The following are the three most common types of reservoirs: 1. Earth Reservoirs 2. Masonry and R.C. Reservoirs 3. Elevated Reservoirs.
Type # 1. Earth Reservoirs:
When large quantity of water is to be stored before the treatment, usually earth reservoirs are provided, because these are the cheapest. These reservoirs are constructed by excavating to the required depth below the ground surface and using the excavated material for the building of embankments to the necessary height above the ground. To make the earthen reservoirs impermeable, core walls are constructed.
The embankments of these reservoirs should have minimum top width of 1.3 m or one-fourth the total height. As far as possible greater top width should be used. The side slopes should not be steeper than 1½ horizontal to 1 vertical. The embankments should be keyed down to the bottom by removing roots, loose soil and permeable material.
To prevent the leakage and loss of water, the sides and bottom of the reservoirs should be properly lined with bricks, stones, asphalts or concrete etc. Outlet pipes should be provided in the embankments walls at various places to minimize seepage of water. Fig. 18.11 shows an earthen reservoir.
Type # 2. Masonry and R. C. C. Reservoirs:
These reservoirs are used for storing and distributing clear water. These are constructed on high natural grounds and are usually made of stones, bricks or plain or reinforced cement concrete. The side walls are designed to take up the pressure of the water, when reservoir is full and the earth pressure when it is empty. The position of ground water table is also considered while designing these reservoirs.
The floors of these reservoirs are constructed with R.C.C. slab or square stone blocks. To obtain water tightness bituminous compounds are used at all construction joints. These reservoirs should be provided with R.C.C. roofs resting on columns.
At the top of roofs about 60 cm thick earth layer is deposited to protect the reservoir from cold and heat. Generally green grass lawns are maintained at the top. For aeration of water and going inside for inspection, ventilation, pipes and stairs are provided respectively. Fig. 18.12 shows a masonry reservoir.
Type # 3. Elevated Reservoirs:
When sufficient high ground above the distribution area is not available for the construction of ground reservoirs, from where water can flow under gravitational force in the distribution system, elevated reservoirs are constructed. The elevated reservoirs reduce the initial cost of pumps, reduce the peak demands on the pumps and reduce the maximum pressure required at the pumps discharge.
ADVERTISEMENTS:
Generally two types of elevated reservoirs are used, which are:
(a) Stand Pipes, and
(b) Elevated Tanks.
ADVERTISEMENTS:
(a) Stand Pipes:
These are usually made of steel and are circular in plan. The useful storage capacity of these is the volume of tank above the elevation of the high point of distribution. Water in tank below this point serves as additional storage for low distribution area which can be used with booster pumps or for fire-fighting where fire pumping engines are used.
Fig. 18.13 shows a stand pipe with inlet, outlet and drain pipe. Main hole is provided at the top with ladder for inspection and repair work.
(b) Elevated Tanks:
ADVERTISEMENTS:
When water is to be distributed at very high pressure and the use of the stand pipes becomes impracticable and uneconomical elevated tanks may be constructed with steel or R.C.C.
Now-a-days R.C.C. elevated tanks are very popular, because they have long life, require very little maintenance and give decent appearance in the locality. Recently pre-stressed R.C.C. tanks are coming up, because they are even economical than plain R.C.C. tanks.
Figures 18.14 and 18.15 show elevated tanks of various shapes. All tanks are provided with inlet, outlet, drain pipe, overflow pipe, water level indicator, manhole, ladder, ventilation pipe, lightening conductor etc. About 60 cm to 100 cm balcony is provided around the tank for inspection and maintenance of the tank. These tanks can be built for storing large quantity of water. The various shapes depend on the designing engineers.
