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201.
The characteristics of foredunes created in a municipal management program on a developed barrier island are evaluated to identify how landforms used as protection structures can be natural in appearance and function yet compatible with human values. Shoreline management zones include a naturally evolving, undeveloped segment; a noneroding, developed segment; eroding and noneroding segments of an “improved beach” where dunes have been built by artificial nourishment; and a privately built, artificially nourished dune on the shoreline of an inlet.A disastrous storm in 1962 resulted in an aggressive program for building dunes using sand fences, vegetation plantings, purchase of undeveloped lots, and sediment backpassing to maintain beach widths and dune elevations. The present nourished and shaped foredune in the improved beach is higher, wider, and closer to the berm crest than the natural dune. Restricted inputs of aeolian sand keep the surface flat and poorly vegetated. A stable section of this engineered shore has a wider beach, and sand fences have created a higher foredune with greater topographic diversity. The cross shore zonation of vegetation here is more typical of natural dunes, but the environmental gradient is much narrower. The privately built dune is low, narrow, and located where it could not be created naturally. Foreshore and aeolian sediments in the undeveloped segment and the improved beach are similar in mean grain size (0.16–0.21 mm) and sorting (0.31–0.39φ), but sediment on the surface of the nourished dune is coarser (28.1% gravel) with a more poorly sorted sand fraction (1.30φ) representing lag elements on the deflation surface.Willingness to enhance beaches and dunes for protection has reduced insurance premiums and allowed the municipality to qualify for funds from the Federal Emergency Management Agency (FEMA) to replace lost sediment, thus placing an economic value on dunes. Success of the management program is attributed to: (i) timing property-purchase and dune-building programs to periods immediately after storms (causing residents to accept high dunes that restrict access or views); (ii) instituting a vigorous education program (reminding residents of hazards during nonstorm periods); (iii) maintaining control over local sediment supplies (to keep pace with erosion and create new shoreline environments); (iv) investing private and municipal economic resources in landforms (qualifying them for external funds for replacement); and (v) maintaining, augmenting, or simply tolerating biodiversity and natural processes (retaining a natural heritage). 相似文献
202.
203.
The variations in sulfur dioxide (SO2) emission from the Summit Craters of Mt. Etna were determined, with particular reference to the period 1993–1995. Vehicle-based
weekly measurements of SO2 flux, using a correlation spectrometer (COSPEC), suggest new input of magma into the main feeder system of the volcano between
1993 and 1995. Minimal flux values (<1000 t/day) preceded the two eruptive events in the period 1987–1995. Only approximately
9.5% of the magma that contributed the SO2 emission was erupted during the same period.
Received: 3 November 1997 / Accepted: 21 September 1998 相似文献
204.
Adrien Berchet Bruno Simon Anthony Beaudoin Pierre Lubin Germain Rousseaux Serge Huberson 《国际泥沙研究》2018,33(3):351-370
Tidal bores may appear in some estuaries when the tides quickly reach a high level. This phenomenon is rare but has a strong impact during its short duration: i.e. the river bed is significantly eroded and sediments are then transported. In this paper, the trajectories of suspended particles induced by this flow are numerically studied. Four undular bores with Froude numbers between 1.1 and 1.2 are studied. Despite similar Froude numbers, various initial flow conditions were selected to produce or not an inversion of the flow direction during the bore passage. The particle trajectories associated with each distinct flow configuration are presented and analyzed. These trajectories, estimated by solving the Maxey-Riley equation, appear to be very different even though the Froude numbers of flows are similar. These observations are important because the Froude number is often used to characterize a tidal bore as it describes well the free surface, however, it cannot describe the sediment transport. Finally, Chen's model of wave-current interactions is adapted to fit the cases studied and is applied to the four bores simulated. The results highlight that this latter model can reproduce the observed trajectories and dissociate their different components. From this model, it is shown that the inertial and Basset history effects can be neglected compared to the gravity and flow entrainment effects due to the viscous drag when one wants to determine the long-term trajectories of suspended particles. 相似文献
205.
