Towards defining geomorphic rarity and vulnerability; use of River Styles in High Ecological Value Aquatic Ecosystems (HEVAE)

Unlike in the field of ecology, defining geomorphic rarity of river systems has received relatively little attention. The fluvial geomorphology literature contains references to forms of rarity, denoting uncommonness (continental to basin scale rarity), unique geo-ecological relationships or vulnerability to alteration or
destruction since European occupation of Australia. In this paper, we present a process to identify rarity in identified river forms defined using the River Styles Framework (Brierley and Fryirs 2005). A definition of geomorphic rarity for use in High Ecological Value Aquatic Ecosystems (HEVAE) has been made on the basis
of: uncommonness meaning absolute rarity or endemism of a River Style, fragmentation where isolated remnants of a particular River Style occur, susceptibility where a River Style has a very low proportion of reaches in good condition or in moderate condition with rapid potential for geomorphic recovery, and vulnerability to alteration whereby geomorphic forms are under threat - directly or indirectly. Completion of NSW River Styles mapping now allows more detailed examination of risk to in-stream value matched to hydrologic stress modelling.