Iluka community plans for emergency management during adverse weather events, including storm and flood, progressing thanks to local ICOPE

Clarence Valley Independent, 12 April 2023:

In a community first for the Clarence Valley, ICOPE – Iluka Community Organisation Planning for Emergencies has been approved to run a Community Managed Evacuation Centre in the event of wild weather or disasters isolating locals.

ICOPE President Cheryl Dimmock said the group had been working with the Clarence Valley Local Emergency Management Committee LEMC since October 2022 to have a Community Managed Evacuation Centre CMEC in Iluka, which would take in residents from Woody Head, The Freshwater, and if access is available, Woombah.

Ms Dimmock said the group was motivated to act to establish the CMEC by the predicted increase in wild weather induced by climate change and the fact Iluka can be isolated for several days in times of flood.

“We had to put an action plan together to present to the LEMC and we’ve had it approved that we could have a Community Managed Evacuation Centre CMEC,” she said.

“ICOPE will be allowed to run the CMEC if it is activated by the Local Emergency Operations Controller (high ranking local police officer).

“The CMEC would be at the Iluka Community Hall in Spencer Street, in the event that it was safe to evacuate to the community hall.

“The reason why we have been so proactive in doing this is because we get cut off, there is only one road in and one road out, we get cut off for days, and we don’t want to see the community in a situation like what has happened in Lismore.”

In addition to the CMEC, Ms Dimmock said ICOPE plans to transform the Iluka Community Hall over the next year.

“We are hoping to work with council to get grants and make improvements to the hall and we’re hoping to have Iluka Community Hall as a hub where the community can actually come…say on a Saturday morning where they can come and have cuppa and a chat about disaster preparedness and community events,” she said.

“We want to encourage the community to prepare for disasters, we don’t want it to be scary, but we want them to prepare and be ready in the event that something happens, that they will know what to do, where to go, and the communication they receive comes from one central place, so they are getting information that is current and from a reliable source.”…..

So, you are looking to buy a house or land in Yamba on the Clarence Coast in NSW?

 

A recent local newspaper article of 12 October 2022 stated that Clarence Valley Council would not release the results of a circa 2014 floor level survey of an unstated number of Yamba homes.

This survey was apparently undertaken to assess flood risk vulnerability against potential flood height modelling for Yamba township and environs.

The reason Council gave for withholding this information appears to be; “Premature release of the floor level data might (for instance) result in one or more sales falling through without the statutory immunity of Council being assured.”

By Census Night in August 2021 there were 4,073 residential dwellings recorded for a Yamba population of 6,376 people.

It is possible that conservatively between 30% to 53% of this housing stock is vulnerable to varying degrees during heavy rainfall associated with adverse weather events and Lower Clarence River flooding. A smaller percentage of Yamba dwellings above flood height on Pilot Hill and environs may be still be at risk - from land slippage during prolonged heavy rain and high seas.

Now according to propertyvalue.com.au there have been 142 houses sold in Yamba and environs in the last twelve months with a median price of $925,000.

Looking at online real estate sites there are also a number of dwellings in the town currently for sale – ranging from modest houses on manufactured relocatable housing estates through to 3-4 bedroom brick family homes and onto million dollar plus residences of up to 5 bedrooms & 2 bathrooms with all the mod cons.

There’s no easy way to establish floor levels in Yamba just by viewing real estate websites or looking at documents currently publicly available on Council’s own website. The only historic information publicly available ‘guesses’ dwelling floor heights in many of the town’s streets based on the surveyed height of the adjacent road surface.

An estimation method which clearly had its drawbacks in March 2022 when this overview of a section of Yamba Road was taken.

Embed from Getty Images

If Clarence Valley Council is determined to cloak in secrecy a more accurate extant list of floor heights, perhaps it’s time that the Yamba community began to help people who want to move here make informed choices before committing themselves to a mortgage or spending their hard-earned retirement savings?

