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131.
The moisture content ws of a beach surface strongly controls the availability of sand for aeolian transport. Our predictive capability of the spatiotemporal variability in ws, which depends to a large extent on water table depth, is, however, limited. Here we show that water table fluctuations and surface moisture content observed during a 10-day period on a medium-grained (365μm) planar (1:30) beach can be predicted well with the nonlinear Boussinesq equation extended to include run-up infiltration and a soil–water retention curve under the assumption of hydrostatic equilibrium. On the intertidal part of the beach the water table is observed and predicted to continuously fall from the moment the beach surface emerges from the falling tide to just before it is submerged by the incoming tide. We find that on the lower 30% of the intertidal beach the water table remains within 0.1–0.2 m from the surface and that the sand is always saturated (ws≈20%, by mass). Higher up on the intertidal beach, the surface can dry to about 5% when the water table has fallen to 0.4–0.5 m beneath the surface. Above the high-tide level the water table is always too deep (>0.5 m) to affect surface moisture and, without precipitation, the sand is dry (ws < 5 − 8%). Because the water table depth on the emerged part of the intertidal beach increases with time irrespective of whether the (ocean) tide falls or rises, we find no need to include hysteresis (wetting and drying) effects in the surface-moisture modelling. Model simulations suggest that at the present planar beach only the part well above mean sea level can dry sufficiently (ws < 10%) for sand to become available for aeolian transport. ©2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
132.
Saverio Romeo Lucio Di Matteo Laura Melelli Corrado Cencetti Walter Dragoni Andrea Fredduzzi 《Landslides》2017,14(4):1457-1465
On October 30, 2016, a seismic event and its aftershocks produced diffuse landslides along the SP 209 road in the Nera River Gorge (Central Italy). Due to the steep slopes and the outcropping of highly fractured and bedded limestone, several rockfalls were triggered, of which the main event occurred on the slope of Mount Sasso Pizzuto. The seismic shock acted on a rock wedge that, after an initial slide, developed into a rockfall. The debris accumulation blocked the SP 209 road and dammed the Nera River, forming a small lake. The river discharge was around 3.6 m3/s; the water overtopped the dam and flooded the road. By a preliminary topographic survey, we estimated that the debris accumulation covers an area of about 16,500 m2, while the volume is around 70,000 m3. The maximum volume occupied by the pre-existing talus mobilized by the rockfall is about 20% of the total volume. Besides blocking the road, the rockfall damaged a bridge severely, while, downstream of the dam, the water flow caused erosion of a road embankment. A rockfall protection gallery, a few hundred meters downstream of the dam, was damaged during the event. Other elastic nets and rigid barriers were not sufficient to protect the road from single-block rockfalls, with volumes around 1–2 m3. Considering the geological and geomorphological conditions, as well as the high seismicity and the socioeconomic importance of the area, a review of the entire rockfall protection systems is required to ensure protection of critical infrastructure and local communities. 相似文献
133.
134.
Patricia M. Clayton Ching‐Yi Tsai Jeffrey W. Berman Laura N. Lowes 《地震工程与结构动力学》2015,44(12):2093-2110
Previous research has shown that self‐centering steel plate shear walls (SC‐SPSWs) are capable of achieving enhanced seismic performance at multiple hazard levels, including recentering following design‐level earthquakes. When modeling SC‐SPSWs numerically, these studies considered an idealized tension‐only steel plate shear wall (SPSW) web plate behavior. Research has shown that web plate behavior is more complex than predicted by the idealized model, and web plates can provide more strength, stiffness, and energy dissipation than predicted by the idealized model. The idealized model of web plate behavior is used widely in SPSW numerical models where the moment‐resisting boundary frame provides supplemental hysteretic damping and stiffness; however, in SC‐SPSWs, where the post‐tensioned boundary frame is designed to remain elastic during an earthquake, accounting for the more complex web plate behavior can have a significant impact on seismic performance estimates from numerical simulation. This paper presents different methods for modeling SC‐SPSWs. Responses from these models are compared with experimental results. A simple modification of the tension‐only model, referred to as the tension‐compression strip model, is shown to provide a reasonable approximation of SC‐SPSW behavior. Results from nonlinear response history analyses of SC‐SPSWs with the tension‐only and tension‐compression web plate models are compared to assess how the approximation of web plate behavior affects SC‐SPSW seismic performance. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
135.
Recent shifts in coastline change and shoreline stabilization linked to storm climate change 总被引:1,自引:0,他引:1 下载免费PDF全文
Jennifer M. Johnson Laura J. Moore Kenneth Ells A. Brad Murray Peter N. Adams Richard A. MacKenzie III John M. Jaeger 《地球表面变化过程与地形》2015,40(5):569-585
Since cuspate coastlines are especially sensitive to changes in wave climate, they serve as potential indicators of initial responses to changing wave conditions. Previous work demonstrates that Cape Hatteras and Cape Lookout, North Carolina, which are largely unaffected by shoreline stabilization efforts, have become increasingly asymmetric over the past 30 years, consistent with model predictions for coastline response to increases in Atlantic Ocean summer wave heights and resulting changes in the distribution of wave‐approach angles. Historic and recent shoreline change observations for Cape Fear, North Carolina, and model simulations of coastline response to an increasingly asymmetric wave climate in the presence of beach nourishment, produce comparable differences in shoreline change rates in response to changes in wave climate. Results suggest that the effect of beach nourishment is to compensate for – and therefore to mask – natural responses to wave climate change that might otherwise be discernible in patterns of shoreline change alone. Therefore, this case study suggests that the effects of wave climate change on human‐modified coastlines may be detectable in the spatial and temporal patterns of shoreline stabilization activities. Similar analyses of cuspate features in areas where the change in wave climate is less pronounced (i.e. Fishing Point, Maryland/Virginia) and where local geology appears to exert control on coastline shape (i.e. Cape Canaveral, Florida), suggest that changes in shoreline configuration that may be arising from shifting wave climate are currently limited to sandy wave‐dominated coastlines where the change in wave climate has been most pronounced. However, if hurricane‐generated wave heights continue to increase, large‐scale shifts in patterns of erosion and accretion will likely extend beyond sensitive cuspate features as the larger‐scale coastline shape comes into equilibrium with changing wave conditions. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
136.
