Economic Level of Leakage (ELL)

Transcription

1 Conferenze sulle Strategie di Gestione delle Perdite Idriche 1 Economic Level of Leakage (ELL) Stuart Trow United Kingdom Leakage Consultant and Director of CaL Solutions Ltd Approaches to Estimating and Achieving ELL

2 2 Estimating ELL Estimating ELL is one of the first things that should be done before starting a major programme of investment in leakage management ELL estimation is an ongoing process not a one-off off This presentation summarises the latest IWA thinking on ELL methodologies I have been involved with leakage management in the UK for 27 years, and with target setting based on ELL for 20 years. Please take the opportunity to ask questions StuartTrow@aol.com

3 3 An Economic Optimum If little or nothing is spent on leakage control, the value of the water lost will be excessive If too much is spent on leakage control, the cost will outweigh the savings which result from the expenditure Between these two extremes there is an economic level of leakage at which the costs and benefits are optimised

4 4 Defining ELL Report : It is clearly uneconomic to ensure that pipelines and reservoirs will never leak. It is also clear that there is an economic limit to the loss of water that should be tolerated through leakage Managing Leakage Report C 1994: That level of leakage where the marginal cost of active leakage control equals the marginal cost of the leaking l water CIWEM Approach 2003: Economic level of leakage can be defined, ---- as that level of leakage at which any further reduction would incur costs in excess of the benefits derived from the savings Latest WLTF Definition: The level of water losses which results from a policy under which the marginal cost of each individual activity for managing losses can be shown to be equal to the marginal value of water in the supply zone In other words: Do everything that makes economic sense and the ELL is the level of leakage which results from such a strategy

5 5 Time and Money Water supply organisations carry out leakage control in order to save money It is important to recognise that there are different kinds of money; money is time dependent The time horizon of leakage control expenditure is very important in the analysis of ELL It also makes ELL estimation complicated The new IWA methodologies attempt to simplify the ELL process in a practical way based on experience

6 6 Facts about ELL ELL is specific to an individual water supply zone ELL is time dependent; short-run run and long-run Short run ELL is a function of: The current variable cost of water (CV) The cost of active leakage control interventions (CI) The Rate of Rise of un-reported leakage (RR) Long run ELL is a function of: The future cost of water depending on the available supply The changes in short-run run ELL due to cost - effective investments on the water supply network

7 7 Diminishing Returns A fundamental fact about leakage control is that every possible leakage control measure follows a law of diminishing returns. As more money is spent, the return in terms of water saved due to lower losses, becomes progressively less. Some level of each activity will form part of an economic strategy.

8 8 Short, Medium and Long Term Short term measures: Leak detection and repair Medium term measures: Pressure Management District metering Long term measures: Mains and service renewal

9 9 ALC Cost Curve Economic Range Annual Cost Water Cost Total Cost Leakage Level ALC Cost Policy Minimum

10 10 ALC Marginal Cost Curve Marginal Cost ELL Leakage Level Water Cost ALC Cost Policy Minimum

11 11 Short Run vs Long Run ELL Vary Active Leakage Control: Optimise against variable cost of Water (CV) This is short run ELL Consider capital investment in leakage management options: Pressure control, rehabilitation, sectorisation etc. Hypothesis interventions work out discounted cost, benefit and derive Average Incremental Cost (AIC) Rank and implement in order Strictly need to reassess benefit of schemes after implementation of other schemes This is long run ELL

12 12 Water Resource Headroom

13 ELL vs. other Supply Demand Measures IWA Water Loss Task Force Visit Italy 13

14 Use the IWA water balance to calculate the Current Annual Real Losses (CARL) with 95% confidence limits Measure system pressures: check for the presence of surges, identify excess pressure above minimum standard of service, and any pressure below the minimum standard of service Twin-Track approach to Benchmarking and Management of Real Losses Calculate Unavoidable Annual Real Losses (UARL) using average system pressure Identify opportunities for achieving economic management of operating pressures, to reduce frequencies of new bursts leaks, and flow rates of running leaks Calculate the Infrastructure Leakage Index ILI = CARL / UARL Operate to economic ALC intervention times Calculate Economic Intervention times and Economic Annual Real Losses (EARL) using cost of water Identify economic speed and quality of repairs, extent and size of sectors Calculate the Economic Leakage Index ELI = CARL / EARL Identify opportunities for achieving economic infrastructure management activities: assets, mains and service connections IWA Water Loss Task Force Visit Italy Benchmark the operational performance in managing Real Losses by comparing the ILI and ELI with international, national and sub-system data ILI data UARL < CARL < EARL 14

