WRM Water & Environment Pty Ltd (WRM) was commissioned by Moree Plains Shire Council (MPSC) to review the Moree and Environs Flood Study/Floodplain Risk Management Study and Plan. Volume 1 (this report) represents the first stage of the study to undertake the data collection and flood study components of the floodplain risk management process. The Gwydir River is a major tributary of the Murray Darling River system. It covers an area of some 26,000 square kilometres, commencing in the Great Dividing Range near Uralla flowing in a generally north-westerly direction through Moree to the Barwon River near Collarenebri. It is separated from the Border Rivers catchment to the north by the Mastermans Range and from the Namoi catchment to the south by the Nandewar Range.

The approach and methodology employed to achieve this phase of the study involved:

• the compilation and review of available flood related data;
• the development and calibration of a computer based hydrological model to derive catchment flows for the historical floods downstream of Gravesend;
• the development and calibration of a computer based hydraulic model to simulate the movement of floodwaters across the floodplain using the recorded Gwydir River flows at Gravesend in combination with a rainfall runoff routing model of the catchment downstream of Gravesend;
• the estimation of Gwydir River design flood discharges by annual series flood frequency analysis of the recorded flows; and
• the use of the computer model results to derive design flood extent maps and preliminary hydraulic flood hazard maps.