particular efficiency of the pump, and the system selection largely depends
on the discharge–head requirements and on pump efficiency.
13.3.3 Variations in sump level, pumping demand, and friction losses
During the operational period of a pumping system the demand may
increase or decrease, the water level in the sump well may change (e.g.
variation in drawdown of a well) and the wall roughness of the pipeline
may increase with age; even partial clogging of the suction pipe (e.g. clog-
ging of the well screen) may occur.
A system initially designed with its characteristic as (a) correspond-
ing to a discharge Q 1 is shown in Fig. 13.5. If the water table in the well, for
example, decreases by an amount ∆S (dry period) the system curve
changes to (b), delivering a reduced discharge of Q 2. A larger pump with a
differentQ(Hm) characteristic may be necessary to maintain the original
dischargeQ 1 with the new system characteristic. If the conditions return to
normal (i.e. ∆S0; wet period) the original system curve (a) controls the
operation, giving a discharge Q 3 Q 1. If no storage facilities are available
556 PUMPING STATIONS
Fig. 13.5 Pipeline and pump characteristics with varying sump levels
