When is a Flood Impact Assessment required for a DA?

1. Your site is mapped in a flood-prone area

If your property falls within a flood-affected zone under the local council's flood mapping, you will likely need a Flood Impact Assessment as part of your development application.

NSW planning regulations require councils to manage flood risk in accordance with their Local Environmental Plan (LEP) and Development Control Plan (DCP).

Town planning teams regularly review council flood maps to determine early if a DA approval is likely to trigger flood-related concerns.

Even if only a small section of your land is affected, the requirement for a flood study can still apply.

2. You're proposing major earthworks or altering site levels

Raising or cutting the ground level on flood-prone land can significantly affect stormwater flows and neighbouring properties.

A planning consultant will often recommend a hydraulic engineer to prepare a site-specific flood assessment if your DA includes retaining walls, cut-and-fill plans or slab elevation changes.

This is especially important for townhouse developments, new dwellings or dual occupancies in low-lying suburbs like Canterbury-Bankstown, Blacktown or the Central Coast.

We frequently provide planning advice to clients on whether their proposed changes to landform or drainage systems will trigger council approval conditions related to flooding.

3. You're increasing site coverage or building footprint

Developments that increase impervious surfaces such as concrete driveways or large roof areas can lead to more runoff.

Councils often ask for a flood study to demonstrate how the new built form will interact with overland flow paths or existing stormwater infrastructure.

In these cases, town planning input is critical in coordinating architectural design and drainage plans before lodging the development application.

4. The site has a history of overland flow or stormwater surcharges

Even if a site is not on a floodplain, a DA can trigger a flood impact assessment if there's known overland flow or regular pooling of water.

A local planning consultant familiar with NSW planning policies will know how to interpret council flood certificates and determine what level of flood documentation is required.

For example, in Ryde and Inner West councils, even minor alterations on lots with past drainage complaints may require a basic flood statement.

5. You're building critical infrastructure or basements

If the proposal includes underground parking, basements or sensitive uses like childcare centres, flood impact assessments are usually mandatory.

These types of development require a higher standard of protection and safe evacuation criteria under NSW planning legislation.

Our town planning team has guided developers through complex DA approvals where carpark entries needed to be raised or flood gates installed based on the hydraulic modelling results.

6. The council includes a standard flood clause in zoning controls

Many LEPs and DCPs in NSW automatically require a flood impact assessment when development is proposed in flood planning areas.

This is often triggered by the zoning, regardless of whether recent floods have occurred.

A key part of our planning advice service is identifying when these automatic triggers apply and helping streamline the DA process by liaising directly with council planners.

7. You're unsure if your site is flood-affected

The best first step is to speak to a town planning expert who can review your lot against council mapping tools, obtain relevant flood certificates and speak to council officers directly.

Getting clear planning advice early can prevent costly delays and unnecessary redesigns later.

At Town Planning Sydney, we assist homeowners, builders and architects with accurate site assessments and fast-tracked council approval pathways, even in complex flood-prone areas.