Flood Mitigation Guide

What Flood Mitigation Means

Flood mitigation refers to measures that may reduce the likelihood, severity or consequences of water entering or affecting a property.

It is different from simply knowing that a flood risk exists. Flood risk review identifies where water may come from and what it may affect. Flood mitigation focuses on practical controls that may reduce, manage or prepare for that exposure.

Flood Mitigation May Include

• Flood barriers at exposed openings
• Drainage improvements or better drainage maintenance
• Pump and sump systems for below-ground or low-lying areas
• Backflow prevention devices where connected systems may reverse flow
• Maintenance routines for flood-related systems
• Flood risk records, photos and site documentation
• Emergency planning, communication and post-event review processes

Mitigation Should Follow The Water Pathway

The best starting point is to understand how water may approach the property, where it may collect, which openings may be exposed and what systems may be affected. Mitigation measures should be chosen around that pathway.

For that first exposure review, see the Flood Risk Guide. For a practical checklist approach, see Flood Resilience Checklists.

Flood Barriers As Mitigation

Flood barriers may help reduce water entry through selected openings such as doorways, garage doors, roller doors, loading docks, basement ramps, driveways and low-level access points.

A barrier should be selected for the specific opening and site conditions. It should not be treated as a general answer to all flood exposure around a property.

Barrier Options May Include

• Demountable flood barriers for doors, garages, loading docks and wide openings
• Self-activating flood barriers for suitable driveways, ramps or access points
• Doorway or garage flood barriers for residential and small commercial openings
• Temporary flood barriers where there is enough warning time and safe deployment
• Integrated barrier systems forming part of walls, thresholds or civil works

Barrier Planning Questions

• Which specific opening or area is being protected?
• Where is water expected to approach from?
• Can water bypass the barrier through nearby openings or low points?
• Is manual deployment realistic before floodwater arrives?
• How does the barrier interact with drainage, pumps or access?
• Who is responsible for inspection, maintenance and records?

Flood barriers are often most effective when they are planned with drainage, access, maintenance and site responsibilities in mind.

For barrier selection, see Flood Barrier Options For Property Owners. For homes and commercial sites, see the Residential Flood Barrier Guide and Commercial Flood Barrier Guide.

Drainage And Surface Water Controls

Drainage management is a key part of flood mitigation because water usually follows surface levels before reaching a doorway, driveway, ramp, drain or low-lying area.

Blocked pits, undersized grates, poor surface falls, landscaping changes, debris build-up and uncontrolled overflow paths can all affect how water moves during heavy rain.

Drainage Items To Review

• Surface water flow paths across driveways, hardstand areas and paved areas
• Drainage pits, grated drains and trench drains
• Low points where water may pond or collect
• Overflow paths if drains are blocked or overwhelmed
• Downpipes and roof water discharge points
• Recent paving, landscaping or building works that may change surface falls

Surface Water Mitigation Questions

• Does water flow toward or away from the building?
• Can water bypass existing drains?
• Where does water go if a pit or grate blocks?
• Are drains clear, visible and maintained?
• Does water collect in front of or behind a flood barrier?

Drainage design, stormwater capacity and hydraulic performance should be reviewed by suitably qualified professionals where technical decisions are required.

For detailed drainage checks, see Drainage Management. For below-ground parking and ramps, see Basement Car Park Flood Risk.

Pumps, Backflow And Building Systems

Some properties rely on pump and sump systems to remove water from below-ground or low-lying areas. Others may be exposed to backflow through stormwater, sewer, drainage or plumbing connections.

These systems can affect flood mitigation even when the main flood entry point appears to be a doorway, ramp or driveway.

Pump And Sump Items To Consider

• Sump pit and pump locations
• Pump controls, float switches and alarms
• Power supply and backup arrangements where relevant
• Discharge pipework and outlets
• Service records, testing history and fault reports
• Areas that drain into the sump system

Backflow Items To Consider

• Low-level drains, floor wastes and plumbing fixtures
• Stormwater, sewer and drainage connections
• Backflow prevention devices where present
• Inspection, testing and maintenance records
• Warning signs such as surcharge, odour, gurgling or water marks
• Previous backflow events or near misses

For more detail, see Pumps And Sump Systems and Backflow Prevention.

Maintenance And Documentation

Flood mitigation measures need to be maintained and documented. A barrier that cannot be accessed, a blocked drain, a pump alarm nobody receives or missing inspection records can all reduce the usefulness of a mitigation plan.

Documentation also helps property owners, strata managers, facility managers, contractors and future decision-makers understand what has been installed and what has been checked.

Maintenance Items To Include

• Flood barriers, seals, posts, panels, fixings and storage locations
• Drainage pits, grates, trench drains and surface water flow paths
• Pump and sump systems, including controls and alarms
• Backflow prevention devices and inspection records where relevant
• Low vents, service penetrations and wall openings
• Plant rooms, electrical rooms, lift pits and other exposed services

Useful Records To Keep

• Photos of flood risk areas and protected openings
• Flood barrier product information, installation records and manuals
• Drainage, pump and backflow servicing records
• Maintenance reports, contractor notes and repair records
• Flood event or near-miss photos and observations
• Action lists showing issues, responsibilities and follow-up dates

Records should be clear, current and stored somewhere authorised people can access. This is especially important for strata buildings, commercial sites and properties where responsibility may change over time.

For more detail, see Regular Maintenance and the Flood Risk Documentation Checklist.

Planning And Responsibility

Flood mitigation is easier to manage when responsibility is clear. Different properties may involve owners, tenants, strata committees, building managers, facility managers, contractors or site operators.

A practical mitigation plan should explain who checks the systems, who arranges maintenance, who keeps records and who acts before or after severe weather.

Responsibility Questions

• Who is responsible for checking flood barriers?
• Who arranges drainage, pump or backflow servicing?
• Who keeps manuals, photos, records and reports?
• Who deploys manual or demountable barriers where relevant?
• Who monitors warnings or communicates with occupants?
• Who records post-event photos, damage or follow-up actions?
• Who reviews the mitigation plan after building or site changes?

Review Triggers

• After heavy rain, flooding or a near miss
• After flood barrier installation, servicing or repair
• After drainage, pump, alarm or backflow issues
• After building, paving, landscaping or drainage changes
• When responsible people, managers, tenants or contractors change
• Before internal risk reviews or insurance-related discussions where records are being prepared

A mitigation plan should stay usable over time, not depend on one person remembering every detail.

For preparation, safety and post-event actions, see Emergency Planning. For strata-specific planning, see the Strata Flood Planning Guide.

Flood Mitigation Checklist

Use this checklist as a starting point when reviewing practical flood mitigation measures around a property.

Summary

Flood mitigation means practical measures that may help reduce flood exposure and improve property preparedness.

Useful mitigation areas may include flood barriers, drainage management, pumps, sump systems, backflow prevention, regular maintenance, documentation and emergency planning.

The most effective mitigation approach is usually site-specific and based on the likely water pathway, exposed openings, available systems, maintenance responsibilities and records.