15 15 Squeezing the Box For any system the Economic Level of Leakage comprises 3 Principal Components: 1. A level of background losses which results from an optimised entry and exit policy for DMA management, or exit policies for regular survey 2. A level of leakage from reported bursts with optimised repair time policy 3. A level of leakage from unreported (hidden) bursts resulting from an economic intervention policy for leak detection and repair

16 Pressure Management Management Unavoidable Annual Real Losses Speed Active and Quality Leakage of Repairs Control Current Annual Real Losses Speed Active and quality Leakage of repairs Control Pipeline and Pipe Assets Materials Management: Management: selection, Selection, installation, maintenance, Installation, Maintenance, renewal, IWA Water replacement Loss Renewal, Task Force Visit Italy Genova Replacement Ferrara May

17 IWA WLTF approach: Squeezing the Box IWA Water Loss Task Force Visit Italy 17 For any system achievement of the ELL comprises 4 inter- related activities: 1. An optimised overall Pressure Management policy: - identify presence of surges and minimise their adverse effects - basic simple reduction of excess pressures 2. An optimised Repair Time policy for all bursts 3. An economic Intervention Policy for awareness, location and repair of unreported (hidden) bursts - influenced by level of investment in leakage management infrastructure ructure i.e. Telemetry/SCADA, DMAs,, advanced pressure management - influenced by exit level (background and other leaks remaining after interventions) 4. An economic level of Investment in mains and services renewals which takes account of all other factors

18 An economic approach to prioritising Pressure Management Areas (PMAs) IWA Water Loss Task Force Visit Italy Number of Properties in Scheme PRA property count Cost per property metre Cost Per PM Schem e Reference

19 19 Repair Times Additional Cost / Repair Uneconomic Economic? Repair Time Days

20 Graph 1: Predicting Economic Intervention Frequency for Regular Survey CI/MaC = Intervention survey cost ( /service conn)/ Marginal cost of water ( /m 3 ) Economic Period between Interventions Te (months) Rate of rise of unreported leaks (S) (litres/connection/day, per year) CI/MaC=100 m3/sc CI/MaC=50 m3/sc CI/MaC=20 m3/sc CI/MaC=10 m3/sc CI/MaC=5 m3/sc CI/MaC=2 m3/sc Source of data: ALCCalcs IWA Water Loss Task Force Visit Italy 20

21 Economic Approach to Coverage by DMAs IWA Water Loss Task Force Visit Italy 21 Cost per Mld Saved Economic Uneconomic % DMA Coverage

22 Economic approach to Mains and Service Pipe Replacement IWA Water Loss Task Force Visit Italy 22 Length km / Mld saved Limit based on value of water Economic Uneconomic Scheme

23 23 Selecting Mains for Replacement Burst Rate Distribution Busrt Rate no/km/yr % 20% 40% 60% 80% 100% Cumulative % of network

24 Relative costs of reducing leakage (UK, late 1990 s) IWA Water Loss Task Force Visit Italy 24

25 Economic ILI Pressure Management Management Economic Level of Real Losse Unavoidable Annual Real Losses Speed Active and Quality Leakage of Repairs Control Potentially Recoverable Real Losses Speed Active and quality Leakage of Control repairs Pipeline and Pipe Assets Materials Management: Current Annual Real Losses : selection, Selection, installation, Installation, maintenance, Maintenance IWA Water, renewal, Loss Renewal, replacement Task Force Visit Italy Replacement 25