Glossary of Drainage Terms and Definitions

Glossary of Drainage Terms and Definitions

Here at Flo-Well educating our customers on how best to look after their drainage systems is one of our top priorities. While we strive to explain things in the simplest terms possible, it can sometimes feel like your drainage technician is speaking an entirely different language, which is why we’ve put together this handy blog to cover some of the more popular drainage terms to help aid communication between yourself and your drainage specialist.

“Aco” style channel drain – Aco style drains are channels which are covered with a grating and are designed to drain surface water from a hardstanding such as a driveway along the entire length instead of from one point like a yard gully.

Adoption of sewers – Transferring responsibility of the upkeep and maintenance of a sewerage system to a sewage undertaker.

Aesthetic pollution – Solid, visible sewage materials that have little environmental impact.

Anti-flood valve – Designed to be installed in sewers or gravity drains to stop the backflow from a sewer towards a property or collection of properties.

Attenuation tank – Attenuation tanks are designed to hold a high volume of water during very heavy rainfall which in a normal system would overload the main sewer have a flow control chamber which releases the stored water before running into the drainage system.

Back inlet gully – Although this has the appearance of a standard gully at ground level, this design has below ground connections and therefore the connecting pipework does not discharge onto the grating.

Backfall – During the installation of some drainage systems, the pipework has not been laid to a good falling gradient, sometimes flat or with the downstream section higher than the direction the water is coming from and where the water is not flowing away it is pooling which causes the accelerated accumulation of debris deposits.

Branch connections / Lateral connection – Branch connections are drains that are not the main section of pipework running upstream and downstream but a drain that connects to the side of either a manhole chamber or underground section of pipework.

Brownfield site – A site which is being redeveloped because of pollution issues.

Catchment pit – An empty chamber installed in the surface water drainage system for intercepting silt and debris deposits being carried along the pipework.

Cavitation – Implosion of air in water at high velocity – something which can cause damage.

Collection system – A series of underground pipes located in wastewater which receives and carries stormwater and/or domestic or industrial sanitary wastewater.

Combined sewer – A sewer network collecting foul water and rainfall from both impervious surfaces and domestic and commercial sources.

Combined sewer overflow – Prevents a sewer or sewage treatment works from reaching its maximum capacity by allowing excess, diluted sewage to drain into a different disposal point.

Communal drainage – Since the “Transfer of Sewers” Act in 2011, the Local Water authorities are responsible for most of the sewer network. Private contractors are not permitted to work on these drains and should you be planning to build within 3.0m of these assets, a build over agreement will be required.

Contributing area – A catchment area which contributes storm runoff to a sewerage system directly.

Control structure – Used to limit the rate of flow, this is a hydraulic device.

Culverts – A covered pipeline or channel.

Depression storage – Natural depression on the ground’s surface that needs rainfall to be filled.

Detention tanks (balancing tanks) – Constructed in a sewerage system, these tanks temporarily store water during peak flows.

Discharge – An indeterminate amount of liquid which flows through a section of conduit per unit of time.

Domestic wastewater – Overflows from sinks, toilets, washing machines and other household items and services.

Drain – An underground pipeline specifically designed to carry surface or wastewater to a sewer.

Drainage – A series of channels, pipes and other engineering works designed to carry stormwater away from an environment which is built up.

Drain tracing – A method of inspection to locate blockages, collapsed drains and concealed manholes in areas that would be otherwise difficult to reach.

Dry weather flow – A flowing drainage system which hasn’t been caused by direct rainfall.

Dye testing – If the configuration of the drainage prevents passage of the camera, fluorescein dye is dropped into the system to confirm a connection.

Effluent – Effluent is the name for wastewater that has been either partially treated, completely treated or in its natural state.

Erosion – The movement of sedimentary deposits or soil caused by the flow of water, such as within a pipe or over the ground surface.

Evaporation – The process which dries out the ground surface.

Event (rainfall) – A single occurrence of rainfall both before and after a sufficient dry spell, therefore influencing certain sewer systems.

Extreme event – An event which occurs infrequently (such as large storms or long droughts).

Flap gate – A gate which, when opened, releases water whilst also preventing it from going back into the system.

Foul sewage – Waterborne waste coming from commercial or domestic sources where rain or surface water hasn’t contributed.

Foul system – A sewerage system, drains or pipes that have been specifically designed to carry foul sewage only.

French drain / Filter drain – A granular trench that has been filled with stone to carry and infiltrate stormwater runoff.

Gradient – The angle of the pipe’s inclination which also dictates its velocity of flow as well as its capacity.

Gravity system – A sewerage system or a particular drain whereby flow occurs due to the force of gravity. The pipeline is specifically designed to operate below its capacity when required.

Greywater – Wastewater coming from domestic appliances, baths, showers, and sinks.

