Environmental protection

Functional performance monitoring checks whether the NBS is improving water quality as intended. The focus is on pollutant removal, hydraulic behaviour, and whether water is passing through the intended treatment pathway rather than bypassing the system. For high-value or regulated assets, use paired inflow/outflow monitoring; for lower-risk assets, combine inspections with periodic sampling. [2]

Practical monitoring approaches: Suitable approaches include inflow–outflow sampling, event-based grab sampling after rainfall, field measurements, water-level logging, and periodic laboratory analysis. In City Blues, LoRaWAN-sensors were tested for water level and soil moisture. Also, a sample of the infiltrating soil/material can also be taken and tested for loading with contaminants.

Suggested parameters: Typical parameters include turbidity, total suspended solids, nitrogen and phosphorus species, conductivity, pH, temperature, hydrocarbons, metals, pathogens where relevant, infiltration performance, drawdown time, and hydraulic residence time.

Realistic monitoring frequency: Monitoring is usually more intensive during the first year of operation and after significant storm events. The further monitoring should be adjusted to local permit conditions, receiving-water sensitivity, climate, and asset criticality (usually quarterly to annual). Also tests of the infiltrating soil/material for loading with contaminants must be added to the monitoring plan.

Example action triggers: Action is needed when pollutant removal falls persistently below the target, drawdown is much slower than expected, or outlet water quality deteriorates over time. Additional triggers must be defined based on local conditions. The infiltrating soil/material must be replaced when it is loaded. [2, 3]

Condition and asset-health monitoring checks whether the NBS is physically capable of continuing to perform well. Many failures first appear as visible deterioration before they are reflected in water-quality data. [2]

Practical monitoring approaches: The main methods are structured visual inspections supported by photographs and simple field checks. In City Blues digital manual inspection forms as a low-tech option were tested. Visual inspection also can be updated with Unmanned aerial vehicles (UAVs or drones) equipped with RGB and multispectral cameras to quickly survey large areas and assess structural condition and vegetation health. Observation can also be supported by citizen or residents (citizen science).

Suggested parameters: Key aspects include vegetation cover and health, sediment accumulation, erosion at inlets and outlets, clogging of soil or filter media, underdrain and overflow condition, structural integrity, invasive species, and debris accumulation.

Realistic monitoring frequency: Monitoring should be frequent during establishment and then seasonal/quarterly or event-based after heavy rainfall according to local permit conditions, receiving-water sensitivity, climate, and asset criticality.

Example action triggers: Action is required when vegetation declines significantly, sediment reduces storage or treatment area, erosion becomes active, or clogging affects infiltration and drainage. Different triggers apply to different NBS types. [2, 3]

Practical monitoring approaches: In practice, this is monitored through post-event inspections, water-level observations, complaint records, and routine operational checks. Here also the City Blues technologies digital manual inspection forms, citizen science or LoRaWAN-sensors could help to improve the monitoring.

Suggested parameters: Important concerns include early overflow, repeated bypass of untreated water, blocked outlets, unstable side slopes or embankments, standing water, mosquito or nuisance conditions, and unsafe public access

Realistic monitoring frequency: Monitoring should be done event-based after heavy rainfall and according to local permit conditions, receiving-water sensitivity, climate, and asset criticality.

Example action triggers: Action should be triggered when overflow occurs during moderate rainfall, outlet performance is impaired, stagnation persists, or site safety risks are identified. [2, 3]

This part of monitoring focuses on what maintenance action is required and how quickly it is delivered. The purpose is to ensure that issues identified through inspection are translated into timely maintenance and not simply recorded. [2]

Practical maintenance reporting options: Monitoring methods include maintenance logs, work orders, inspection follow-up records, and supervisor review.

Suggested parameters: Key aspects include unresolved defects, response time for urgent issues, repeated faults at the same location, maintenance access constraints, and completion of routine tasks.

Realistic monitoring frequency: The maintenance needs corresponding response time should be monitored on a regular base.

