Frequently Asked Questions

1. Overview of Hazard/Danger Management

What are the typical hazards/danger local government deals with?

Natural hazards are essentially meteorological and/or geological phenomena that have the potential to create emergency or disaster situations for communities and the environment. The economic, social and environmental losses can be significant and maybe magnified if these events repeatedly affect the same areas. Australia is exposed to arrange of natural hazards that carry with them varying levels of risk. Land use planning contributes to natural hazard risk reduction and consequently improves community safety and sustainability.

Australian natural hazards, listed in decreasing order of cost for the period 1967-99,include:

floods;
severe storms (including tornadoes and hailstorms which may cause wind, rain and hail damage and local flooding);
cyclones (including damage from both high winds and flooding by sea as a result of storm surge);
earthquakes;
bushfires; and
landslides.

Coastal erosion, which may occur without being associated with a hazard event, must also be considered in the land use planning process.

There are a number of direct and indirect losses associated with natural hazards and natural disasters. These losses include:

loss of life;
physical suffering;
emotional suffering;
damage to property;
reduced productivity;
degraded environment;
loss of species and habitats;
damaged infrastructure;
weakened economy;
destabilised community coherence, political situations; and
reduced quality of life.

(Planning Safer Communities EMA 2002 pg 5)

Links

MANUAL 7, Planning Safer Communities Land Use, Planning for Natural Hazards

How significant is Landslide in Australia?

Landslides regularly occur in localised areas across Australia, and pose a serious threat to people and property. They occur over a wide range of velocities and are often at their most damaging when they happen suddenly and without warning.

The economic cost of individual landslide events is typically much lower than the cost of flood or earthquake events. Since 1842 there have been approximately 84 known landslide events, collectively responsible for the deaths of at least 107 people and injury to at least 141 people, as recorded in the Australian Landslide Database (GA 2007). Although many landslides have natural causes, well over half of the landslides that have caused death and injury can be attributed either directly or indirectly to human activity.
(Natural Hazards in Australia p116)

Additional Information

Cost of Landslides

The financial and social consequences posed by landslides are extremely underestimated in Australia. Landslides regularly damage buildings, roads, railways, vehicles, pipelines and communication lines, and have adverse social effects that include death, injury, stress and displacement. Not only is stress detrimental from the psychological and social point of view, it also can have detrimental physical effects that may even lead to fatalities.

The total direct cost of landslides in Australia for the period from 1967 to 1999 is estimated at $40 million. This can be solely attributed to the 1997 Thredbo landslide as only landslides costing $10 million or over were included in the BTE (2001) estimate. However, for the period from 1900 to 1999 the total socioeconomic cost of landslides was estimated at $500 million in 1998 dollars (EMA 1999).

Most damage is the result of many small landslide events, and it is believed they have a significant cumulative cost. Few insurance policies in Australia cover landslides, and it is understood that the majority of landslide costs are absorbed directly by individual property owners as well as by infrastructure authorities.

Costs associated with disaster assistance and road maintenance, relocation and repair are among the greatest public costs resulting from landslides. For example, the Australian Landslide Database indicates that the construction cost of diverting the Lawrence Hargrave Drive coastal route around a cliff face subject to rockfalls was $49 million in 2006 dollars, and it is estimated that from 1989 to 1996 the cost of repairs to railway infrastructure in Wollongong amounted to $175 million. Reconstruction of the Alpine Way after the Thredbo landslide cost $24 million (BTE 2001).

Adding to the complexities of estimating landslide costs are the different types of landslide processes. The costs of extremely slow-moving landslides which cause cracks or irregularities in the fabric of buildings and in the surface of roads, footpaths or pipelines are typically absorbed into general maintenance and repair costs. Other hazards, such as tropical cyclone or flood, may trigger landslides, presenting a challenge in isolating and determining the damage that is a specific consequence of the landslide.

Environmental cost is difficult to quantify in financial terms. Landslide-derived sediment may cause prolonged turbidity in stream channels that, in turn, may adversely impact on water reservoirs or fish habitats. A significant increase in the incidence of landslides on Macquarie Island, Tasmania, is believed to be the consequence of the removal of vegetation by a rapidly expanding population of rabbits. Costs of controlling the rabbit numbers and preventing further landslides are estimated to be $24.6 million (ABC 2007; Parks and Wildlife Service 2007).
(Natural Hazards in Australia p119-120)

Landslides are not as well recognised as some other hazards in Australia, but they do occur and have caused economic loss as well as death and injury. Indeed, the twelve months from September 1996 to August 1997 saw five landslides that killed 30 people and injured five others; they included nine deaths when a 14 metre limestone cliff collapsed at Gracetown (Western Australia) and the Thredbo (New South Wales) landslide that destroyed two chalets and killed 18 people.
(Planning Safer Communities p67)

Landslides cause more problems in Australia than most people think. Many people are aware of the Thredbo landslide, which killed 18 people in 1997, and the Gracetown cliff collapse, which took nine lives in 1996, because these huge tragedies made international news.

However, most Australian landslides kill one or two people and, although this loss of life is just as tragic for those concerned, it is often not widely reported and rarely makes the headlines beyond the local area. In many cases, the victims of these small landslides are children. Fatal accidents have been caused by children digging under a rock to make a cubby house, causing the rock to topple onto them; digging into sand, which collapsed and buried them; or sitting on a rock ledge, which broke off because it could not support their weight. These were all avoidable tragedies.

Since 1842, until the end of 1998, at least 82 people have died in 36 reported landslides. Because small events are not widely reported, it is almost certain that the data in AGSO s Australian Landslide Database are incomplete, and that the number of fatalities is much higher.

Forty eight landslides are known to have caused injury or death. Almost half were caused either directly or indirectly by human activity. One third involved material falling off cliffs. Almost half were rock falls or topples.

Landslides have also caused many hundreds of millions of dollars damage to buildings, roads, railways, pipelines, agricultural land and crops. More than 200 buildings are known to have sustained damage due to at least 53 landslides. The worst case was at Lawrence Vale, Launceston, Tasmania, where 35 houses were destroyed by two adjacent landslides during the period 1956-70.
(Australian Landslides AGSO)

Links

Where are the susceptible areas located?

Fell (1992) provides a regional overview of land instability in Australia, which describes the location and extent of landslides and the conditions and mechanisms which are conducive to slope failure. Most landslides in Australia occur in Tertiary basalt, Tertiary and Cretaceous sediments and older inter-bedded sedimentary and coal measure formations (Fell 1992). Maps which show the distribution of such materials for New South Wales, Victoria, southern Queensland and Tasmania, along with a comprehensive bibliography, are also provided in Fell (1992). Further information is provided by Johnson and others (1995), Michael-Leiba (1999), Michael-Leiba and others (1997), Blong and Coates (1987) and AGS (2007).

The distribution of reported landslide events in the Australian landscape is shown in Figure 8.1, which reflects the results of specific landslide mapping programmes based in Tasmania, southwest Victoria, Wollongong and Newcastle Lake Macquarie in New South Wales, and Brisbane and Cairns in Queensland. The remainder of the landslides depicted were reported by the media or by landslide spotters .
Reproduced from “Natural Hazards in Australia. Identifying Risks Analysis Requirements”. Miriam H. Middlemann (Editor) 2007. Geoscience Australia , Canberra. Chapter 8 Landslides

Links

Natural Hazards in Australia
https://www.ga.gov.au/products/servlet/controller event=GEOCAT_DETAILS&catno=65444
http://www.ga.gov.au/hazards/landslide/landslide-basics/where.html
Figure 8.1: Recorded landslide events in Australia
Source: This map was compiled by Geoscience Australia in August 2007 from data available in the Australian Landslide Database (incorporating records from Geoscience Australia, Mineral Resources Tasmania and the University of Wollongong).Data for southwest Victoria were supplied by Corangamite Catchment Management Authority in association with the University of Ballarat and A.S. Miner Geotechnical.
(Natural Hazards in Australia p118)

Additional Information

The types of landslides that occur in various geomorphic settings in Australia are explained below.

Rockfall

Typical settings where rockfalls may occur include cliffs in coastal zones, mountain sides, gorges, road cuttings or quarry faces. The coastal cliff lines of New South Wales (Kotze 2007) and the dolerite mountains of Tasmania are prominent examples. Rockfalls are characterised by an extremely rapid rate of movement and have been responsible for many of the landslide related deaths in Australia. Depending on local conditions, the run-out distances of rockfalls can be considerable. Although the source areas of these features are generally too steep to build upon, popular beaches and structures such as walking tracks, roads and houses may be located in the run-out area.

