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

Harrison, Lee R.; East, Amy E.; Smith, Douglas P.; Logan, Joshua B.; Bond, Rosealea M.; Nicol, Colin; Williams, Thomas H.; Boughton, David A.; Chow, K. C. Ander; Luna, L.

doi:10.1002/esp.4464

Cited by 19 publications

(59 citation statements)

References 79 publications

(119 reference statements)

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“…Sediment pulses from other dam removals have also been associated with channel fining, including higher-gradient removals such as those on the Elwha River (East et al, 2018) and in lower-gradient channels (Harrison et al, 2018). Channel fining and homogenization is likely a primary explanation for faster recovery of stage than bed elevation, as losses in cross-sectional area due to bed aggradation can be compensated by increases in flow velocity, even given equivalent stage and discharge.…”

Section: Discussionmentioning

confidence: 99%

Channel response to a dam‐removal sediment pulse captured at high‐temporal resolution using routine gage data

Cashman

Gellis

Boyd

et al. 2021

Earth Surf Processes Landf

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In this study, we captured how a river channel responds to a sediment pulse originating from a dam removal using multiple lines of evidence derived from streamflow gages along the Patapsco River, Maryland, USA. Gages captured characteristics of the sediment pulse, including travel times of its leading edge ($7.8 km yr −1 ) and peak ($2.6 km yr −1 ) and suggest both translation and increasing dispersion. The pulse also changed local hydraulics and energy conditions, increasing flow velocities and Froude number, due to bed fining, homogenization and/or slope adjustment. Immediately downstream of the dam, recovery to pre-pulse conditions occurred within the year, but farther downstream recovery was slower, with the tail of the sediment pulse working through the lower river by the end of the study 7 years later.The patterns and timing of channel change associated with the sediment pulse were not driven by large flow or suspended sediment-transporting events, with change mostly occurring during lower flows. This suggests pulse mobility was controlled by process-factors largely independent of high flow.In contrast, persistent changes occurred to out-of-channel flooding dynamics. Stage associated with flooding increased during the arrival of the sediment pulse, 1 to 2 years after dam removal, suggesting persistent sediment deposition at the channel margins and nearby floodplain. This resulted in National Weather Serviceindicated flood stages being attained by 3-43% smaller discharges compared to earlier in the study period.This study captured a two-signal response from the sediment pulse: (1) short-to medium-term (weeks to months) translation and dispersion within the channel, resulting in aggradation and recovery of bed elevations and changing local hydraulics; and (2) dispersion and persistent longer-term (years) effects of sediment deposition on overbank surfaces. This study further demonstrated the utility of US Geological Survey gage data to quantify geomorphic change, increase temporal resolution, and provide insights into trajectories of change over varying spatial and temporal scales.

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Section: Discussionmentioning

confidence: 99%

Channel response to a dam‐removal sediment pulse captured at high‐temporal resolution using routine gage data

Cashman

Gellis

Boyd

et al. 2021

Earth Surf Processes Landf

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“…Our stream geometry data pre‐ and post‐removal (Figures 5‐8) demonstrate how channel shapes change very little when impoundments storing relatively small quantities of mobile sediment are removed from erosion‐resistant streambeds. The channel of the lower Penobscot River was also not sensitive to two ~10‐year floods during the study period, illustrating how a coarse‐bedded/bedrock reach can be resistant to multiple disturbance mechanisms (Harrison et al, 2018).…”

Section: Discussionmentioning

confidence: 89%

“…Our hypothesis for question 2 was “yes” because the coarse substrates bedding each impoundment had interstitial sands (described below). Two approximately 10‐year recurrence interval floods happened during our study, giving us the unexpected opportunity to also provide more information about the effects of floods post‐dam removal, a knowledge gap noted by Harrison et al (2018) as important for anticipating river response.…”

Section: Introductionmentioning

confidence: 86%

“…Many physical studies of dam removals targeted sites storing appreciable quantities of sediment (e.g., Major et al, 2012; Wilcox et al, 2014; Collins et al, 2017; East et al, 2018; Harrison et al, 2018), especially the few investigating dams ≥10 m high (Bellmore et al, 2017; Duda, Johnson, Wieferich, Wagner, & Bellmore, 2020). These locations were chosen for that attribute because there is great interest in how channels respond to large sediment releases.…”

