FAQs and Glossary
Frequently Asked Questions
Download and complete a Property Flood Advice Request Form and email it to email@example.com. If you have a specific development in mind for the property please include details of the proposed development. You can attach plans or sketches of your proposed development to your application for review. A floodplain officer will then assess your flood advice request and respond to you in writing.
There are no fees associated with flood advice.
Not all information is captured in the planning scheme of a local council and therefore it is necessary to contact the CMA to obtain the most up to date information.
Yes, you can apply for flood advice for a property that you don’t own.
No, in the interest of fairness Corangamite CMA responds to flood advice requests in the order that they are received. The Authority will respond to you in writing within 28 days of the date from when the application is recieved.
There are not set finished floor levels for certain areas. A floodplain officer will need to calculate the finished floor level for each individual request. Each flood advice request will be processed in the order that they are received.
Special Building Overlays are planning scheme controls that identify areas prone to overland flooding. Overland flooding (or overland flows) is caused by inundation by local runoff on its way to a waterway and is synonymous with stormwater flooding. Local Councils, as the drainage authority, are the responsible authority for managing stormwater flood risk, including overland flows.
Corangamite CMA does not provide any advice in relation to stormwater flooding including areas identified by a Special Building Overlay (SBO) or land liable to stormwater flooding under the Building Regulations. Please contact your Council directly for any stormwater/SBO related advice or enquiries.
The Corangamite CMA is a recommending authority for flood related planning applications. Council has the authority to make the final decision relating to planning applications. The advice that we give for flood advice requests is the advice that we would give council if they referred a planning application to us. As council are the determining authority, they make the ultimate decision on whether or not to grant planning permits.
Flood levels can vary greatly in a relatively small area. There can be multiple flood levels on one property, so it is important to get flood advice for each property specific to each development.
The insurance industry has recently developed its own database of flood risk Australia wide for individual properties which has regard for both depth of flooding and frequency of flooding for a range of flood events. As such, it is not based solely on whether your property is within a flood overlay or not. It is understood that premiums are based on the flood risk assessed by the individual insurance company and companies may have different criteria for determining premiums.
If you are concerned that a premium is excessive, you may ask for a review by your insurance company or you may consider alternative quotes from other insurance providers.
The 1% AEP flood event means that a flood of that magnitude (or greater) has a 1% chance of occurring in any given year. It is also known as the 100 year Average Recurrence Interval (ARI5) flood; however a flood of this size or greater may occur more frequently than this, and can happen more than once in any year. The Victorian Government has determined that the 1% AEP flood is the appropriate standard to regulate and protect new developments through the planning and building systems. The impacts of floods rarer than the 1% AEP flood (i.e. less than 1% AEP) are not regulated through the planning and building systems.
Apply to the Corangamite Catchment Management Authority via our Property Flood Advice Request Form. You will receive a written report that will indicate flood levels generated by computer models and historical information available. A report may indicate that the Authority does not have information available. This means that the City has no information, but it does not necessarily mean that a property is immune from flooding.
Flood modelling is a term that is used to describe the process of artificially trying to represent a river or floodplain system to determine the magnitude, extent and depth of flooding, how fast floodwaters rise and the implications for flood damage and emergency planning.
Flood maps are based on computer modelling and historical flood records. Because some large and rare floods have often not been experienced since European settlement, computer models are used to stimulate the depths and velocities of major floods. These computer models are normally established and operated by flooding experts employed by local and state government authorities. Because of the critical importance of the flood level estimates produced by the models, such modelling is subject to very close scrutiny before flood information is formally adopted by government.
In general, flood mapping, determined by flood modelling techniques, has been carried out for many cities, and towns. In such areas, flood understanding is critical for land use and flood response planning to determine possible flood mitigation controls. Despite some rural areas throughout Victoria have detailed flood modelling, most flood mapping has, to date, relied on past historical flood information, including aerial photography, satellite imagery, newspaper accounts, recorded peak flood levels, ground contour information etc.