The largest rockfall in Australian history is believed to be a 30 million tonne rockfall which collapsed above the shoreline of the Lake Burragorang Reservoir (Warragamba Dam) in New South Wales in 1965; the rockfall was attributed to underground coal mining (Pells and others 1987). Other examples include the rockfall at Gracetown, Western Australia, in 1996, where 30 tonnes of rock and sand fell from a limestone sea cliff onto people sheltering under an overhang, injuring three and killing nine; a 100 metre rockslide at Mulligans Bluff on the Gwydir Highway, New South Wales, in 2002; and regular rockfalls along Lawrence Hargrave Drive in Wollongong, New South Wales, including notable falls in 1988 and 2003.

Deep-seated Landslide

Deep-seated landslides typically occur in steep terrain. However, they can be observed on slopes with angles as low as a few degrees, because the geological materials involved typically have low shear strength or are subject to high pore pressure. Areas include the Tertiary basalt soils and the Tertiary sediments of eastern Australia (Fell 1992; McGregor and others 2007).

Across Australia, there are many examples of houses and subdivisions built on existing landslide sites or on slopes that are susceptible to failure. While most of these landslide sites may be dormant, some can be reactivated with changes in pore water pressures and/or disturbance through human activities such as property development.

An example of a deep-seated landslide in Tasmania is the Taroona Landslide in Hobart, a very to extremely slow-moving landslide on which two schools and nearly one hundred houses are located (Moon and McDowell 2002; Latinovic and others 2001). Monitoring over a seven-year period indicated that movement occurred at the site every year, although only a few structures were affected by the movement.

Debris Flow

Debris flows can originate on slopes in the range of approximately 16 to 40 degrees, where loose rock and soil materials are subjected to high intensity rainfalls. Where water content is high, debris flows can travel at rapid velocities with considerable destructive potential. Houses and other structures may be situated on or near the source area or run-out path of such features.

The landslide at Thredbo, New South Wales, in 1997 became a debris flow which destroyed two buildings and claimed 18 lives. It was the worst landslide disaster in Australian history, and the ground failure was attributed to a leaking water main.

Debris flows triggered by intense rainfall include: the debris flow at Humphrey Rivulet, Tasmania, in 1972 (Mazengarb and others 2007); the slides which blocked the Captain Cook Highway behind Ellis Beach, north of Cairns, Queensland, in 1951 (Michael-Leiba and others 1999); and the 60,000 tonne debris flow at Montrose in the Dandenong Ranges of Victoria in 1891 (Moon and others 1992).

Shallow Landslide

Shallow landslides occur in areas with a shallow layer of weak material and are often triggered by brief episodes of intense rainfall. They tend to occur on the edge of embankments and on steep natural slopes of 30 degrees or more. The infrastructure most commonly affected is roads and railway lines, although shallow landslides occasionally damage houses and other private property.

Numerous shallow landslides occur during the wet season. For example, they are often associated with tropical cyclones in the Cairns region and along the Cairns Kuranda railway (Michael- Leiba and others 1999).

Reproduced from “Natural Hazards in Australia. Identifying Risks Analysis Requirements. Miriam H. Middlemann (Editor) 2007. Geoscience Australia , Canberra. Chapter 8 Landslides

Brief history of landslide zoning in Australia

Landslides impact localized areas in every state and territory of Australia and have caused fatalities, environmental degradation and millions of dollars worth of damage to buildings, roads and railways. Geoscience Australia (2007) report that the Australian Landslide Database contains a record of 84 landslide events in Australia that were collectively responsible for at least 107 deaths and 141 injuries this certainly is an under-recording of landslide impact. Geoscience Australia also noted although many landslides have natural causes, well over half of the landslides that have caused death and injury can be attributed either directly or indirectly to human activity .

Whilst these records are certainly incomplete, throughout Australia more than 200 buildings have been reported damaged directly by landslides, with the worst single event recorded at Lawrence Vale in northern Tasmania where 35 houses were destroyed in two adjacent landslides in the 1960s. In Geoscience Australia (2007), it is estimated that the total socio-economic cost of landslides was $500 million for the last decade of the 20th century. Within Australia, the recorded fatalities from landslides are about five times greater than those caused by earthquake though, in terms of natural hazards, the Australian population is more at risk from bushfire, flooding and storm (refer to Geoscience Australia 2007).

Notwithstanding the fatalities identified above, prior to the Thredbo landslide, it is fair to say that the Australian population generally perceived the issue of risk associated with landslides as primarily related to loss of property. By way of example, within New South Wales (which has been chosen only because this is the region most familiar to the authors and by no means represents a comprehensive coverage): several residential properties have been damaged in the Wollongong area (colluvial slides in the steep terrain of the Illawarra region); four properties were lost in a single event within Pittwater Council area in 1973 (fill situated upon colluvium in the Northern Beaches area of metropolitan Sydney); shallow flow slides occurred in the Picton area (southwest of Sydney within an extensive shale precinct) with minor damage; an extensive cutting slide occurred during freeway construction (low shear strength tuffaceous claystone) during the 1980s in the Central Coast; in the 1970s, a large rock slide, possibly up to 1 million cubic metres in volume, was associated with underground coal mining adjacent to Lake Burragorang (which is the reservoir for Sydney’s major water supply dam, Warragamba Dam); a rockslide was also associated with adjacent underground coal mining in the Dombarton area near Wollongong in 1969; an earlier rockslide occurred near the Three Sisters at Katoomba in the early 1900s; sub-divisional scale landslides have occurred in Wollongong City (80 km south of Sydney) and Baulkham Hills (north-western Sydney metropolitan area); and there has been loss of land (though not including structures) through rockfall from the near-vertical sandstone cliff line along the Sydney coast, whilst land and dwellings were lost along the New SouthWales coast due to severe beach erosion in several large storm events in the 1980s.

In 1997, a mobile fill landslide demolished two accommodation lodges in the ski resort of Thredbo. This produced a quantum shift in appreciation of risk-to-life from landslides within the Australian population. The Thredbo landslide cost the Australian community the loss of 18 lives, and remediation works to the AlpineWay of the order of $24 million were expended. Other examples of significant landslide events include: in 1996, a cliff line collapse at Gracetown, WA, that cost the loss 9 lives of people sheltering under the cliff; in 1988, two lives were lost in the Coledale failure which involved the failure of an embankment on the South Coast Railway (connecting Sydney and Wollongong); some $100 million was later spent on rectification of the South Coast Railway following large scale instability (over 100 separate sites) in the La Nina event from 1988 to 1990; instability of a 1 km length of the 300 m high (cumulative height) cliff line above Lawrence Hargrave Drive north of Wollongong which involved controlled road closures as safety measures prior to construction of the $49 million off-shore Seacliff Bridge; and two lives were lost and widespread instability occurred across the City of Wollongong from torrential rainfall in 1998. There are many more examples across the nation.

Andrew R. Leventhal , Greg P. Kotze – Landslide susceptibility and hazard mapping in Australia for land-use planning with reference to challenges in metropolitan suburbia

Links

Landslide classification

What is a landslide?

Other explanations exist, such as that offered by the United States Geological Survey, USGS (2008) uses the following explanation: “Geologists, engineers, and other professional often rely on unique and slightly different definitions of landslides. This diversity in definitions reflects the complex nature of the many disciplines associated with studying landslide phenomena. For our purposes, landslide is a general term used to describe the downslope movement of soil, rock and organic materials under the effects of gravity and also landform that results from such movement.” (however, does not mention the impact of groundwater and surface storm water upon instability of slopes, which should not be underestimated). The basic landslide types are: fall, topple, slide, spread or flow.

Ref: US Geological Survey (2008) “The Landslide handbook: a guide to understanding landslides”, Circular 1325, United States Geological Survey and geological Survey of Canada, LM Highland & P Bobrowsky (eds)

There are some excellent video resources on a site called “The Landslide Blog” posted by Dr David Petley

Dave’s Landslide blog

In particular he has a past blog listing 20 best landslide videos which are all pretty impressive and exciting as far as landslides go!

Landslide videos

USGS website

USGS The Landslide Handbook – a guide to understanding landslides

Maierato, Italy February 2010

Wales Rockfall, 2011

Nara Prefecture, Japan, 2004

Landslides occur in many types of materials and are of various types:

The US Transport Research Board (1978) notes that “The factors of geology, topography, and climate that interact to cause landslides are the same regardless of the use to which man puts a given piece of land. The methods for examination of landslides are equally applicable to problems in all kinds of natural or human environment. And the known methods for prevention or correction of landslides are, within economic limits, independent of the use to which the land is put.”

