Flood Levels

What is the flood risk to land or buildings? How high could it flood and how often? Experienced home buyers know that when buying a home, each house on the short list should if possible be inspected during, or just after rain just to get an idea of the capability of water dispersal and/or intrusion on both land and dwelling. Such an inspection whilst useful; won’t reveal the likelihood of flooding on the property. We can provide you with a report that will assess the likelihood and severity of flooding.

Datum

Surveyors can determine levels on any property – these levels being called Reduced Levels and they are heights above or below a reference level or datum. In Australia this datum is called the Australian Height Datum (A.H.D.) which has been set from the average tide gauges on the East Coast. Zero Metres AHD is equivalent to a 0.925 m tide at Fort Denison.

Flood levels

Flood levels and the extent of flooding have been recorded for over 120 years throughout NSW. This data provides the basis for determining the areas of land that are affected by flooding and the expected height of flood waters. The frequency at which various heights of flooding can be expected is referred to as once in 5 years (1:5), once in twenty years (1:20) up to the maximum flood of once in 100 years (1:100).

Surveyor’s Help

Unless the property is obviously in a high position it can be difficult for the inexperienced person to determine whether or not the property is flood-prone – surveyors are experts.

We can investigate records and inquire from all authorities about the flood risk for any property. Observations can be made to determine the extent of risk. Advice can be obtained on precautions required for a new building(s) or the likely depth of flooding which could be expected on existing buildings or land.

Building In A Flood Affected Area

Local councils can issue a building approval in flood-prone areas with the condition that the proposed floor level not be less than a specified reduced level – usually 0.5 m above the 1:100 flood level.

We can provide a reference point near the building site so that the council’s conditions can be met. When the building is erected we can then measure the reduced level of the floor ‘as built’ and provide a report. We can also provide advice on potential problems resulting from flooding. Whatever flood problems there may be can often be overcome with help from a surveyor.