Page 296 - Water Loss Control

Contr olling Real Losses in the Field—Pr oactive Leak Detection 265

When launching a system plans update project, careful thought must be given to
the planning of a process that ensures that the new mapping system is reliably updated
as system changes occur. It is also important to have buy-in from all departments within
the water utility, such as finance and maintenance.

16.3 Leakage Fundamentals
It is important that the utility’s water loss management personnel understand the fun-
damental characteristics of leakage occurrences and appropriate means to control them.
The basics of leakage are given below

16.3.1 Leak Types
Just like there are many different types of infrastructure used in a distribution system
there are also many different types of leaks occurring in a distribution system as given
herein
Main Break or Pipe Fracture
This term is widely used in North America to describe a catastrophic pipe failure
caused by pipe deterioration, fluctuating or excessive pressure, ground movement or a
combination of these factors. Breaks, or bursts, in water mains are relatively easy to
locate as water released in these failures usually becomes quickly and visually apparent
at street or ground surface level, particularly in areas of high pressure. However, on
occasion, main breaks are not visually evident from above ground as the water finds an
escape channel underground. This can make detection difficult, as paradoxically a nota-
ble rupture may not necessarily produce a loud leak noise. This is due to the fact that a
large amount of leaking water often results in dramatically reduced pressure, thereby
resulting in low noise level. A water pocket may also quickly form around the leak,
further diminishing the quality of leak noise. The leak noise from a main break is nor-
mally characterized by a low frequency rumbling rather than a high frequency hissing
and may therefore be difficult to detect audibly by an inexperienced leakage inspector.
In the case of a large volume escaping underground and a reduced pipeline pressure,
evidence of the break in a general area may be detected if the water utility monitors
water pressures across the distribution system and notes a detectable reduction in pres-
sure. A note regarding terminology: while the term “main break” is widely recognized
and utilized in the North American water industry, it is not applied consistently as the
terms “main break” and “leak” are interpreted inconsistently by utilities. This makes
performance comparisons among water utility main break and leak data difficult. Ter-
minology established during the development of component analysis models using
“reported” and “unreported” leakage better defines “main breaks” and “leaks,” respec-
tively, and the reader is referred to Chap. 10 and the Glossary for the basis of these
definitions.

Crack
This term is used to describe a pipe failure mechanism occurring as circumferential or
longitudinal failure that usually results from pipe deterioration or ground movement.
They may go undetected for some time and eventually deteriorate to become a reported
main break or fracture. The quality of the leak noise depends on factors such as pressure
and pipe material, but usually is distinct and of high audible frequency.