DESIGN LAYOUT OF DISTRIBUTION SYSTEMS CE 370

Distribution System Layout Layout of water distribution system is a function of: source of water supply topography of distribution area variation in water consumption

Source of Water Supply water is supplied at one point (i.e. treatment plant) distribution storage (elevated tank or ground-level tank plus booster pump) is required in remote areas to maintain water pressure water is supplied at several points (wells) storage capacity is reduced and pipe sizes required are smaller.

Topography water is supplied at high elevation it flows by gravity through the water network. water is supplied at low elevation must be pumped up into the water network (pipes and storage).

Water Consumption is a function of residential, commercial and industrial demands. planning and zoning is applied to control variations in water consumption. Climate and economical aspects could also influence the layout of a water distribution system.

The objective of an engineer designing a water distribution system is to provide a stable hydraulic gradient to maintain adequate pressure throughout the service area and enough pumping and storage capacities to meet emergency demands. The following figure shows simplified water distribution systems which illustrate the basic principles of design.

EVALUATION OF DISTRIBUTION SYSTEMS

Quantity the water source plus the storage facilities must be able to provide enough water to meet both current and future demands (ten years ahead). records of average daily, peak daily, peak hourly rates of consumption of the past ten years are needed, beside other factors related to community growth, to project the future needs.

Intake Capacity surface water intakes must be large enough to deliver enough water to meet municipal use and treatment plant needs during any day of peak demand. if storage is not available, water intake capacity must be large enough to meet fire demand, maximum hourly flow, and inplant process needs at the same time.

Pumping Capacity Low-lift pumps transport water from the source to the treatment plant. High-lift pumps transport water from the treatment plant to the distribution system. Well pumps deliver water to the treatment facilities or directly to the distribution system. Booster pumps are needed to increase pressure in the distribution system of large communities or in areas with widely varying elevations. Pumping stations must have enough capacity to provide the amount of water at flow and pressure rates needed to meet both daily and hourly peak demand plus fire flow. Pumping stations must be reliable through duplication of units, standby equipment, and alternate sources of power

Piping Network Arterial and secondary feeder mains must be designed to supply water service for 40 or more years after installation. Actual lifetime of pipes of mains under normal conditions is 50 to 100 years. Sub-mains must be at least 6 inches in diameter in residential districts and 8 inches in important districts. Distribution lines are laid out in gridiron pattern Avoid dead-ends Adequate number of valves must be installed to allow shutoff in case of emergency Valves should be located in a way so that no more than one block will be out of service in case of emergency.