THE DESIGN OF A LOW COST GRAVITY MAIN

ABSTRACT
Kiirua sub-location in Buuri Constituency is currently supplied by Muguna Water Supply which
was commissioned 20 years ago. The sub-location is a high-potential rural area and has a rapidly
growing population. In recent years, the area has been experiencing water shortages due to
increasing demand and reduced flow in its primary water source. It has therefore become
necessary to construct a supply main that will augment the existing system. The main is expected
to supply an estimated 850 m³ of water per day while keeping the costs incurred as low as
possible. This project was thus carried out to design a technically viable gravity main between a
river intake 6.915 km away from an existing distribution reservoir in Kiirua while examining the
cost implications of three possible alternatives. The design was carried out in two steps which
involved the determination of suitable pipe diameters and the choice of appropriate pipe pressure
classes and the use of break pressure tanks. Suitable pipe diameters were obtained by employing
the parameters of hydraulic gradient, head loss and piezometric head. Appropriate pressure class
determinations were made by using the static head at different points. A unit cost analysis was
then undertaken and the most cost-effective alternative was that which involved the use of uPVC
pipes of pressure class B, which can withstand up to 90m static head, and two break pressure
tanks.

 

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PROJECT 2014-2015 SANYA NOELLA NAMFUTA F16-34912-2010.pdf1.81 MB