Page 319 - Water Loss Control

288 Cha pte r S i x tee n

calibrated hydraulic models may use their models to calculate expected flow ranges at
the DMA metering point instead of temporary flow measurements.
If initial leakage levels are very high it is recommended to conduct a thorough leak
detection and repair campaign to remove the majority of the leakage backlog before final-
izing the meter design. This will allow the design to be based upon flow characteristics
representative of the desired low leakage operation, and avoid oversizing the meter.
A simple rule of thumb is to limit the number of metered inlets and outlets (if any),
since multiple supply and pass-through locations can give rise to misleading leakage
levels due to the compounding of errors from multiple flowmeter.
16.6.5 DMA Data Monitoring
The economic optimum volume of leakage is a driving factor influencing the selection of
DMA monitoring and data transfer capabilities. In utilities where the cost of water is rela-
tively low it is very likely that there is no financial incentive in detecting small-sized leaks
instantly. This means that it will not be necessary to have real time transmission of DMA
data. The data from the DMA might be transferred and analyzed once a week. If several
leaks occurred over this period, the minimum night flow might only reach the level of inter-
vention after a number of days. Only then does it become necessary to send a leak detection
team into the DMA to conduct a leak survey. However, there are several options to consider
when selecting the optimum interval to collect the DMA flow and pressure data.
Real time data transmission: Supervisory control and data acquisition (SCADA)
systems are commonly used in North American water utilities to provide real time
monitoring and to control pumping stations, remote treatment facilities, reservoir
sites, pressure reducing chambers, and any other desired water supply facilities.
In recent years, the role of the SCADA system has expanded to include security,
video transmission, water quality monitoring, and other parameters not directly
associated with water distribution. If real time data collection is desired, the use of
an existing SCADA system is a viable option for many water utilities. With an
existing SCADA system in place, the cost to outfit and individual meter/PRV site
is basically the cost of one additional SCADA endpoint device, or remote terminal
unit (RTU), and related instrumentation. If a SCADA system does not exist, the
possibility of outfitting multiple DMAs in a SCADA system might be one of a
number of benefits to help justify the cost of a complete SCADA system in the
water utility. Real time monitoring is appropriate if the water utility needs to
respond immediately to an emerging leak or main break in the DMA. However,
most leaks emerge slowly and are initially small in volume and are not identified
until the next minimum nighttime flow period. Therefore, it is not essential to
receive DMA data in real time. For distribution systems with mostly slowly
emerging leaks, the greatest data collection frequency that can be economically
justified is once per day, ideally early in the morning after the minimum nighttime
flow period. Monitoring DMA data through a SCADA system is the most
comprehensive option to monitor DMA data, but is not likely to be cost-justified
strictly based upon DMA use alone. Usually the business case for SCADA systems
is based upon the multiple benefits of monitoring and control of many parameters
at many sites and facilities.
Data transmission through GSM telemetry: Another option of monitoring the DMA
flow and pressure data is by transmitting data through global system for mobile