[US Transport Research Board (1978) “Landslides: analysis & control”, Special Report 176, National Academy of Sciences, Washington DC, Schuster RL & Krizek RJ (eds)]

What is Landslide Zoning?

Zoning is defined as the division of land into homogeneous areas or domains. When applied to landslides, zoning may include categories defined as a ranking of potential occurrence.

Additional Information

Why is zoning needed and why AGS2007?

The identification of situations that are more susceptible to landslide occurrence through landslide zoning would facilitate development planning and landslide risk management. It is the combination of having an area which is potentially subject to landsliding and the scale and type of development of the area that will determine whether landslide zoning is needed for land use planning.
(AGS2007 p17)

Additional Info

2. Overall Roles and Responsibilities

Who are the regulators in Australia and what are their responsibilities?

Generally throughout Australia, the authority responsible for planning control and consent for urban development is Local Government i.e. Cities, Shires, Councils, and Regional Councils.
They have the responsibility for administering planning control and approving developments.
Where available, local government works under State and Federal policy but this seems to be limited in Australia.
State Authorities (Various Park Departments) are responsible for control in state run reserves and parks.

Who undertakes landslide zoning?

Conclusion: The regulator (typically local government) has the responsibility and bears the technical and budgetary impost for preparing Statutory Maps (or Planning Control) for areas susceptible to landslide.
By necessity this will also require Information Maos (inventory) and Advisory Maps (i.e. Susceptibility, hazard and/or risk maps)

Additional Information

Local Government

The majority of mitigation and development controls for slope management are achieved at the local government level (Leventhal and Kotze in press). Most landslide work is also undertaken at this level, with the private sector providing advice and support.

Local governments have principal responsibility for systematically taking proper account of risk assessments in land use planning to reduce landslide risk. Local government agencies are responsible for reducing landslide losses using the best information available (COAG 2004).

Zoning and planning schemes across local government are variable across jurisdictions within each state and territory. Some local governments designate landslide hazard zones which control development within their jurisdictions, while others have not recognised or planned for landslide-related risk (Leventhal and Kotze in press).

While guidance is provided by the Development Assessment Forum (DAF 2007), systematic policy implementation to address landslide hazard is rare across local governments.

Local governments also have a regulatory responsibility, and regulatory approaches vary widely. There are no requirements for building constructions with the capability to withstand a landslide; regulatory control is currently directed toward preventing exposure to landslides (Leventhal and Kotze in press). A number of parties are involved in the landslide risk management process, although pragmatically the regulator sets the tolerable risk levels. Regulators need to appreciate the complexities of landslide risk analysis in order to ascertain the rigour of any geotechnical landslide reports upon which they base their decisions. The regulator is best placed to act in the interests of the community with respect to landslide hazard, particularly for matters relating to transfer of risk upon sale of properties.
(Natural Hazards in Australia p129)

State and Territory Governments

Legislation varies across states and territories in Australia; some have stronger legislative requirements than others. Current Australian legislative controls are outlined in ABCB (2006), Leventhal and Kotze (in press) and Tefler (1988). State and territory governments differ in their approaches to managing landslide hazards. Some have accepted the AGS (2007) predecessor Landslide Risk Management Concepts and Guidelines (AGS 2000) as an industry reference paper within legislation. All play an important role in strengthening partnerships with local governments, and in encouraging and supporting them to undertake disaster risk assessments and mitigation measures.

All state and territory governments, with the exception of the Tasmanian Government, delegate responsibility to their local governments. Mineral Resources Tasmania is the only state government agency that undertakes regional mapping of landslides, maintains a state-wide landslide database, and provides landslide information to the public. Mapping is generally undertaken by the private sector in other jurisdictions.

Planning agencies in each state and territory develop coastal policies and landslide or erosion policies (EMA 2001a; DAF 2007). However, it is believed that some erosion policies do not specifically relate to landslide hazard, which can result in confusion among land owners and members of the general public. One example is the Erosion Management Overlay in Victoria (Golder Associates 2004; DSE 2007b).

Road and rail transport agencies have a responsibility to protect road and rail infrastructure against landslides and to ensure construction does not increase landslide hazard. They do this by liaising strongly with geotechnical consultants.
(Natural Hazards in Australia p128-129)

National: Australian Government

The Australian Government’s overarching goal in the management of landslide risk is to ensure the development of safer communities. The Australian Government offers some financial assistance for landslide studies and landslide mitigation measures, through its funding programmes aimed at reducing the risk of natural disasters. It maintains the Australian Landslide Database and provides overarching emergency management and land use planning guidelines.

The Australian Government plays a role in “raising awareness of landslide hazard though education and training programmes (EMA 2001a; EMA 2001b), and contributes to innovative research to assist the mining industry through the development of models which assess the geotechnical stability of artificial slopes. The Australian Government also underpins and coordinates a number of intergovernmental organisations and groups, particularly those directed to planning and building codes, such as the Development Assessment Forum.
(Natural Hazards in Australia p128)

3. Planning Schemes and the Approvals Process

How does the control of the landslide danger vary around Australia and what is the approval process in my state?

State and territory governments differ in their approaches to managing landslide hazards. Some have accepted the AGS (2007) predecessor Landslide Risk Management Concepts and Guidelines (AGS 2000) as an industry reference paper within legislation. All play an important role in strengthening partnerships with local governments, and in encouraging and supporting them to undertake disaster risk assessments and mitigation measures.

Planning agencies in each state and territory develop coastal policies and landslide or erosion policies (EMA 2001a; DAF 2007). However, it is believed that some erosion policies do not specifically relate to landslide hazard, which can result in confusion among landowners and members of the general public. One example is the Erosion Management Overlay in Victoria (Golder Associates 2004; DSE 2007b).

While guidance is provided by the Development Assessment Forum (DAF 2007), systematic policy implementation to address landslide hazard is rare across local governments.
(Natural Hazards in Australia p128-130)

Additional Information

Overview Of Planning Instruments In Australia

Table 2 lists key planning legislation, development controls and strategic planning
documents in Australia s states and territories. The Table is included to demonstrate how the risk management and planning issues addressed in the manual relate to specific instruments in the states and territories.

It should be noted that both the web sites and the instruments may be subject to change in the longer term. However, the planning agencies cited in Table 2 regularly update their web sites, which can provide a wide range of information on current and pending planning controls. The web sites for the states and territories are a good source for new planning initiatives.

As well as the state and territory legislation, there are intergovernmental agreements and a large number of Commonwealth Acts, Regulations and Instruments that need to be considered in the land use planning process. Examples include:

The Inter-Governmental Agreement on the Environment, signed in 1992 by the Commonwealth Government, State and Territory Governments and the Australian Local Government Association;
The Native Title Act 1993, amended in 1998 – planning authorities have an obligation to comply with the Act in areas where native title exists or may exist; and
The Environment Protection and Biodiversity Conservation Act 1999, which established a Commonwealth administered environmental assessment and approval system operating in addition to but separate from state and territory systems. Information on Commonwealth instruments is available through the Development Assessment Forum at www.daf.gov.au. This contains:
- Commonwealth Planning Instruments – a database of all Commonwealth Acts,
- Regulations, Agreements, Policies and the like that impact upon planning and
- development assessment systems and processes.
- State of Play a report that compares planning systems in Australian states and territories.
- Many of the Acts and Regulations, and some of the planning instruments, are available in full through the Australian Legal Information Institute site at www.austlii.edu.au (Planning Safer Communities Appendix 2)

Links

http://www.ga.gov.au/hazards/our-capabilities/case-studies/natural-hazards-in-australia-report.html
https://www.ga.gov.au/products/servlet/controller?GEOCAT_DETAILS&catno=65444
http://www.ema.gov.au/www/emaweb/rwpattach.nsf/VAP/(3273BD3F76A7A5DEDAE36942A54D7D90)~Manual07-PlanningSaferCommunities.pdf/$file/Manual07-PlanningSaferCommunities.pdf
Table 2 – Overview of planning instruments in Australia

What are the 5 basic steps to be considered in the approvals process?

