Technical terms explained simply
In our glossary, we explain key terms from the field of water management — concise, clear, and practical. Ideal for clients, planners, and anyone interested in sustainable infrastructure.
It indicates the rainfall that does not infiltrate or evaporate, but instead runs off. A distinction is made between peak and average runoff coefficients, depending on the given period or scenario.
Hygienic and chemical safety measure towards surface waters used for bathing. In the EU, the bathing water quality and its management is based on the Directive 2006/7/EC.
It represents the top soil layer in technical or nature-based systems where microorganisms break down pollutants and purify water through biological processes.
It represents the rainfall events statistics over different return periods (e.g., 2 years, 5 years, etc.) used to design drainage systems. The data are, for example, provided as “KOSTRA-Daten” by the German Weather Service (DWD).
A sewage treatment system that filters water through vegetated soil layers, with either vertical or horizontal flow. It is commonly used in small-scale wastewater treatment plants, as well as for rainwater or surface water management.
Replacement of contaminated or unsuitable soils with appropriate material, depending on the intended purpose (e.g., to enhance water infiltration).
Water intended for technical, commercial, or domestic use that does not need to meet drinking water quality standards, such as for toilet flushing and irrigation.
Green roof substrate layer designed to retain rainwater, enhance the microclimate, and decrease runoff. It can be part of a retention roof system.
A parameter defining the temporal length of rainfall events, typically derived from the “KOSTRA” dataset. Duration steps, ranging from 5 minutes to 72 hours, are crucial for the design of drainage systems and retention storage, since intense events require different considerations than long-lasting, lower-intensity rainfall.
Technical system used to remove excess water from soils or structures. It can also be used to convey water into infiltration systems, such as infiltration trenches or soakaways.
Controlled water discharge limitation from retention structures, typically implemented using flow control devices. In Berlin, it is permitted on a case-by-case basis, with a maximum of 10 l/s per hectare.
A regulatory permit for discharging wastewater or rainwater into a watercourse or the public sewer system. In rainwater management, direct discharge releases water, after any required treatment, directly into a surface water body, while indirect discharge routes water first into the public sewer system for subsequent transport and treatment if necessary.
The removal of deposited sediment from water basins or water bodies to preserve their functionality and water quality. It also eliminates nutrients, such as phosphorus, that can lead to eutrophication
The restoration of natural infiltration, evaporation, and hydrological balance by dismantling sealed areas. This measure helps adapt to heavy rainfall events and enhances groundwater recharge.
The excessive accumulation of nutrients, particularly phosphorus and nitrogen, in water bodies. It can cause algal blooms, oxygen depletion, and degradation of aquatic ecosystems. Treatment measures, such as vegetated soil filters, can help mitigate these effects.
Evaporation of water from, for example, soil, vegetation, or open water surfaces is a key process in the natural water cycle. As evaporation withdraws heat from the surrounding environment, measures that enhance evaporation are an important component of climate adaptation in urban areas.
The process of sealing land surfaces through various constructions, which limits infiltration, evaporation, and other essential soil functions.
Lightly polluted wastewater from showers, bathtubs, or washbasins. After technical treatment, it can be reused as service water.
Process in which water infiltrates into deeper soil layers, contributing to groundwater recharge. Technical measures, such as swales or infiltration trenches, can enhance this process.
Infiltration is the process by which water penetrates the soil through unsealed surfaces. In stormwater management, infiltration is a key factor in the proper functioning of systems such as swales, infiltration trenches, or soakaway pits. The infiltration capacity depends on the soil type and is quantified, the kf-value. For example, sandy soils are particularly well suited for infiltration. It is essential to ensure that the soil can absorb the incoming rainfall within specified timeframes to maintain effective drainage.
The Kf-value, also known as the permeability coefficient, indicates the water permeability of the soil. It is a key parameter for designing infiltration systems and assessing a site’s suitability for infiltration.
The collection and derivation of stormwater from paved surfaces such as roads, pathways, or plazas using channel drains.
The provision of water for fire protection, for example from hydrants, (artificial) water bodies, retention basins, or cisterns.
A drainage system in which both wastewater and stormwater are conveyed together through a single sewer to a treatment plant. During heavy rainfall events, however, the system can overload. In such cases, excess water is discharged into surface waters through so-called combined sewer overflows. This can result in untreated wastewater and stormwater entering rivers or lakes, potentially impacting water quality. Therefore, retention volumes and treatment facilities are essential components to reduce such discharges.
