A flood issue identified after a concept design, planning application or building layout has been prepared can force expensive redesign. The best flood survey questions establish what is known about the site, which levels govern the project and what information council or a hydraulic engineer will need before decisions are locked in.
For Victorian landowners, builders, architects and developers, the useful questions are not limited to whether a property has flooded before. Flooding is assessed through mapped information, site levels, drainage paths, nominated flood levels and planning controls. A licensed surveyor can provide the accurate spatial and level data that supports these assessments, but the required scope depends on the project.
Start with the planning and site context
1. Is the land affected by a flood-related planning overlay?
Ask whether the property is affected by a Land Subject to Inundation Overlay, Floodway Overlay, Special Building Overlay or another relevant planning control. The applicable overlay can affect building locations, floor levels, earthworks, access and the supporting material required with a planning permit application.
Do not assume an absence of obvious water on site means there is no constraint. Mapping can reflect riverine flooding, local drainage behaviour, overland flow or other catchment conditions. The planning scheme and advice from the responsible authority should be checked early, particularly on sites near waterways, low points, drains or established flood-prone areas.
2. What flood information already exists for the property?
Existing information may include council flood advice, a drainage authority response, historic plans, engineering reports, planning permit conditions or a previous flood study. Ask for the source, date and intended purpose of each document. A level shown on an old plan is not automatically suitable for a new development decision.
The key question is whether the information is current, tied to a recognised datum and relevant to the proposed works. A survey can accurately locate the site in relation to this information, while a hydraulic engineer or relevant authority may need to confirm the flood criteria that apply.
3. Which authority needs to be consulted?
The responsible authority is often the local council, but Melbourne Water, a catchment management authority or another drainage authority may also have a role. Their requirements can differ by location and by the type of development proposed.
Clarifying this early reduces duplicated work and avoids preparing a survey that does not include a level, extent or feature required for assessment. For a subdivision or multi-dwelling project, authority input should be considered before lot layouts and finished levels become fixed.
Questions that define the survey scope
4. What datum should all site and flood levels use?
This is one of the most important flood survey questions. Levels need a common reference, usually Australian Height Datum (AHD), so that existing ground, floor, road, drainage and nominated flood levels can be compared with confidence.
Ask how the datum will be established and whether it is suitable for the accuracy required. A flood level has limited value if the building floor level has been derived from a different or uncertain reference. Clear documentation of datum and benchmarks helps architects, engineers, builders and authorities work from the same information.
5. Do we need a flood level survey, a feature and levels survey, or both?
A flood level survey may focus on recording relevant levels and relating the property to specified flood information. A feature and levels survey has a broader purpose. It can show boundaries, buildings, site features, contours, drainage structures, adjoining conditions, road levels and services visible at the time of survey.
For a simple assessment of an existing dwelling, a targeted level survey may be appropriate. For a new home, extension, commercial build or subdivision, a detailed feature and levels survey is commonly the more useful starting point because design teams need more than a single flood level. The right scope depends on what is being designed and what the authority has requested.
6. Which site features could influence overland flow?
Ask the surveyor to identify features that may affect how water moves across or into the land. These can include pits, drains, kerbs, channels, retaining walls, driveways, low points, embankments, fences and building thresholds.
Site observations do not replace hydraulic modelling, but they provide the accurate base information required for it. They also reveal practical constraints that may otherwise be missed in desktop mapping, such as a driveway that falls towards a garage or an adjoining retaining wall that directs water to a boundary.
7. Should adjacent road, footpath and neighbouring levels be captured?
Often, yes. Water does not stop at a title boundary. The relationship between the site and the road reserve, drainage infrastructure and neighbouring land can be material when assessing access, stormwater discharge, overland flow or proposed earthworks.
The extent of survey should be agreed before fieldwork begins. Capturing enough surrounding detail at the outset is usually more efficient than arranging a return visit when an engineer or council officer requests additional information.
Questions for design and approval decisions
8. What is the nominated flood level, and who has confirmed it?
A surveyor can measure existing levels precisely, but the nominated flood level for design is generally determined through advice from the relevant authority or a qualified hydraulic assessment. Ask for the formal source of that level and the event or condition it represents.
This distinction matters. The highest observed water mark, a neighbour’s recollection and a mapped contour are not necessarily the design flood level accepted for a permit or building outcome. Project records should state the source clearly so the design team is not working from an assumption.
9. Is freeboard required above the nominated flood level?
Freeboard is an additional vertical allowance above a flood level. It may be required by an authority, recommended by an engineer or adopted as a risk-management measure for the particular site. The applicable allowance can vary, so it should not be selected by copying a nearby project.
Ask whether the finished floor level, electrical services, access route, garages or other critical elements need to meet separate criteria. Raising the building may improve resilience, but it can also affect accessibility, streetscape, overlooking, driveway grades, retaining and construction cost.
10. Can the proposed building footprint and access remain functional during a flood event?
The answer may affect more than the house or commercial building itself. A raised floor level is of limited benefit if vehicle or pedestrian access becomes unsafe, if stormwater is trapped against the structure, or if the proposed works redirect water towards adjoining land.
This is where survey information, architectural design, civil engineering and hydraulic advice need to align. On constrained inner-suburban sites, even modest changes to driveway or paving levels can create knock-on issues at boundaries and the kerb.
11. Will filling, retaining walls or landscaping trigger further assessment?
Earthworks can alter storage, flow paths and drainage behaviour. Ask what existing ground levels must be retained, whether cut and fill volumes are proposed, and whether any walls, decks or landscape works could obstruct water movement.
A detailed survey establishes the existing condition before works commence. That record can be valuable for design, permit documentation and resolving questions about whether proposed works will adversely affect neighbouring properties.
12. What deliverables will the consultant team need?
Before commissioning the survey, confirm the format and detail required by the architect, engineer, planner, builder and council. This may include a signed plan, contours, spot levels, a digital drawing file, photographs, benchmark details, title information or level schedules.
For larger projects, ask how the survey will be coordinated with subdivision design, construction set-out, drainage design and future as-constructed information. A well-scoped survey package reduces rework and gives each consultant a dependable base for their part of the project.
Avoid two common assumptions
First, a flood overlay does not automatically mean development is impossible. It means the proposal must respond to the relevant planning and flood considerations. Suitable floor levels, design changes, supporting reports or permit conditions may be required, depending on the site and authority advice.
Second, a survey alone does not determine flood risk. Accurate levels are essential evidence, but flood behaviour can require specialist hydrology or hydraulic analysis. The most effective approach is to obtain the right survey data early, then use it with the appropriate planning, engineering and authority advice.
For projects across Melbourne and wider Victoria, Melbourne Land Surveyors can help define a survey scope that gives your design and consultant team reliable levels from the start. Asking these questions before plans are finalised is a practical way to protect programme, budget and approval pathways.