Dam removal: Listening in Foley, M. M.; Bellmore, J. R.; O'Connor, J. E. ...
Water resources research,
July 2017, 2017-07-00, 20170701, Letnik:
53, Številka:
7
Journal Article
Recenzirano
Dam removal is widely used as an approach for river restoration in the United States. The increase in dam removals—particularly large dams—and associated dam‐removal studies over the last few decades ...motivated a working group at the USGS John Wesley Powell Center for Analysis and Synthesis to review and synthesize available studies of dam removals and their findings. Based on dam removals thus far, some general conclusions have emerged: (1) physical responses are typically fast, with the rate of sediment erosion largely dependent on sediment characteristics and dam‐removal strategy; (2) ecological responses to dam removal differ among the affected upstream, downstream, and reservoir reaches; (3) dam removal tends to quickly reestablish connectivity, restoring the movement of material and organisms between upstream and downstream river reaches; (4) geographic context, river history, and land use significantly influence river restoration trajectories and recovery potential because they control broader physical and ecological processes and conditions; and (5) quantitative modeling capability is improving, particularly for physical and broad‐scale ecological effects, and gives managers information needed to understand and predict long‐term effects of dam removal on riverine ecosystems. Although these studies collectively enhance our understanding of how riverine ecosystems respond to dam removal, knowledge gaps remain because most studies have been short (< 5 years) and do not adequately represent the diversity of dam types, watershed conditions, and dam‐removal methods in the U.S.
Key Points
Dam removal is an increasingly common approach to river restoration in the United States
Dam‐removal studies provide insights on key controls influencing the physical and ecological responses to dam removal
Although many aspects of physical and ecological systems react quickly to dam removal, overall response trajectories depend on how and where dams are removed and overall watershed conditions
Until recently, uncertainty quantification in low energy nuclear theory was typically performed using frequentist approaches. However in the last few years, the field has shifted toward Bayesian ...statistics for evaluating confidence intervals. Although there are statistical arguments to prefer the Bayesian approach, no direct comparison is available. In this work, we compare, directly and systematically, the frequentist and Bayesian approaches to quantifying uncertainties in direct nuclear reactions. Starting from identical initial assumptions, we determine confidence intervals associated with the elastic and the transfer process for both methods, which are evaluated against data via a comparison of the empirical coverage probabilities. Expectedly, the frequentist approach is not as flexible as the Bayesian approach in exploring parameter space and often ends up in a different minimum. We also show that the two methods produce significantly different correlations. In the end, the frequentist approach produces significantly narrower uncertainties on the considered observables than the Bayesian. Our study demonstrates that the uncertainties on the reaction observables considered here within the Bayesian approach represent reality more accurately than the much narrower uncertainties obtained using the standard frequentist approach.
The evolution of single-particle strengths as the neutron-to-proton asymmetry changes informs us of the importance of short- and long-range correlations in nuclei and has therefore been extensively ...studied for the last two decades. Surprisingly, the strong asymmetry dependence of these strengths and their extreme values for highly asymmetric nuclei inferred from knockout reaction measurements on a target nucleus are not consistent with what is extracted from electron-induced, transfer, and quasi-free reaction data, constituting a two-decade old puzzle. This work presents the first consistent analysis of one-nucleon transfer and one-nucleon knockout data, in which theoretical uncertainties associated with the nucleon-nucleus effective interactions considered in the reaction models are quantified using a Bayesian analysis. Our results demonstrate that, taking into account these uncertainties, the spectroscopic strengths of loosely bound nucleons extracted from both probes agree with each other and, although there are still discrepancies for deeply bound nucleons, the slope of the asymmetry dependence of the single-particle strengths inferred from transfer and knockout reactions are consistent within 1σ. Both probes are consistent with a small asymmetry dependence of these strengths. The uncertainties obtained in this work represent a lower bound and are already significantly larger than the original estimates.
Understanding river response to sediment pulses is a fundamental problem in geomorphic process studies, with myriad implications for river management. However, because large sediment pulses are rare ...and usually unanticipated, they are seldom studied at field scale. We examine fluvial response to a massive (~20 Mt) sediment pulse released by the largest dam removal globally, on the Elwha River, Washington, United States, in an 11‐year before‐after/control‐impact study of channel morphology and grain size. We test the hypothesis that for a given flow magnitude, greater geomorphic change occurs under sediment‐rich conditions than under sediment‐starved conditions. Channel response to flow forcing was significantly different during the sediment‐pulse peak, 1–2 years after dam removal began, than earlier or later. During peak sediment supply our hypothesis was supported; major geomorphic change occurred under low flows and unit stream power ≤60 W/m2. However, by 4–6 years after dam removal began, rates of geomorphic change and sensitivity to stream power had decreased substantially such that our hypothesis was no longer unequivocally supported. These findings are consistent with a two‐phase conceptual model of dam‐removal response, involving a transport‐limited state followed by a more supply‐limited state. From comparisons with other dam removals and natural sediment pulses, we infer that the longevity of sediment‐pulse signals in gravel‐bed rivers depends upon gradient, river discharge, valley morphology, and sediment grain size. Stream power associated with substantial geomorphic change varies with sediment supply, such that assigning a general threshold stream power to gravel‐bed rivers may be untenable.
