Page 348 - Water Loss Control

Contr olling Real Losses—Pr essur e Management 317

18.10 Understanding the Hydraulics of Your
System Prior to Implementation
In addition to using hydraulic models for the location of pressure control stations and
field measurements to locate critical data, it is also very important to understand exactly
how the system functions hydraulically.
This analysis is normally undertaken in the demand analysis phase of the project
and should identify:
• Percentage of direct pressure consumption
• Percentage of consumption from individual storage tanks
• Distribution feeds, by pump or by gravity
• Breakdown of consumer categories, residential, commercial, and industrial
• Level controls for elevated storage
• Pump shut off controls
The results of this research will form the basis of the control scheme, providing
limits of control and cost to benefit assumptions.

18.11 Using Statistical Models to Calculate
the Potential Benefit of a Scheme
Once we have identified an area, made field measurements, and identified how the water
is used within the sector, we can proceed to the decision-making stage. During this phase
we identify how much control we can effect without disrupting normal supply and what
benefit this control will have on reduction of leakage volume, reduction of new leak fre-
quency, deferral of new source schemes, and in some cases water conservation.
A simple model can be constructed by most users of excel following the guidelines
shown in Chap. 10, however there are also various commercial models available for
purchase. The decision to purchase a model or construct one should really lie with the
type of staff a utility has and time that they have available. While the calculations are
not really complex, it can in some cases be false economy to try to build your own
model when a small investment will buy a tried and tested version.
Most commercial models are flexible however care should be taken to ensure that
the model purchased takes into account the hydraulic characteristics of the utility sys-
tem in question. As discussed earlier there are significant differences between hydraulic
characteristics of demand for a system, which uses residential storage, and a system,
which has direct pressure feed.

18.12 Calculating Cost to Benefit Ratios
Once the data has been entered into the model and calibrated to a certain degree of
confidence, the model can be used to analyze the cost of a potential project and its esti-
mated benefit. The components and the diameters to be installed, the type of bypass
and chamber, the ground type, the type of control to be effected, and the type of main-
tenance program to be put into action after installation dictate the cost. An additional