Page 324 - Water Loss Control

Contr olling Real Losses in the Field—Pr oactive Leak Detection 293

If the reservoir is found to be leaking, then one way of finding the actual leaks is to
send in a diver with fine sand. The fine sand is sprinkled along the walls of the reservoir
and the base and is drawn into patterns where the suction of the leak takes effect. In
many cases, though, if the leakage is significant, the reservoir should be programmed
to be lined, as long as the basic structure is still structurally sound. Determining the
presence of leakage will help to justify the cost the reservoir lining project.
Storage overflow losses are more common where storage is in a remote location and
water is not obviously visible or evident from above-ground, as it would be in an urban
situation. Overflows usually happen at off-peak times when head losses and demand
are low in the system and storage is filling. Overflows occur most typically from mal-
functioning level instruments or control equipment and/or inattentive operators who
fail to halt a filling operation at the proper level.
Overflow pipes should be inspected to see if there are obvious markings on the ground
or wet patches where water has been ejected. Another simple method is to wedge a ball or
object into the pipe during the day. If the object moves, it is likely that there has been an
overflow situation. A more detailed analysis can be undertaken by using a high-resolution
level logger. When the level of the overflow pipe is reached, loss starts to occur. Coupled
with a temporary meter at the inlet to the tank, it is easy to calculate the volume and value
of the loss. Once the value of the loss is calculated, a suitable and cost-effective method of
intervention may be installed. The simplest forms of level control are mechanical float
valves or altitude valves, which are discussed in Chap. 18. However, utilities often use
remote control systems and SCADA systems to control tank levels. In some cases tank over-
flows occur because this equipment malfunctions due to lightning strikes or other causes.
Sometimes the problem is no control or inefficient manual control, and sometimes
the problem is lack of maintenance on simple mechanical controls. In all cases the loss
should be resolved in a cost-effective fashion.
Utilities with SCADA or telemetry systems in place can utilize these systems to
periodically read zonal meters and analyze the condition of the losses through periodic
modeling and assessment.

16.8 Summary
In this chapter we have discussed the methods of cost-effective leakage management. The
intent of this chapter is to provide guidance on effective and innovative methods and tech-
nologies to control water distribution system leakage, particularly underground, nonvisible
(unreported) leakage. A variety of methods can be considered, in developing the leakage
management strategy, and each distribution system should be evaluated individually
before a commitment is made to one methodology or approach. However, without active
leak detection, leakage in a water distribution system will only worsen!

References
1. Fanner, V. P., R. Sturm, J. Thornton, et al. Leakage Management Technologies. Denver,
Colo.: AwwaRF and AWWA, 2007.
2. Fanner, V. P., J. Thornton, R. Liemberger, et al. Evaluating Water Loss and Planning Loss
Reduction Strategies. Denver, Colo.: AwwaRF and AWWA, 2007.
3. “District Metered Areas Guidance Notes,” IWA Water Loss Task Force, 2007.
4. UK Water Industry Research Limited. A Manual of DMA Practice. Report Ref. No.
99/Wm/08/23, UKWIR: UK 1999.