The London Stored Water System comprises the Thames Valley Stored Water System (SWS) in the west of London and the Lee Valley SWS in the east of London.
The Thames Valley SWS comprises 10 raised storage reservoirs, supplied with raw water drawn from the River Thames by 5 pump stations. The reservoirs supply 4 water treatment plants (WTPs) via an interconnected system of tunnels and pipe mains. The figure above illustrates the system and transmission mains.
The Lee Valley SWS comprises 13 storage reservoirs which are supplied with raw water drawn from the River Lee by 2 pump stations and a gravity aqueduct. These reservoirs are also supplied with groundwater pumped from boreholes and water pumped from the River Thames and transferred via the Thames-Lee-Tunnel. The reservoirs supply 2 WTPs via a system of tunnels and pipe mains. A third WTP (Hornsey) draws water directly from the River Lee (New River) and boreholes. Raw water is also supplied to Essex & Suffolk Water Company from the reservoirs via the Lower Hall pump station.
The prolonged period of low rainfall over 2005 -2006 resulted in a depletion of the stored water in the Lee Valley SWS early in 2006. Storage in the Thames Valley SWS (which supplies the west London WTPs) was also low. As part of the action plan, an optimization model was developed to review the operations of the Thames Valley SWS and the Lee Valley SWS as part of the DSF (Decision Support Framework) in support of Thames Water’s contingency planning to assist in developing the operational and business strategies for coping with a drought event.
The main objectives to the project were:
- Assure that the system is operated in the most efficient manner during the dry months;
- Assure that reservoir levels are sufficiently high to accommodate the required flows;
- Increase the security of supply during the drought, and
- Maintain good quality of raw water as supplied to all of the WTPs.
As part of this study, two optimization-simulation models for both the Lee Valley and Thames Valley raw water reservoirs systems were developed to derive a strategy for operating reservoirs down to a low level and for testing the operating control strategies associated with different rainfall scenarios.
The main operational objectives of the study were to maximize operational usage of the total storage volume in the reservoirs of strategic importance, in particular the Queen Mary Reservoir, and to meet the water demands at the four WTPs while maintaining water levels at the reservoirs within the defined low and high level set points and not exceeding the hydraulic capacities of the pipe mains, aqueducts and tunnels in the system. All the daily river flows and demands for the whole simulation period are taken from the outputs of Thames Water’s WARMS model.
The decision variables are the daily flow into and discharge from each reservoir.
The main simulation-optimization results include:
- the storage profiles for all reservoirs together with their time-series inflows and outflows.
- inflows to each of the treatment works and its composition, together with the blended water quality index
As the result of this development, operators at Thames Water can now simulate the operations of the raw water input and distribution system under different scenarios for the purposes of testing the management strategy before its implementation.
The software can also be used for optimizing the short-term (weekly) production plans, including configuration of abstraction and supply routes and percentage of abstraction/supply for each route by taking account of projected demands as well as scheduled maintenance plans, such as tunnel inspections and responding to unscheduled failures or outages.