Example action triggers: Action is needed when critical issues remain unresolved beyond the defined response time, routine tasks are missed repeatedly, or recurring problems indicate deeper design or operational weaknesses. [7]

Automated

Automated methods include sensors, data loggers (e.g. LoRaWAN-sensors), telemetry (UAVs), and event-triggered sampling systems. They are best suited to water levels, overflow behaviour, conductivity, turbidity trends, and storm-event response. Their main strength is high temporal resolution. Their limitations include sensor fouling, calibration needs, power or communication failures, and higher operational cost. [3]

Inspection-based

Inspection-based methods rely on structured visual checks by trained staff or also by citizen science using e.g. digital manual inspection forms. They are especially useful for identifying clogging, sediment build-up, erosion, damage at inlets and outlets, vegetation problems, and safety issues. Their main strength is direct operational relevance; their limitation is that they cannot by themselves quantify pollutant removal. [2]

Field testing

Field testing uses portable instruments for parameters such as pH, conductivity, temperature, dissolved oxygen, turbidity, and simple infiltration checks. It is valuable for rapid operational diagnosis, but usually less precise than laboratory analysis. [3]

Analytical

Analytical monitoring uses laboratory testing of water, sediment, or media samples. It is most appropriate for nutrients, metals, hydrocarbons, pesticides, pathogens, and contaminated sediments or filter media. Its strengths are accuracy and suitability for compliance or performance verification; its limitations are cost and sampling logistics. [8]

User / operator feedback

User- citizen science– or operator-based monitoring includes maintenance records, incident reports, complaint logs, and day-to-day operational observations, e.g. using digital manual inspection forms. It is useful for identifying recurring issues, odour, access constraints, nuisance conditions, or unusual ponding behaviour. Its value is highest when observations are recorded in a standardised way. [2, 3, 7, 8]

A balanced program usually combines inspection-based monitoring as the default, field tests for rapid diagnosis, lab analysis for validation or regulated parameters, and automation on high-value or event-sensitive assets. Surveys in Melbourne’s constructed wetlands show that monitoring often fails not because parameters are unknown, but because funding, expertise, maintenance integration, and practical guidance are weak. [9]

Establishment-phase maintenance

During establishment, the priority is to confirm that the NBS is functioning as designed and that vegetation, soils, and hydraulic pathways are stabilizing. Practical tasks include watering and replanting, weed and invasive control, mulch replacement where applicable, erosion repair, checking media settlement, verifying inlet and outlet levels, removing construction sediment, and confirming that early flows are distributed through the treatment area rather than short-circuiting. This stage is most relevant to the establishment stage, but the findings also feedback to design-stage lessons learned. [5]

Routine maintenance

Routine maintenance keeps water-quality treatment pathways open and reliable. Typical tasks are litter and debris removal, inlet/outlet cleaning, mowing or trimming where needed, vegetation thinning or replanting, invasive species control, forebay cleaning, minor scour repair, inspection of underdrains and overflows, and recording ponding duration after rainfall. This is mainly an operation-stage activity. [2, 7]

Periodic maintenance

Periodic maintenance includes larger, planned interventions to restore treatment performance. Examples include sediment excavation, media replacement or rehabilitation, underdrain flushing, wetland vegetation renewal, structural repair of embankments and energy dissipators, pond dredging, replacement of damaged liners or control structures, and recalibration or replacement of sensors. This is relevant to operation stage and long-term adaptive management. [2, 3, 7]

Event-caused maintenance

Event-caused maintenance is triggered by storms, spills, floods, drought, vandalism, fire, or abnormal monitoring results. Typical actions include post-storm debris and sediment removal, emergency erosion repair, blockage clearance, contamination investigation and sampling, removal of polluted sediment, rapid replanting of washed-out areas, and urgent public-safety controls. This is critical to operation stage and long-term adaptive management. [1, 2, 7]

Maintenance decisions should be based on simple and practical trigger rules. Water remaining in the system longer than the design drawdown period often indicates clogging, poor infiltration, or outlet blockage and should trigger inspection and rehabilitation.

Declining pollutant removal may indicate sediment overload, short-circuiting, vegetation failure, or exhausted media. Dead or sparse vegetation should trigger replanting and review of soil, irrigation, and scour conditions.

