In the past, various activities were undertaken to straighten rivers, such as the stabilisation of river banks with concrete or other types of retention walls.ﾠ Such actions limited riversﾒ natural movements, leading to degradation of the river, increased water flow, increased erosion and decreased biodiversity.ﾠ Natural bank stabilisation reverses such activities, allowing rivers to move more freely.ﾠ Where bank stabilisation is nevertheless necessary, such as in residential areas, natural materials such as roots or gravel can be used.ﾠ Natural materials are preferable as they allow water to infiltrate into the bank.ﾠ They also provide better living conditions for aquatic fauna.
- Based on Stella definitions, adapted by NWRM project experts and validated by the European Commission

"Approaches to manage surface water that take account of water quantity (flooding), water quality (pollution)ﾠ and amenity issues are collectively referred to as Sustainable Drainage Systems (SuDS).
SuDS mimic nature and typically manage rainfall close to where it falls. SuDS can be designed to slow water down (attenuate) before it enters ﾠstreams, rivers and other watercourses, they provide areas to store water in natural contours and can be used to allow water to soak (infiltrate) into the ground or evaporated from surface water and lost or transpired from vegetation (known as evapotranspiration)." (Source: susdrain)

"Supplementary" measures are those measures designed and implemented in addition to the basic measures, with the aim of achieving the objectives established pursuant to Article 4 of the WFD. Part B of Annex VI contains a non-exclusive list of such measures. Member States may also adopt further supplementary measures in order to provide for additional protection or improvement of the waters covered by this Directive, including in implementation of the relevant international agreements referred to in Article 1.

EU definition:
Green Infrastructure is addressing the spatial structure of natural and semi-natural areas but also other environmental features which enable citizens to benefit from its multiple services. The underlying principle of Green Infrastructure is that the same area of land can frequently offer multiple benefits if its ecosystems are in a healthy state. Green Infrastructure investments are generally characterized by a high level of return over time, provide job opportunities, and can be a cost-effective alternative or be complementary to 'grey' infrastructure and intensive land use change. It serves the interests of both people and nature.
Clarification points:
From the perspective of Natural Water Retention Measures (NWRM), green infrastructure refers to new methods of managing water, favouring as much as possible the restoration of natural ecosystems or at least of their key functionalities in terms of water management. It consists of land management or engineering measures which use vegetation, soils, and other natural materials to restore the natural water retention capacity of the landscape. Green infrastructure measures use natural and man-made materials to enhance or improve longitudinal and lateral hydrological connectivity and natural hydrologic processes, including infiltration and runoff control but also purification processes. Green infrastructure can exist at a range of spatial scales, ranging from the very local, to the scale of a neighbourhood, a city or a whole region.
Local scale green infrastructure includes green roofs, permeable pavements and downspout disconnections, all of which can contribute to greater natural infiltration, reduced load on wastewater management systems, and limitations of peak runoff.
At the scale of a city or neighbourhood, green infrastructure can support sustainable urban drainage systems that mimic nature by soaking up and storing water or biodiversity promotion with fish ladders.
At a regional scale, green infrastructure can include the mosaic of managed semi-natural and natural areas that provides habitat, flood protection, cleaner air, and cleaner water. Thus land management strategies such as afforestation and retention of natural water retaining features in agricultural areas such as riparian buffers, ponds and wetlands can be considered as Green infrastructures designed to manage flood risks in downstream urban areas.
One key feature of Green infrastructure is its multi-functionality. The underlying principle of green infrastructure is that the same area of land can offer multiple benefits if the natural or man-made ecosystem is in a socio-ecologically sustainable state. Benefits of green infrastructure include a more natural hydrological cycle and ecosystem services related to biodiversity and human amenity. Green Infrastructure investments are generally characterized by a high level of return over time, provide job opportunities, and can be a cost-effective alternative or be complementary to 'grey' infrastructure and intensive land use change. Green infrastructure serves the interests of both people and nature.

Basins and ponds store surface run-off.ﾠ Detention basins are free from water in dry weather flow conditions but ponds (e.g., retention ponds, flood storage reservoirs, shallow impoundments) contain water in dry weather, and are designed to hold more when it rains.
- Based on Stella definitions, adapted by NWRM project experts and validated by the European Commission

The (monetary) value of resources deployed for the implementation of any NWRM, which includes upfront capital expenditures, either from new investments or the replacement of assets in past investments; depreciation allowances (annualised cost or replacing the accounting value of existing assets in the future); operating expenditures (those incurred to keep the NWRM running in an efficient manner); maintenance expenditures (for preserving existing or new assets in good functioning order throughout their useful life); and decommissioning costs (those incurred at the end of the lifecycle of the NWRM).

Targeted planting of forests in headwater areas (e.g. with a slope) can help to stabilize hillslopes, thereby reducing erosion and potentially leading to greater water retention in montane areas. Afforestation may have beneficial effects on the hydrograph by reducing peak flows and helping to maintain base flows. The potential for water retention must be balanced against the increased ET and pollutant trapping that may be associated with forests.
- Based on Stella definitions, adapted by NWRM project experts and validated by the European Commission

Negative impacts connected with the actual or potential degradation of natural assets or environmental quality due to economic activities.

Sacrifice associated to the use of available resources to one means instead of another (so that any economic cost is indeed an opportunity cost) or of following one course of action instead of the best available alternative. As applied to NWRM, it refers to those negative impacts in terms of welfare, either direct or indirect, that may be linked to the implementation of any measure.
The difference between explicit and implicit costs depends on whether there is an unequivocal monetary payment (or at least one which is straightforward to infer) or not. The term ﾓdirect (economic) costﾔ does actually refer to those costs that fall directly on the promoter of the NWRM. Hence, as opposed to direct costs, indirect costs are those incurred by others (those who are not under the direct scope of the NWRM implementation).

A gabion (from Italian gabbione meaning "big cage"; from Italian gabbia and Latin cavea meaning "cage") is a cage, cylinder, or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineering, road building, and military applications.