Swales are a key element of decentralized stormwater management, combining infiltration, retention, and treatment. They are shallow, vegetated systems capable of storing up to 30 cm of water. Rainwater is purified as it passes through the biologically active soil zone, where pollutants are removed or broken down through biological, chemical, and physical processes.
Spaces that can be used as open public areas and also serve for stormwater management, for example for temporary retention or infiltration of rainwater.
An open water basin that purifies, temporarily stores, and infiltrates rainwater. It can be integrated into landscape planning and serve as a recreational area and habitat.
Charge for the discharge of rainwater, which is exempted if the water evaporates, infiltrates, or is reused on-site.
Additional pathway for stormwater that diverts water when the regular sewer or retention systems are overloaded, helping to prevent flooding.
a concept in which all rainwater is retained, infiltrated, or reused on-site, so that no runoff enters the sewer system.
A system using wetland vegetation and soil to filter and treat rainwater or wastewater through biological processes. Plants and microorganisms break down pollutants, improving water quality..
Measures and systems for the controlled use, storage, infiltration, and discharge of rainwater. Their aim is to prevent flooding, reduce the load on sewer systems, promote groundwater recharge, and minimize the input of pollutants and nutrients into water bodies.
Temporary storage of rainwater for delayed discharge or reuse. The goal is to reduce peak flows during heavy rainfall and retain water as close to its source as possible. To achieve this, retention roofs, cisterns, infiltration trenches, or multifunctional areas can be used.
A roof system designed for the temporary storage and controlled, delayed discharge of rainwater. When combined with green roofing, it helps relieve drainage systems and improve the urban climate.
Controlled circulation of water in artificial water bodies using pumps and treatment systems to remove nutrients, improve water quality, and mix the entire water body.
Underground, permeable storage structures where rainwater is collected, stored, and infiltrated. In gravel trenches, the storage medium consists of gravel or crushed stone, while modular infiltration trenches are typically made of plastic modules that provide a high storage capacity.
Refers to the amount of contaminants, suspended solids, and nutrients carried by rainwater from sealed surfaces into the sewer system or water bodies. It is quantified, among other methods, using the aggregate parameter AFS63.
A system for removing particles from rainwater through sedimentation. It serves as a preliminary treatment before the water is further treated, infiltrated, or discharged.
A vertical structure to infiltrate rainwater. In Type A, both the walls and the base are permeable, allowing water to infiltrate directly into the surrounding soil. In Type B, the shaft is watertight except for the permeable base, so water infiltrates solely through the bottom.
A precipitation event with high intensity (large amounts of rain fall in a short period) potentially causing flooding and overloading sewer and stormwater systems. The German Weather Service (DWD) often defines such events based on return periods, for example, 30-year or 100-year rainfall events.
Underground channels that temporarily store rainwater and release it in a controlled manner to prevent overloading the sewer system during heavy rainfall events.
Planting area that temporarily stores rainwater and allows it to infiltrate slowly. Its function is similar to a swale but is more space-efficient, making it suitable, for example, as a roadside installation.
The process by which water evaporates from plant leaves, returning rainwater to the atmosphere and influencing the natural water cycle.
Drainage system in which wastewater and stormwater are collected and conveyed separately, reducing the load on treatment plants and preventing flooding.
Legally designated area in drinking water catchment zones where stricter requirements for rainwater infiltration apply to protect drinking water from contamination.
Mandatory assessment to ensure that heavy rainfall does not cause unacceptable flooding on private properties or public areas. The requirements and methods are specified in DIN 1986.
Measures to prevent or reduce damage from flooding, such as retention areas, emergency drainage routes, and floodable surfaces.
Technical facility that directs rainwater into the ground in a controlled manner to promote groundwater recharge and reduce surface runoff. To achieve this swales, infiltration trenches and soakaway shafts can be used.
The entirety of the water cycle in a given area, including precipitation, evaporation, infiltration, and runoff.
Statistical average time after which a specific rainfall event of a defined intensity is expected to occur once. Events with return periods of 30 or 100 years are often considered, based on data from the KOSTRA system of the German Weather Service (DWD)
Underground tank for the storage and use of rainwater. It can also serve as a retention volume, functioning like a rainwater retention basin.