Floods can be devastating for property and business owners, but the extent of damage can often be significantly reduced with some good planning and preventative measures.
Floods can be devastating for property and business owners, but the extent of damage can often be significantly reduced with some good planning and preventative measures.
Floods affect more people around the world each year than any other form of natural disaster. Indeed, two of the most costly insured events to take place in Australia in the past 40 years were caused by floods.
The 1974 Brisbane floods, triggered by heavy rainfall from a weakening cyclone Wanda, rank fourth in the Insurance Council of Australia’s (ICA’s) ‘7 most costly insured events’, while Newcastle's 2007 storms rank sixth. According to the ICA, inland floods historically account for nearly a third of insured losses, with the worst affected states from an insurance perspective being NSW and Victoria, followed by Queensland and Western Australia. The ICA says the worst time of year for flooding is typically between April and October.1
Given the high prevalence of flooding in Australia, some of your clients are likely to be located in flood-prone areas, for example in close proximity to a river/natural waterway (whose banks can overflow), near the coast (and vulnerable to storm surge) or situated in low-lying urban areas, where flash floods can occur during heavy rainfall.
Without a doubt, the best flood minimisation strategy is to find an elevated location that’s low-risk. But given most Australian towns are located adjacent to rivers or by the coast, that’s not always possible. Now, thanks to the wonders of modern technology, clients can construct new premises or modify an existing building to increase its capacity to withstand water inundation and reduce flood damage. Quite often, modifying an existing property can be relatively inexpensive and make the premises habitable in less time following a flood.
Sizing up the risks
When devising a flood protection plan, important factors your clients need to consider are:
- Potential sources/types of flooding
- Likely frequency of flooding
- Predicted maximum flood levels for the location
- Likely flood duration.
The type and impact of potential flooding will determine the degree of flood protection that should be installed in your client’s premises. The first stage in the planning and design strategy is to determine the types or sources of flooding and which of these is likely to impact on the site.
Flood sources can include:
- Creeks, rivers, streams, natural watercourses
- Sea/storm surge
- Groundwater
- Overland flow
- Ruptured town water mains
- Blocked or overloaded drains and sewers.
While these sources can act collectively, one or two will usually represent the greatest threat to your client’s property. Development has increased the risk of flooding from rivers and streams in many areas by reducing the natural capacity of floodplains and increasing the rate of overland surface water run-off into rivers and streams. Indeed, urbanisation can increase water runoff by two to six times above what would be expected to occur on natural terrain.
There are several potential information sources that can help your clients determine their site’s potential maximum flood level and the likely frequency/duration of flood events. These include previous flood records and flood modelling, which may be available from the local council, local water authority, state/territory government department responsible for emergency planning and/or an insurer. Data availability varies from state to state.
Identifying the potential business impacts
After identifying the flood risks, your clients need to work out what the main impacts of this event are likely to be on their business, such as:
- Personal injury or death of staff
- Exposure to hazardous materials
- Loss of business records
- Damage to stock, plant and equipment
- Damage to furniture, floor coverings and fittings
- Loss of business and loyalty with customers
- Damage to reputation or image
- Time taken to resume trading
- Loss of production
- Cost of clean-up and debris removal
- Customers unable to physically access premises
- Employees unable to come to work.
Your clients need to put in place a contingency plan to help mitigate these risks.
Flood-proofing techniques
Numerous options are available to help your clients make their existing buildings more resistant to flood damage. Permanent/automatic measures, which require no human intervention, can include things like installing back-pressure reflux valves on drains or locating hard-to-move equipment and critical machinery, stock and spares to elevated areas.
Meanwhile, contingent flood-proofing measures (ie activated when there’s a threat of flooding) can include things like putting in place movable flood walls and free-standing barriers. For example, Floodgate Australia, which manufactures flood protection systems, recently installed a one-metre high barrier for a row of inner city stores in Lismore to protect them from water and debris that could flow down the embankment from an adjacent car park. The Floodgate ‘Fast-Fit’ system allows the shopkeepers to store system components on the premises and rapidly deploy a temporary wall in an emergency. See box for more examples of permanent and contingent flood-proofing tactics.
Designing flood-resistant buildings
If your client is constructing a new building, some relatively simple design measures can make the premises more flood-resilient. These include:
- Elevating the facility on walls, piers, columns or compacted fill above the predicted flood level
- Diverting drainage away from buildings
- Installing permanent flood protection barriers
- Raising door thresholds (allowing for disabled access)
- Locating service entry points and meters (e.g. gas, electricity, water and telephone) above predicted maximum flood levels
- Locating internal service walls above flood levels
- Locating windows above flood levels
- Installing solid, water-resistant external doors
- Avoiding the use of glass doors, large windows or large glass areas (susceptible to damage from hydrostatic and hydrodynamic forces)
- Fitting anti-backflow valves on sewers and drains
- Avoiding the use of plasterboard and gypsum-based materials
- Coating external walls with a water-resistant membrane or render
- Increasing external wall thickness of masonry to increase its resistance to flood-water penetration.
Consideration also needs to be given to design features that can enhance or speed up the drying process in the event of flooding. These range from installing additional weep holes at the bottom of cavity walls (to allow water to drain out) to using low permeability lime-based paints (to allow walls to dry out more quickly) and installing periscope air vents in walls. If the risk of flooding is significant, it may be worthwhile pre-purchasing dehumidifiers and blowers to enable a swift recovery.
Flood-protection measures for buildings and property
Permanent/automatic flood measures
- Installing non-return check valves in sewerage waste pipes and outlets to prevent backflow into the facility.
- Reinforcing wall structures to resist water pressure where the anticipated flood depth is greater than one metre.
- Sealing/facing/rendering walls to prevent or reduce seepage into the building’s interior.
- Building watertight walls around key or susceptible equipment/work areas.
- Installing permanent watertight external doors.
- Constructing flood walls or levees outside the facility to keep flood waters away.
- Landscaping the site to divert flood waters away from buildings.
- Building low bunds around the site or buildings.
- Installing sills/thresholds on doorways/openings with ramp access.
- Elevating the facility on walls, piers, columns or compacted fill.
- Installing permanent submersible pumps in basements to remove flood waters.
- Installing a diesel generator for back-up power.
- Backing-up computer data regularly and storing it in a safe, off-site location.
- Purchasing dedicated hydraulic lifts to raise key equipment prior to flooding.
Contingent/manual interventions
- Enacting the facility emergency shutdown procedure and isolating services (eg gas, electricity and water).
- Installing watertight barriers (eg flood shields, gates, skirts or covers) to prevent the passage of water through openings (eg doors, windows, air vents etc).
- Constructing movable flood walls and free-standing barriers.
- Sealing around doors and low openings.
- Installing temporary submersible pumps to remove flood waters.
- Moving mobile plant/vehicles to higher ground.
- Raising machinery/equipment on dedicated hydraulic lifts.
- Raising stock above the lower rack level and off the floor.
- Unplugging portable electrical equipment and storing at higher levels.
- Moving equipment that is outside to higher ground, particularly if it could float away and cause further damage to property.
- Securing equipment/tanks that cannot be readily moved but may float around (especially if fed by electricity, gas or water lines).
- Closing gas mains, cylinder tank valves, oil drums and other fuel containers and securing gas cylinders.
- Raising dangerous (ie flammable, explosive or toxic) chemicals.
- Filling windows, doors or other openings with water-resistant materials, such as concrete blocks or bricks (assuming the structure can withstand flood waters).
1 “Current Issues Brief: Australian Catastrophe Information”, ICA.