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1.
During the summer of 2004, four hurricanes (Charley, Frances, Ivan, and Jeanne) affected Florida between August 13 and September 27. Two storms (Frances: category 2 and Jeanne: category 3) made landfall in the southern portion of the Indian River Lagoon (IRL) on the east-central coast of Florida. The presence of Florida Fish and Wildlife Conservation Commission's long-term fisheries monitoring program in the IRL provided a unique opportunity to examine the effects of large tropical events on estuarine fish communities. Increased sampling efforts to monitor the effects of tropical disturbances on the fish community within the IRL and one of its major tributaries (St. Sebastian River) were initiated within days after the passing of the last hurricane (Jeanne). The objectives of the study were to characterize changes to the composition of the fish community within the lagoon and river immediately after the passage of two hurricanes, and to examine the recovery of the fish communities. Analyses indicated that immediately after the last hurricane passed, community diversity within the estuary decreased following these storms due to the absence of many marine species, whereas the fish community within the St. Sebastian River shifted to one containing a greater percentage of freshwater species. Recovery of the community structure to pre-hurricane conditions was evident within several weeks following the last hurricane, and by mid December 2004 (ca. 3 mo after the last storm), there was little difference between the pre-hurricane and post-hurricane fish communities.  相似文献   

2.
On August 13, 2004, Hurricane Charley came ashore in the Charlotte Harbor watershed. Surface winds at the time of landfall were estimated at 130 knots. The track of the hurricane roughly followed the floodplain of the Peace River, causing massive defoliation and mortality of native vegetation and planted citrus groves, as well as substantial damage to human habitation and various infrastructure elements. Eight days after landfall, a water quality monitoring effort documented hypoxic (<2 mg I−1) to nearly anaerobic (<0.5 mg I−1) dissolved oxygen (DO) values throughout the vast majority of the Peace River's c. 6,000 km2 watershed. Low DO values appeared to be related to high values of both dissolved organic matter and suspended materials. Hypoxic conditions in Charlotte Harbor itself, occurred within 2 wk of landfall. Approximately 3 wk after the landfall of Hurricane Charley, Hurricane Frances struck the east coast of Florida, causing further wind damage and bringing substantial amounts of rain to the Charlotte Harbor watershed. Three weeks later still, Hurricane Jeanne caused similar damage to the same area. In response to the combined effects of these three hurricanes, DO values in the Peace River did not recover to pre-hurricane levels until approximately 2–3 mo later. The spatial and temporal pattern of DO fluctuations appeared to be related to the proximity of sampling locations to the path of the eyewall of the first of the three hurricanes. Within the Harbor itself, the duration of hypoxic conditions was less than that recorded within the Peace River, perhaps reflecting greater dilution of oxygen-poor waters from the watershed with less-affected water from the Gulf of Mexico.  相似文献   

3.
Regional-scale washover deposits along the Florida Gulf and Atlantic coasts induced by multiple hurricanes in 2004 and 2005 were studied through coring, trenching, ground-penetrating radar imaging, aerial photography, and prestorm and poststorm beach-profile surveys. Erosional and depositional characteristics in different barrier-island sub-environments, including dune field, interior wetland and back-barrier bay were examined. Over the eroded dune fields, the washover deposits are characterized by an extensive horizontal basal erosional surface truncating the old dune deposits and horizontal to slightly landward-dipping stratification. Over the marshes in the barrier-island interior, the washover deposits are characterized by steep tabular bedding, with no erosion at the bottom. Overwash into the back-barrier bay produced the thickest deposits characterized by steep, prograding sigmoidal bedding. No significant erosional feature was observed at the bottom. Washover deposits within the dense interior mangrove swamp demonstrate both normal and reversed graded bedding. The washover deposits caused by hurricanes Frances (2004) and Jeanne (2004) along the southern Florida Atlantic coast barrier islands are substantially different from those along the northern Florida barrier islands caused by Ivan (2004) and Dennis (2005) in terms of regional extension, erosional features and sedimentary structures. These differences are controlled by different overall barrier-island morphology, vegetation type and density, and sediment properties. The homogeneity of sediment along the northern Florida coast makes distinguishing between washover deposits from Ivan and Dennis difficult. In contrast, along the Atlantic coast barrier islands, the two overwash events, as demonstrated by two phases of graded bedding of the bimodal sediments, are easily distinguishable.  相似文献   

