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RedR TSS

My first advice would be don’t do it!  Pipes laid on the surface would be subject to mechanical damage from passing people, animals (do you have elephants where you are?) and vehicles as well as more vulnerable to anyone along the 6km route that might want to gain access to water through an illegal connection.  I guess, however, that you are limited by cost or time so if you do have to lay the pipes on the surface then it would be most advisable to use strong pipe such as galvanised iron.  Again there is a cost implication so you may be limited to plastic pipes, in which case use a thick walled HDPE pipe.  At all costs avoid the use of PVC pipe which becomes brittle and cracks when exposed to sunlight.  If you are using High Density Polyethylene (HDPE) then ensure that it is at least buried at any point where it would be more subject to damage such as where it crosses tracks.  Also try to ensure that no sharp stones or other edges are pressing against the pipe.  If it is any comfort, I have seen surface laid HDPE for the complete water supply system on the island of Rodrigues which is part of Mauritius.

 

You have a 480m head difference between the top and the bottom of the pipe which is equivalent to 48 bars of pressure at the downhill end, ignoring head losses due to friction along the 6km of pipe.  The head losses will depend on the flow rate and the pipe size and you should size the pipes to comfortably handle the flow from the spring.  Tables of flow rate/pipe size/head loss are available in various publications such as “Engineering in Emergencies” as well as from the manufacturers and on-line.   Once you have an estimate of the maximum head likely to be experienced along the pipeline you can specify the pipe by the Nominal Pressure Class PN which I believe goes up to PN20 or 20bar (200m vertical column of water) of pressure.  The Pressure Class is related to the wall thickness of the pipe. If your pressure is still too high you might need to include break pressure tanks or a pressure reducing valves along the pipe run.    

 

Don’t forget that you will also need air valves to allow air to escape from high points along the pipe run and wash-out valves at low points, especially where there is likely to be a build-up of sediment. 

 

Best regards

 

Martin