Rafael Almar Alexandre Nicolae Lerma Bruno Castelle Timothy Scott 《Ocean Dynamics》2018,68(7):899-909
The reflection of incident gravity waves over an irregular swash zone morphology and the resulting influence on surf zone dynamics remains mostly unexplored. The wave-phase resolving SWASH model is applied to investigate this feedback using realistic low-tide terraced beach morphology with well-developed beach cusps. The rhythmic reflection generates a standing wave that mimics a subharmonic edge wave, from the superimposition of incident and two-dimensional reflected waves. This mechanism is enhanced by shore-normal, narrow-banded waves in both direction and frequency. Our study suggests that wave reflection over steep beaches could be a mechanism for the development of rhythmic morphological features such as beach cusps and rip currents. 相似文献
206.
Precipitation as a proxy for climate variables: application for hydrological modelling 总被引:1,自引:1,他引:0
Ayan Fleischmann Fernando Fan Bruno Collischonn Walter Collischonn Paulo Pontes Anderson Ruhoff 《水文科学杂志》2019,64(3):361-379
It has been proposed that linear regression curves can be used to estimate monthly climate variables from observed precipitation. This approach was explored by applying the MGB hydrological model to the Paraná Basin (Brazil). Linear regressions were obtained for 54 climate gauges, and most of them showed at least six months of significant correlation between monthly climate variables (sunlight hours and relative humidity) and precipitation. The regression equations were applied to 5201 raingauges to estimate monthly climate variables and evapotranspiration, and the results were compared with a scenario using long-term climate averages only. The main differences occurred in wetter periods, where negative correlations between monthly precipitation and evapotranspiration were obtained when using precipitation as a proxy. Long-term changes in the hydrological regime were assessed and showed that the effect of precipitation on relative humidity and sunlight hours seems to have a minor effect on the alterations observed in river discharge in the Paraná Basin. 相似文献
207.
Bruno Lansard Christophe Rabouille Lionel Denis Christian Grenz 《Estuarine, Coastal and Shelf Science》2009,81(4):544-554
Biogeochemical processes in sediments under the influence of the Rhône River plume were studied using both in situ microelectrodes and ex situ sediment core incubations. Organic carbon (OC) and total nitrogen (TN) content as well as stable carbon isotopic composition of OC (δ13COC) were analysed in 19 surface sediments to determine the distribution and sources of organic matter in the Rhône delta system. Large spatial variations were observed in both the total O2 uptake (5.2 to 29.3 mmol m−2 d−1) and NH4+ release (−0.1 to −3.5 mmol m−2 d−1) rates at the sediment–water interface. The highest fluxes were measured near the Rhône River mouth where sedimentary OC and TN contents reached 1.81% and 0.23% respectively. Values of δ13COC ranged from −26.83‰ to −23.88‰ with a significant seawards enrichment tracing the dispersal of terrestrial organic matter on the continental shelf. The amount of terrestrial-derived OC reaches 85% in sediments close to the Rhône mouth decreasing down to 25% in continental shelf sediments. On the prodelta, high terrestrial OC accumulation rates support high oxygen uptake rates and thus indicating that a significant fraction of terrestrial OC is remineralized. A particulate organic carbon (POC) mass balance indicates that only 3% of the deposited POC is remineralized in prodelta sediments while 96% is recycled on the continental shelf. It was calculated that a large proportion of the Rhône POC input is either buried (52%) or remineralized (8%), mostly on the prodelta area. The remaining fraction (40%) is either mineralized in the water or exported outside the Rhône delta system in dissolved or particulate forms. 相似文献
208.