Plain Language Summary
In this 11‐year study we investigated sedimentary and geomorphic response to a massive sediment pulse released by the largest dam removal globally, on the Elwha River, Washington, United States. In the most detailed look thus far at river response to a large dam removal, we show that the major response was brief, lasting 5 months, and that the river recovered quickly after this large disturbance. We conclude that the amount of change that happens in a river channel for a certain sized flood depends on how much sediment the river is carrying, as well as on its recent flow history preceding that flood.
Key Points
We present a high‐resolution evaluation of sedimentary and geomorphic response to the largest dam removal thus far
The peak magnitude of dam‐removal response was brief (5 months), as the sediment pulse was exported efficiently from the river
Stream power capable of causing major geomorphic change is sediment‐supply dependent
The English case-control Infectious Intestinal Disease Study (1993-1996) failed to detect an enteric pathogen or toxin in 49% of cases of gastroenteritis. In the present study, polymerase chain ...reaction (PCR) assays were applied to DNA and cDNA generated from 4,627 faecal samples from cases and controls archived during the original study for the detection of norovirus, rotavirus, sapovirus, Campylobacter spp., Salmonella spp., enteroaggregative Escherichia coli, Cryptosporidium spp., and Giardia spp. The percentage of archived samples from cases and from controls in which at least one agent (or toxin) was detected increased from 53% in the original study to 75% and from 19 to 42%, respectively, after the application of PCR assays. Among cases, the following percentages of enteric pathogens were detected: norovirus 36%, rotavirus A 31%, sapovirus 4%, Salmonella spp. 6%, Campylobacter jejuni 13%, Campylobacter coli 2%, other Campylobacter spp. 8%, enteroaggregative E. coli 6%, Giardia spp. 2%, and Cryptosporidium spp. 2%. The present study provides additional insight into the aetiology of infectious intestinal disease in England and highlights the occurrence of viral infections in cases as well as in asymptomatic individuals. Other notable findings include the frequent presence of Campylobacter spp. other than C. jejuni or C. coli, the high frequency of multiple agents in 41% of cases and in 13% of controls, and the variation in the aetiology and rate of infection found for different age groups. The results demonstrate the greater sensitivity of PCR-based methods compared to current conventional methods.
Large wood is an integral part of many rivers, often defining river‐corridor morphology and habitat, but its occurrence, magnitude, and evolution in a river system are much less well understood than ...the sedimentary and hydraulic components, and due to methodological limitations, have seldom previously been mapped in substantial detail. We present a new method for this, representing a substantial advance in automated deep‐learning‐based image segmentation. From these maps, we measured large wood and sediment deposits from high‐resolution orthoimages to explore the dynamics of large wood in two reaches of the Elwha River, Washington, USA, between 2012 and 2017 as it adjusted to upstream dam removals. The data set consists of a time series of orthoimages (12.5‐cm resolution) constructed using Structure‐from‐Motion photogrammetry on imagery from 14 aerial surveys. Model training was optimized to yield maximum accuracy for estimated wood areas, compared to manually digitized wood, therefore model development and intended application were coupled. These fully reproducible methods and model resulted in a maximum of 15% error between observed and estimated total wood areas and wood deposit size‐distributions over the full spatio‐temporal extent of the data. Areal extent of wood in the channel margin approximately doubled in the years following dam removal, with greatest increases in large wood in wider, lower‐gradient sections. Large‐wood deposition increased between the start of dam removal (2011) and winter 2013, then plateaued. Sediment bars continued to grow up until 2016/17, assisted by a partially static wood framework deposited predominantly during the period up to winter 2013.
Plain Language Summary
We measure the large wood in the Elwha River, Washington, USA, during and after dam removal. The presence of two dams had previously limited the movement of sediment and wood through the system. The removal of those dams liberated large amounts of sediment and wood from the former reservoir bottoms, which traveled downstream and deposited in the river channel. We develop an Artificial Intelligence (AI) model to measure all wood and sediment in the Elwha River corridor downstream of the two former dams, from a time‐series of high‐resolution imagery collected from aircraft. These measurements, accurate to within 15% of true values, provide a unique opportunity to understand how large wood occurs and behaves over multiple years and tens of kilometers. We found that the deposition of large wood on bars was coincident with and promoted the growth of sediment bars. The AI model we made could be powerful enough to find large wood in other places and images for similar purposes. Our data sets and models are made available to stimulate further studies of changes in river form resulting from interactions between water flow, wood, sediment, and vegetation.