In order to develop planning controls and building regulations, local government (or other regulators) must ensure that it has the statutory means to:

Through a planning scheme and using the principles in AGS (2007a), identify the areas that are susceptible to or at risk from landslides.
Require planning and/or building approvals for all land use and development within the areas zoned as susceptible to landslides.
Ensure there is a proper process for assessment in relation to existing and proposed development, including the requirement for completion of LRM reports in accordance with this Practice Note.
Provide appropriate risk tolerance criteria for loss of life and property so that there is a means to determine whether it is appropriate for development to occur or the required land use to proceed.
Apply, if necessary, consent conditions on the land use and/or development approval, including conditions requiring maintenance that will appropriately manage the landslide risk for that use and/or development.

It can be seen from the above that zoning in accordance with AGS (2007a) becomes the initiator under the planning scheme and building approvals process to determine whether LRM controls are required and whether more detailed LRM consideration is required.
(AGS2007c pg 67)

Additional Information

4. Implementing Landslide Zoning for Land Use and Planning

What definitions and terminology do I need to understand?

Definitions for terms used in landslide zoning and risk management are given in Appendix A. These definitions are based on IUGS (1997), with some amendments in matters of detail based on internationally adopted definitions prepared by The International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE) Technical Committee 32. These definitions should be used for all zoning, reports and land use planning documents. It is recommended that the definitions are attached to these documents so there is no misunderstanding of the terms.

Definitions of the main terms are:

Landslide: The movement of a mass of rock, debris, or earth (soil) down a slope.
Landslide Inventory: An inventory of the location, classification, volume, activity and date of occurrence of individual landslides in an area.
Landslide Susceptibility: A quantitative or qualitative assessment of the classification, volume (or area) and spatial distribution of landslides which exist or potentially may occur in an area. Susceptibility may also include a description of the velocity and intensity of the existing or potential landsliding.
Hazard: A condition with the potential for causing an undesirable consequence. The description of landslide hazard should include the location, volume (or area), classification and velocity of the potential landslides and any resultant detached material and the probability of their occurrence within a given period of time. Landslide hazard includes landslides which have their source in the area or may have their source outside the area but may travel on to or regress into the area.
Risk: A measure of the probability and severity of an adverse effect to health, property or the environment. Risk is often estimated by the product of probability and consequences. However, a more general interpretation of risk involves a comparison of the probability and consequences in a non-product form.

For these guidelines risk is further defined as:

(a) For life loss, the annual probability that the person most at risk will lose his or her life taking account of the landslide hazard and the temporal spatial probability and vulnerability of the person.

(b) For property loss, the annual probability of the consequence or the annualised loss taking account of the elements at risk, their temporal spatial probability and vulnerability.

Elements at Risk: The population, buildings and engineering works, economic activities, public services utilities, infrastructure and environmental features in the area potentially affected by the landslide hazard.
Vulnerability: The degree of loss to a given element or set of elements within the area affected by the landslide hazard. It is expressed on a scale of 0 (no loss) to 1 (total loss). For property, the loss will be the value of the damage relative to the value of the property; for persons, it will be the probability that a particular life (the element at risk) will be lost, given the person(s) is (are) affected by the landslide.
Zoning: The division of land into homogeneous areas or domains and their ranking according to degrees of actual or potential landslide susceptibility, hazard or risk.

In this guideline use of the word ‘landslide’ implies both existing (or known landslides) and potential landslides which a practitioner might reasonably predict based on the relevant geology, geometry and slope forming processes. Such potential landslides may be of varying likelihood of occurrence.

The term landslip is sometimes used to describe landslides but is not the recommended term.

It is noted that the term ?zoning? has particular application by planners in Australia. This document uses the term as it best describes the process and is used internationally. To avoid confusion, those preparing landslide zoning using this document should always refer to ? landslide susceptibility zoning?, ?landslide hazard zoning? and ?landslide risk zoning?.
(AGS2007a pg 14-15)

ADDITIONAL INFORMATION

LINKS

http://australiangeomechanics.org/downloads/

What is the preferred system of Landslide classification and terminology?

It is important that those carrying out landslide mapping use consistent terminology to classify and describe the landslides. It is recommended that the classifications of Cruden and Varnes (1996), Varnes (1978) or Hutchinson (1988) and terminology described in IAEG (1990) be used. These are reproduced in AGS (2007c).
(AGS2007a pg15)

Links

AGS Downloads/

What is the Landslide Risk Management Framework used as the basis for landslide zoning?

Since the publication of AGS (2000), many local government authorities have required a quantitative risk assessment approach for assessment of life loss risk for individual building developments. They have generally accepted qualitative or semi-quantitative assessment of property risk. These assessments are carried out using the risk based framework described in AGS (2000) and AGS (2002).

Figure 1 summarizes the framework for landslide risk management. This is taken from Fell, et al. (2005) and represents a framework widely used internationally. It was the basis for the State of the Art papers and invited papers at the International Conference on Landslide Risk Management held on Vancouver in May 2005 and is consistent with AGS (2000), AGS (2002) and AGS (2007c).

It is recommended that this general framework be used for landslide susceptibility, hazard and risk zoning whether a quantitative or qualitative approach is being taken.
(AGS2007a pg 15)

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What are the different types of zoning I might consider?

The different types of landslide zoning are as follows:

Landslide Susceptibility Zoning involves the classification, volume (or area) and spatial distribution of existing and potential landslides in the study area. It may also include a description of the travel distance, velocity and intensity of the existing or potential landsliding. Landslide susceptibility zoning usually involves developing an inventory of landslides which have occurred in the past together with an assessment of the areas with a? potential to experience landsliding in the future, but with no assessment of the frequency (annual probability) of the occurrence of landslides. In some situations susceptibility zoning will need to be extended outside the study area being zoned for hazard and risk to cover areas from which landslides may travel on to or regress into the area being zoned. It will generally be necessary to prepare separate susceptibility zoning maps to show landslide sources and areas onto which landslides from the source landslides may travel or regress.

Landslide Hazard Zoning takes the outcomes of landslide susceptibility mapping, and assigns an estimated frequency (annual probability) to the potential landslides. It should consider all landsliding which can affect the study area including landslides which are above the study area but may travel onto it and landslides below the study area which may retrogressively fail up-slope into it. The hazard may be expressed as the frequency of a particular type of landslide of a certain volume or landslides of a particular type, volume and velocity (which may vary with distance from the landslide source) or, in some cases, as the frequency of landslides with a particular intensity where intensity may be measures in kinetic energy terms. Intensity measures are most useful for rock falls.

Landslide Risk Zoning takes the outcomes of hazard mapping and assesses the potential damage to persons (annual probability the person most at risk loses his or her life) and to property (annual value of property loss) for the elements at risk, accounting for temporal and spatial probability and vulnerability.

(AGS2007a pg 16-17)

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Where is landslide zoning useful for land use planning?

Landslide zoning for land use planning is most commonly required at the local government level for planning urban development, but may be required by state or federal governments for regional land use planning or disaster management planning. It may also be required by land developers, those managing recreational areas or those developing major infrastructure such as highways and railways. The following are some examples of situations that are more susceptible to landslide occurrence. Their identification through landslide zoning would facilitate development planning and landslide risk management. It is the combination of having an area which is potentially subject to landsliding and the scale and type of development of the area that will determine whether landslide zoning is needed for land use planning.

The following are examples of topographical, geological and development situations where landsliding is potentially an issue in land use planning:

Where there is a history of landsliding e.g:
- Deep-seated sliding on natural slopes.
- Widespread shallow slides on steep natural slopes.
- Rock falls from steep slopes and cliffs.
- Rock falls from coastal cliffs.
- Landslides in cuts, fills and retaining walls on roads, railways and associated with urban ?development.
- Large currently inactive landslides subject to undercutting by active erosion of the toe or subject to reactivation by development.
- Debris flows and earth slides from previously failed slopes.
- Widespread shallow creep type landslides in slopes of any inclination.
Where there is no history of sliding but the topography dictates sliding may occur. e.g:
- Cliffs (coastal and inland).
- Natural slopes steeper than 35o (landslide travel is likely to be rapid).
- Natural slopes between 20o and 35o (rapid landslide travel is possible).
- Steep, high road or rail cuttings.
- Steep slopes degraded by recent forest logging, forest fires and/or construction of roads.
- Large currently inactive landslides subject to rising groundwater regimes; e.g. by forestry and agricultural operations.
When there is no history of sliding but geological and geomorphologic conditions are such that sliding is possible e.g:
- Weathered basalt overlying other more competent rocks (sliding often occurs on the boundaries).
- Weathered granitic and volcanic rocks.
- Weathered interbedded rocks (such as claystone, shale and siltstone) and sandstone or limestone.
- Sand dunes.
- River banks in soil subject to floods and/or active erosion.
- Steep natural slopes in regions affected by large earthquakes.
- Slopes in highly sensitive weak clays (e.g. quick clays).
- Where there is active undercutting of slopes by rivers or the sea.
- In seismically active regions slopes in loose saturated soil which are susceptible to liquefaction.
Where there are constructed features which, should they fail, may travel rapidly e.g:
- Loose silty sandy fills (residual/extremely weathered granite; ripped sandstone etc).
- Other side cast fills on steep slopes.
- Large retaining walls.
- Mine overburden spoil and mine waste dumps, particularly those sited on hillsides.
- Tailings dams constructed using upstream construction methods.
Forestry works and agricultural land clearing where landsliding may lead to damage to the environment by degrading streams and other receiving water bodies.

