The Griffith Floodplain Risk Management Study and Plan were completed by Worley Parsons for Council in 2011. Following the completion of the study the Riverina region suffered from some of the worst flooding in recorded history. During the March 2012 flood event the community of Yenda was severely impacted. The source of flooding in Yenda was from Mirrool Creek flood waters overtopping the irrigation infrastructure and spilling into the catchment of Main Drain J. The existing Floodplain Risk Management Study had only considered flooding from runoff within the Main Drain J catchment and not from external sources. A review of the Study was therefore required to investigate the implications of flood contributions from Mirrool Creek. The Griffith Main Drain J and Mirrool Creek Flood Study was prepared for Griffith City Council (Council) by BMT WBM in 2014 to define the flood behaviour of the catchment, both in terms of local catchment runoff and flood flow contributions from Mirrool Creek. The study produced information on flood flows, velocities, levels and extents for a range of flood event magnitudes under existing catchment and floodplain conditions.

The outcomes of the revised Flood Study established the basis for subsequent floodplain management activities. The Floodplain Risk Management Study (FRMS) aims to derive an appropriate mix of management measures and strategies to effectively manage flood risk in accordance with the NSW Government Floodplain Development Manual. The findings of the study will be incorporated in a Plan of recommended works and measures and program for implementation.

The objectives of the Griffith Main Drain J Catchment Floodplain Risk Management Study and Plan are to:

• Identify and assess measures for the mitigation of existing flood risk;
• Identify and assess planning and development controls to reduce future flood risks; and
• Present a recommended floodplain management plan that outlines the best possible measures to reduce flood damages in the Main Drain J catchment.

This report documents the Floodplain Risk Management Study and presents a recommended Floodplain Risk Management Plan for the Main Drain J catchment.