Flood Risk Guide

What Flood Risk Means

Flood risk is not only about whether a property has flooded before. It is also about whether water could reach vulnerable areas under certain conditions.

A property may have flood exposure because of its level, location, surrounding land, drainage arrangement, building openings, basement access, surface water flow paths or connected stormwater and plumbing systems.

A Practical Flood Risk Review Should Consider

• Where water may approach the property from
• Which openings, access points or low areas may be exposed
• Whether water can collect or pond near the building
• Whether drains, pits, pumps or backflow points may be involved
• Which rooms, services, storage areas or access routes could be affected
• What photos, plans, reports or maintenance records are available

The purpose of an initial review is not to design a solution straight away. The purpose is to understand the likely water pathway before deciding what controls, records or professional assessments may be needed.

Once the water pathway is understood, the Flood Mitigation Guide can help explain the practical control measures that may be considered.

Where Water May Come From

Floodwater may not always come from the most obvious direction. During heavy rain, water can move across roads, footpaths, driveways, paved areas, neighbouring land, gardens, courtyards and car parks before it reaches a building.

Water may also rise or reverse through connected drainage, stormwater, sewer or pump systems. This means surface flooding and backflow risk should both be considered where relevant.

Common Water Sources To Review

• Street runoff moving toward the property
• Water flowing across driveways, footpaths or hardstand areas
• Water draining from neighbouring land or shared accessways
• Overflow from pits, grates, trench drains or stormwater systems
• Water moving down basement ramps or driveway entries
• Creek, river, canal or overland flow where relevant
• Backflow from stormwater, sewer, drainage or plumbing connections

Useful Questions

• Where does water naturally flow during heavy rain?
• Does water move toward the building or away from it?
• Are there visible debris lines, ponding marks or staining after rain?
• Can water bypass the existing drains or grates?
• Has recent paving, landscaping or construction changed the flow path?

For more detail on pits, grates, overflow paths and surface water movement, see Drainage Management.

Entry Points And Low-Lying Areas

Flood risk often becomes more serious where water can reach a low opening, threshold, ramp, door, vent, drain or service penetration.

Some entry points are obvious, such as a driveway or doorway. Others may be harder to see in dry weather, such as low vents, wall penetrations, floor wastes, drainage pits or basement service areas.

Common Entry Points

• Doorways and pedestrian entries
• Garage doors and roller doors
• Driveways and basement ramps
• Loading docks and service yards
• External stairwells and below-ground access points
• Low vents, grilles and wall penetrations
• Floor drains, stormwater pits or connected plumbing fixtures

Low-Lying Areas To Identify

• Basement car parks
• Driveway low points
• Ground floor entries below surrounding paving
• Low courtyards or enclosed paved areas
• Plant rooms, pump rooms and electrical rooms
• Lift pits and basement service areas
• Storage areas, garages and loading areas

Identifying low-lying areas helps show where water may collect and which parts of the property may need closer review.

For barrier selection around exposed openings, see Flood Barrier Options For Property Owners. For homes and businesses, see the Residential Flood Barrier Guide and Commercial Flood Barrier Guide.

Site Conditions That Affect Risk

Flood risk can be affected by small site details. A minor level change, blocked grate, raised garden bed, new driveway surface or poorly directed downpipe can alter how water behaves during heavy rain.

A site review should consider both permanent features and changing conditions that may affect water movement over time.

Site Features To Review

• Ground levels around the property
• Driveway slopes and ramp gradients
• Threshold levels at doors, garages and entries
• Drainage pits, grates and trench drains
• Downpipes and roof water discharge points
• Retaining walls, garden beds and landscaping
• Hardstand areas, paving and car parks
• Fences, walls or kerbs that may redirect water

Changes That May Increase Risk

• New paving that changes surface falls
• Landscaping that directs water toward the building
• Blocked or covered drainage grates
• Debris collecting at low points
• Building works that alter ground levels or drainage paths
• New walls, fences or structures that obstruct overflow routes

Systems That Can Change Risk

Flood risk is often affected by how different systems work together. A flood barrier may reduce water entry at one opening, but drainage, pumps, backflow prevention, maintenance and emergency planning may still affect the final outcome.

This is why flood risk should be reviewed as a site system rather than a single product decision.

Systems To Consider

• Flood barriers at doors, ramps, loading docks or driveways
• Drainage pits, grates, trench drains and stormwater outlets
• Pumps and sump systems in below-ground or low-lying areas
• Backflow prevention devices and connected plumbing systems
• Maintenance routines for flood-related systems
• Emergency planning and communication procedures
• Site records, photos, reports and contractor information

System Interaction Questions

• If a flood barrier is installed, where does water go?
• If a drain blocks, what area does water move toward?
• If a pump fails, which areas are affected?
• If backflow occurs, where could water appear?
• If access is unsafe, who knows what actions should stop?
• Are maintenance records current enough to support future reviews?

These questions help identify whether the issue is mainly surface water, entry points, drainage, pump capacity, backflow, maintenance or a combination of factors.

For the supporting system guides, see Pumps And Sump Systems, Backflow Prevention, Regular Maintenance and Emergency Planning.

Recording Flood Risk Information

Flood risk information is more useful when it is recorded clearly. Photos, notes, plans, maintenance records and contractor details can help future owners, strata managers, building managers or site operators understand what has been observed.

Good records also make it easier to decide which specialist pages, contractors or professional reviews may be needed next.

Useful Information To Record

• Photos of flood-prone areas and likely water approach directions
• Photos of doorways, ramps, drains, pits, pumps and barriers
• Notes from heavy rain events, near misses or previous flooding
• Known low points and ponding areas
• Maintenance records for drainage, pumps, barriers or backflow devices
• Contractor reports, inspections or recommendations
• Follow-up actions and review dates

Keep Records Simple And Current

A useful flood risk file should be easy to find, easy to update and clear enough for someone else to understand. The best records are usually practical, dated and linked to specific locations around the property.

For a detailed record-keeping structure, see the Flood Risk Documentation Checklist. For a shorter multi-topic review, see Flood Resilience Checklists.

Flood Risk Review Checklist

Use this checklist as a starting point when reviewing general flood risk around a property.

Summary

A flood risk guide should help property owners, strata managers and commercial site operators understand the basic water pathway before choosing flood controls.

Useful starting points include water approach directions, entry points, low-lying areas, drainage features, pumps, backflow risk, maintenance records and site documentation.

The aim is to build a clearer picture of flood exposure so the right next step can be chosen, whether that is a flood barrier review, drainage inspection, pump servicing, documentation update or professional assessment.