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Sewers for Adoption 8 (Sneak Preview #1)


One of the founding elements of a drainage design is the calculation of flow rates…..

and that is looking to change.

With previous editions of Sewers for Adoption guidelines, several figures have been used to calculate flow rates.

Although deemed relatively accurate it assumes that each house discharges the same amount.

What it doesn’t take account of is that bigger developments may discharge less per house.

Simple isn’t it!?!

How does this affect me?

Foul sewers (including pump stations) will soon have to be sized according to the new method potentially meaning manholes and discharge pipes may be larger on some smaller developments.

Although this is new for the water authorities of the UK it is heavily used throughout the M&E industry and is known as Discharge Units.

What are Discharge Units?

It is a method of calculating the amount of water usage units (like sinks and baths) to determine peak flow out of a building

What difference does this make?

Smaller developments look to have a greater flow rate, but larger ones look to decrease from current calculations.

When will this take effect?

Sewers for Adoption 8th Edition is supposed to be released later this year but may take a while for all the water authorities to review it and no doubt write their own addendums.


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