Remembering that the Lower Clarence River estuary has flooded on average every three years since the 1990s, looking at Google Earth as well as basic digital flood modelling that Clarence Valley Council has available online and, then sampling from the over 50 dwellings currently advertised for sale for an example of each of the three aforementioned housing types:

• that sweet little 3 bedroom home in one of Yamba’s manufactured home estates is probably only est. 4m above mean sea level and, if its floor level doesn’t turn out to be at least 2.84m AHD then there is a statistical 1 in 100 chance in any given year that it will have stormwater and/or floodwater running across the bedroom carpeting;

• the 4 bedroom brick home with a tidy garden is probably est. 4m above mean sea level but if its floor level isn’t high enough then there is a statistical 1 in 50 chance in any given year that flood water will enter the property and threaten the house. There is also a 1 in 100 chance in any given year that with a floor below or even at 2.84m AHD the river will come knocking at the door and take possession of the house for as many days as it pleases;

• when it comes to one of those houses with the million dollar plus price tag, well it is an est. 3-4m above mean sea level. However if its floor level falls short of 2.84m AHD then it may be uncomfortable to live in as there is a statistical 1 in 50 chance in any given year that flood water will enter the property but possibly not the house. However, there is also a 1 in 100 chance in any given year that storm water and/or flood water will enter the property and threaten the ground floor areas of this house.

Needless to say all three example residences are highly likely to be inundated during an extreme flood event given that modelled flood water heights would reach above the ceiling of the average single storey house design and above ceiling level on the ground floor of the average two-story design.

I rather suspect that Council is not voluntarily offering up that information to prospective home buyers, unless they happen to ask a precisely framed question in writing over the signature of their solicitor and perhaps not even then – given how many hundreds of land or house & land packages property developers are hoping to sell over the next five to twenty-five years in Yamba and how attractive future increases in rate income are to local government. 

Although quite frankly with Australia’s climate already having warmed on average by 1.44 ± 0.24 °C since national records began in 1910 [Dept. Planning and Environment, AdaptNSW 2022] and the possibility being canvassed that the world and Australia will reach long-term 1.5°C warming as early as the 2030s, Clarence Valley Council has more to worry about than riverine flooding.

In a worst case scenario due to the expected increase in sea-level rise this warming will bring, a significant amount of land within Yamba town precincts will be begin to go under water at high tide in another 8-17 years time.

Climate Central Inc. interactive mapping
Sea-level rise at 1.5°C global warming
Click on image to enlarge

Quote of the Week

“Prime Minister Anthony Albanese says stopping development on flood plains, especially in western Sydney, will go a long way towards saving communities already reeling from multiple natural disasters. "The obvious answer is to stop development on flood plains," he said on Friday.”

[The West Australian, 7 October 2022] 

So you built, purchased or rent housing on flood prone land - what comes next beside an upgraded personal flood plan?

 

2022 may be the year that brought home to many on the Australian east coast what it really means in a changing climate to have built, purchased or rented a freestanding house, townhouse, unit or flat on flood prone land or on floodplain.

Right now, ten months into the third year of a triple La Niña event, individuals and couples may well be wishing that the real estate agent, local council, individual who did the property conveyancing, a neighbour, friend or family member, had been a little more forthcoming about what moving to a particular street, town, local government area or region actually meant when it came to hazard risks from storms, heavy rainfalls and local or widespread flooding.

Whether it is your first home, your retirement dream home or just an affordable rental in which you are happily settled, for literally thousands of people the limitations of the dwelling in which they currently live is becoming apparent.

While devastated souls in catastrophically affected areas are trying to come to grips with trauma and loss as they assess their options.

Where to start with looking at your home with fresh eyes, before deciding if it will withstand the worst floods or whether you need to modify the dwelling, move the house to higher ground or look for a brand new home on land in a safer area? Big decisions.

In mid-2021 a report was published looking at certain options available for flood prone buildings.

Bushfire & Natural HAZARDS CRC, COST-EFFECTIVEMITIGATION STRATEGY DEVELOPMENT FOR FLOOD PRONE BUILDINGS, Final project report, July 2021, excerpt:

Globally, floods cause widespread impacts with loss of life and damage to property. An analysis of global statistics conducted by Jonkman (2005) showed that floods (including coastal flooding) caused 175,000 fatalities and affected more than 2.2 billion people between 1975 and 2002. In Australia floods cause more damage on an average annual cost basis than any other natural hazard (HNFMSC, 2006). The fundamental cause of this level of damage and the key factor contributing to flood risk, in general, is the presence of vulnerable buildings constructed within floodplains due to ineffective land use planning.

