The Main Drain ‘J’ catchment covers an area of nearly 1,000 square kilometres, forming a moderately sized sub-catchment of the Murrumbidgee River Valley. The catchment extends approximately 60 kilometres north of Griffith along a wide floodplain that is bound by the Cocoparra Range to the east and the McPhersons and Melbergen Ranges to the west. The catchment is characterised by undulating and lightly timbered grasslands in the upper reaches that transitions to flat open farmland in the lower reaches around the villages of Yenda, Yoogali and Hanwood. The objectives of the study are:

• to review relevant studies previously carried out;
• to identify the nature and extent of historical floods;
• to develop predictive tools (computer models) which reproduce historical flood behaviour;
• to define best estimates of peak water levels and velocities for the design 20, 100 and 200 year recurrence floods as well as the Probable Maximum Flood (PMF);
• to produce maps showing the likely extent of inundation for the design floods; and,
• to produce maps showing provisional flood hazard categories.