Gully – Typically fitted with a grit tap and a grating, this is a structure permitting the entry of surface water runoff into the sewerage system.

Head-discharge – The relationship between the water level and the discharge rate.

Highway drainage system – A sewer or drain constructed in order to drain a highway of excess surface water.

Hydraulic capacity – The maximum capacity that a pipe can carry based on its slope, roughness, and dimension. It’s also referred to as pipe-full capacity.

Hydraulic simulation – A computational process done by way of a computer model to analyse how the system behaves because of an external influence, such as rainfall.

Impermeable surface – A surface which resists water infiltration.

Inflatable packer – Used to position a patch repair liner by pushing it out against the internal surface of the damaged pipe.

Inflow – The flow of water and other liquids which enter the sewerage system. It can be generated by industrial discharge or rainfall, for example.

Inlet – A connection joining the catchment area and a drain for surface or stormwater to enter. It’s also used to describe a structure which sits at the entrance of a conduit. An inlet also refers to the upstream end of a structure that water flows through.

Inline trap – Installed to prevent the escape of foul smells and vermin from the communal sewers however as they are not accessible from a manhole and do not have rodding access, there are usually difficulties clearing blockages which are known to build up in the u-bend of traps.

Interceptor trap – Interceptor traps are usually found in the outlet of the last manhole chamber, and this is the favoured design to prevent the escape of foul smells and passage of vermin from the communal sewers as there is incorporated rodding access.

Inspection chamber – Provides access to the sewer or drain to service it. This is done using equipment that’s remotely operated – no personnel access.

Invert – The lowest portion of a closed conduit. Usually, this can be found in its internal cross-section.

Land drains – Land drains are used in agriculture and building construction to drain wet or swampy ground. They usually carry excess water to an open ditch or natural water source.

Lateral drains – A private sewer or drain carrying drainage flows from an individual property to a public sewer.

Longitudinal fracture – A longitudinal fracture runs down the length of the pipe usually from a joint and will allow the loss of water into the surrounding ground area, possibly leading to subsidence. These fractures are usually easy to repair by drain lining/sleeving if there is adequate access.

Macerator – Used to break up solid waste with blades, making it easier to pump the liquid sewage uphill or vertically. Commonly used in basement toilets where it is not possible to install a gravity system.

Manhole – A structure providing access to the sewer or drain for servicing.

Misconnection – An improper connection between an inlet or drain to a drain or sewer that isn’t designed to carry a particular element of flow.

Model – Mathematical computer-generated equations that are developed and used to replicate the behaviour of a certain system.

Network – A collection of connected links, drainpipes, and manholes.

Obstruction – Obstructions in the drainage system restrict the free flow of waste. Water usually holds behind an obstruction which prevents a clear view of the cause however it can be anything from a build-up of non-disposable wipes and nappies, a roots mass or collapsed section of pipework.

Orifice – A pipeline constriction that controls the rate of flow.

Overflow – The discharge of sewage into the environment before it has been treated.

Overflow weir – a structure or device which relieves excess water from the conduit, or another container, when it reaches full capacity.

Patching – Like a drain liner but used to repair isolated defects or small damaged sections of a drain, sewer or pipe.

Pervious surface – Ground surface that allows the infiltration of water to occur, although it’s still subject to some surface runoff.

Primary treatment – The treatment of wastewater at a dedicated facility.

Private sewer – Typically, this is collectively owned and maintained by the owner of the building the sewer network is connected to.

Public sewer – A sewer where the responsibility falls to public authorities to maintain it.

Pitch fibre pipework – Pitch fibre was a material used predominately in the 1960’s and was subsequently found to be inherently defective, becoming deformed and blistered over a period of years causing the pipework to block completely, requiring excavation and renewal.

Pop-up valve – A specialized end of a drainage system that allows for manual opening when more rapid drainage is needed.

Radial fracture – Many drainage systems are of earthenware or clay construction and although strong, it is a material known to fracture. A radial fracture runs partly around the pipe and will allow the loss of water into the surrounding ground area, possibly leading to subsidence.

Rat blocker – Rat blockers are usually installed in place of interceptor traps to prevent the passage of vermin from the communal sewers into the private drainage system.

Recessed manhole cover – Standard manhole covers are not aesthetically pleasing so it may be decided that a recessed cover is used as they allow for bricks or slabs to be installed to match the surrounding area, making it blend into the floor but still allowing full access.

Redundant drain – It is possible that some drains are no longer in use, and we often find that these have just been left open or poorly capped at the end of the run with a builder’s plastic rubble sack. We advise these runs are sealed at the manhole chamber as rats prefer to nest in these sections and can escape inside houses.

Rain gauge – a device used to record the level of rainfall at a specific location.

