Knowledge Hub Glossary

An arch bridge is a structure that carries load primarily in compression through its curved form, transferring thrust to abutments or surrounding soil. Modern buried corrugated steel arches provide rapid, low-carbon alternatives to concrete bridges.

Attenuation crates are modular plastic geocellular units assembled into an underground void that stores surface water run-off and releases it at a controlled rate. They are one of two main forms of below-ground attenuation storage used on UK developments, alongside prefabricated steel tanks.

What Is an Attenuation Tank? An attenuation tank is an underground structure designed to temporarily store excess stormwater runoff during periods of heavy rainfall. By holding water and releasing it at a controlled rate, attenuation tanks prevent downstream flooding, reduce peak discharge, and help developments meet local drainage requirements. How Does an Attenuation Tank Work? […]

A balancing pond is a surface storage basin that temporarily holds storm run-off and releases it downstream at a controlled rate, limiting flood risk. Underground attenuation tanks perform the same function where land is constrained.

A box culvert is a rectangular-section culvert — most commonly in reinforced concrete (pre-cast or cast in situ) or corrugated steel — used to convey watercourses, drainage flows or small fauna under roads, railways and embankments.

A bridge abutment is the end support of a bridge. It carries the vertical and horizontal reactions from the deck down to the foundation while retaining the approach embankment behind it, which makes it simultaneously a substructure element and a retaining wall.

A catchpit is an access chamber with a sump below the outgoing pipe invert, positioned on a drainage run to collect silt and grit before they reach downstream storage, treatment or an outfall. The sump below invert is what distinguishes it from an ordinary inspection chamber.

A crib wall is a gravity retaining wall built from interlocking precast concrete or timber units stacked to form open cells, which are filled with free-draining granular material. The mass of the filled crib resists the earth pressure behind it.

What Is a Culvert? A culvert is a closed conduit or tunnel-like structure that conveys water — typically a stream, drainage channel, or stormwater flow — beneath an obstruction such as a road, railway, embankment, or trail. Culverts are fundamental to transport and civil engineering infrastructure, preventing water from eroding road foundations while maintaining natural […]

A culvert pipe is a pipe-form culvert that carries a watercourse, drainage flow or small-fauna passage under a road, railway or embankment. Common materials are corrugated steel, pre-cast concrete and structured-wall HDPE.

Erosion control is the application of measures and materials that prevent or reduce the loss of soil and sediment caused by water, wind or ice. Common UK methods include rock armour, gabions, erosion control mats, geotextiles and vegetation.

Flood risk management is the structured process of identifying, assessing and reducing the risk of flooding to people, property, infrastructure and the environment.

A footbridge is a bridge designed to carry pedestrians — and often cyclists and equestrians — over roads, railways, watercourses or other obstacles, designed in the UK to the Eurocodes and DMRB.

A French drain is a gravel-filled trench, normally containing a perforated drainage pipe wrapped in geotextile, that intercepts and redirects subsurface water.

What Is a Gabion? A gabion is a wire mesh cage or basket filled with rock, stone, or other durable material. Gabions are used extensively in civil engineering and landscape construction for retaining walls, erosion control, channel lining, and slope stabilisation. Their flexibility, permeability, and ability to conform to ground movement make them a versatile […]

A geocell is a three-dimensional honeycomb cellular confinement system, expanded on site and filled with soil, aggregate or concrete to reinforce ground, protect slopes and line channels.

A geocomposite is a manufactured product that combines two or more geosynthetic materials — typically a geotextile, geogrid, geomembrane or geonet — into a single composite product engineered to deliver multiple functions simultaneously.

A geogrid is a planar polymeric reinforcement product with an open mesh structure that interlocks with soil or aggregate to provide tensile reinforcement. Geogrids are used to stabilise weak subgrades, reinforce retaining walls and steep slopes, and reduce aggregate layer thickness.

A geomembrane is a synthetic, low-permeability sheet used as a fluid barrier in civil engineering — most commonly to contain liquids and gases in landfills, contaminated land, reservoirs, ponds, tanks and tunnels.

A geonet is a polymeric geosynthetic with intersecting ribs that form open, in-plane drainage channels, used to convey liquids and gases within landfill linings, retaining walls and below-ground structures.

A geosynthetic clay liner (GCL) is a low-permeability barrier consisting of a layer of sodium bentonite clay sandwiched between two geotextiles (or bonded to a geomembrane). When hydrated, the bentonite swells to form a self-sealing, near-impermeable barrier.

Geosynthetics are polymer products used in contact with soil or rock to perform one or more of six engineering functions: separation, filtration, drainage, reinforcement, containment and erosion control. The family includes geotextiles, geogrids, geomembranes, geocells, geonets, geocomposites and geosynthetic clay liners.

A geotextile is a permeable textile manufactured from synthetic fibres — typically polypropylene or polyester — used in contact with soil or other materials in civil engineering applications to separate, filter, drain, reinforce or protect.

Ground reinforcement is the application of structural elements — geosynthetics, piles, columns or chemical stabilisers — to increase the bearing capacity, reduce settlement or improve stability of soils.

A headwall is the retaining structure built at the inlet or outlet of a culvert or pipe. It retains the embankment around the opening, anchors the pipe end against flotation and displacement, improves hydraulic entry conditions and provides a fixing point for safety grilles and handrails.

An inspection chamber is a shallow access point on a drainage run that allows a pipe network to be inspected, rodded and jetted from the surface without entry. It differs from a manhole, which is sized and constructed to allow a person to enter the chamber.

