Abstract:
The objective of this study is to investigate the hydraulic adequacy of the existing
water distribution network in the urban areas of Dhaka city for fire protection. For this
purpose, four pilot areas from different operational zones of Dhaka Water Supply and
Sewerage Authority (DWASA) have been selected on the basis of their development
pattern. These are Baridhara DOHS, Banani Old DOHS, Niknuja and Nimtoli (a
portion of old Dhaka). As an effective fire fighting device, street hydrants have been
proposed with the pipe network at some suitable locations in the study area following
some international standards. Besides the minimum and maximum fire-flow
requirements for these hydrants have been derived from the Bangladesh National
Building Code (BNBC, 2011) guidelines. As there are no well defined hydraulic
specifications readily available for street hydrants in BNBC and other local standards,
therefore pressure-flow constraints have been set on the basis of existing network
behavior and supply characteristics.
A WaterCAD v8i hydraulic network model has been developed for each area in order
to perform fire flow analysis. Necessary network information and consumer demand
characteristics have been collected from field survey and processed for model input.
Besides, different local and international water standards such as BNBC, AWWA,
ISO and NFPA have been utilized to define several model variables. Then all the
models have been simulated at steady state condition for one of the worst case
scenarios e.g. under peak demand period during a day. In addition, ten critical
scenarios have been analyzed in each model to evaluate the system response and
pressure-flow hydraulics at the hydrant locations. Simulation results dictate the
Available Fire-Flow (AFF) at the hydrant nodes under different scenarios. Based on
the AFF quantity, the adequacy of individual model has been assessed. Besides the
most critical and most reliable hydrant locations have been also identified according
to overall performance at those locations under different worse case scenarios. A total
of 141 street hydrant locations have been proposed and recommended in the study
areas. Among them, five in Baridhara DOHS and twenty two in Nikunja have been
identified as the critical hydrant nodes. Meanwhile the network of Nimtoli is found
adequate for fire fighting with thirty one hydrant locations. Note that the net AFF has
been determined at individual hydrant in any of the four models in the base scenario
for a minimum residual pressure of 1 m.
Overall hydraulic evaluation of study areas depict that the system has reasonable
adequacy for fire protection under general circumstances. Therefore, proposed fireflow
nodes in the study areas can be used for detailed design, flow-rating and
installation of street hydrants. This will ensure and enhance the reliability of the
existing water distribution network. Besides the report also provides a comprehensive
guidelines for setting a suitable fire flow water requirement which can be utilized in
other parts of Dhaka city. Finally the study provides a primary technical reference for
evaluation of fire fighting network in the water distribution system of Dhaka.
