La necessitat d'utilitzar unes habilitats de raonament que no són pròpies de la seva edat

A. Storage Capacity

 A service reservoir shall be designed to store or contain within its storage compartment a maximum volume of water equivalent to a cumulative day’s estimated total water demand from all types of premises located within its demarcated service area. The service area could either be a single development area or a number of development areas receiving water only from one reservoir.

Estimation of stored water volume shall be based on the unit water demand rates pertaining to specific premise types (Table B.1), and the total numbers of each premise type located within the reservoir service area.

B. Hydraulic Requirements

 Design of external reticulation systems supplied from an service reservoir shall be based on (a) the reservoir's BWL, and (b) the minimum residual pressure available at the HSL of a premise shall be a minimum of 7.5 m.

 The following residual pressure requirements shall be satisfied at the service reservoir:

- Minimum residual pressure at reservoir/ tank’s Top Water Level (TWL) shall not be less than 4.5m, where the connection source of incoming main has no connection to any other reticulation main.

- Minimum residual pressure at reservoir/ tank’s Top Water Level (TWL) shall not be less than 7.5 m where the incoming main has direct connection to reticulation pipe.

- Maximum residual pressure above HSL at any case shall not exceed 15 m for a gravity fed reservoirs/ tanks and 5 m for pumping fed reservoirs/ tanks.

 Reservoirs with storage capacities above 5 million litres shall be provided with compartments.

 Reservoirs shall be designed to permit the ingress and egress of air as the water level falls and rises. Appropriate ventilation systems shall be screened by non-corrosive mesh to prevent intrusion by insects, small animals, etc.

 There shall be proper circulation within reservoirs and suction cisterns. Inlets and outlets shall be located at the far side of each other. Inlets shall be placed at an angle to promote circulation.

 Outlets shall be designed in order to prevent pick up of sediments accumulated within the reservoir.

C. Boundary Setback

 Setbacks from the edge of structural foundations to the facility’s boundary shall be flat all-round and shall be at least 6.0 m for ground reservoirs, suction cisterns and pumping station structures, and 9.0 m for elevated reservoirs. Minimum distance between two (2) structures shall be 3.0 m.

 Subject to the minimum setback condition as specified above, the competent person shall determine the distance between service reservoir and the toe or crest of a slope.

D. Materials and Measures

 All materials used in the construction of an service reservoir shall conform to those registered with the Commission.

 Service reservoirs and suction cisterns shall preferably be constructed from reinforced concrete. However, service reservoirs of other materials may be used in special cases such as where there are constraints in the available size or shape of the land, or when the reservoir needs to be completed within a short duration. The Commission/Certifying Agency shall have the right to decide on the final selection of reservoir construction materials for different applications.

 Service reservoirs with a capacity of more than 454,000 litres should be of reinforced concrete or of other materials registered with the Commission.

 Elevated service reservoirs of the reinforced concrete type, or storage cisterns, shall be limited to capacities of less than 4.54 million litres.

The allowable capacity of elevated service reservoirs constructed from other materials shall be determined by the Commission.

 The effective water depth in service reservoirs built from reinforced concrete shall be limited to five (5) metres for capacities of less than 4.54 million litres, or seven (7) metres for capacities of 4.54 million litres and above. The water depth for non-reinforced concrete service reservoirs or storage cisterns shall not be more than five (5) metres.

 Inspection gallery with access door shall be provided for ground reservoirs of 4.54 million litres capacity, or more.

E. Pipelines located inside of Service Reservoirs and Storage Cisterns

 All pipes installed within service reservoirs or storage cisterns shall either be of stainless steel or ductile iron and coated with suitable anti-corrosion paint system or other materials as approved by the Commission.

 All vertical pipes shall be anchored and supported with stainless steel brackets and bolts and nut bolted into the wall of the reservoir.

 Overflow pipes shall be at least one size larger than the inlet pipe diameter.

 The scour pipe shall be designed to empty the full capacity of an service reservoir or storage cistern at least within six (6) hours.

 Generally, if water is supplied to a storage reservoir by gravity flow, the inlet pipe at the reservoir shall be of side or bottom inlet, whilst if water is supplied by forced pumping the inlet pipe shall be of top-inlet (bellmouth) type. The outlet pipe shall be of side or bottom outlet.