Severe sediment accumulation should trigger removal and upstream source-control review. Erosion at inlets or outlets should trigger stabilisation and hydraulic review. Abnormal sensor readings should be checked in the field before action is taken. Visible contamination, discolouration, odour, or oil sheen should be treated as potential pollution incidents requiring immediate investigation. [2, 3, 7, 8]

• Restore the regulated streams as Bueris Stream and Ravnbakke Stream
• “Catchment-based” approach: treating the entire hydrological area (streams, runoff, land use) rather than just individual spots.
• Integrate solutions for flood mitigation, erosion control, water quality improvement and enhancing nature and people’s wellbeing via green/blue infrastructure.
• Stakeholder co-creation and planning from early stages

Monitoring campaign: digital manual inspection forms and LoRaWAN sensors

• Prevent flooding, erosion, and poor water quality in the Riseberga Stream watershed (challenging and complex water body with many different landowners)
• Development of a watershed-wide development plan for nature-based solutions —close collaboration with a wide range of stakeholders

Monitoring campaign: sensor-based monitoring, UVAs, and digital manual inspection forms

• Flood management
• Bioswales, street trees, green roofs, permeable pavements

• Reduce flooding the old residential areas in Lake Iidesjärvi catchment
• Improve the ecological status and water quality of the Vuohenoja stream and Lake Iidesjärvi
• Prepare for increasing water volumes due to climate change and changes in land use in the upstream area for resilient urban watersheds
• Increase biodiversity; combat invasive alien species
• Improve the recreational value of the area

Monitoring campaign: continuous measurements and water samples, citizen science approach

• Flood risk and biodiversity
• Cascade of NBS

EcoDaLLi (EU-Projekt): The project is developing a methodology for monitoring nature-based solutions (NBS) in the Danube region (“Methodology for Mission-Relevant NBS Assessment”) to improve water quality and ecological connectivity.

RECONECT (EU-Projekt): The project aims to demonstrate large-scale nature-based solutions that reduce water-related risks while improving water quality.

Securing key nature-based solutions of urban water bodies (IGB Berlin): The Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) has developed guidelines for monitoring urban aquatic nature-based solutions (NBS). This includes monitoring water quality, vegetation, invertebrates, and hydromorphological conditions.

UNaLab (EU-Projekt): UNaLab (“Urban Nature Labs”) has developed a “Nature-Based Solutions Implementation Handbook” and a “Best Practices Booklet“. These resources provide specific tools for monitoring nature-based solutions (NBS) aimed at enhancing water and climate resilience in cities.

UPSURGE (EU-Projekt): The project has published a “Quick Guide for monitoring Nature Based Solutions“. This guide focuses on monitoring NBS in urban environments, including the assessment of water quality, air quality, and biodiversity.

Water Resources East (WRE): On behalf of WRE, the University of East Anglia has developed guidelines for monitoring nature-based solutions (NBS) for water security, including measures to improve water quality through riparian restoration and flow regulation.

Climate-ADAPT: The European Climate Adaptation Portal provides detailed information on Nature-based Solutions (NBS), including the Natural Water Retention Measures (NWRM) platform, which focuses on measures related to water retention and water quality.

Connecting Nature Resource Centre: Here you can find information about the project, cities, and all the relevant tools, guidebooks, reports, papers, innovations, policy briefs, videos, podcasts and blogs produced during the project.

EIP-AGRI Focus Group: The European Innovation Partnership (AGRI) has conducted an in-depth examination of nature-based solutions (NBS) for water management in agriculture, including reports on improving water quality

NbS Case Study Platform: Examples of best practice Nature-based Solutions from around the globe.

Network Nature: This platform serves as a central hub for NBS in Europe. It offers a resource library and a case study finder that focus specifically on improving water quality, addressing non-point source pollution, and implementing the Water Framework Directive (WFD) through NBS.

OPPLA: A leading platform for knowledge sharing on natural capital and nature-based solutions. It offers a wide range of case studies, products, and tools.