It is inevitable that floods of various magnitudes will continue to occur in the future. As the size of a flood increases, the smaller the chance that it will occur. Because some of these rare floods have been experienced since European settlement, the height of future floodwaters is normally predicted using computer models. These computer models simulate flood levels and velocities for a range of flood sizes and flood probabilities. Given the importance of estimating flood levels accurately, experts are used to establish and operate the computer models. From time to time the computer models are revised and predicted flood levels can change. The resultant change in flood levels however is normally very small. The reasons why the computer models are revised can include:
- New rainfall or ground topography information becomes available
- New floods occur which provide additional data from which to fine-tune the models. New flow data of large flood can influence the flood probabilities that sometime alter the design 100-year ARI flood levels
- Better computer models become available as the science of flood modelling improves and computer capabilities increase or
- Flood mitigation works may have been carried out, or development within the catchment may have occurred, that was not previously simulated in the models
(Source: Victorian Floodplain Management Strategy 2016, Department of Environment, Land, Water and Planning)
Adjustment in response to actual or expected climate change or its effects, which moderates harm or exploits beneficial opportunities.
Annual Exceedance Probability (AEP)
The likelihood of the occurrence of a flood of a given or larger size occurring in any one year, usually expressed as a percentage. For example, if a peak flood flow of 500 m3/s has an AEP of 5%, it means that there is a 5% (one-in-20) chance of a flow of 500 m3/s or larger occurring in any one year (see also average recurrence interval, flood risk, likelihood of occurrence, probability).
Average annual damage (AAD)
Depending on its size (or severity), each flood will cause
a different amount of flood damage to a flood-prone
area. AAD is the average damage per year that would occur in a nominated development situation from flooding over a very long period of time. If the damage associated with various annual events is plotted against their probability of occurrence, the AAD is equal to the area under the consequence–probability curve. AAD provides a basis for comparing the economic effectiveness of different management measures (i.e. their ability to reduce the AAD).
Average Recurrence Interval (ARI)
A statistical estimate of the average number of years between floods of a given size or larger than a selected event. For example, floods with a flow as great as or greater than the 20-year ARI (5% AEP) flood event will occur, on average, once every 20 years. ARI is another way of expressing the likelihood of occurrence of a flood event (see also Annual Exceedance Probability).
Australian Rainfall and Runoff (ARR)
ARR is a national guideline for the estimation of design flood characteristics in Australia published by Engineers Australia. ARR aims to provide reliable (robust) estimates of flood risk to ensure that development does not occur in high risk areas and that infrastructure is appropriately designed. The edition is currently being revised. The revision process includes 21 research projects, which have been designed to fill knowledge gaps that have arisen since the 1987 edition was published.
The rapid abandonment of a river channel and the formation of a new river channel. Avulsions occur as a result of channel slopes that are much lower than the slope that the river could travel if it took a new course. Avulsions typically occur during large floods that carry the power necessary to rapidly change the landscape.
The area of land draining to a particular site. It is related to a specific location and includes the catchment of the main waterway as well as any tributary streams.
Short-term retreat of sandy shorelines as a result of storm effects and climatic variations.
Coastal flooding (inundation)
Flooding of low-lying areas by ocean waters, caused by higher than normal sea level, due to tidal or storm-driven coastal events, including storm surges in lower coastal waterways.
Coastal hazard assessments
Coastal hazard assessments commonly define the extent of land expected to be threatened by coastal hazards (inundation, coastal erosion, coastal recession) over specific planning periods. They are typically used for development assessment purposes and to inform land-use planning considerations. In particular such assessments include consideration of future sea level rise scenarios, typically to the year 2100.
The outcome of an event or situation affecting objectives, expressed qualitatively or quantitatively. Consequences can be adverse (e.g. death or injury to people, damage to property and disruption of the community) or beneficial.
The land occupied by a dwelling and its yard, outbuildings, etc, actually enclosed or considered as enclosed.
