In Australia and other countries, small private dams in agricultural catchments pose both disastrous individual and cumulative dam failure flood threats to downstream communities; threats that can be exacerbated by increased rainfall intensities caused by climate change. This paper addresses the need for a low cost, scientifically acceptable mechanism and policy guidance to help dam owners and governments better understand and manage these risks and assure community safety. To this end an innovative, cost-effective farm dam flood safety review/design tool is developed and tested in Australia, including hydrology-diverse Tasmania, to complement best practice dam safety assurance policy. The tool's development involved generating complex catchment data to represent hydrologically homogenous regions using best practice water engineering methods, to derive simple regionalised dam flood capability prediction relationships of acceptable accuracy. Results demonstrate the tool's successful development and potential transferability to different hydrological regions; how the relationships can be refined by future research and potentially made to account for climate change; and how the tool can be applied within a best practice dam safety assurance policy which includes additional farmer-friendly elements. The findings are potentially transferable to any region to assure communities that cumulative safety threats posed by rural catchment dams are minimised.