It should be noted that rapid sliding is important because of the potential for life loss. However slow and very slow moving landslides are also of importance because they may also lead to property damage.
(AGS2007a pg 17-19)

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What are some of the principles behind the selection of the type and level of landslide zoning?

Landslide zoning is carried out for regional, local and site specific planning. The outputs are usually in the form of one or more of the following: landslide inventory, susceptibility, hazard and risk zoning maps and associated reports. The type and level of detail of the zoning and the scale of the maps depends on the purpose to which the landslide zoning is to be applied and a number of other factors:

The stage of development of the land use zoning plan or engineering project: Susceptibility and hazard zoning are more likely to be used in preliminary stages of development with hazard and risk zoning for more detailed stages. However the choice depends mostly on the intended purpose of the zoning in land use management.
The type of development: Risk zoning is more likely to be used for existing urban developments where the elements at risk are defined or for existing and planned road and railway developments where the elements at risk (the road or rail users) are readily predicted. However, the elements at risk often vary with time so risk zoning needs to be up-dated regularly.
The classification, activity, volume or intensity of landsliding: Risk zoning is more likely to be required where the landslides are likely to travel rapidly and or have a high intensity as measured by the combination of volume and velocity (e.g. rock fall, debris flows, rock avalanches). For these situations life loss is more likely so it is useful to use risk zoning as this allows land use zoning to be determined using life loss risk criteria.
Funds available: While the purpose should determine the level of zoning and the scale of the maps, the funding available may be a practical constraint. Landslide susceptibility zoning is lower cost than hazard zoning, and hazard zoning is somewhat lower cost than risk zoning, so land use planners may opt for a lesser type and level of mapping at least in a staged introduction of landslide land use planning.
The amount and quality of available information: Only susceptibility zoning is performed where data on frequency of landslides either do not exist or are so uncertain as to not be relied on.
History of land use: The history of the area being zoned and its evolution in terms of land use must be carefully taken into account as human activities may modify the slope instability environment and modify the susceptibility to and likelihood of landsliding and hence the hazard.
Degree of quantification: Qualitative methods are often used for susceptibility zoning and sometimes for hazard zoning. It is better to use quantitative methods for both susceptibility and hazard zoning. Risk zoning should be quantified. More effort is required to quantify the hazard and risk but there is not necessarily a great increase in cost compared to qualitative zoning.
The required accuracy of the zoning boundaries: Where statutory land use planning constraints are proposed large scale maps with appropriate levels of inputs should be used. In this regard it should be noted that State and Local governments may have different requirements. The largest scale required will determine the level and scale of landslide zoning.
Linkage to the proposed planning controls: The use of complementary or linking processes such as planning schedules and development control plans whereby the landslide zoning initiates a more detailed assessment at site scale. In this case, the use of landslide susceptibility mapping which defines a planning control area may be sufficient to identify where a more detailed landslide risk assessment is needed.

(AGS2007a pg19)

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What are the recommended types and levels of zoning and map scales?

Table 1 shows the recommended types of zoning, zoning levels and mapping scales that depend on the purpose of the zoning. The table is applicable to land use planning for urban development. The table is broadly applicable to other uses such as managing landslide hazard and risks for new and existing roads and railways.

It will usually be appropriate to carry out landslide susceptibility zoning as a first stage in the development of landslide hazard or risk zoning for planning purposes. Staging will allow better control of the process and may reduce the costs of the zoning by limiting the more detailed zoning only to areas where it is necessary.

It should be noted that it will seldom be necessary to carry out landslide zoning at an advanced level because the costs will potentially be so much larger than the costs for intermediate level zoning and this will potentially outweigh the benefits.

The levels of zoning and descriptors of susceptibility, hazard and risk are given in the following sections. It is recommended that these descriptors be used by all involved in landslide risk management.

(AGS2007a pg19)

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What is meant by the Levels of Zoning?

Table 2 in AGS2007a defines the levels of landslide inventory, susceptibility, hazard and risk zoning in terms of geotechnical and other input data. The definitions of the levels of the input data are given in Section 8 in AGS2007a. It is important to match the level of the zoning to the required usage, the scale of mapping and in turn match these to the level of the input data. It is not possible, for example, to produce a satisfactory advanced level hazard zoning without at least intermediate level assessment of frequency of landsliding. If only a basic level assessment of frequency can be made then the result will be no better than preliminary level and there is no point spending large resources getting the other inputs to a intermediate or, in particular, to a sophisticated level. On the other hand, if a preliminary level hazard zoning is required then the inputs may be at the basic level.

Table 2 – Levels of activity required for susceptibility, hazard and risk zoning levels.

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What are the Scales for Landslide Zoning Maps and their Application?

Table 3 summarises map scales and the landslide inventory, susceptibility, hazard and risk mapping to which they are usually applied. Landslide zoning maps should be prepared at a scale appropriate for displaying the information needed at a particular zoning level. In practical terms the scale of mapping may be controlled by the scale of the available topographic maps.

Table 3 -Landslide zoning mapping scales and their application

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What are the common descriptors used in landslide zoning and why should they be used?

There will be considerable benefits if those carrying out landslide zoning use common descriptors to describe the degree of landslide susceptibility, hazard and risk. It will allow geotechnical professionals doing the zoning to relate to each other and allow legislators and those developing building controls to refer to these descriptors in the knowledge that they have a uniform meaning. This Section defines susceptibility, hazard and risk descriptors.

In general the standard descriptors used are:, very low, low moderate, high and very high. AGS2007a provides further details and explanations of the? recommended descriptors for landslide susceptibility, hazard and risk zoning in sections 7.2.2, 7.2.3, 7.2.4 and 7.2.5.

(adapted from AGS2007a pg 20-23)

LINKS

http://australiangeomechanics.org/downloads/

What are the requirements when documenting a landslide zoning scheme?

It is essential that the landslide zoning process be well documented in a report. The report should include:

Zoning maps and legends.
The definitions of the susceptibility, hazard and risk zones.
The basis upon which the zoning has been carried out including data sources, zoning methodology, the time period covered by the landslide inventory if one has been used to assess landslide frequency.
A description of any limitations of the zoning including accuracy of zone boundaries.
Other information to explain the use of the landslide zoning as required for the particular project.

This informs those who are using the landslide zoning and facilitates peer review.

(AGS2007a pg 28)

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What are some of the limitations involved in developing a landslide zoning scheme?

There are a number of potential sources of error in the zoning process. These include:

Limitations in the landslide inventory upon which the susceptibility and hazard zoning maps are based.
Limitations in the stability of temporal series. For example the relationship between the triggering factor (e.g. rainfall) and the frequency of landslides may change if the area is deforested.
Limitations in the level of detail available of topography, geology, geomorphology, rainfall and other input data.
Model uncertainty, meaning the limitations of the methods used to relate the inventory, topography, geology, geomorphology and triggering events such as rainfall to predicting landslide susceptibility, hazard and risk.
Limitations in the skill of the persons carrying out the zoning.

It must be recognised that landslide zoning is not a precise science and the results are only a prediction of performance of the slopes based on the available data. In general, intermediate or advanced level zoning will be less subject to error than preliminary level zoning with each done at a suitable zoning map scale

(AGS2007a pg 29)

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What is the role of mapping?

For most zoning studies for land use planning there should be a peer reviewer appointed to provide independent assessment of the susceptibility, hazard and risk zoning. The peer reviewer should have a high level of the skills and experience listed in Section 11.2.The peer reviewer should meet with those carrying out the study at the beginning of the study and, depending on the scale of the projects, perhaps after initial mapping and then as the zoning is being finalised. This process is a basic form of quality control and a form of validation if the peer reviewer has appropriate wide experience.

