Water Storage reservoirs are constructed with square shape water storage reservoirs, rectangular shapes water storage reservoirs and circular shapes water storage reservoirs. Special shapes like in the type, conical and spherical types are elegant in appearance but are expensive. Service reservoirs of different shapes are shown below. Service reservoir with circular shape in plan is the most economical shape and easier for construction. However the rectangular shape is preferred when the land available for constructing the service reservoir is rectangular with L : B ratio greater than 2. Further the space below the rectangular tank in the staging can be put into beneficial purposes like office or commercial complexes.
(d) Spherical r type.
The storage depth of service reservoir should be neither shallow nor deeper. Temperature effects are felt in the shallow depth tanks, which stimulate biological growth of the organisms leading the impairment of water quality. Further shallow depth increases the floor-area and thus necessitating more number of supporting columns, resulting in expensive installation. Larger storage depth of service reservoir, on the other hand increases the pumping head to fill the reservoir and causes wide variation of pressure in the d-system when the depth of water in the tank fluctuates. Most economical depth is, therefore, determined by the optimization techniques using computer software, considering the installation and O&M costs of the entire system. The recommended depths for different capacities of Storage reservoirs are furnished in below Table
The outlet pipe from the reservoir should be placed 15 cm above the floor and is usually provided with a strainer of perforated cast iron. The reservoirs filled by gravity are provided with ball valves of the equilibrium or other type which close when water reaches full tank level. The overflow pipe should be of sufficient size (equal to the inlet pipe size) to take away by gravity the maximum flow that may be delivered to the reservoir. The top of overflow pipe fitted with a bell mouth may be kept flush with the maximum water level of the tank. Scour outlet connected to a down take pipe with valve control is provided with the top of scour outlet with bell mouth kept flush with the floor of the tank. The tank floor is finished sloping towards the scour outlet. When there are two or more compartments, each compartment should have separate inlet and outlet arrangements, while the scour from each compartment with control valve and overflow downfall pipes may be connected to a single line. To.avoid waste of energy, it is advantageous to form the opening of the outlet, scour and overflow with a configuration by providing with a bell mouth at the openings. The different pipe connections to the elevated reservoir is shown above table.
Pump control system is a device at the elevated tank to measure the water level in the tank and transmit the level signal to a central pump control unit. The central control unit is programmed to turn on one or more pumps when the tank level drops to a set point level and to turn the pump, or pumps, off when the level rises to a higher set point level.
Pumps may run for hours to raise the tank level to the shutoff set point. Running pumps continuously for long time periods is preferable to avoid pumps start and stop frequently to minimize power and maintenance costs.
Evaluations considering larger-scale sub-regional combined water supply systems will often indicate the need for less overall storage than if evaluations are conducted on an individual, smaller community basis. Such evaluations on a sub-regional basis could also provide additional options for system interconnection.