Economic Intervention

Rate of Rise of Unreported Leakage

Calculating Active Leakage Control economic frequency and budgets

Calculation of economic intervention frequencies for active leakage control (ALC), based on continuous night flow measurements in small District Metered Areas (DMAs), commenced in the UK in the early 1990s. However, outside the UK, a simpler less data-intensive practical method, based on regular survey, was needed to promote the wider use of active leakage control and quickly estimate ALC budget requirements.

The approach adopted by IWA Task Force members (2005M and 2005Q) is based on Rate of Rise of Unreported Leakage, which can be quickly estimated in several different ways; it had initially been proposed in a 1998 Financial Times Energy publication authored by Lambert, Myers and Trow.

 Rate of Rise of Unreported Leakage, which can be quickly estimated in several different waysThe figure is a simplified view of the three components of leakage in a system – background leakage (pink), unreported leakage (grey) and reported leaks (red). Following an active leakage control intervention, unreported leakage starts to rise, and at some time (T) another intervention will be needed; the process repeats itself. How can economic intervention time (Te) and annual ALC budget be calculated?

If the Rate of Rise of unreported leakage can be estimated, even approximately, then it can be shown that the economic intervention time Te occurs when the monetary value of the unreported leakage volume (represented by the volume of the grey triangle times CV, the Variable Cost of leakage) equals the cost of an intervention (CI). Te is then simply calculated as:

Te = √(CI/(0.5 x CV x RR))

Once Te has been calculated, the Economic Intervention Frequency (EIF), the Annual Budget for Intervention (ABI) and the Economic Annual Unreported Real Losses (EAURL) can also be quickly and easily calculated (2005P, 2005Q).

This practical approach can be applied to a whole Utility distribution system, or to any individual Zone within the system.

Three methods are given for assessing Rate of Rise of unreported leakage, but because the Economic Intervention time Te varies with the square root of the Rate of Rise, an approximate value of RR is sufficient to enable calculations to proceed. They can be refined later, as each time an intervention is made, Rate of Rise can be recalculated (based on the unreported leaks found, and the time since the last intervention); so the approach can become self-calibrating for each Zone within a distribution system.

Because Rate of Rise has unusual units, Lambert and Fantozzi developed a 5 stage international grading system (Very Low/ Low/ Moderate/ High/ Very High) for Rate of Rise, and Confidence levels for the calculations. The results below, from the 2009 Australian version of ALCCalcs provided to Australian WSAA Utilities, show that this simplified approach produces ‘mimimum cost’ solutions of the same form as more complex UK Economic Leakage Level calculations based on continuous minimum night flows.

3 apr table ilmss b

Because Rate of Rise has unusual units, ALCCalcs software also includes a 5 stage international grading system

This approach to Economic Intervention also greatly simplifies the assessment of Short-Term Economic Leakage Levels