Luigi Sorrentino Laura Liberatore Luis D. Decanini Domenico Liberatore 《Bulletin of Earthquake Engineering》2014,12(5):2299-2331
In this study the damage suffered by churches during the 2012 Emilia seismic sequence in Italy is analysed, based on surveys and inspections carried out in the area. Similarly to what was observed after other Italian earthquakes, the damage to churches was severe. However, the Emilia churches present some characteristic features such as the use of unreinforced clay brick masonry. In order to appropriately address the performance of this class of buildings, typical architectural layouts and construction techniques are described. Such techniques are interpreted also in the light of the local seismic catalogue. Fifty churches are then selected and their damage is studied, with reference to typical local-collapse mechanisms of different macro-elements. The study highlights that the damage is often concentrated at the top section of the façade, in the clerestory walls, in the vaults and in the bell towers. Structural analyses are performed to explain some of the observations. The overturning of the top section of the façade is analytically addressed, modelling the friction interlocking. With reference to the case study of San Francesco in Mirandola, non-linear static and dynamic analyses allow us to correlate the directionality of damage to the higher seismic demand along the NS direction, to point out the negligible role of the large vertical component of ground motion and to emphasise the relevance of the buttresses for the seismic response of the façade. 相似文献
137.
138.
Between 2001 and 2005, a large debris rock slide occurred on the western slope of the Cordillera de Santa Cruz in the southeast
Andean corner of the Province of San Juan (31°40′ S–70°16′ W). The landslide material accumulated in a downstream gorge as
a natural dam of the Santa Cruz river, forming a large-volume lake. In November 2005, probably as a result of the increasing
pressure of the water volume, this natural dam breached off with a violent and unexpected flash flood. In addition to life-threatening
instances lived by some people downstream, this flood caused great economic loss to main localities of the Department of Calingasta,
as well as considerable damage to one of the most relevant projects of the Province, the Caracoles Hydropower Project dam
on the San Juan river. Considering the high costs of any physical remediation for a natural dam located in this high, remote,
and inaccessible mountain area with no reliable road access, the main protective measures left to be pondered are the installation
of a flash-flood early-warning system connected to downstream localities, along with a program of hydrological monitoring
at the dam-forming area and annual satellital monitoring to verify the evolution of accumulated mass movements. 相似文献
139.
Jennifer L. Lewicki George E. Hilley Laura Dobeck Bruno D. V. Marino 《Bulletin of Volcanology》2012,74(1):135-141
Use of eddy covariance (EC) techniques to map the spatial distribution of diffuse volcanic CO2 fluxes and quantify CO2 emission rate was tested at the Horseshoe Lake tree-kill area on Mammoth Mountain, California, USA. EC measurements of CO2 flux were made during September–October 2010 and ranged from 85 to 1,766 g m−2 day−1. Comparative maps of soil CO2 flux were simulated and CO2 emission rates estimated from three accumulation chamber (AC) CO2 flux surveys. Least-squares inversion of measured eddy covariance CO2 fluxes and corresponding modeled source weight functions recovered 58–77% of the CO2 emission rates estimated based on simulated AC soil CO2 fluxes. Spatial distributions of modeled surface CO2 fluxes based on EC and AC observations showed moderate to good correspondence (R
2 = 0.36 to 0.70). Results provide a framework for automated monitoring of volcanic CO2 emissions over relatively large areas. 相似文献
140.
Laura Sandri Gill Jolly Jan Lindsay Tracy Howe Warner Marzocchi 《Bulletin of Volcanology》2012,74(3):705-723
By using BET_VH, we propose a quantitative probabilistic hazard assessment for base surge impact in Auckland, New Zealand.
Base surges resulting from phreatomagmatic eruptions are among the most dangerous phenomena likely to be associated with the
initial phase of a future eruption in the Auckland Volcanic Field. The assessment is done both in the long-term and in a specific
short-term case study, i.e. the simulated pre-eruptive unrest episode during Exercise Ruaumoko, a national civil defence exercise.
The most important factors to account for are the uncertainties in the vent location (expected for a volcanic field) and in
the run-out distance of base surges. Here, we propose a statistical model of base surge run-out distance based on deposits
from past eruptions in Auckland and in analogous volcanoes. We then combine our hazard assessment with an analysis of the
costs and benefits of evacuating people (on a 1 × 1-km cell grid). In addition to stressing the practical importance of a
cost-benefit analysis in creating a bridge between volcanologists and decision makers, our study highlights some important
points. First, in the Exercise Ruaumoko application, the evacuation call seems to be required as soon as the unrest phase
is clear; additionally, the evacuation area is much larger than what is recommended in the current contingency plan. Secondly,
the evacuation area changes in size with time, due to a reduction in the uncertainty in the vent location and increase in
the probability of eruption. It is the tradeoff between these two factors that dictates which cells must be evacuated, and
when, thus determining the ultimate size and shape of the area to be evacuated. 相似文献