River Channel Change Following Dam Removal in an Ephemeral Stream

Abstract

Dam removal is becoming increasingly common for both small and large structures and is motivated by both environmental (e.g. re-establishing longitudinal connectivity) and engineering (e.g. safety) issues. Fluvial systems respond to dam removal by adjusting their forms through various processes and at varying rates. While limited research has investigated these adjustment mechanisms in perennial systems, little is understood regarding these mechanisms in ephemeral systems. The aim of this study is to analyse the geomorphic responses of the ephemeral Bushrangers Creek, central western New South Wales, Australia, following the 2002 removal of a 15 m high dam. Comparisons of pre- and post-dam removal survey data indicate that there has been repeated base-level lowering upstream of the former dam site. Longitudinal profiles of the thalweg before and after dam removal show an average bed lowering of 0.5 m and reveal that a 90 m long channel with a slope in excess of two-times greater than the pre-dam removal channel has formed upstream of the former dam wall.