Water Storage and Balancing Reservoirs

STORAGE AND BALANCING RESERVOIRS

• Storage Resevoirs - store the treated water until it is pumped into the service reservoir or distribution reservoirs.

The capacity of storage reservoirs should be 14 to 16 hours of average daily flow.

•  Distribution Reservoirs - provide storage to meet the widely fluctuating demands, for fire-fighting and during emergencies.

Distribution Reservoirs serve the following purposes:

(i) They absorb the hourly variations in demand.

(ii) The pumps can be run at constant rate.

(iii) Reduction in pipe sizes, pumps and treatment units (economical)

(iv) They serve as storage for emergencies such as fire/ failure of pumps/ bursting mains etc.

(v) They maintain desired pressure even in remote areas.

(vi) Operation of distribution system becomes very easy.

 

Types of Storage and Distribution Reservoird:

1. Surface Reservoirs

2. Elevated Reservoirs

3. Stand Pipes

 

1. Surface Reservoirs (Ground Reservoirs)

 

• Made of masonry or concrete; circular or rectangular; constructed at ground level or below the ground level.

• Lining is provided with concrete or asphalt to check leakage of water. tonis

• They are constructed at high points in the city to achieve gravity flow.

• Sometimes pumps are used to convey water from surface storage reservoirs to muminin elevated distribution reservoirs.

The reservoir has two or more compartments to facilitate cleaning and repair.

• Overflow pipes are provided at full supply level to maintain constant water level.

• Ventilators are provided at roof slab for free circulation of air.

• The sludge settled in the reservoir due to storage of water is removed through washout pipes.

• The cement concrete floor is sloped towards the central washout pipes. doidwaysb msbo

 

2. Elevated Reservoirs (Overhead Tanks)

• Rectangular, circular or elliptical tanks.

• Supported on towers at suitable elevation above ground level.

• Used where pressure requirements are high.

• Used where combined gravity and pumping system of distribution are adopted.

• Water is pumped into these elevated reservoirs from surface reservoirs and then supplied to consumers.

• These tanks are made of RCC, steel, stone masonry or prestressed concrete

• Steel tanks corrode and have short life.

• Masonry tanks require very heavy supporting towers.

• Hence, RCC overhead tanks are preferred as they are cheaper, do not corrode iiguous band requires less maintenance.

• Intze type RCC tank is popular due to its structural stability and economy. bai Juodas leineo odi abawat beg

• Prestressed concrete elevated tanks are also preferred in modern days, which gives considerable savings in steel and concrete.

• The elevated reservoirs are provided with top roof cover to avoid contamination of water.

•  Other accessories of elevated reservoir are:

(i) Inlet pipe for entry of water

(ii) Outlet pipe for supplying water to distribution mains.

(iii) Overflow pipe to maintain constant water level.

(iv) Float gauge for indicating depth of water.

(v) Wash-out pipe (drain pipe) for removing settled sludge.

(vi) Ladders and manholes for cleaning and inspection.

(vii) Ventilator for fresh air circulation.

 

3. Stand Pipes

• They are elevated tanks without towers.

• They are tall cylindrical shells resting on ground.

• They are 15 to 30 m high and 10 to 15 m in diameter.

• They are made of RCC or Steel

• RCC stand pipes are not used for heights above 15 m as it cannot bear the high stresses.

• Stand pipes are provided where high heads are required.

• Like elevated reservoirs, stand pipes are also provided with inlet pipe, outlet pipe, wash-out or drain pipe, overflow pipe, manholes, ladders etc.

• The storage volume of the cylindrical tank includes an upper portion (useful storage) which is above the discharge pipe and a lower portion (supporting

• The entire capacity of tank can be used during fire-fighting or by locating the stand pipes on hills or high grounds.

 

Location of the Distribution Reservoirs

Following points are considered in deciding the location of distribution reservoir :

(i) They should be centrally located to have maximum command of the area.

(ii) They must be near to the area of distribution.

(iii) They should be located on high grounds/ elevations to maintain adequate pressure.

(iv) They should be close to the places of heavy demands to reduce the head losses.

(v) Located so as to reduce the length of pipelines and friction losses.

(vi). The distribution reservoir may be located in two ways:

 (b) Placed at farther end of distribution area.

In the former case (a) elevation of reservoir is high, length of pipeline is less and head loss is less.

In the latter case, (b) it is vice versa. However, the total head for pumping will remain the same for both cases.