New flood mapping covering much of the Byron Shire could affect future development controls, with a major new study recommending that planning decisions be based on whichever flood source – river flooding or overland flow – produces the highest flood level.
The draft Byron Shire Overland Flood Study, endorsed unanimously by the Floodplain Risk Management Advisory Committee on 25 June, extends flood mapping beyond traditional river flooding and identifies areas affected by local overland flow, sometimes known as flash flooding.
Prepared by consultants Engeny in the wake of the 2022 floods, the study examines local overland flooding across the Byron Shire.
Overland flooding and river flood mapping
It states that in areas where overland flooding overlaps with existing river flood mapping, ‘peak flood levels from each flood source should be assessed, with planning controls applied based on the flood mechanism that produces the highest flood level’.
The new mapping will help strategic land use policy, and flood-related development controls across the Shire.
Unlike river flooding, overland flooding occurs when intense rainfall overwhelms drainage systems or flows across land before reaching creeks and waterways.
While the mapping has implications for future planning and development controls across the Shire, the study also identifies seven locations where flooding impacts are considered severe enough to warrant further investigation of mitigation works.
Hotspots identified
The report says the hotspots were identified because they involve concentrations of flood-affected properties or significant inundation.
They are located at Parkway Drive in Ewingsdale, Coomburra Crescent and Rajah Road in Ocean Shores, Fingal Street in Brunswick Heads, New City Road and Hollingsworth Lane in Mullumbimby, and Yelgun Creek and Palmer Avenue in South Golden Beach.
Preliminary mitigation options identified for these sites include upgrades to a culvert crossing and channel works at Parkway Drive, property acquisition, drainage channel works, drainage upgrades at Coomburra Crescent, additional stormwater infrastructure at Fingal Street, and new drainage pipes at Hollingsworth Lane.
At Rajah Road, the study identifies a new stormwater pipe network as a possible solution, while at Yelgun Creek it proposes upgraded pipes, additional pits and a pump system.
A bund and a detention basin have been identified as potential measures at Palmer Avenue.
The report notes that these mitigation options are preliminary only and require further assessment.
Future planning and design
It states that ‘future planning and design should be aimed at reducing the flood risk in these hotspot locations’.
The identified works carry a price tag of approximately $13.4 million.
The study also notes that some flooding problems may not be fully resolved even if mitigation works proceed, with some properties likely to remain vulnerable to inundation.
Public exhibition of the draft study is expected later this year, with community feedback to be incorporated into the final report before it is ultimately adopted by Council.
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