An oil separator is a below-ground treatment chamber that removes free oils and fuels from surface water run-off before discharge to a sewer or watercourse, specified in the UK to BS EN 858 as Class 1 or Class 2, full retention or bypass.

Permeability — also known as hydraulic conductivity or k-value — is a measure of how easily water moves through a porous medium such as soil, rock or a geosynthetic. It is normally expressed in metres per second (m/s) and is central to geotechnical and drainage design.

Permeable paving is a surfacing system that allows rainfall to pass through the surface and into a granular sub-base.

A pipe arch is a corrugated steel culvert with an elongated, arch-shaped cross-section — wider than it is tall — that maximises hydraulic capacity while requiring less cover than an equivalent circular pipe.

Rainwater harvesting is the practice of collecting, storing and reusing rainwater that falls on roofs and hard surfaces, typically for non-potable applications such as WC flushing, irrigation, vehicle washing and process water.

A rainwater harvesting tank is the storage vessel — typically buried underground or installed in a basement — that holds captured rainwater between collection and reuse. UK tanks are sized to BS 8515 and constructed in concrete, GRP, HDPE or corrugated steel.

A rainwater tank is any storage vessel — above ground or buried — used to hold rainwater collected from roofs or hard surfaces. Tanks may serve rainwater harvesting reuse, stormwater attenuation or a combination of both functions.

A reno mattress is a shallow, wide gabion unit — typically 150 to 300 mm deep — divided into internal cells and filled with small stone. It is used as a flexible erosion-resistant lining for channel beds, banks and slopes, where its low profile and large plan area suit revetment work rather than retaining.

What Is a Retaining Wall? A retaining wall is a structure designed to resist the lateral pressure of soil, rock, or water and hold back earth where a change in ground elevation occurs. Retaining walls are essential in road and railway construction, site development, slope stabilisation, and flood defence — enabling engineers to create level […]

A revetment is a protective facing placed on a sloping bank or embankment to absorb wave and flow energy and prevent erosion. Unlike a retaining wall it does not hold back the soil mass; it armours the surface of a slope that is already stable.

A road bridge is a structure that carries vehicular traffic over an obstacle such as a watercourse, valley, railway or other road. UK road bridges are designed to the Design Manual for Roads and Bridges (DMRB) and the structural Eurocodes.

A road gully is the surface inlet that collects run-off from a carriageway or paved area and passes it into the drainage network. It comprises a grating and frame, a gully pot with a sediment sump, and a connection to the carrier drain or sewer.

Rock armour — also known as riprap — is a layer of large, durable, interlocking rock placed to protect shorelines, river banks, embankments and structures from erosion and scour.

A silt trap is a chamber or structure that intercepts and retains silt, sand and sediment carried by surface water run-off before it enters a drainage system, soakaway or watercourse.

Slope stabilisation covers the engineering measures used to increase the factor of safety of a cutting or embankment against sliding, and to prevent surface erosion of the face. Methods range from regrading and drainage through geosynthetic reinforcement to soil nailing and structural retention.

A soakaway is a sub-surface infiltration structure — typically a pit, trench or modular crate system filled with granular material — that disposes of surface water run-off by allowing it to soak into the surrounding ground.

Soil nailing reinforces an existing soil mass in place by installing closely spaced passive steel bars into the ground and connecting them to a face. The nails mobilise tension as the ground tends to move, creating a coherent reinforced block that acts as a gravity structure.

Soil stabilisation is the modification of soil properties to improve its load-bearing capacity, strength, durability or volume stability.

A sponge city is an urban planning concept where the built environment is designed to absorb, store, filter and reuse rainwater — rather than channel it rapidly away — to reduce flood risk, mitigate urban heat, improve water quality and recharge groundwater.

Stormwater attenuation is the process of temporarily storing surface water run-off during a storm event and releasing it at a controlled, reduced rate to limit downstream flooding and meet discharge consents.

Stormwater management is the planning, design and operation of systems that control rainfall run-off from developed surfaces. The aim is to limit flood risk, protect water quality, support amenity and biodiversity, and meet UK planning policy requirements.

Surface water drainage is the system that collects and conveys rainwater run-off from roofs, paved areas and other hard surfaces.

What Are Sustainable Drainage Systems (SuDS)? Sustainable Drainage Systems — commonly known as SuDS — are a collection of water management practices that aim to mimic natural drainage by managing rainfall close to where it falls. Rather than conveying stormwater as quickly as possible into piped networks, SuDS slow the flow, reduce peak runoff volumes, […]

A swale is a shallow, broad vegetated channel that conveys, stores and filters surface water run-off at low velocity. Swales are a core conveyance component of Sustainable Drainage Systems (SuDS) in the UK.

A temporary bridge is a structure designed and installed for short-term use — typically months to a few years — to provide crossing during construction work, after a permanent structure has been damaged, or for events and emergencies.

Underground drainage systems are networks of pipes, chambers and ancillary structures installed below ground level to convey foul water, surface water or combined flows from buildings and hard surfaces to a sewer, watercourse or soakaway.

An underpass is a grade-separated crossing that carries pedestrians, cyclists, vehicles, livestock or wildlife beneath a road, railway or other infrastructure, commonly built as a buried concrete or corrugated steel structure.

A vortex separator is a hydrodynamic stormwater treatment device that uses induced rotational flow to remove sediment, silt, oil and floatable debris from surface water run-off before discharge to sewer or watercourse.

A wildlife crossing is a structure designed to enable animals to safely cross a road, railway or other linear infrastructure. UK crossings range from large vegetated green bridges to small mammal pipes and amphibian tunnels, designed per DMRB LA 109 and CIEEM guidance.