Christian Tamburini Madeleine Goutx Catherine Guigue Marc Garel Dominique Lefvre Bruno Charrire Richard Sempr Stphane Pepa Michael L. Peterson Stuart Wakeham Cindy Lee 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1533-1546
We used a new experimental device called PASS (PArticle Sinking Simulator) during MedFlux to simulate changes in in situ hydrostatic pressure that particles experience sinking from mesopelagic to bathypelagic depths. Particles, largely fecal pellets, were collected at 200 m using a settling velocity NetTrap (SV NetTrap) in Ligurian Sea in April 2006 and incubated in high-pressure bottles (HPBs) of the PASS system under both atmospheric and continuously increasing pressure conditions, simulating the pressure change experienced at a sinking rate of 200 m d−1. Chemical changes over time were evaluated by measuring particulate organic carbon (POC), carbohydrates, transparent exopolymer particles (TEP), amino acids, lipids, and chloropigments, as well as dissolved organic carbon (DOC) and dissolved carbohydrates. Microbial changes were evaluated microscopically, using diamidinophenylindole (DAPI) stain for total cell counts and catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) for phylogenetic distinctions. Concentrations (normalized to POC) of particulate chloropigments, carbohydrates and TEP decreased under both sets of incubation conditions, although less under the increasing pressure regime than under atmospheric conditions. By contrast, dissolved carbohydrates (normalized to DOC) were higher after incubation and significantly higher under atmospheric conditions, suggesting they were produced at the expense of the particulate fraction. POC-normalized particulate wax/steryl esters increased only under pressure, suggesting biochemical responses of prokaryotes to the increasing pressure regime. The prokaryotic community initially consisted of 43% Bacteria, 12% Crenarchaea and 11% Euryarchaea. After incubation, Bacteria dominated (90%) the prokaryote community in all cases, with γ-Proteobacteria comprising the greatest fraction, followed by the Cytophaga–Flavobacter cluster and α-Proteobacteria group. Using the PASS system, we obtained chemical and microbial evidence that degradation by prokaryotes associated with fecal pellets sinking through mesopelagic waters is limited by the increasing pressure they experience. 相似文献
209.
Hydrographic mesoscale structures in the North-western Alboran Sea show a high variability induced by a number of different factors. One of the most important is the differences in atmospheric pressure over the Mediterranean basin when compared to the Gulf of Cádiz. This difference modulates the zonal wind field in the Alboran Sea and the intensity of the Atlantic inflow through the Strait of Gibraltar, also affecting the formation and extension of the Western Alboran Gyre (WAG). When westerly winds are dominant, lower atmospheric pressure in the Mediterranean enhances the inflow of Atlantic waters causing the Atlantic Jet to be located in the vicinity of the Spanish shore, creating a well-defined frontal zone in front of Estepona Cove. In this situation, the coastal upwelling is enhanced, leading to a minimum in sea surface temperature and a maximum of surface nutrient concentrations located in the coastal area. The vertical position of the chlorophyll maximum found in these circumstances appeared to be controlled by the nutrient availability. On the other hand, when easterly winds prevail, higher atmospheric pressure in the Mediterranean leads to a reduced inflow and the oceanographic and biological structures are clearly different. The Atlantic Jet moves southward flowing in a south-eastern direction, changing the structure of the currents, resulting in an enhanced cyclonic circulation extending throughout the North-western Alboran Sea basin. These physical alterations also induce changes in the distribution of biogeochemical variables. Maximum nutrient and chlorophyll concentrations are located further off the coast in the central area of the newly created cyclonic gyre. During these easterlies periods coastal upwelling stops and the distribution of phytoplankton cells seems to be mainly controlled by physical processes such as advection of coastal waters to the open sea. 相似文献
210.
Post-rift volcanism and high heat-flow at the ocean-continent transition of the eastern Gulf of Aden
Francis Lucazeau Sylvie Leroy Julia Autin Alain Bonneville Bruno Goutorbe Louise Watremez Elia d'Acremont Doga Düsünur Frédérique Rolandone Philippe Huchon Nicolas Bellahsen Patrick Tuchais 《地学学报》2009,21(4):285-292
A high heat-flow (∼900 mW m−2 ) has been observed over a volcanic structure at the Ocean-Continent Transition in the Eastern Gulf of Aden (Oman margin). The anomaly is superposed to a progressive increase of heat-flow across the margin and can be interpreted either by (1) heat refraction, (2) fluid discharge or (3) cooling magma. The two first explanations cannot be ruled out definitely by modelling analysis, but require unlikely thermal conductivity or permeability values. The third one implies that the latest activity of the volcano was about 100 000 years old and therefore continued c. 18 Ma after the break-up of Africa and Arabia. This potential mechanism is consistent with other lines of evidence of post-rifting activity in the Gulf of Aden and could invalidate the conventional assumption that rifted-margins become passive after the break-up of continents. 相似文献