For more important advanced level mapping projects there can be a process of validation within the study. To do this the landslide inventory is randomly split in two groups: one for analysis and one for validation. The analysis is carried out in part of the study area (model) and tested in another part with different landslides. An alternative approach for advanced mapping projects is for an analysis to be carried out with landslides that have occurred in a certain period whilst validation is performed upon landslides that have occurred in a different period. Validation can also be carried out by this process after the mapping and land use planning scheme has been in place for some time. This is really only practical for high frequency landsliding because of the time frame required to gather performance data.

(AGS2007a pg 29-30)

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How does a regulator prepare a brief for a zoning study?

The following are some matters which should be considered in preparing a brief for a landslide zoning study:

Define the purpose of the zoning and how it will be used.
Define the area to be zoned.
Define what type of zoning is required: landslide susceptibility, hazard or risk.
Define the level of zoning required and whether it will be staged.
Identify the various stake holders and their interests.
Describe what, if any, public consultation process will be required.
State relevant legal and regulatory controls.
Set out the documentation required for the results of the zoning, including details of what maps are required, map scales, and electronic formats and the supporting report describing the zoning processes, methods used, validation and limitations.
Set a program for the study.
Set a budget consistent with the scope and expectations of the study.
Describe the peer review process which will apply.
List the available data and the format it is in.
Detail the expected method for the study.
Define the terminology to be used to describe susceptibility, hazard and risk.

In so far as possible, this is best done in consultation with prospective consultants so there is a clear understanding of what is required.

Landslide susceptibility, hazard and risk zoning is a science that should be done by well qualified geotechnical professionals who are experienced in mapping and who understand slope processes, risk assessment and geotechnical slope engineering. This will usually mean that a team of professionals will be needed including an engineering geologist, geomorphologist (for zoning of natural slopes where geomorphology mapping is required) and a geotechnical engineer. It should be noted that only a few engineering geologists and geotechnical engineers are experienced in geomorphologic mapping. It is essential that geotechnical engineers who understand the soil and rock mechanics of slope processes pre and post-failure are involved in the landslide susceptibility, hazard and risk assessments.

Consultants proposing to carry out landslide zoning should demonstrate they have personnel who will work on the project with the relevant skills and experience. It is not sufficient that a geotechnical company has done such studies because it is the personnel directly involved that are important

(AGS2007a pg 30-31)

5. Policy Requirements

Why does a Regulator need a specific policy?

The regulator should have a specific policy which sets out the requirements for LRM assessments as part of the development application documentation and process. The need for such a policy should be determined by zoning studies in accordance with AGS (2007a).

(AGS2007c pg 67)

Additional Information

A natural hazard is a naturally occurring situation or condition with the potential for loss or harm to the community or environment. Natural hazards do not have to become natural disasters. Effective land use planning is an important means of reducing the community’s vulnerability to natural hazards and promoting resilient communities.

Natural disasters are a significant and rising cost to the community. They are estimated to have cost Australia $37.8 billion (in 1997 prices) in direct and indirect tangible costs between 1967 and 1999. In addition, there are significant intangible costs associated with loss of life, injury, human suffering, loss of productivity and environmental degradation.

Inappropriate development in areas susceptible to natural hazards significantly increases the risks (and associated costs) to the community. A specific landslide policy should aim to minimise these risks by ensuring that the potential adverse impacts of natural hazards are adequately considered when development applications are assessed, when planning schemes are made or amended and when land is designated for community infrastructure.

(Adapted from SPP1/03 Queensland State Government)

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When should a LRM assessment be undertaken?

The need for a LRM assessment is usually related to a Susceptibility or Hazard Zoning Study or some other plan or criteria defining areas or types of development which are to be included or excluded for assessment.

(AGS 2007c pg 67)

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What competencies should I expect and ask for from those doing this work?

Practitioners undertaking LRM assessments should typically be required to have LRM as a core competency

A method of demonstrating core competency in LRM is being addressed by the Australian Geomechanics Society and Engineers Australia as a specific area of practice within the National Professional Engineers Register (NPER). Some regulators may choose to define another method of demonstrating competency.

(AGS 2007c pg 67)

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What are the basic requirements of a LRM report?

The basic requirements of LRM reports which should be based on compliance with the requirements of the AGS2007 Practice Note (AGS2007c). The report on the risk assessment is to document the data gathered, the logic applied and conclusion reached in a defensible manner.

The practitioner will gather relevant data, will assess the relevance of the data and will reach conclusions as to the appropriate geotechnical model and basic assessment of the slope forming processes and rates. Full documentation of these results provides evidence of completion, provides transparency in the light of uncertainty, enables the assessment to be re-examined or extended at a later date and enables the assessment to be defended against critical review. The process often identifies uncertainties or limitations of the assessment which also need to be documented and understood.

The data to be presented includes:

List of data sources.
Discussion of investigation methods used, and any limitations thereof.
Site plan (to scale) with geomorphic mapping results.
All factual data from investigations, such as borehole and test pit logs, laboratory test results, groundwater level observations, record photographs.
Location of all subsurface investigations and/or outcrops/cuttings.
Location of cross section(s).
Cross section(s) (to scale) with interpreted subsurface model showing investigation locations.
Evidence of past performance.
Local history of instability with assessed trigger events.
Identification of landslides, on plan or section or both, and discussed in terms of the geomorphic model, relevant slope forming process and process rates. Landslides need to be considered above the site, below the site and adjacent to the site.
Assessed likelihood of each landslide with basis thereof.
Assessed consequence to property and life for each landslide with basis thereof.
Resulting risk for each landslide.
Risk assessment in relation to tolerable risk criteria (e.g. regulator?s published criteria where appropriate).
Risk mitigation measures and options, including reassessed risk once these measures are implemented.

Where any of the above is not or cannot be completed, the report should document the missing elements, including an explanation as to why.

The report needs to clearly state whether the risk assessment is based on existing conditions or with risk treatment measures implemented. In some cases, the assessment for both existing and after treatment should be documented to demonstrate the effect of risk control measures on reducing risk.

(AGS2007c pg 81)

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What types of risks need to be considered in a LRM report?

All LRM assessments as a minimum should consider risk to life and risk to property. Other risks which might also be consider may include risk to the environment, loss of business , community confidence etc.

Generally AGS2007 recommends an assessment of risk to life as part of a LRM report should be completed in a quantitative basis. Risk of damage to property or infrastructure may be completed either qualitatively or semi-quantitatively.

(adapted from AGS2007c)

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What terminology and methods should we adopt?

AGS2007 recommends the adoption of the preferred qualitative terminology given in Appendix C of the Practice Note (AGS2007c) for risk to property so that the regulator can become accustomed to the terminology adopted and implications arising there from. If alternative terminology is to be adopted for LRM, the regulator should only accept non standard schemes where the terms have been clearly defined, the terms have been explained in relation to the preferred terminology and it can be reasonably demonstrated by the practitioner that the alternative is better suited to the particular circumstances of the assessment.

(AGS2007c pg 68)

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How can I control the quality of submissions and the approvals process?

As part of a structured policy AGS2007 recommends the regulator adopt and provide a number of Quality Assurance(QA) forms to control the submissions and approvals process. Examples of such forms are provided in Appendix D of AGS2007c which can be adapted to suit the specific needs of an individual regulator.

(adapted from AGS2007c)

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Who specifies the acceptance criteria under which a decision will be made?

It is the sole responsibility of the regulator to specify the criteria under which a decision will be made for both the scope/nature of developments and the appropriate tolerable risk criteria being adopted.

(adapted from AGS2007c)

6. Processing Requirements

How do the use of QA forms proposed by the AGS help with the approvals process?

The regulator should use a number of forms to provide appropriate QA process control and documentation records of the submitted LRM assessment and subsequent compliance with the approval conditions.

The forms need to be appropriate to each stage of the development application, approval, detailed design, construction and maintenance of the development. Essential contents will include:

Name and qualification of the practitioner responsible for the LRM assessment.
A list of supporting documents including the architectural, civil design and structural engineering design drawings, as appropriate, to fully define the extent and scope of the proposed development.
A statement of compliance with the requirements of this Practice Note. In some cases the statements will be required to include details of how compliance is achieved.
Document reference details (date, reference number, report title) for the relevant LRM assessment submission.

