The Shifting Sands of Stockyard Creek: the geomorphic response to large wood reintroduction in a sand-bed stream

Abstract

Key Points 場he reintroduction of wood through the construction of Engineered Log Jams (ELJs), can successfully increase geomorphic diversity and stability in an incised, partly confined sand-bed stream 堅LJs can provide a stable pool habitat that would otherwise have not existed without intervention. 堅LJ design and frequency can significantly affect patterns of pool and bar development 堔he increased habitat provided by constructed ELJs is further enhanced by natural wood recruitment and the colonisation of in-channel vegetation within sand-bed streams Abstract In April 2002, 26 Engineered Log Jams (ELJs) were built within a 2 km treatment reach of what was a degraded ephemeral sand-bed stream at Stockyard Creek, Wollombi, NSW. Coupled with ~ 20 years of ongoing native revegetation this project aimed to increase the geomorphic diversity and ecological characteristics of the ephemeral stream. The experiment was set up as a standard Before-After Control-Impact (BACI) design, with a control reach situated in the upstream limit of the study site and the incorporation of an external control reach in an adjacent valley. This paper aims to assess the geomorphic response to the re-introduction of wood by comparing treatment and control reaches. Since construction, the ELJs have experienced a 5 year period of low or no flow conditions, as well as two major bed mobilising flood events which occurred in June 2007 and February 2013, and a number of smaller flow events. Four detailed topographic surveys of the study reach were completed during the 11 year study period and have been used to construct Digital Elevation Models (DEMs) of the in-channel bed topography. Geomorphic change detection analysis suggests the magnitude of change within the treatment reaches was much greater than that of the control, with the most pronounced response to ELJ introduction being the development of persistent pool habitat