Glossary
- Aggregate
- Granular material used in construction. Aggregate may be natural, manufactured or recycled.
- Aggregate, Primary
- Natural or primary aggregates may be crushed rock, sands and crushed or uncrushed gravels, extracted from quarries or sand pits.
- Aggregate, Recycled
- Materials that have previously been used in construction and then reprocessed to make them suitable for incorporation in asphalt; examples are spent Rail Ballast and crushed concrete.
- Aggregate, Secondary
- Manufactured aggregates and by-products of industrial processes; examples are Blast Furnace Slag, Steel Slag, Slate Waste and Calcined Bauxite
- Attenuation
- Runoff water is retained or stored then released at a controlled rate to reduce peak flow and increase the duration of the flow event.
- Catchment
- The area contributing surface water flow to a point on a drainage or river system; may be divided into sub-catchments. For example, where roof water is fed into a porous pavement, the catchment for the SUDS system is the roof and the pavement.
- CBR
- The California Bearing Ratio is a standard measure of the resistance of the subgrade to deformation under load.
- Contained / Tanked System
- A system with a sealed water storage layer below the pavement surface that retains water. The stored water can be re-used or released through a controlled outflow to achieve a prescribed rate of discharge.
- Controlled Outflow
- The flow rate of water from the storage reservoir of a SUDS system to a public water course such as an existing sewerage system. The rate of flow may be prescribed by the Environment Agency.
- Discharge
- Discharge is another term for stream flow; it is the measured volume of water that moves past a point in a given amount of time and is usually expressed in litres per second or cubic metres per second.
- Evapotranspiration
- The process of transferring moisture from the Earth’s surface to the atmosphere by evaporation of water and transpiration from plants.
- Filter Drain
- A linear drain or trench filled with a permeable material, such as coarse aggregate, which provides an easy route for water collection and infiltration into the subgrade or to a managed outflow; may have a perforated pipe in the base of the trench to conduct water to the outflow.
- Filtration
- The act of removing sediment or other particles from a fluid by passing it through a filter.
- First Flush
- The initial runoff from a site or catchment following the start of a rainfall event. As runoff travels over a catchment it will pick up or dissolve pollutants and the “first flush” portion of the flow may be the most contaminated as a result. This is especially the case in small or more uniform catchments, however, in larger or more complex catchments pollution wash-off may contaminate runoff throughout a rainfall event.
- Flood
- A flood is any relatively high streamflow that overtops the natural or artificial banks of a river. A flood occurs when the flow of water into a system exceeds the flow of water out of the system.
- Flood Frequency
- The probability of a flowrate being equalled or exceeded in any year.
- Floodplain
- The floodplain is the relatively flat lowland that borders a river, usually dry but subject to flooding. Floodplain soils actually are former flood deposits.
- Flow Control Deveice
- A device used to manage the movement of surface water into and out of an attenuation facility.
- Greenfield Runoff
- This is the method of surface water runoff from a site before development, or the existing site conditions for brownfield redevelopment sites.
- Greywater
- Wastewater from household appliances such as baths showers and washing machines that is captured before it reaches the sewer.
- Groundwater
- Water that is below the surface of the ground in the saturation zone; for instance in the water table.
- Hydraulic Conductivity
- Hydraulic conductivity describes the ease with which water can move through pore spaces or fractures. TarmacDry has a Hydraulic Conductivity rating of 5000mm/hr, whilst a 1 in 100 year storm event in the UK is the equivalent of 130mm/hr.
- Hydrograph
- A hydrograph is a graph that shows changes in discharge or river stage over time. The time scale may be in minutes, hours, days, months, years, or decades.
- Impermeable
- Will not allow water to pass through.
- Impermeable Surface
- An artificial surface that generates surface water runoff after rainfall.
- Impermeable Membrane
- An impermeable, puncture-proof membrane used to line the storage area of tanked / contained systems.
- Infiltration Potential
- The rate at which water flows through a soil (mm/hr).
- Infiltration System
- A water storage layer below the pavement surface that allows the water to soak into the subgrade over time.
- Infiltration Trench
- A trench, usually filled with stone, designed to promote infiltration of surface water to the ground.
- In-Situ Voids
- The voids in a layer once it has been placed and compacted; “the amount of fresh air in it”
- Permeable or Porous Pavement
- A paved surface (may be asphalt, concrete or blocks) that allows the passage of water to through the surface to a storage area (subbase), for capture or infiltration to the subgrade.
- Permeabiity
- The capability of a porous material to permit the flow of water. This depends on the material’s properties including shape, size and connectivity of pores or voids.
- PMB Binder
- Polymer Modified Bitumen Binder – bitumen that has been blended with polymers to achieve desired characteristics.The process map shows clearly how enquiries should progress through the business, highlighting the enquiry ownership at each phase.
- Porous Pavement
- Porous pavement, is a term used to describe paving methods for roads, car parks and footpaths that allow the movement of water and air through the paving material. Whether porous asphalt, concrete, paving stones or bricks, all these pervious materials allow precipitation to percolate through areas that would traditionally be impervious and instead infiltrates the stormwater through to the soil below.
- Proper Outfall
- An outfall to a watercourse, public sewer and in some instances an adopted highway drain. Under current legislation and case law, the existence of a proper outfall is a prerequisite in defining a sewer.
- Rainwater Harvesting
- A system that collects rainwater from where it falls rather than allowing it to drain away. It includes water that is collected within the boundaries of a property, from roofs and surrounding surfaces. A TarmacDry tanked system can be used to harvest rainwater.
- Recurrence Interval
- The average number of years between floods of a certain size is the recurrence interval or return period. The actual number of years between floods of any given size varies a lot because of the naturally changing climate
- Retention Pond
- A pond where surface water runoff is detained (e.g. for several days) to allow settlement and biological treatment of some pollutants.
- Runoff
- Water flow over the ground surface to the drainage system. This occurs if the ground is impermeable, is saturated or if rainfall is particularly intense.
- SEPA
- Scottish Environment Protection Agency.
- Soakaway
- A subsurface structure into which surface water is conveyed to allow infiltration into the ground.
- Source Control
- The control of runoff or pollution at or near its source.
- Streamflow
- Streamflow is the measured volume of water that moves past a point in a given amount of time and is usually expressed in litres per second or cubic metres per second.
- Subbase
- The subbase is the first significant structural layer in the construction of a pavement, the thickness of which is determined by the supporting strength of the subgrade. In a porous pavement, the subbase is highly voided as it must provide the reservoir space to store water.
- Subgrade
- The existing ground, or the surface of an excavation, upon which a pavement is built. This can be hard or soft, permeable or impervious. Its supportive strength is measured by California Bearing Ratio which is a standard measure of the resistance of the subgrade to deformation under load.
- Sustainable Drainage Systems (SuDS)
- Sustainable Drainage Systems (SuDS) are designed to reduce the potential impact of new and existing developments with respect to surface water drainage discharges. The SuDS concept is to try to replicate natural systems that use cost effective solutions with low environmental impact to drain away dirty and surface water run-off through collection, storage, and cleaning before allowing it to be released slowly back into the environment, such as into water courses. This is to counter the effects of conventional drainage systems that often allow for flooding, pollution of the environment - with the resultant harm to wildlife - and contamination of groundwater sources used to provide drinking water.
- Surface Water Management
- The management of runoff in stages as it drains from a site.
- Swales
- A shallow vegetated channel that provides temporary storage for storm water; a gradual soak-away.
