Economic Aspects of Decision Making in Reliability Assessment of Water Distribution Networks - Pattern Recognition for Reliability Assessment of Water Distribution Networks - page 211

the most economic solution is finally selected from such a diagram (option 2), the question is
how that solution can be perceived from the perspective of supply in irregular situations.
Moreover, in case additional funds are to be invested to improve the network reliability, some
kind of guidelines should suggest either investing into increasing of the pumping i.e.
operational costs (option 1), or additional pipe capacity (option 3) would yield better results.

8.4 DESIGN ALTERNATIVES BASED ON TOPOGRAPHY

Good hydraulic design of water distribution network will aim to utilise the topography of the
area covered by the network to the largest possible extent, in order to reduce the energy input.
This can be taken as a principle, because the situations where this philosophy would lead to
more expensive design alternative are mostly theoretical. Even if the energy supply would
prove to be so much cheaper than the investment costs of the network, high energy input into
the water distribution may not be justified from the environmental point of view, the least.
Hence, were gravity supply is possible, it should also be provided, as Figure 8.5 shows.

Secondly, the topography plays important role as far the pressure in the network. Additional
pumping or storage may be needed to supply water to the areas far away from the source(s).
This eventually results in combined supply configurations where the storage will be mostly
elevated at higher elevations and pumping at lower elevations.

Figure 8.5 Typical cross section of gravity supply landscape

Reservoirs and pumping stations are always designed to operate in synchronised way. Pumps
will either supply from the source reservoir to the network or fill a reservoir that has to
supply (part of) the network by gravity. To provide sufficient balancing of the demand, the
volume of the reservoir and size of the pump will be designed to satisfy the minimum
pressure, accordingly. Location of the storage, pump and consumers can be correlated to five
typical terrain configurations:
1. Flat . Both the source and consumers are located on similar altitudes. The supply will
mostly take place by direct pumping and the storage plays role only on the suction side of
the pump, to balance the demand with the average source production. Possible tanks
within the consumers' area will be elevated (water towers) with primary purpose to
stabilise pressures rather than to balance the demand.