A suite of example forms is given in AGS 2007 c in Appendix D for modification by each regulator to be consistent with their policy. The aim of the forms is to provide appropriate documentary control of the stages required through to completion of a development.

(AGS2007c pg 68)

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What roles does peer review / independent third party review play in the processing requirement?

Where the regulator has specific concerns in relation to the adequacy of a submission, or the conclusions reached, or if required by a Hazard Zoning study, the submission may be subject to peer review or independent specialist advice to the regulator as an audit process or as part of mediation for an agreement. The reviewer should independently review the LRM assessment report in terms of adequacy of compliance with this Practice Note and the reasonableness of the assessment conclusions and risk control measures specified. The review should also consider the specific development proposals as defined by the design drawings.

(AGS2007c pg 68)

Additional Information

Circumstances under which a regulator would not support an application might include the following:

Where an application is not supported by a geotechnical report complying with the requirements of the regulators planning control guidelines ( typically a schedule, development control plan or code).
Where the supporting geotechnical report has been prepared or verified by a geotechnical engineer or engineering geologists with qualifications not meeting the requirements of the regulator.
Where risks identified within the original Geotechnical report are estimated to be not acceptable.
Where independent 3^rd party review assesses risks to be higher than those adjudged in submitted report and deemed to be not acceptable.
Where acceptable risk is fully contingent on ongoing mitigation and maintenance of the site or related lands.

(Adapted from Draft Policy on the use and application of the Erosion Management Overlay. Report to Corangamite Catchment Management Authority by ASMG 2006)

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What are typical circumstances when a final approval for a DA is not granted?

Where construction is completed but all aspects of the Approval Conditions have not been completed with appropriate documentation or justification, then the final approval by the regulator should not be given until sufficient information is provided to demonstrate compliance.

It is anticipated that completion of Forms F and G in appendix D of AGS2007c with suitable annotation would help identify where non compliance exists. If the regulator does not have a strong procedure for enforcement of, or auditing of, compliance with consent conditions, then there may be subsequent liability issues for the regulator if non-compliance becomes an issue at a later date.

(AGS2007c pg 68)

7. Setting Risk Criteria

Who establishes the risk criteria to be used in the evaluation of risk?

The regulator is responsible for setting the Risk Criteria for loss of life and property loss

(AGS2007c pg 68)

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What is meant by Tolerable Risk and Acceptable Risk?

It is important to distinguish between “acceptable risks” and “tolerable risks”.

Tolerable Risks are risks within a range that society can live with so as to secure certain benefits. It is a range of risk regarded as non-negligible and needing to be kept under review and reduced further if possible.

Acceptable Risks are risks which everyone affected is prepared to accept. Action to further reduce such risk is usually not required unless reasonably practicable measures are available at low cost in terms of money, time and effort.

(Commentary on AGS2007c pg 133)

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What risk criteria and levels does the AGS recommend for consideration by the regulator?

After due consideration of these factors and taking account of the criteria which were included in AGS (2000, 2002) AGS suggests that for most development in existing urban areas criteria based on Tolerable Risks levels are applicable because of the trade-off between the risks, the benefits of development and the cost of risk mitigation.

The recommended Tolerable loss of life risk values for the person most at risk for different situations are shown in Table 1 of the Practice Note.

Table 1 – AGS Suggested Tolerable loss of life individual risk.

It is recommended that risks be assessed only for the person most at risk,

The recommended values are higher for existing slopes than for new slopes.

Regulators may decide to apply ‘acceptable risk’ criteria for high consequence cases, such as schools, hospitals and emergency services in recognition of the importance of these structures and as a way of covering societal risk concerns. This is also reflected in the recommended criteria for property loss for different Importance Levels of structures presented in table C10 in the Commentary on the practice note.

Table C10 -AGS suggested Acceptable qualitative risk to property criteria.

Notes

Refer to Appendix A, Practice Note
Based on Appendix C, Practice Note
Existing Slopes in this context are slopes that are not part of a recognizable landslide and have demonstrated nonfailure performance over at least several seasons or events of extended adverse weather, usually being a period of at least 10 to 20 years.
Existing Development includes existing structures, and slopes that have been modified by cut and fill, that are not located on or part of a recognizable landslide and have demonstrated non-failure performance over at least several seasons or events of extended adverse weather, usually being a period of at least 10 to 20 years.
New Constructed Slope includes any change to existing slopes by cut or fill or changes to existing slopes by new stabilisation works (including replacement of existing retaining walls or replacement of existing stabilisation measures, such as rock bolts or catch fences).
New Development includes any new structure or change to an existing slope or structure. Where changes to an existing structure or slope result in any cut or fill of less than 1.0 m vertical height from the toe to the crest and this change does not increase the risk, then the Existing Slope / Existing Structure criterion may be adopted. Where changes to an existing structure do not increase the building footprint or do not result in an overall change in footing loads, then the Existing Development criterion may be adopted.
Existing Landslides have been considered likely to require remedial works and hence would become a New Constructed Slope and require the lower risk. Even where remedial works are not required per se, it would be reasonable expectation of the public for a known landslide to be assessed to the lower risk category as a matter of ?public safety?.
Tolerable risk levels would be one class higher (for example Moderate where Low is acceptable). Consideration should be given by regulators to adopting Tolerable risk to property for Existing Slope and Existing Development situations in a similar vein to the recommended differentiation for risk to life.

(Commentary on AGS2007c pg 135)

8. Policy and Processing Roles and Responsibilities

What information should the Regulator maintain to facilitate better LRM outcomes for all stakeholders?

The local Council, or other regulator, should maintain an inventory of past landslide events as discussed in AGS (2007a) and make this information available to all practitioners.

Detailed information of landslide inventories is contained in AGS2007a and its commentary.

(Adapted from AGS2007c pg 68)

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What does the Regulator expect of the Practitioner?

The practitioner has the role of providing technical input in relation to the specialized aspect of LRM. Such input will be subject to the specific requirements of any policy instituted by the regulator. The regulator may require specific levels of qualification and competence of practitioners providing the regulator with advice in relation to compliance with the risk acceptance criteria.

It is the responsibility of the practitioner to carry out LRM assessments in accordance with this Practice Note and within the requirements of his/her professional Code of Ethics. The practitioner must provide advice to the client and regulator in an unbiased manner.

The qualifications and experience of suitable practitioners are to be accordance with the regulators planning and regulatory protocols

(AGS2007c pg 69)

Who undertakes landslide zoning?

Conclusion: The regulator (typically local government) has the responsibility and bears the technical and budgetary impost for preparing Statutory Maps (or Planning Control) for areas susceptible to landslide.
By necessity this will also require Information Maos (inventory) and Advisory Maps (i.e. Susceptibility, hazard and/or risk maps)

Additional Information

Local Government

While guidance is provided by the Development Assessment Forum (DAF 2007), systematic policy implementation to address landslide hazard is rare across local governments.

State and Territory Governments

National: Australian Government

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Can the terms Risk Analysis, Risk Assessment and Risk Management be used interchangeably because they have the same meaning but perhaps a different emphasis?

Terminology used in papers discussing Risk in relation to landslides has evolved and changed over the years. When referring to published papers, the reader has to be very careful as to the definitions adopted for the various terms. Unfortunately many papers do not define the terms used and therefore it is easy to confuse the terminology with that now adopted as defined in AGS 2007c.

These terms now have clear and different definitions.

These terms describe different parts of the overall process of Risk Management.

Risk Analysis refers to the evaluation of risk, by the product of likelihood and consequence.

Risk Assessment includes the Risk Analysis but then compares the risk against acceptance criteria, such as those set by the Regulator

Risk Management includes Risk Assessment but then includes risk treatment options to control or reduce risks to acceptable or tolerable levels.

Formal definitions are given in AGS 2007c Appendix A.

Why is scope definition an important part of the LRM process?

Implicit in the scope will be compliance with the requirements of the regulator’s policy. Such requirements are likely to be derived from studies in accordance with the AGS (2007a).

Such studies, and resulting policy, may determine a particular minimum scope or level of study, as discussed in Section C5.2. If the minimum scope is not completed, then the reasons for departure from such a scope should be documented by the practitioner.

In more complex studies, staged study may be appropriate, so that increasing complexity of study is only adopted if the results obtained from the initial studies show it to be warranted. It may be appropriate to discuss with the client the alternative levels of study and implications arising therefrom.

Frequently a lay client will not have sufficient knowledge to question whether the scope is appropriate. If there may be a need to extend the scope of the assessment, based on the results of the initial assessment or response from the regulator, then it would be “good practice” to advise the client at the earliest opportunity of the possibility of such an extension.

