Flood risk management

Main goal

Reduce flood risk

  • Store stormwater
  • Increase infiltration
  • Delay runoff
  • Safely convey excess water
  • Reduce local flood impacts

Typical NBS types

  • Swales
  • Rain gardens
  • Permeable pavements
  • Wetlands
  • Detention basins
  • Green roofs
  • Restored watercourses

Monitoring flood risk prevention

  • Is the NBS reducing runoff and flood peaks as intended?

    Performance parameters

    • Runoff reduction
    • Peak flow reduction,
    • Peak delay
    • Infiltration rate
    • Drawdown time
    • Storage use

    Monitoring approaches

    • Sensors
    • Rainfall-event assessment
    • Infiltration tests
    • Hydraulic checks

    Frequency

    • Continuous/event-based
    • Post-storm
    • Annual testing

    Action trigger

    • Slow drawdown
    • Repeated overflow
    • Declining infiltration
    • Missed attenuation target

  • Is the NBS physically healthy enough to keep performing well?

    Performance parameters

    • Sediment
    • Blockage
    • Clogging
    • Erosion
    • Vegetation health
    • Litter
    • Structural damage

    Monitoring approaches

    • Routine inspections
    • Checklist walks
    • Photo points
    • Sediment checks

    Frequency

    • Monthly
    • Seasonal
    • After major storms
    • Annual review

    Action trigger

    • Blocked inlet
    • Visible erosion
    • Heavy sediment
    • Dead vegetation
    • Prolonged ponding

  • Does the system still work safely under stress conditions?

    Performance parameters

    • Overflow events
    • Alarm activation
    • Nuisance flooding
    • Unsafe ponding
    • Control failure

    Monitoring approaches

    • Alarm logs
    • Incident review
    • Operator notes
    • Post-event inspection

    Frequency

    • Continuous for alarms
    • Event-based after threshold storms
    • Annual resilience review

    Action trigger

    • Repeated failures
    • Unsafe ponding
    • Blocked controls
    • Exceedance route not functioning

  • What action is needed, and how quickly is it being taken?

    Performance parameters

    • Open issues
    • Repeated defects
    • Response time
    • Backlog
    • Vegetation replacement need

    Monitoring approaches

    • Maintenance logs
    • Work orders
    • Inspection-to-action checklist
    • Contractor records

    Frequency

    • Ongoing logging
    • Monthly review
    • Quarterly and annual summary

    Action trigger

    • Repeated issue pattern
    • Missed tasks
    • Growing backlog
    • Performance loss linked to maintenance

  • Automated

    Best for

    • water levels
    • flows
    • rainfall
    • overflow events

    Inspection-based

    Best for

    • vegetation
    • blockage
    • erosion
    • sediment

    Field testing

    Best for

    • infiltration rate
    • permeability
    • local diagnostics

    Analytical

    Best for

    • event comparison
    • peak attenuation
    • design checks

    User / operator

    Best for

    • complaints
    • field notes
    • recurring problems

Maintenance actions for flood risk reduction

  • Establishment-phase maintenance

    • Water and establish the plants
    • Control weeds early
    • Replace the plantings
    • Check settlement and initial flow paths

    Routine maintenance

    • Remove litter and debris
    • Clean inlets and outlets
    • Care for vegetation and control weed
    • Remove minor sediment
    • Inspect overflow structures

    Periodic maintenance

    • Remove deeper sediment
    • Replant and replace vegetation
      Repair erosion
      Renew the soil/media
      Carry out structural repairs

    Event cause maintenance

    • Clear the blockage immediately.
    • Repair after repeated overflow
    • Communicate about safety after an incident
    • Adjust the hydraulics or redesign as needed

  • Observation Likely issue Required action Urgency
    Water remains too long after rainfall Clogging or poor infiltration Inspect, test infiltration, clean or rehabilitate High
    Inlet blocked Debris or sediment Clear blockage and re-check after next event High
    Vegetation dieback Poor establishment or water stress Replace plants and adjust management Medium
    Visible erosion Excessive flow velocity Repair and stabilize flow path High
    Repeated issue pattern Underlying design or operation problem Escalate to annual review / redesign discussion Review

Learn more

  • (Links missing)

    • General NbS monitoring guidance
    • SuDS operation and maintenance guidance
    • Flood-focused green infrastructure assessment literature
    • Guidance on adaptive management and indicator selection

  • (Links missing)

    • City examples of flood-focused rain gardens and swales
    • Monitoring setups for detention basins and wetlands
    • Lessons learned from maintenance-heavy sites
    • Examples comparing manual and sensor-based monitoring

Further additions for the JOM site

  • Downloadable monitoring checklist
  • Template inspection form
  • Glossary links for technical terms
  • References to project partner outputs