undergound pipe

8/7/2019 UNDERGOUND PIPE

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A Sewer is defined as an underground pipe orchannel owned and maintained by a statutorybody (usually one of the privatised water

companies) and used to carry waste water orsewage.

A Drain is most commonly defined as a pipe orchannel owned by an individual, usually theproperty owner.

A Private Sewer is a drain shared by a group ofresidents/property owners.



All drainage systems, both above ground and below

ground, work by creating a slope and relying on gravity tocause the water (or other liquids) to flow from the highpoint to the low point. This is known as the 'fall' and canexpressed in a number of ways, usually either a percentageor as a ratio. All gradients are defined as the amount of rise(or fall) in height above a fixed point over a given distance

(the run). Gradients are expressed in a number of ways,including Ratios [eg: 1 in 60 or 1:60] and Percentages [eg:9%].

For 100mm pipes, the type normally used for residentialdrainage, the minimum acceptable falls are 1:40 for FoulWater and 1:100 for Surface Water. Larger diameter pipes

may have gentler gradients in certain circumstances



Foul water used water from any building orprocess. This includes water from toilets, baths,showers, washing machines, kitchen sink, dish

washers etc. Sometimes it referred to as 'grey'water, effluent, soil water or waste water.



Surface water also referred to as Storm Water.Clean (ish) water that has been drained directlyfrom the ground, a pavement or a roof. It is

also known as 'run off'.



Water held by the soil, subsoil or bedrock. Theupper level of the groundwater is known as the'water table' or 'saturation line'.



Backfall is the term used to describe a gradientthat is counter to what would normally beexpected. In the footpath example from above,

a footpath that sloped away from the roadwaywould be said to be back falling. Backfall in adrain is usually bad news - it indicates thatwater/sewage may find itself trapped at a low

point



This is a term that seems to have been specificallydesigned to befuddle students and others outside thetrade, but is actually a much needed term for the sakeof clarity on site. It refers to the height above/below

a benchmark of the lowest part of the pipe channel at agiven point on the drainage system. The key point isthat it refers to the level of the floor of the pipe on theinside, not the base of the pipe on the outside, whichcan be 10mm or lower still, depending on the thicknessof the pipe.

In a manhole or access chamber, the invert level (oftenabbreviated to IL), is taken to be the lowest point in thepipe channel that is still within the chamber, that is, thelevel of the pipe channel just as it exits the chamber



The highest point of a manhole (or other access chamber) is thecover level (CL), which is the height of the cover above abenchmark level, and the difference between Cover Level (CL)and Invert level (IL) is the overall depth of the chamber. On

drainage plans, manholes are often annotated with figures for ILand CL, and the difference between the IL figures for successivepoints of a drain run (usually manholes or other chambers) areused to calculate endfall.

undergound pipe

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