Communication of the scope adopted and inherent limitations arising therefrom becomes “good practice” for the practitioner as a liability risk management issue. It is essential that the client be informed of the limitations of the particular risk assessment and inherent uncertainty.

What are the field investigations required to formulate the geotechnical model?

Field Investigation Requirements

Does the collation of landslide inventory result in an objective measure of the landslide likelihood?

Does the assessed likelihood take into account the probability of spatial impact?

The equations to calculate the quantitative risk to either property or life (refer to Section 7.1 of AGS 2007c) consider the probability of spatial impact as part of the equation.

However if a qualitative assessment is being completed the risk matrix in AGS 2007c Appendix C does not appear to make specific allowance for this partial factor to be taken into account. Where relevant, the probability of spatial impact can be taken into account by modifying the “Likelihood” term by the value of the probability of spatial impact.

Further advice on probability of spatial impact is given in AGS 2007c Section 5.4.3 and Section 5.4.3 of AGS 2007d.

Why should the extent of damage to property be expressed in terms of market value?

PDF AGS 2007c Section 6.3

PDF AGS 2007d Section C6.3

How can I estimate the vulnerability of persons, that is, the likelihood of death, should they be impacted by a landslide?

AGS 2007c Section 6.3

AGS 2007d Section C6.3

Is there a preferred qualitative terminology that should be adopted for assessment of risk to property?

AGS 2007c Section 7.3

AGS 2007d Section C7.3

Can risk to life be expressed in a qualitative terminology?

AGS 2007d Section C7.4

What is the difference between “tolerable risk” and “acceptable risk”?

PDF AGS 2007c Section 8.2

PDF AGS 2007d Section C8.2What are the AGS recommended values for Tolerable risk to life for the person most at risk?

What are the AGS recommended values for tolerable risk to life for the person most at risk?

Notes

Existing Slopes in this context are slopes that are not part of a recognizable landslide and have demonstrated nonfailure performance over at least several seasons or events of extended adverse weather, usually being a period of at least 10 to 20 years.
Existing Development includes existing structures, and slopes that have been modified by cut and fill, that are not located on or part of a recognizable landslide and have demonstrated non-failure performance over at least several seasons or events of extended adverse weather, usually being a period of at least 10 to 20 years.
New Constructed Slope includes any change to existing slopes by cut or fill or changes to existing slopes by new stabilisation works (including replacement of existing retaining walls or replacement of existing stabilisation measures, such as rock bolts or catch fences).
New Development includes any new structure or change to an existing slope or structure. Where changes to an existing structure or slope result in any cut or fill of less than 1.0m vertical height from the toe to the crest and this change does not increase the risk, then the Existing Slope / Existing Structure criterion may be adopted. Where changes to an existing structure do not increase the building footprint or do not result in an overall change in footing loads, then the Existing Development criterion may be adopted.
Existing Landslides have been considered likely to require remedial works and hence would become a New Constructed Slope and require the lower risk. Even where remedial works are not required per se, it would be reasonable expectation of the public for a known landslide to be assessed to the lower risk category as a matter of public safety.

Acceptable risks are usually considered to be one order of magnitude lower than the Tolerable Risks.

It is important to distinguish between acceptable risks and tolerable risks.

AGS suggests that for most development in existing urban area criteria based on Tolerable Risks levels are applicable because of the trade-off between the risks, the benefits of development and the cost of risk mitigation.

The Commentary discusses Individual and Societal risk to loss of life. Usually Societal risk need not be considered for a risk evaluation in relation to a single dwelling. Societal risk should be evaluated for buildings having high numbers of occupants, such as schools, hospitals, hotels or motels where many lives are at risk. This then addresses society?s aversion to loss of many lives from single landslide events.

The Tolerable Risk Criteria for property loss may be determined by the Importance Level of the development (Appendix A) as discussed in the Commentary.

What are the options for risk management?

AGS 2007c 9.1

AGS 2007d C9.1

What design life should be adopted for design of risk mitigation measures?

AGS 2007c 9.3

AGS 2007d C9.3

What principles should be adopted for risk assessment of minor works?

AGS 2007c 11.1

What should the practitioner do if part of the site is found not to have an acceptable level of risk?

AGS 2007c 11.2

AGS 2007d C11.2

Should a Landslide Risk Assessment report limit consideration to a nominated site area regardless of dangers from outside the site which may affect the site?

AGS 2007c 11.3

AGS 2007d C11.3

How can a subjective or “degree of belief” assessment by a practitioner be improved?

AGS 2007d Section C5.4.1 (Part IV)

Additional Material

Boulder Falls:

Simple event tree example:

Example of partitioning probability:

Thoughts on effect of Climate Change:

Example of rainfall data analysis:

Example of Groundwater modeling:

Where can I get help?

Refer to Australian GeoGuides (AGS 2007e) and the suite AGS (2007), as well as your local Council. Every Council in Australia was provided with a copy of AGS (2007) in both hard and soft copy.

What are the differences between landslides in rock and those in soil?

See Australian GeoGuides:

Water and Drainage

One way or another, water usually plays a critical part in initiating a landslide (GeoGuide LR2). For this reason, it is a key factor to be controlled on sites with more than a low landslide risk (GeoGuide LR7).

Read Australian GeoGuide LR05 – Water & Drainage

Retaining walls

Design of retaining walls more than 900mm high should be undertaken by a geotechnical practitioner or structural engineer and normally require local council approval.

Read Australian GeoGuide LR06 – Retaining Walls

Examples of good and poor practice

Sensible development practices are required when building on hillsides, particularly if the hillside has more than a low risk of instability (GeoGuide LR7). Only building techniques intended to maintain, or reduce, the overall level of landslide risk should be considered.

Read Australian GeoGuide LR08 – Construction Practice

Effluent and surface water management

All households generate effluent and wastewater. The disposal of these products and their impact on the environment are key considerations in the planning of safe and sustainable communities. Cities and townships generally have reticulated water, sewer and stormwater systems, which are designed to deliver water and dispose of effluent and wastewater with minimal impact on the environment. However, many smaller communities and metropolitan fringe suburbs throughout Australia are un-sewered. Some of these are located in hillside or coastal settings where landslides present a hazard.

Read Australian GeoGuide LR09 – Effluent and Surface Water Disposal

Coastal environment and sea-level variation

The coast presents a particularly dynamic environment where change is often the norm. Hazards exist in relation to both cliffs and sand dunes. The coast is also the most heavily populated part of Australia and always regarded as ?prime? real estate, because of the views and access to waterways and beaches.

Read Australian GeoGuide LR10 – Coastal Landslides

Should records be kept?

It is strongly recommended that records be kept of all construction, inspection and maintenance activities in relation to developments on sloping blocks. In some local authority jurisdictions, maintenance requirements form part of the building consent conditions, in which case they are mandatory.

Australian GeoGuide LR11 – Record Keeping

Additional Information

Geoscience Australia (“Natural Hazards in Australia, identifying risk analysis requirements”, Middlemann MH (ed)

Frequently Asked Questions

1. Overview of Hazard/Danger Management

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Additional Information

Cost of Landslides

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Additional Information

Rockfall

Deep-seated Landslide

Debris Flow

Shallow Landslide

Brief history of landslide zoning in Australia

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Maierato, Italy February 2010

Maierato, Italy February 2010

Wales Rockfall, 2011

Nara Prefecture, Japan, 2004

Additional Information

Additional Info

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2. Overall Roles and Responsibilities

Who undertakes landslide zoning?

Additional Information

Local Government

State and Territory Governments

National: Australian Government

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3. Planning Schemes and the Approvals Process

Additional Information

Overview Of Planning Instruments In Australia

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Table 2 – Overview of planning instruments in Australia

Additional Information

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4. Implementing Landslide Zoning for Land Use and Planning

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Table 2 – Levels of activity required for susceptibility, hazard and risk zoning levels.

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Table 3 -Landslide zoning mapping scales and their application

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5. Policy Requirements

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6. Processing Requirements

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Additional Information

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7. Setting Risk Criteria

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Table 1 – AGS Suggested Tolerable loss of life individual risk.

Table C10 -AGS suggested Acceptable qualitative risk to property criteria.

Notes

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8. Policy and Processing Roles and Responsibilities

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Who undertakes landslide zoning?

Additional Information

Local Government

State and Territory Governments

National: Australian Government

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