A mechanistic understanding of channel evolution following dam removal

Bedload tracing with RFID tags in gravel‐bed rivers: Review and meta‐analysis after 20 years of field and laboratory experiments

“…The employment of RFID tracers for evaluating the effect of hydraulic structures (dams, weirs and check‐dams) on the longitudinal sediment continuity is an emerging topic of the last 3 years, with several dedicated field experiments in gravel‐bed rivers of Europe (Brenna et al, 2020; Brousse, Arnaud‐Fassetta, et al, 2020; Casserly et al, 2020, 2021; Galia et al, 2021; Gilet et al, 2021; Peeters et al, 2020) and North America (Fields et al, 2021; Magilligan et al, 2021). This reflects the growing concern of water management policies (e.g., EU Water Framework Directive) in restoring the connectivity of fragmented fluvial reaches, which are now common with the multiplication of in‐channel barriers (Belletti et al, 2020).…”

“…PIT tags were also recently used to document the effect of dam removal in a gravel-bed river of NE France (Gilet et al, 2021) and showed that the bedload continuity has been efficiently restored, but the downstream channel morphology remained unchanged. Critical shear stress over the course of channel recovery following dam removal has been constrained with smart rocks equipped with PIT tags and accelerometers, providing evidences of the rapid post-removal formation of a threshold channel (Fields et al, 2021).…”

Six years of fluvial response to a large dam removal on the Carmel River, California, USA

“…East et al (2018) and Ritchie et al (2018) observed only modest downstream geomorphic change on the Elwha River, Washington, due to a 10‐year flood 4 years after the removal of two large dams (64 and 32 m high), whereas earlier in the dam‐removal time frame abundant sediment transport and geomorphic change had occurred under low to moderate flows (East et al, 2015; Magirl et al, 2015). Based on hydraulic modelling of reach morphology after removal of a 4 m‐high dam, Fields et al (2021) proposed that the rate of geomorphic adjustment after dam removal depends on the time needed for temporarily elevated critical Shields values (caused by increased fine‐sediment supply) to decrease below that expected for the 2‐year flood. Having measured the response of the Carmel River, California, to removal of a 32 m‐high dam and erosion from a partially sequestered reservoir‐sediment deposit, Harrison et al (2018) proposed that large floods early in the post‐dam‐removal time frame are relatively more important in driving downstream fluvial response than large floods occurring later.…”

Channel Response and Reservoir Delta Evolution From Source to Sink Following an Extreme Flood

“…First, a sediment flux decay is a characteristic post‐disturbance channel response (Dadson et al., 2004; Major et al., 2000; Nelson & Dubé, 2016; Pitlick, 1993; Rathburn et al., 2018; Umbal, 1997), although in one setting sediment flux increased over time (Dethier et al., 2016). Second, narratives or conceptual models of post‐disturbance rivers are common and include pathways of response controlled by hydraulic variables such as shear stress relative to incipient motion (Rathburn & Wohl, 2003), bankfull Shields criteria compared to Shields criteria (Fields et al., 2021), a response progression from lahar to fluvial to ecological response (Gran & Montgomery, 2005), response that leads to long‐term sediment persistence (Grimsley et al., 2016; Moody & Martin, 2001), or revegetation of flood sediments by native species (Costa, 1974) or encroachment of upland species (Schook et al., 2017) that stabilize the landscape. Finally, most post‐disturbance studies span 1–5 years (Dadson et al., 2004; Moody & Martin, 2001; Nelson & Dubé, 2016; Pitlick, 1993), with many fewer studies over an intermediate time scale of 6–10 years (e.g., 8 years in Gran & Montgomery, 2005), and even fewer multi‐decadal, post‐disturbance data sets (Moody & Meade, 2018; Major et al., 2000, 2021).…”