Design flood event (DFE)
In order to identify the areas that the planning and building systems should protect new development from the risk of flood, it is necessary to decide which level of flood risk should be used. This risk is known as the design flood event.
Development may be defined in jurisdictional legislation or regulation. It may include erecting a building or carrying out work, including the placement of fill; the use of land, or a building or work; or the subdivision of land.
New development is intensification of use with development of a completely different nature to that associated with the former land use or zoning (e.g. the urban subdivision of an area previously used for rural purposes). New developments generally involve rezoning, and associated consents and approvals. Major extensions of existing urban services, such as roads, water supply, sewerage and electric power may also be required.
Infill development refers to the development of vacant blocks of land within an existing subdivision that are generally surrounded by developed properties and is permissible under the current zoning of the land.
Redevelopment refers to rebuilding in an existing developed area. For example, as urban areas age, it may become necessary to demolish and reconstruct buildings on a relatively large scale. Redevelopment generally does not require either rezoning or major extensions to urban services.
Greenfield development refers to building in a currently undeveloped area or development that is unrestrained by prior work.
Flooding that is sudden and unexpected, often caused by sudden local or nearby heavy rainfall. It is generally not possible to issue detailed flood warnings for flash flooding. However, generalised warnings may be possible. It is often defined as flooding that peaks within six hours of the causative rain.
A natural phenomenon that occurs when water covers land that is normally dry. It may result from coastal or catchment flooding, or a combination of both (see also catchment flooding and coastal flooding).
An appreciation of the likely effects of flooding, and a knowledge of the relevant flood warning, response and evacuation procedures. In communities with a high degree of flood awareness, the response to flood warnings is prompt and effective. In communities with a low degree of flood awareness, flood warnings are liable to be ignored or misunderstood, and residents are often confused about what they should do, when to evacuate, what to take with them and where it should be taken.
Flood class levels
The terms minor, moderate and major flooding are used in flood warnings to give a general indication of the types of problems expected with a flood
Minor flooding: Causes inconvenience. Low-lying areas next to watercourses are inundated. Minor roads may be closed and low-level bridges submerged. In urban areas inundation may affect some backyards and buildings below the floor level as well as bicycle and pedestrian paths. In rural areas removal of stock and equipment may be required.
Moderate flooding: In addition to the above, the area of inundation is more substantial. Main traffic routes may be affected. Some buildings may be affected above the floor level. Evacuation of flood-affected areas may be required. In rural areas removal of stock is required.
Major flooding: In addition to the above, extensive rural areas and/or urban areas are inundated. Many buildings may be affected above the floor level. Properties and towns are likely to be isolated and major rail and traffic routes closed. Evacuation of flood-affected areas may be required. Utility services may be impacted.
The tangible (direct and indirect) and intangible costs (financial, opportunity costs, clean-up) of flooding. Tangible costs are quantified in monetary terms (e.g. damage to goods and possessions, loss of income or services in the flood aftermath). Intangible damages are difficult to quantify in monetary terms and include the increased levels of physical, emotional and psychological health problems suffered by flood-affected people that are attributed to a flooding episode.
Education that raises awareness of the flood problem to help individuals understand how to manage themselves and their property in response to flood warnings and in a flood event. It invokes a state of flood readiness.
Flood emergency management
Emergency management is a range of measures to manage risks to communities and the environment. In the flood context, it may include measures to prevent, prepare for, respond to and recover from flooding.
Potential loss of life, injury and economic loss caused by future flood events. The degree of hazard varies with the severity of flooding and is affected by flood behaviour (extent, depth, velocity, isolation, rate of rise of floodwaters, duration), topography and emergency management.
The maximum flow occurring during a flood event past a given point in the river system (see also flow and hydrograph). The term may also refer to storm-induced flood peaks and peak ocean or peak estuarine conditions.