 Stainless steel strainer shall be installed at the outlet pipe of the reservoir or storage cistern. The invert level of outlet pipe shall be at least 150 mm above the floor of the reservoir.

F. Control Valves

 Water flowing by gravity into a suction cistern or service reservoir shall be controlled by a mechanical control valve; except in the case of pumped flows which shall be controlled by electrodes or level sensors.

 Inlet control valves shall be a one way flow full bore altitude valve complete with strainer and by-pass system installed in one common chamber, with butterfly valves introduced for isolating and by-passing water flows. This requirement is exempted when the incoming main is below 300mm and the inlet position is at the top end of a reservoir.

 By-pass pipes shall be provided and shall be of the same size as the incoming pipes.

 The altitude valve shall be of the diaphragm or piston type for sizes of less than 450 mm diameter, and only of the piston type for sizes of 450 mm diameter and above.

 The control valves shall be fitted with sluice valves/ butterfly valves for isolation and maintenance purposes.

 All valve chambers shall either be well drained, or equipped with an installed dewatering system.

G. Pipes Strainers

 All incoming mains to the suction cistern and gravity flow to service reservoirs shall be fitted with pipe strainers.

 A pipe strainer shall be fitted after the sluice valve and installed together in a common valve chamber. The size of the valve chamber shall be constructed to suit the fittings of the sluice valve and pipe strainer.

 The strainer shall be of 10 - 15 mm size of mesh stainless steel screen (net).

H. Miscellaneous

 Stairs placed external to an elevated or ground service reservoir shall be of reinforced concrete and shall be fenced complete with mild steel doors. All external walk up stairs for ground reservoirs shall have brick wall enclosure. Walk up stairs inside an service reservoir shall be of reinforced concrete or stainless steel (SS304). All walk-up stairs shall be fixed with hand railings.

 All service reservoirs or suction cisterns shall be fitted with 'Dial' type level indicators. The size of level indicator for ground type service reservoirs or cisterns, and for elevated reservoirs or cisterns shall not be less than 600 mm diameter and 900 mm diameter respectively.

Only stainless steel grade cable (of tangle-free design) shall be permitted.

 Top water level, bottom water level and capacity of an service reservoir or suction cistern shall be printed on the reservoir or cistern wall.

 Water sampling stations shall be provided at every service reservoir outlet.

 All valve chambers shall protrude above the ground level by not more than 300 mm, and shall be tightly fitted with a suitable cover.

 Platform drainage, overflow drains and slope drainage shall be designed as per Table B.11. The type of slope drainage shall be reinforced concrete V-drain as shown in Figure B.1.

Table B.11 : Storm drainage system design requirements

Drain Type Design Flow

General platform drainage 5 years ARI + check 100 years ARI Overflow discharge drain to

approved discharge point

5 years ARI + check 100 years ARI or

5 years ARI + Overflow whichever is the greater

Slope drainage 5 years ARI + check 100 years ARI Note: ARI is an average recurrent interval

Figure B.1 : Typical Details of Slope Drainage

 Security fences for service reservoirs and/or suction cisterns and pumping stations shall be built along the boundary of the reserve (in accordance with the Standard Drawing No. SPAN/WS/STD/035), and the boundary shall be marked with boundary stones at 6 meter intervals.

 All level ground within an external service reservoir, suction cistern and pumping station compound shall be premixed in accordance with criteria specified in Table B.12.

Table B.12 : Premix road pavement structures

Pavement Structure

Thickness (mm) Subject to traffic

loads

Not subject to traffic loads

Road Base (crusher run) 250 150

Base / Binder Course

Surfacing 60 60

 Dedicated access metalled roads servicing an service reservoir, suction cistern and pumping station site shall be at least 6 m wide with 1 m shoulder on both sides. The maximum gradient of an access road should not exceed 10%.

 Service reservoirs and cisterns shall be painted as per WDL’s requirements.

 All markings on service reservoirs or suction cisterns and pumping stations shall be subject to the WDL’s approval.

 All ferrous type saddles used shall have protective coating against corrosion.

 Saddles for High Density Polyethylene (HDPE) pipe should be of electro-fusion tapping.

 All bolts and nuts placed below ground shall be of stainless steel.

B.4.3 Pumping Stations