Below Ground Drainage Flashcards
What is a sewer?
Sewers are public authority drains to which private house drains are connected
What is the purpose of a below ground drainage system?
To remove all the water carried waste from a household or community
List 6 rules of the bgds?
- Provide adequate acess points
- system must be water tight including inspection chambers
- drains should not be run under buildings unless it’s unavoidable
- minimum internal diameter is 100mm
- be adequately protected from tree routes
- all entry points should be trapped
Explain the combined system of bgd?
Both foul and surface water are discharged into the same sewer
List two advantages of the combined bgd?
Cheaper to install
Sewer gets flushed clean through heavy rainfall
List 3 disadvantages of the combined bgd?
- Can flood through heavy rainfall giving raw sewage on the streets
- Treatment plants have double the capacity too treat
- Can’t cope with expanding towns
What is the minimum drain size for underground drainage?
100mm
Explain the separate system of bgd?
Has 2 sewers and is the most commonly employed method of waste water disposal in new towns and urban areas
List 2 advantages of the separate system?
Reduces loading on sewage treatment works
No surcharging during heavy rainfall
List two disadvantages of the seperate system?
Cross connections can occur
Sewer does not get a flushing out during rainfall
Explain the partially seperate system?
It requires two sewers one carrying water from paved areas and part of the roof and the other carrying foul water and water from the remainder of the roof
Why would access points be provided in the bgd system?
To avoid the possibility of a blockage
List 3 types of access fitting used?
Bend
Branch
Gully
Define the term manhole?
If the chamber is large enough too work in it’s a manhole