Land susceptible to flooding by the largest probable flood event. Flood-prone land is synonymous with the floodplain. Floodplain management plans should encompass all flood-prone land rather than being restricted to areas affected by defined flood events.
Flood proofing of buildings
A combination of measures incorporated in the design, construction and alteration of individual buildings or structures that are subject to flooding, to reduce structural damage and potentially, in some cases, reduce contents damage.
An ability to react within the effective warning time (see also flood awareness and flood education).
The potential risk of flooding to people, their social setting, and their built and natural environment. The degree of risk varies with circumstances across the full range of floods. Flood risk is divided into three types – existing, future and residual. Existing flood risk refers to the risk a community is exposed to as a result of its location on the floodplain. Future flood risk refers to the risk that new development within a community is exposed to as a result of developing on the floodplain. Residual flood risk refers to the risk a community is exposed to after treatment measures have been implemented. For example: a town protected by a levee, the residual flood risk is the consequences of the levee being overtopped by floods larger than the design flood; for an area where flood risk is managed by land-use planning controls, the residual flood risk is the risk associated with the consequences of floods larger than the DFE on the community.
A qualitative indication of the ‘size’ of a flood and its hazard potential. Severity varies inversely with likelihood of occurrence (i.e. the greater the likelihood of occurrence, the more frequently an event will occur, but the less severe it will be). Reference is often made to major, moderate and minor flooding (see also flood class levels).
A comprehensive technical assessment of flood behaviour. It defines the nature of flood hazard across the floodplain by providing information on the extent, depth and velocity of floodwaters, and on the distribution of flood flows. The flood study forms the basis for subsequent management studies and needs to take into account a full range of flood events up to and including the largest probable flood. Flood studies should provide new flood mapping for Planning Scheme inclusion, data and mapping for MEMPs, and a preliminary assessment into possible structural and non-structural flood mitigation measures.
A Total Flood Warning System (TFWS) encompasses all the elements necessary to maximise the effectiveness of the response to floods. These are data collection and prediction, interpretation, message construction, communication and response. Effective warning time refers to the time available to a flood-prone community between the communication of an official warning to prepare for imminent flooding and the loss of evacuation routes due to flooding. The effective warning time is typically used for people to move farm equipment, move stock, raise furniture, transport their possessions and self-evacuate.
An area of land that is subject to inundation by floods up to, and including, the largest probable flood event.
The prevention activities of flood management together with related environmental activities (see also floodplain).
The rate of flow of water measured in volume per unit time, for example, megalitres per day (ML/day) or cubic metres per second (m3/sec). Flow is different from the speed or velocity of flow, which is a measure of how fast the water is moving, for example, metres per second (m/s).
The height above the DFE or design flood used, in consideration of local and design factors, to provide reasonable certainty that the risk exposure selected in deciding on a particular DFE or design flood is actually provided. It is a factor of safety typically used in relation to the setting of floor levels, levee crest heights and so on. Freeboard compensates for a range of factors, including wave action, localised hydraulic behaviour and levee settlement, all of which increase water levels or reduce the level of protection provided by levees. Freeboard should not be relied upon to provide protection for flood events larger than the relevant design flood event. Freeboard is included in the flood planning controls applied to developments by LGAs.
The measure of likelihood expressed as the number of occurrences of a specified event in a given time. For example, the frequency of occurrence of a 20% Annual Exceedance Probability or five-year average recurrence interval flood event is once every five years on average (see also Annual Exceedance Probability, Average Recurrence Interval, likelihood and probability).
A source of potential harm or a situation with a potential to cause loss.
The study of water flow in waterways; in particular, the evaluation of flow parameters such as water level, extent and velocity.
The study of the rainfall and runoff process, including the evaluation of peak flows, flow volumes and the derivation of hydrographs for a range of floods.
A risk that, following understanding of the likelihood and consequences of flooding, is so high that it requires consideration of implementation of treatments or actions to improve understanding of, avoid, transfer or reduce the risk.
