Page 134 - Water Loss Control

116 Cha pte r Ni ne

effect of changes in operating regime on leakage. There is a very high level of monitoring,
and hence data availability, within England and Wales, for example, 15 minutes flow and
pressure data on each sector. Most companies now have fully calibrated all mains hydrau-
lic models of their networks. As a result of the drought in 1995–96 a number of companies
initiated major leakage management programmes based on economic assessment out-
lined in this paper. One of these involved the construction and implementation of over
2000 pressure management schemes within a 3-year period. As a result of this, a company
supplying over 3.2 million properties reduced their average night time pressure from
over 50 m to less than 40 m. All companies implemented a free or heavily subsidised
3
programme for the repair or replacement of customer supply pipes in order to speed the
repair of leaks that previously required the serving of statutory notices.
9.6.2 International Experience
The situation in other parts of the world is quite different from England and Wales.
Water supply is often still in the hands of local municipal authorities each covering a
relatively small number of properties. Most connections are metered, but it is common
for supplies to be intermittent due to resource shortages. Sectorization is very rare and
proactive leakage control is limited. The benefits of pressure management are not
widely appreciated and there is generally no assessment of the economic level of leak-
age. Only limited data is available and there are generally very few hydraulic models.
There is therefore the need for advice on the application of ELL in a staged manner in
the situation of limited data.

9.7 Practical Application
Application of the ELL analysis in many situations has shown that pressure management is
12
by far the most cost-beneficial activity. Its benefit in reducing burst frequency is such that
pressure-reducing schemes will often have payback periods significantly less than 12 months.
In fact, the initial schemes can have such a quick and direct influence on the repair budget
that they will free up sufficient money to pay for further pressure management schemes,
and also some leakage detection resources to start proactive leakage detection. If this
resource can be effectively targeted to identify backlog leaks, then it will be found that leak-
age can be reduced significantly within the existing budget.
The priority in terms of the identification of pressure management schemes
should be

• Identify any occurrence of surges or instability in pressure on the network using
very short-time interval logging and identify solutions to the problem.
• Identify and, where possible, move from fixed to variable speed pumps.
• Look for areas of high pressure (greater than 40 m) that can be controlled by
pressure management.
• Look for areas with high diurnal flow and pressure variation and look to control
these using flow-modulated pressure control valves.
As the benefits of pressure management start to be achieved, the economic level of
4
regular sounding can be calculated and appropriate targets can be implemented. If the
area is sectorized, then economic leakage detection can be applied practically at sector
level. 5,6