Reintroducing wood to streams in agricultural landscapes: changes in velocity profile, stage and erosion rates

Abstract

Historically, perceived increases in erosion and flooding levels have been attributed to in-stream wood and used to justify its removal from streams and rivers around the world. More recently, recognition of the adverse morphological and biological impacts caused by this removal has led to rehabilitation projects that actively reintroduce wood to streams. However, a perception remains amongst some members of the general community that wood additions increase the likelihood of flooding and erosion in the target streams.To test whether there was a basis for this perception, we experimentally added wood to eight streams across southwest Victoria and Gippsland, Australia. The velocity, stage and bed and bank erosion rates were compared with those of unaltered reaches. We detected localized changes in the velocity and stage parameters but that these were unlikely to operate at the reach-scale. Bed erosion rates, where maximum erosion was assumed if pins were not recovered, showed increased erosion due to wood additions but this was not supported by channel shape analyses, which identified short-term increases in the variability of the channel shape, followed by longer-term stability at treatment sites.We found no clear evidence of increased longer-term rates of erosion or flooding associated with the introduction of wood to streams over the 18-month study period. It remains important to carefully design rehabilitation works, but the lack of adverse effects on stream morphology and increased variability of the in-stream environment suggests improved habitat diversity, supporting the use of wood addition as a stream rehabilitation technique.

Does reintroducing large wood influence the hydraulic landscape of a lowland river at multiple discharges?

“…These results reject both hypotheses. Our study results contrast those of previous studies that have shown that reintroducing large wood had positive influences on hydraulics when assessed at smaller scales (sites or individual pieces; Lehane et al, ; Lester & Wright, ; Shields, Knight, Morin, & Blank, ). However, this study reinforces the findings of a study by Matheson et al (in press), which showed little difference between managed and control reaches over a sequence of low flows.…”

Log‐jams and avulsions in the San Antonio River Delta, Texas

“…Perceived increases in flooding are commonly attributed to in‐stream wood, but several studies have shown that in most cases LWD effects on river stages are minimal, though other significant hydraulic impacts occur locally (Young, ; Lester and Wright, ; Phillips and Park, ). However, very high densities of wood, particularly at constrictions, can dam channels sufficiently to increase flooding.…”

Effects of fine wood on macroinvertebrate drift in four boreal forest streams

“…In small streams, FW can contribute substantially to the stream wood load (Triska & Cromack, 1980) and probably play a significant ecological role. Several authors recognise that FW ought to affect stream-dwelling organisms (Triska & Cromack, 1980;O'Connor, 1991;Hoffmann & Hering, 2000;Collier & Bowman, 2003;Lester & Wright, 2009). For instance, very small pieces of wood can serve as invertebrate habitat (Hoffmann & Hering, 2000) of high structural complexity.…”

“…Stream wood is an important habitat structure for stream invertebrates and fish (Angermeier & Karr, 1984;Benke & Wallace, 2003;Kimbirauskas et al, 2008;Lester & Wright, 2009). Large wood (LW) can affect streams by changing the characteristics of flow and structure (Bilby & Ward, 1989;Beechie & Sibley, 1997), by increasing the retention of nutrients and energy (Smock et al, 1989) and by providing sites for invertebrate attachment and feeding (Eggert & Wallace, 2007;Spänhoff & Cleven, 2010).…”