WATER SUPPLY DISTRIBUTION On completion of this module you should be able to Describe a water supply distribution system describe the components of pipe distribution systems appreciate the Queensland Planning Guidelines for Water Supply and Sewerage design simple gravity and rising mains determine the required storage capacities and location in a water supply distribution

WATER DISTRIBUTION SYSTEMS A network of pipes & storage tanks to meet demand at satisfactory pressure Grid or branching layout Supply zones and storage tanks Design flow rates

Reticulation pipe networks Branching system Grid system Reticulation pipe networks

PIPE APPURTENANCES Stop, butterfly valves reflux or non-returning valves pressure reducing, pressure sustaining valves pressure relief valves (surge) air valves hydrants

PIPE APPURTENANCES

Design of Urban Water Supply Schemes Trunk main from headworks to distribution reservoirs must cater for MDMM capacity Supply mains from service reservoirs and reticulation network must achieve MH demand Maximum pressure 80 m head in pipelines Minimum pressure 22 m (12 m under firefighting)

Some design parameters Annual demand is the total demand for a community, ML/year Average daily demand (ADD) = Annual demand/365, ML/d Mean day maximum month (MDMM) = 1.5 x ADD Maximum day (MD) = 1.5 x MDMM Maximum hour (MH) = MD/12 or 2.25 x ADD/12

Design of Gravity Main Determine the maximum capacity Select pressure at load centre, check for pressure at high and low points Ascertain TWL of service reservoir and total losses Static head must not be excessive. Consider adjusting elevations or introduce break-pressure tank Design for appropriate pipe diameter through a process of iteration

Design of Gravity Main

Maximum capacity This depends on the location of the delivery system For trunk main from the headworks to the distribution storage tank, the design capacity is MDMM For other mains and within the reticulation system, the pipe must be designed to carry the maximum instantaneous flow i.e. MH demand.

Hydraulic equations Use Darcy-Weisbach and Moody equations Determine the head losses (friction and minor) Friction loss = f L v2 /(2gD)

Design of Rising Main Operating hours must be less than 24 hours Operating cost and not construction cost may be a significant factor Pump power is directly related to head losses which increases with the square of flow velocity Use economic analysis

Service Reservoir Provides adequate pressure and acts as a buffer between supply and demand Operating storage Breakdown storage Firefighting

Types of Service Reservoirs Surface tank Standpipe Elevated tank

Location of Storage Reservoir Storage reservoir is an essential component of a distribution system. A strategic location is important in terms of cost and service Locate centrally and as close as possible to the area it serves to minimise head losses and capital construction costs Locate at an elevation (natural or constructed) high enough to provide adequate pressures To accommodate fluctuation in demand, high and low supply operations regimes are to be provided

Reservoir location influences pressure distribution

Use of rise and fall main

End of Module 19 - Water distribution systems