Glossary

This glossary is copied from the Stormwater Manual of Western Australia Chapter 11: Further Information. References are available from this chapter.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

R

Rational method: A means of computing storm drainage flow rates (Q) by use of the formula Q = CIA, where C is a coefficient describing the physical drainage area, I is the rainfall intensity and A is the area.

Receiving environment: Areas that receive stormwater runoff, including wetlands, waterways, coastal waters/dunes, groundwater and bushland areas.

Receiving water bodies: Include waterways, wetlands, coastal marine areas and shallow groundwater aquifers.

Recharge: Water infiltrating to replenish an aquifer.

Recycled water: Treated stormwater, greywater or black water suitable for a range of uses, e.g. toilet flushing, irrigation, industrial processing or other suitable applications (ARMCANZ & ANZECC 2000).

Regulatory controls: One of the five principal categories of non-structural BMPs for stormwater management. Includes controls such as enforcement of local laws to improve erosion and sediment control on building sites, the use of regulatory instruments such as environmental licences to help manage premises likely to contaminate stormwater or groundwater, and programs to minimise illicit discharges to stormwater management systems (e.g. drains).

Remobilisation: The transformation of sedimented contaminants by microbial or chemical processes into a dissolved form and transfer by diffusion from the sediment pore water into the water column (ARMCANZ & ANZECC 2000).

Re-suspension: The physical entrainment of sedimented particles by elevated flows, or as a result of sediment bio-turbation (ARMCANZ & ANZECC 2000).

Retention/retain: Retention is defined as the process of preventing rainfall runoff from being discharged into receiving water bodies by holding it in a storage area. The water may then infiltrate into groundwater, evaporate or be removed by evapotranspiration of vegetation. Retention systems are designed to prevent off-site discharges of surface water runoff, up to the design ARI event. It is the difference between total precipitation and total runoff.

Retrofitting: Retrofitting employs additional or alternative stormwater management devices or approaches which are installed or undertaken in an existing developed area. Retrofitting can occur at the lot, block/neighbourhood or catchment scale.

Riffles: High points in the channel floor, representing bedrock bars or accumulations of relatively coarse material. Water flow is typically relatively shallow, fast and rough over riffles. (Water and Rivers Commission 2002.)

Riparian vegetation: Vegetation growing within the channel and the along banks of waterways, extending laterally away from the bank and ending at the extent of the floodplain.

Riprap: Rock riprap consists of a layer or layers of well-graded rocks placed on stream banks to protect them from erosion.

Risk: The chances of something happening that will have an impact on objectives. It is measured in terms of consequences and likelihood. (Standards Association of Australia 1999.)

Risk assessment: The process of risk analysis and risk evaluation.

Roughness coefficient: A factor in velocity and discharge formulas representing the effect of channel roughness on energy losses in flowing water. Manning’s n is a commonly used roughness coefficient.

Runoff: Water that flows over the surface of a catchment area, including streams.

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