Section: Introductionmentioning

confidence: 99%

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River channel response to dam removals on the lower Penobscot River, Maine, United States

Collins

Kelley

Lombard

2020

River Research & Apps

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Most geomorphology studies of dam removals have focused on sites with appreciable quantities of stored sediments. There is great interest in channel responses to sediment releases because of potential effects on aquatic and riparian habitats and human uses of these areas. Yet, behind many dams in the Northeast U.S. and other regions of the world only minor accumulations of sediment are present because of small impoundments, run‐of‐river dam design and management (inflow ≈ outflow), low watershed sediment yield, and/or channel beds dominated by coarse sediment and/or bedrock. The two lowermost dams on the Penobscot River in Maine, United States, removed in 2012–2013, exemplified those conditions. Great Works and Veazie dams were about 6 and 10 m high, respectively. Pre‐project geophysical surveys showed coarse substrates dominated the reservoir beds and little sediment was stored in either impoundment—functions of reach geology, late Quaternary history, and upstream dams. Repeat cross‐section surveys in each impoundment, as well as the upstream and downstream reaches, were completed from 2009 to 2015 to evaluate channel morphology responses to the removals. Bed‐sediment grain size and turbidity were also measured to characterize changes in bed texture and suspended sediment. Pre‐ and post‐removal survey comparisons confirmed the expectation that bed elevations, channel shapes, and channel positions would not change substantially. Changes were often within, or close to, our estimated random measurement error. Our study shows that large‐scale physical changes are likely to be minimal when impoundments storing relatively little sediment are removed from erosion‐resistant streambeds. Many dams eligible for removal have these characteristics, making these observations an important case study that is largely unrepresented in the dam removal literature.

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“…Morgan (2018) reports that bar-pool relief decreased for a doubling of sediment supply in an experimental channel forced by sinusoidal width variations. East et al (2015) and Harrison et al (2018) report on downstream observations following the removal of dams on the Elwha and Carmel Rivers, respectively, and indicate that the immediate channel response to a significant increase of bedload sediment is a tendency to increase bed elevations on average, the filling of pools, and fining of the bed surface. However, the details of local channel response depend on many different contributing factors, including downstream distance from sediment supply sources, the sequence and magnitude of floods following sediment releases, as well as the relative confinement and valley/active river width ratios of downstream reaches (e.g., East et al, 2015;Morgan, 2018;Müller & Hassan, 2018;Nelson et al, 2015;Pizzuto, 2002).…”

Section: Pool-riffle Response To Upstream Supply Changesmentioning

confidence: 99%

Pool‐Riffle Adjustment Due to Changes in Flow and Sediment Supply

Hassan

Radić

Buckrell

et al. 2021

Water Resources Research

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How do gravel bed pool‐riffle streams adjust to changing upstream water and bedload sediment supplies, and what analysis techniques can help to effectively identify how change occurs? Here, we use a mixture of field and experimental data to examine these problems and apply a suite of traditional and novel analysis approaches to highlight dynamics which might otherwise go undetected. Eleven years of monitoring channel morphology in a small forested watershed indicate that pool‐riffles persist through large changes in upstream water and bedload supply and that bed architecture relief is correlated to flow magnitude. A flume experiment consisting of eight runs was conducted to examine the field case in more detail. The experimental design splits the eight runs into four runs of relatively high water and sediment supply and four of relatively low water supply, with no upstream sediment supply. Experimental results corroborate the field‐based measurements of pool‐riffle persistence, which is due to a coupling between downstream width variations, and spatial patterns of flow velocity and bedload transport. More specifically, measurements made during the flume experiments along a prominent pool‐riffle pair indicate that temporal and spatial changes to topography, flow hydraulics, and bed surface sediment texture are more rich and nuanced than existing generalizations offer. For example, clustering analysis completed using self‐organizing maps indicates that sediment sorting between pools and riffles is not simply a binary type response of finer versus coarser described by some characteristic grain size.

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

Cited by 19 publications

References 79 publications

Channel response to a dam‐removal sediment pulse captured at high‐temporal resolution using routine gage data

Channel response to a dam‐removal sediment pulse captured at high‐temporal resolution using routine gage data

River channel response to dam removals on the lower Penobscot River, Maine, United States

Pool‐Riffle Adjustment Due to Changes in Flow and Sediment Supply

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