A qualitative description of probability and frequency (see also frequency and probability).
Likelihood of occurrence
The likelihood that a specified event will occur (see also Annual Exceedance Probability and average recurrence interval).
Local overland flooding
Inundation by local runoff on its way to a waterway, rather than overbank flow from a stream, river, estuary, lake or dam. Can be considered synonymous with stormwater flooding.
Permanent or temporary measures (structural and non-structural) taken in advance of a flood aimed at reducing its impacts.
Municipal Flood Emergency Plan
A sub-plan of a flood-prone municipality’s Municipal Emergency Management Plan. It is a step-by-step sequence of previously agreed roles, responsibilities, functions, actions and management arrangements for the conduct of a single or series of connected emergency operations. The objective is to ensure a coordinated response by all agencies having responsibilities and functions in emergencies
Planning Scheme zones and overlays
Planning Schemes set out the planning rules – the state and local policies, zones, overlays and provisions about specific land uses that inform planning decisions. Land use zones specify what type of development is allowed in an area (e.g. urban (residential, commercial, industrial), rural, environmental protection). Overlays specify extra conditions for developments that are allowed in a zone. For example, flooding overlays specify that developments must not affect flood flow and storage capacity of a site, must adhere to freeboard requirements, and not compromise site safety and access.
A statistical measure of the expected chance of flooding. It is the likelihood of a specific outcome, as measured by the ratio of specific outcomes to the total number of possible outcomes. Probability is expressed as a number between zero and unity, zero indicating an impossible outcome and unity an outcome that is certain. Probabilities are commonly expressed in terms of percentage. For example, the probability of ‘throwing a six on a single roll of a dice is one in six, or 0.167 or 16.7% (see also Annual Exceedance Probability).
The rate at which rain falls, typically measured in millimetres per hour (mm/h). Rainfall intensity varies throughout a storm in accordance with the temporal pattern of the storm (see also temporal pattern).
Regional Coastal Boards
Members of Victoria’s three coastal boards have been appointed by the Minister for Environment and Climate Change because of their experience and expertise in areas such as local government, coastal planning and management, tourism and recreational use of the coast. The functions of the Western, Central and Gippsland Coastal Boards, set out under the Coastal Management Act 1995, include developing regional coastal plans and providing advice to the Minister on regional coastal development issues.
Risk is usually expressed in terms of a combination of the consequences of an event and the associated likelihood of its occurrence. Flood risk is based upon the consideration of the consequences of the full range of flood events on communities and their social settings, and the natural and built environment. Risk analysis in term of flooding is a combination of defining what threat exists (see flood risk) and what steps are taken (see risk management) (see also likelihood and consequence).
The systematic application of management policies, procedures and practices to the tasks of identifying, analysing, assessing, treating and monitoring flood risk.
Inundation of normally dry land when water overflows the natural or artificial banks of a stream, river, estuary, lake or dam. Riverine flooding generally excludes watercourses constructed with pipes or artificial channels considered as stormwater channels.
The amount of rainfall that drains into the surface drainage network to become stream flow; also known as rainfall excess.
The increases in coastal water levels above the predicted tide level resulting from a range of location dependent factors such as wind and waves, together with any other factors that increase tidal water level.
The inundation by local runoff caused by heavier than usual rainfall. It can be caused by local runoff exceeding the capacity of an urban stormwater drainage systems, flow overland on the way to waterways or by the backwater effects of mainstream flooding causing urban stormwater drainage systems to overflow (see also local overland flooding).
The degree of susceptibility and resilience of a community, its social setting, and the natural and built environments to flood hazards. Vulnerability is assessed in terms of ability of the community and environment to anticipate, cope and recover from flood events. Flood awareness is an important indicator of vulnerability (see also flood awareness).
Water Management Scheme
The formal process set out in the Water Act 1989 that can be applied to a flood mitigation infrastructure development and its ongoing management. It can be based on and carried out in parallel with a floodplain management study.