Logjam controls on channel:floodplain interactions in wooded catchments and their role in the formation of multi-channel patterns

Abstract

The role of wood in the formation and maintenance of complex dynamic floodplain surfaces is important and to date has received relatively limited attention compared to in-channel habitat processes. This paper explores the role of logjams as important agents of channel:floodplain interaction. We draw on a specific case study as well as examples from the literature to show that although the processes of interaction differ, the resulting dynamic floodplain patchwork is a common feature of rivers with logjams. In addition, we contend that the presence of logjams is an important factor in the evolution and maintenance of multiple channel patterns in both montane and lowland river environments. These observations have important implications for the definition of reference targets for river restoration. The specific results of this research show:1) The presence of a range of types of multiple channel network dissecting the floodplains of low order channels that are strongly associated with the presence of logjams. 2) The relatively rapid formation of floodplain channels following logjam formation.3) The dynamic nature of logjams within headwater channels on both seasonal and annual timescales that lead to a highly dynamic habitat mosaic on the floodplain surface. 4) An increased frequency of overbank flooding and high rates of floodplain sediment accumulation upstream of logjams and along floodplain channel networks that create the complex topography observed in the case study forested floodplains.

Natural vs anthropogenic streams in Europe: History, ecology and implications for restoration, river-rewilding and riverine ecosystem services

“…Similarly, low width:wood ratios promote the formation of logjams, that force floodplain dissection by overflow channels, and increased water levels upstream of jams. Rates of sediment and organic matter transport from headwaters are strongly influenced by logjam dynamics (Assini and Petiti, 1995;Sear et al, 2010). However, by c. 2,200 BP (the late European Iron Age) human-induced alluviation had changed floodplain and channel morphology and ecology throughout temperate Europe, and floodplains were extensively used for agriculture (Brown, 1997a;Stobbe, 1996Stobbe, , 2012.…”

Scaling down hyporheic exchange flows: from catchments to reaches

“…Wood also interacts with groundwater dynamics: debris dams positioned along gaining stream segments have an effect comparable to tight meander bends, driving water into the subsurface, where it travels along short hyporheic flow paths (Lautz et al, 2006;Boano et al, 2006). Interactions between flow and wood also produce spatial heterogeneity in deposits of sediments and organic matter (Gregory et al, 1991;Naiman et al, 2005;Latterell et al, 2006, Sear et al, 2010Osei et al, 2015). Fines and organic rich sediments are retained, eventually driving higher spatial 20 heterogeneity in HEF (Section 5.2 and 6).…”

“…Creek, a Sonoran Desert stream - Schade et al, 2002Schade et al, , 2005 where soils are often highly impermeable and the presence of riparian vegetation is dependent on stream flows and shallow groundwater tables (Stromberg and Patten, 1991;Stromberg et al, 1996;Schade et al, 2002;Schade et al, 2005). Arid catchments are potentially a sink for streamwater N (Peterjohn and Correll 1984; Hill et al, 1998;Hill 2000) by transformation of N and P by rooted vegetation.…”

“…Wood that is large relative to the river channel significantly impacts flow hydraulics, sediment transfer, and habitat conditions (Osei et al, 2015). Several studies have documented the importance of woody debris in shaping the channel patterns and floodplain evolution in a variety of environments (Piégay and Marston, 1998;Collins and Montgomery, 2002; 30 Abbe and Montgomery, 2003;Jeffries et al, 2003;Millington and Sear, 2007;Sear et al 2010)…”

Wood-mediated geomorphic effects of a jökulhlaup in the Wind River Mountains, Wyoming

“…Wood alters bed-surface grain size and sediment storage (Faustini and Jones, 2003;Ryan et al, 2014) to the point of creating forced-alluvial reaches of lower gradient than might otherwise be present (Montgomery et al, 1995(Montgomery et al, , 2003 and alters bedform configuration (Baillie and Davies, 2002;Gomi et al, 2003). Wood increases resistance of the channel boundary to erosion (Brooks et al, 2003) and creates jams that promote channel avulsion, anastomosing channel planform, and overbank flow (Collins and Montgomery, 2001;Jeffries et al, 2003;O'Connor et al, 2003;Montgomery and Abbe, 2006;Collins et al, 2012), as well as enhanced floodplain deposition (Sear et al, 2010).…”