Retrospective analysis show large benefits from disaster risk reduction (DRR) in the contexts of many developed and developing countries. A study conducted by the U.S. Federal Emergency Management Agency (FEMA) found an overall benefit-cost ratio of four suggesting that DRR can be highly effective in future loss reduction (MMC, 2005). However, in spite of potentially high returns, there is limited research in Australia on assessing benefits of different mitigation strategies with consequential reduced investment made in loss reduction measures by individuals and governments. This is true not only at an individual level but also at national and international levels. According to an estimate, international donor agencies allocate 98% of their disaster management funds for relief and reconstruction activities and just 2% is allocated to reduce future losses (Mechler, 2011).

The Bushfire and Natural Hazards Collaborative Research Centre project entitled Cost-effective mitigation strategy development for flood prone buildings is examining the opportunities for reducing the vulnerability of Australian residential buildings to riverine floods. It addresses the need for an evidence base to inform decision making on the mitigation of the flood risk posed by the most vulnerable Australian building types and complements parallel CRC projects for earthquake and severe wind.

This project investigates methods for the upgrading of the existing residential building stock in floodplains to increase their resilience in future flood events. It aims to identify economically optimal upgrading solutions so the finite resources available can be best used to minimise losses, decrease human suffering, improve safety and ensure amenity for communities.

This report describes the research methods, project activities, outcomes and their potential for utilisation.

Flood mitigation strategies mentioned in the report

Elevation

Elevation of a structure is one of the most common mitigation strategies where the aim is to raise the lowest habitable floor of a building above the expected level of flooding. This can be achieved by extending the walls of an existing structure and raising the floor level; by constructing a new floor above the existing one; or through raising the whole structure on new foundations (walls, piers, columns or piles)as shown in Figure 3.

Technical considerations that need to be taken into account in raising buildings are structure type, construction material, foundation type, building size, flood characteristics and other hazards. Other factors to take into consideration when elevating existing structures are additional loading on foundations, additional wind forces on wall and roof systems and any seismic forces (FEMA, 2012).

Generally the least expensive and easiest building to elevate is a low-set single storey timber frame structure (USACE, 2000). The procedure becomes complicated and more expensive when other factors are included such as slab on-grade construction, walls of masonry or concrete or application to a multistorey building (USACE, 1993). Elevation is one of the strategies which currently can result in incentives from the insurance industry in the form of reductions in annual premiums for flood insurance (Bartzis, 2013).

Relocation

Relocation of a building is a dependable flood mitigation technique. However, it is generally the most expensive as well (USACE, 1993). Relocation involves moving a structure to a location that is less prone to flooding. Relocation normally involves placing the structure on a wheeled vehicle, as shown in Figure 4. The structure is then transported to a new location and set on a new foundation (FEMA, 2012). Relocation is much easier and cost effective for low-set timber frame structures. The relocation of slab-on-grade structures is more complicated and expensive.

Relocation is most appropriate in areas where flood conditions are severe such as a high likelihood of deep flooding, or where there is high flow velocity with short warning time and a significant quantity of debris. Technical considerations for relocation include the structure type, size and condition. Light weight timber structures are easy to transport compared to heavy masonry and concrete buildings. Similarly, the relocation of single storey compact size structures is far easier than for large multi-storey structures.

Dry floodproofing

Dry floodproofing essentially attempts to keep floodwaters out of the house. The portion of a structure that is below the expected flood level is sealed to make it substantially impermeable to floodwaters. This is achieved by using sealant systems which include wall coatings, waterproofing compounds, impervious sheeting over doors and windows and a supplementary leaf of masonry (FEMA, 2012). The expected duration of flooding is critical when deciding which sealant systems to use because seepage can increase with time making flood proofing ineffective (USACE, 1993). Preventing sewer backflow by using backwater valves is also important in making dry floodproofing effective (Kreibich et al. 2005; FEMA, 2007).