Key Points
We develop automated methods for detection and mapping of large wood, sediment, vegetation, and water from a time‐series of orthoimagery
High‐resolution, reach‐wide measurements reveal wood dynamics in two Elwha River reaches adjusting to upstream dam removals over 5.5 years
Large wood deposition increased after dam removal, then plateaued, and bars continued to grow assisted by a partially static wood framework
The low-spin structure of the semimagic 64Ni nucleus has been considerably expanded: combining four experiments, several 0+ and 2+ excited states were identified below 4.5 MeV, and their properties ...established. The Monte Carlo shell model accounts for the results and unveils an unexpectedly complex landscape of coexisting shapes: a prolate 0+ excitation is located at a surprisingly high energy (3463 keV), with a collective 2+ state 286 keV above it, the first such observation in Ni isotopes. The evolution in excitation energy of the prolate minimum across the neutron N=40 subshell gap highlights the impact of the monopole interaction and its variation in strength with N.
This work presents a wideband hybrid-fed ±45º linear dual-polarized patch antenna design for sub- 6 GHz 5G base stations. Two polarizations are created by a slot-coupling with rectangular H-slot ...(+45) and a capacitive coupling with modified L-probe (−45). Antenna exhibits wideband −10 dB impedance bandwidths of 40.7% and 35.6% for slot-fed and probe-fed ports, respectively. Due to the special design of suspended stacked patches with hybrid-fed excitations, high port isolation (< −47 dB) and high cross-polar discrimination (> 38 dB) are achieved. Symmetric and directional radiation patterns with stable gain are obtained in E and H planes for each polarization. Compared to its bandwidth, antenna is low-profile (10.6 mm) with front-to-back ratio greater than 22 dB. Simulations and experimental results are reported and discussed.
Fire facilitates erosion through changes in vegetation and soil, with major postfire erosion commonly occurring even with moderate rainfall. As climate warms, the western United States (U.S.) is ...experiencing an intensifying fire regime and increasing frequency of extreme rain. We evaluated whether these hydroclimatic changes are evident in patterns of postfire erosion by modeling hillslope erosion following all wildfires larger than 100 km2 in California from 1984 to 2021. Our results show that annual statewide postfire hillslope erosion has increased significantly over time. To supplement the hillslope erosion modeling, we compiled modeled and measured postfire debris‐flow volumes. We find that, in northern California, more than 50% of fires triggering the top 20 values of sediment mass and sediment yield occurred in the most recent decade (between 2011 and 2021). In southern California, the postfire sediment budget was dominated by debris flows, which showed no temporal trend. Our analysis reveals that 57% of postfire sediment erosion statewide occurred upstream of reservoirs, indicating potential impacts to reservoir storage capacity and thus increased risk to water‐resource security with ongoing climate change.
Plain Language Summary
Large amounts of soil erode following wildfire, particularly if heavy rainfall occurs on the burned area within the first year after the fire. Climate change is increasing wildfires as well as extreme rain in many regions, including California. We investigated whether documented changes in fire and climate in California in the years 1984–2021 resulted in measurable changes in the amount or patterns of sediment produced from soil erosion following wildfire. Using a combination of models and measurements, we estimated annual postfire sediment erosion statewide, and separately for northern and southern California. We found that postfire erosion increased statewide over the time frame of interest. In southern California, postfire sediment erosion is dominated by debris flows, which are a liquefied mix of rock, mud, and soil, and no clear temporal patterns are apparent. In northern California, most cases of major postfire erosion occurred recently between 2011 and 2021. Most of the sediment mass eroded postfire statewide in the years 1984–2021 occurred upstream of reservoirs, rather than in places where sediment would move downstream directly to the ocean. These results indicate increasing pressure on water resources from postfire erosion with ongoing climate change.
Key Points
First multi‐decadal assessment of postfire sediment mobilization in a region with rapidly intensifying fire and hydroclimate regimes
The mass of sediment eroded from hillslopes after wildfire has increased significantly in California since the 1980s
Most postfire sediment erosion occurred upstream of reservoirs, indicating a growing risk to water security
Precise measurements of the lifetimes of the first excited 2+ states in the stable even-A Sn isotopes 112–124Sn have been performed using the Doppler shift attenuation technique. For the isotopes ...112Sn, 114Sn and 116Sn the E2 transition strengths deduced from the measured lifetimes are in disagreement with the previously reported values and indicate a shallow minimum at N=66. The observed deviation from a maximum at mid-shell is attributed to the obstructive effect of the s1/2 neutron orbital in generating collectivity when near the Fermi level.
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