River-channel topography, grain size, and turbidity records from the Carmel River, California, before, during, and after removal of San Clemente Dam

East, Amy E.; Harrison, Lee R.; Smith, Douglas P.; Bond, Rosealea M.; Logan, Joshua B.; Nicol, Colin; Chow, K. C. Ander

doi:10.5066/f74m93hf

Cited by 2 publications

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“…If the downstream sites were recovering spawning gravel through additions from upstream sources, we would expect the upstream sites to be showing the recovery first. The 3 km long reach of river immediately downstream of the former dam (sites DM and SH; Figure 1) were armored by large cobble and boulder bed material at the time that the dam was removed (East et al, 2017). Following dam removal those sites remained generally too coarse for steelhead nests, except for pools and runs, which were filled by sand and fine gravel that was too fine (Chow et al, 2016;Harrison et al, 2018).…”

Section: Resultsmentioning

confidence: 99%

“…We have two main goals. First, we further evaluate the magnitude and duration of the post-dam sediment pulse on the Carmel River by extending and reanalyzing the data (East et al, 2017) used by Harrison et al (2018). Second, we fully describe and interpret several fire-mediated debris flows impacting the Carmel River near two of our long-term study sites, a rare opportunity afforded by the 2020 Carmel Fire.…”

Section: Study Goalsmentioning

confidence: 99%

“…Using a habitat suitability model modified from Dettman and Hanna (1991), they found that in addition to spawning-gravel impairment along most of the river, gravel deposition immediately downstream of the former dam had locally improved spawning habitat (Harrison et al, 2018). Our work reanalyzes the 2013 to 2017 Harrison et al (2018) grain size data set (East et al, 2017), and adds an additional four years (2018-2021) to further assess the temporal and spatial substrate impacts generated by the post-San Clemente Dam sediment pulse.…”

Section: Introductionmentioning

confidence: 95%

“…A sustainable source of spawning sized gravel in the Carmel River is required to foster recovery of steelhead in the post-dam era. Gravel of the appropriate size for redd construction was abundant upstream of the relict reservoir material in 2017 (site "CR" of Figure 1; Harrison et al, 2018;East et al, 2017), but that material did not reach the lower river in significant quantity in 2017 despite the potential for bedload transport generated by two 10-year and one 25-year to 30-year flood event in that year (Harrison et al, 2018;Smith et al, 2020). The long-term reestablishment of significant gravel transport might therefore hinge on removal of Los Padres Dam, located 7 km higher in the watershed (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Influence of a Post-dam Sediment Pulse and Post-fire Debris Flows on Steelhead Spawning Gravel in the Carmel River, California

et al. 2021

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Spawning gravel scarcity is a limiting factor for successful recovery of federally-threatened anadromous fish like steelhead of central California. A BACI-experimental design using bed particle counts from 2013 through 2021 shows that spawning-sized gravel (32–90 mm) diminished downstream of the former San Clemente Dam site in 2017, following dam removal in 2015. High flows in 2017 transported a pulse of sand and fine-gravel that filled pools and runs throughout the river below the dam. The bed material in the 3 km closest to the dam remained too coarse for redds in riffles and too fine in pools and runs. Time-series bathymetric data of the Los Padres Dam reservoir located in the upper Carmel watershed shows that nearly all bed material (including spawning gravel) in the upper Carmel River watershed was recruited during wet winters that immediately followed expansive wildfires. We studied that effect in detail following the Carmel Fire of August 2020, which preconditioned the slopes adjacent to the Carmel River for debris flows. Our analysis of several fire-mediated debris flows in 2021 show that they contained virtually no mud and held approximately 45% spawning-sized gravel. Although the debris flows contained abundant spawning gravel, and several flow snouts terminated in the Carmel River, the material was dispersed downstream rather than forming bars and patches that could be used for steelhead nest building. The generally small volume of material in the flows relative to the size of the river channel and impediments to debris flow runout limited the contribution of spawning-size gravel to the river.

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Section: Resultsmentioning

confidence: 99%

Section: Study Goalsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Influence of a Post-dam Sediment Pulse and Post-fire Debris Flows on Steelhead Spawning Gravel in the Carmel River, California

et al. 2021

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River response to large‐dam removal in a Mediterranean hydroclimatic setting: Carmel River, California, USA

Harrison

East

Smith

et al. 2018

Earth Surf Processes Landf

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Dam removal provides a valuable opportunity to measure the fluvial response to changes in both sediment supply and the processes that shape channel morphology. We present the first study of river response to the removal of a large (32‐m‐high) dam in a Mediterranean hydroclimatic setting, on the Carmel River, coastal California, USA. This before‐after/control‐impact study measured changes in channel topography, grain size, and salmonid spawning habitat throughout dam removal and subsequent major floods. During dam removal, the river course was re‐routed in order to leave most of the impounded sediment sequestered in the former reservoir and thus prevent major channel and floodplain aggradation downstream. However, a substantial sediment pulse occurred in response to base‐level fall, knickpoint migration, and channel avulsion through sediment in the former reservoir above the newly re‐routed channel. The sediment pulse advanced ~3.5 km in the first wet season after dam removal, resulting in decreased riverbed grain size downstream of the dam site. In the second wet season after dam removal, high flows (including a 30‐year flood and two 10‐year floods) transported sediment > 30 km downstream, filling pools and reducing cross‐channel relief. Deposition of gravel in the second wet season after dam removal enhanced salmonid spawning habitat downstream of the dam site. We infer that in dam removals where most reservoir sediment remains impounded and where high flows follow soon after dam removal, flow sequencing becomes a more important driver of geomorphic and fish‐habitat change than the dam removal alone. © 2018 John Wiley & Sons, Ltd.

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River-channel topography, grain size, and turbidity records from the Carmel River, California, before, during, and after removal of San Clemente Dam

Cited by 2 publications

References 0 publications

Influence of a Post-dam Sediment Pulse and Post-fire Debris Flows on Steelhead Spawning Gravel in the Carmel River, California

Influence of a Post-dam Sediment Pulse and Post-fire Debris Flows on Steelhead Spawning Gravel in the Carmel River, California

River response to large‐dam removal in a Mediterranean hydroclimatic setting: Carmel River, California, USA

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