Dry floodproofing is generally not recommended in flood depths exceeding one metre based on tests carried out by the US Army Corps of Engineers as the stability of the building becomes an issue over this threshold depth (USACE, 1988; Kreibich et al. 2005). Dry floodproofing is also not recommended for lightweight low-set structures or structures with a basement. These types of structure can be susceptible to significant lateral and uplift (buoyancy) forces. Dry floodproofing may also be inappropriate for light timber frame structures and structures that are not in good condition and may not be able to withstand the forces exerted by the floodwater (FEMA, 2012).

Wet floodproofing

In this measure floodwater is allowed to enter the building to equalise the hydrostatic pressure on the interior and exterior of the building, thus reducing the chance of building failure due to a pressure differential on components. As all the building components below the flood level are wetted, all construction material and fit-outs should be water-resistant and/or can be easily cleaned following a flood. Flood resistant materials can help reduce flood damage and facilitate cleanup to allow buildings to be restored to service as quickly as possible. FEMA (2008) provides a detailed list of building materials classified as acceptable or unacceptable for wet floodproofing based on cleanability and water resistance.

Wet floodproofing involves raising utilities (heating, ventilation, and air conditioning (HVAC), electrical systems etc.) and important contents above the expected flood level.

Wet floodproofing may not be suitable in floods with duration of more than a day as longer duration can lead to damage to structural components of the building and can also result in the growth of algae and mould (FEMA, 2007). Also wet floodproofing can only reduce loss from floods but cannot eliminate loss as some amount of cleanup and cosmetic repair will always be necessary (USACE, 1984). Although using flood damage resistant materials can reduce the amount and severity of water damage, it does not protect buildings from other flood hazards, such as the impact of flood borne debris.

Flood barriers

Flood barriers considered here are those built around a single building and are normally placed some distance away from it to avoid any structural modifications to the building. There are two kinds of barriers: permanent and temporary.

An example of a permanent barrier is a floodwall which is quite effective because it requires little maintenance and can be easily constructed and inspected. Generally, it is made of reinforced masonry or concrete and has one or more passageways that are closed by gates. An example of a floodwall is shown in Figure 5.

There are also several types of temporary flood barriers available on the market which can be moved, stored and reused. There are a number of considerations with regard to the use of these barriers such as the need for prior warning and enough time to be set up in order to be effective (Kreibich et al. 2011). They also require periodic inspection and maintenance to address any repair required. Further, access to the building could be difficult (FEMA, 2007).

A number of vendors make temporary flood barriers that can be assembled relatively easily and moved into place. Some of the temporary flood barrier options are presented below and shown in Figure 6.

Sandbags: This is a traditional and less expensive way to construct a barrier up to 1m high in front of a building and its openings. However, it requires considerable time and effort to set up.

PVC tubes: These consist of two flexible tubes laid side by side and joined permanently to form a twin element with high stability. They can be made ready quite quickly, generally in less than 15 minutes, and are available in 1m height and 10m length units.

Metal boards/fence: This fence system consists of two boards in compact flat packs that are lifted into place after transportation to the site and the system is stabilised by water pressure.

Flexible barriers: These barriers are able to dam or redirect flowing water up to 1m high and can be set up very quickly on almost all surfaces.

Box wall: A freestanding flood barrier for use on smooth surfaces. These can be attached and placed next to each other to build a 0.5m high wall around a building.

Box barrier: An effective temporary flood barrier (0.5m high) that can be aligned easily and rapidly. After positioning, the box can be filled with water to hold it in place.

The report looks at vulnerability to flood risks of various types of housing from: Timber Frame (raised floor); Cavity Masonry - Victorian Terrace (raised floor); Cavity Masonry (raised floor); Brick Veneer (raised floor); and Brick Veneer (slab-on-grade).

The report also examines the strength of selected building components and generally the cost effectiveness of building material for use in flood prone buildings.

The full report can be downloaded at:

https://www.bnhcrc.com.au/file/13042/download?token=2Iqm6aEk