Page 323 - Water Loss Control

292 Cha pte r S i x tee n

Figure 16.19 depicts an example of continuous DMA measurements and the rise of
leakage volume in this DMA. Based on economic optimum analysis of real losses for
this particular DMA an optimum threshold level for intervention against real losses
was set. Once this level is reached, a leak detection team is sent to the DMA to detect the
running leaks and bring down real losses to the exit level where further leak detection
efforts would not be cost-effective.

16.6.8 DMA Management
Like any other part of the distribution system, DMAs need to be managed and main-
tained in order to achieve the expected results. DMA related equipments such as DMA
flowmeters and PRVs should be properly maintained to ensure that high quality DMA
data is collected. It is vital for the success of the DMA that the integrity is maintained by
keeping all boundary valves closed and by ensuring that boundary valves are not leak-
ing or passing water into a neighboring zone. However, boundary valves can be opened
temporarily for operational purposes as long as they are properly closed again after-
ward and normal operating conditions are confirmed. It is a good practice to keep
records about events, locations, and durations of boundary valve operations. Boundary
valves should be clearly labeled on maps and in the field so that they are not operated
inadvertently. This information will assist the leakage management team in interpret-
ing high flows as leaks and breaks rather than an open boundary valve.
For each DMA a file should be established containing key information including
number of all types of customers, location of sensitive customers and their contact
information, number of hydrants and fire sprinkler systems, pressure information, and
assessed minimum nighttime consumption volumes. Creating a map with as much
information as possible is another important part of DMA management. Records should
be kept for future component analysis on all leaks found, their location, type of pipe
failure or defect, material, and size of the pipe on which the break was detected.

16.7 Testing for Reservoir Leakage
Large amounts of leakage can be lost through either leakage from the structure of the
reservoir or from reservoir overflow. Leakage from the structure itself is probably more
common in older underground brick or masonry reservoirs which have not been lined,
but leakage can occur in other forms of storage too.
The easiest way to check for leakage is to isolate the reservoir from the system by
closing the inlet and outlet valves. This is usually done at night. Once the reservoir is
isolated, a depth test over time can be performed
either by simply measuring carefully the drop in
A level drop test can be level over time or by installing a high-resolution
level data logger to measure the drop over time. It is
performed to check whether
then just a matter of calculating the area of the reser-
reservoir leakage is present.
voir, calculating the volume per area times the drop
measurement, and calculating the volume of loss.
Care must be taken to ensure that the outlet valve is not letting some water escape.
Calculations are more difficult when the shape of the structure is not prismatic, as the
unit volume per increment of level changes as the level drops. Most water utilities
should have accurate as-built drawings showing exact measurements.