Reservoir storage – a volume of flow will be temporarily stored in a length of pipe, surface, or channel as the rate of flow and depth increases. The storage will deplete following a storm.

Reforming – Pitch fibre pipework is prone to “squashing” and therefore re-rounding is a technique used to return the drain to its original circular shape.

Rest bend – Vertical downpipes that do not discharge to a gully are connected to the underground system with a rest bend. This 90° bend has a long sweeping angle to allow the waste to flow smoothly and usually has a footing to help absorb the force of the flushed water as it hits the base.

Rodding access – Found on interceptor traps, new style gullies and some sections of above ground pipework to allow entry to the drainage system, mainly to attempt to clear a blockage however CCTV camera inspections can also be carried out from these points.

Root ingress – Occurs when a crack forms in an underground pipe which allows water to escape. Nearby tree roots will benefit from this, subsequently leading the roots to the crack in the pipe.

Runoff – Water that flows from a surface, eventually reaching a sewer or drain.

Screen – A device used to remove or retain floating solids in wastewater or flowing water.

Scum board – A board or plate that sits below the water level, thus retaining a build-up of scum and other suspended or floating debris.

Sediment transport – The movement of solids through flowing water and other liquids.

Self-cleansing (velocity) – Velocity needed to keep solids floating to prevent reduced capacity or blockages in the future.

Separate system – A system made up of two pipelines – one carrying surface water and another carrying wastewater.

Septic tank – A container used for collecting and partially treating sewage.

Sewage – Surface water or wastewater conveyed by a sewer or drain.

Sewer – A conduit or pipe that carries drainage water or wastewater which serves more than one property.

Sewer flooding – The unexpected escape of wastewater from a sewerage system.

Sewerage – Also referred to as a drainage collection system.

Settlement tank – This is the tank where most solids settle and are removed from the crude sewage that flows into the primary settlement tank.

Sewerage system – A network of pipelines carrying surface and/or wastewater from drains for treatment or another place of disposal.

Silt – Fine sand, clay, or other material carried by running water and deposited as a sediment

Sludge – Sludge is a mixture of solids and water that is produced during the treatment of wastewater and sewage from both private sewage treatment systems and public sewage treatment works. Sludge is removed from the treatment system via a process known as ‘desludging’.

Sluice gate – A gate which slides open and closed which allows flow to take place.

Snaking – When there is a bad clog in a drain or pipe, drainage technicians can use a snaking system to remove it. The “snake” is a flexible auger that can be fed deeply down the drain to reach the source of the clog.

Soakaway – A pit that surface water is drained into to infiltrate the ground.

Soffit – The top part of the inside of a conduit or pipe.

Source control – Reducing pollutants and runoff to prevent them from entering drainage systems.

Soil and vent pipe / vent stack – Drainage systems need ventilation to allow the escape of gasses, most properties have a soil and vent pipe where the top of the pipe is opened to let air circulate.

Storm tanks / storm drains – Specifically designed to hold high volumes of stormwater in treatment works or sewers.

Stub stack – These are short sections of above ground pipework that serve waste pipes and toilets but do not extend to the top of the property with a vent.

Sub-catchment – A drain at ground surface level leading directly to a gully or collection of gullies.

Surface wash off – Rainfall runoff carries surface debris, dissolved pollutants and sediments into the sewer system or drain.

Surface water system – a sewer system or drain specially designed to only carry surface water.

Suspended solids – insoluble solids that are suspended or floating in water or wastewater.

Sustainable drainage (SUDS) – drainage techniques that are beneficial to the environment.

Sump pump – A pump system placed in basements, cellars, and low points in some yards where immediate drainage is not installed. The pump will siphon pooling water and send it down an attached hose, where it can discharge as needed at the other end.

Swan neck – Swan necks are used in vertical downpipes to allow for a difference in the structure of a building such as the gutter on the edge of a roof to the rainwater pipe adjoined to the wall.

Swale – A small concrete tunnel that helps direct water away from areas where it can collect. Swales often run alongside driveways so discharge can easily reach the street’s gutter.

Time of entry – The time taken for surface runoff to enter the pipe system.

Wastewater – Water used and subsequently discharged to a drain.

Water quality – Chemical, physical and biological properties of water to determine its suitability for varying purposes.

Watercourse – Either a natural or artificial channel allowing water to pass through.

Water table – The water table is the upper level of an area of saturation. This means it’s the upper level of an area of land where the soil or rocks are permanently saturated with water.

Vacuum tanker – A specialist tanker used to pump and collect liquid waste.

These are just some of the terms that you may come across when dealing with a drainage problem. While the technical jargon can seem complicated, here at Flo-Well we aim to make it understandable.

As always, if you have any questions, or are unsure our friendly team of drainage professionals are always happy to help. Contact us today for a drainage quote!