml/d they can utilise the bankside storage.

Regulation Spreadsheet Daily Mean Flow Data Input Montford, Walcot, Buildwas, Bewdley Flow Data, daily recessions & naturalised flows Hampton Loade demand, Chelmarsh storage Abstractions upstream of Bewdley Shelton, Ironbridge, HL, Trimpley Actual and Predicted abstractions Calculation block Releases from reservoirs Predicted recessions at Bewdley Lagged releases 5-day mean flow and daily flow Vyrnwy Bank allocation and reservoir storages

Naturalised Bewdley flow without influence of losses from abstractors and inputs from Reservoirs and groundwater (lagged accordingly) Combined abstraction from Trimpley, HL, Ironbridge, Shelton Daily Mean Flow from Bewdley

Based on predicted recessions and lagged response from water sources we get a predicted daily mean flow for Bewdley Spreadsheet then calculates the 5-day mean based on the average of the 5-daily mean flows as shown previously