Braidwood Floodplain Risk Management Study and Draft Plan

⁠⁠⁠Braidwood is located in the Palerang Local Government Area of NSW (Figure A1) on the Kings Highway and is a popular tourist stopping point as it lies approximately halfway between the ACT and the NSW South Coast. The town of Braidwood (which has a population of around 1,100) is located in the upper reaches of the Shoalhaven River catchment.

Through its Floodplain Risk Management Committee Council proposes to prepare a comprehensive floodplain risk management plan for the study area (Figure A2) in accordance with the Manual. The first key stage of the process has been undertaken with the completion of the Braidwood Flood Study (Cardno Willing, April 2005) which was adopted by Council on 26 April 2005. The subject of this brief is the second key stage of the process, the Floodplain Risk Management Study and the preparation of a draft Floodplain Risk Management Plan.

Braidwood is located at the confluence of three minor creek systems: Gillamatong Creek, Monkittee Creek and Recreation Ground Creek. Each creek has a number of tributaries, and the total catchment has an area of approximately 77km2 upstream of Braidwood. The major land uses in the catchment area include beef cattle and wool production.

In April 2005, the consultant Cardno Willing and Palerang Council completed the Braidwood Flood Study and, in accordance with the Manual, the preparation of a Floodplain Risk Management Study and draft Plan for the study area shown on Figure A2 is the next key stage in progressing to a preparation of a Floodplain Risk Management Plan.

The Braidwood Flood Study investigated the 20%, 5%, 2%, 1% AEP events together with the PMF in Gillamatong Creek, Flood Creek and Recreation Ground Creek. The Hydraulic model used was XP RAFTS/SWMM. Hydraulic categories for the 1% AEP event were determined, as were the provisional hazard categories for the 1% AEP event. A qualitative description of the local overland flow flooding was not provided. The flood study did not estimate flood damages for the design floods investigated and no Average Annual Damage (AAD) have been estimated. The study found that 70 lots would be affected by flooding in a 1% AEP event. In a PMF these numbers increased to 175 lots. It should be noted that not all lots have structures on them.

At Braidwood, flood prone land is generally characterised by floodways and flood fringe with limited flood storage areas. The Flood Study carried out by Cardno Willing identified that the survey collected for the study did not allow accurate definition of flooded extents and hazard categorisation.

A large portion of Braidwood is listed on the NSW Heritage Register (Item 01749) as "Braidwood and its Settings". The State Heritage Registers describes Braidwood and its setting as "an excellent surviving example of a Georgian period town plan, dating from the late 1830s". The listing introduces strict requirements related to the construction of works within the listed area. As such, it is important that heritage considerations be taken into account during the development of the Floodplain Risk Management Plan.

The study area lies within the Shoalhaven River catchment. As such, the area also falls within the remit of WaterNSW (formerly the Sydney Catchment Authority). It will be critical that all works recommended by the Floodplain Risk Management Plan consider the requirements of this body.