4.
Shoreline changes are largely dependent on coastal morphology. South-west coast of India is a high energy coast characterised by monsoon high waves, steep beach face and medium-sized beach sand. Waves are generally from west and west south-west during rough monsoon season and from south-west during fair weather season. Shoreline change along this coast is studied with reference to coastal morphological features. Various morphological features, modifications and chronological positions of shoreline are analysed with the information derived from multidated satellite imageries, toposheets and GPS shoreline mapping along with extended field survey. Image processing and GIS techniques have been used for the analysis of data and presentation of results. Sediment accumulation on the leeward side of artificial structures such as harbour breakwaters and groynes is used as a sediment transport indicator. Artificial structures such as seawalls, groynes and harbour breakwaters modify morphology. Shoreline south of headlands/promontories and breakwaters are stable or accreting due to net northerly longshore sediment transport while erosion tendency is observed on the north side. Lateritic cliffs fronting the sea or with seasonal beach undergo slumping and cliff edge retreat as episodic events. Spits adjoining tidal inlets are prone to shoreline variations due to oscillations of inlet mouth. Interventions in the form of inlet stabilization and construction of coastal protection structures trigger erosion along adjoining coasts. Seawalls constructed along highly eroding coasts get damaged, whereas those constructed along monsoon berm crest with frontal beaches for protection against monsoon wave attack are retained. Fishing gaps within seawalls are areas of severe temporary erosion during rough monsoon season. Accretion or erosion accompanies construction of harbour breakwaters in a stable coastal plain. Close dependence of shoreline changes on morphology necessitates detailed understanding of impacts on morphology prior to introducing any intervention in the coastal zone.  相似文献   

5.
Storm response along the transgressive Chandeleur barrier-island arc southeast of the Mississippi delta plain is variable because of local differences in sediment supply, shoreline orientation and barrier morphology. A study of the morphological impact of Hurricane Frederic (1979) affirmed that tropical storms are the primary agents causing erosion and migration of this barrier arc.Frederic's greatest impact was in the duneless southern Chandeleurs, where sheet-flow overwash caused flattening of the barrier profile, destruction of a strip of marsh 50–100 m wide, and shoreline retreat of approximately 30 m. In contrast, overwash in the northern Chandeleurs was confined between dunes in channels established by previous storms. This channelized overwash breached the northern Chandeleur barriers in nineteen places. As Frederic passed, return flow through these channels transported overwashed sediment back to the nearshore zone. These ebb deposits were a source for longshore drift sediments, which quickly sealed storm channels, reestablishing a coherent northern Chandeleur barrier arc.These storm response patterns may help explain long-term changes in barrier morphology. During an 84-yr period (1885–1969) the southern Chandeleurs decreased 41 % in area, with an average retreat rate of 9.1 m yr?1, compared to a 15% increase in area and an average shoreline retreat rate of 7.2 m yr?1 for the northern Chandeleurs.  相似文献   

6.
Hurricane Andrew, one of the strongest storms of the century, crossed the southern part of the Florida peninsula on 24 August 1992. Its path crossed the Florida Everglades and exited in the national park across a mangrove-dominated coast onto the shallow, low-energy, inner shelf. The storm caused extensive breakage and defoliation in the mangrove community; full recovery will take decades. It produced no extensive sedimentation unit; only local and ephemeral ebb-surge deposits. The discontinuous shelly storm beach ridge was breached at multiple locations, and it moved landward a few meters. After seven months, there was little geologic indication that the storm had passed. It is likely that the stratigraphic record in this area will not contain any recognizable features of the passage of Hurricane Andrew.  相似文献   

7.
Recent projections of global climate change necessitate improved methodologies that quantify shoreline variability. Updated analyses of shoreline movement provide important information that can aid and inform likely intervention policies. This paper uses the Analyzing Moving Boundaries Using R (AMBUR) technique to evaluate shoreline change trends over the time period 1856 to 2015. Special emphasis was placed on recent rates of change, during the 1994 to 2015 period of active storm conditions. Small segments, on the order of tens of kilometers, along two sandy barrier island regions on Florida’s Gulf and Atlantic coasts were chosen for this study. The overall average rate of change over the 159-year period along Little St. George Island was ??0.62?±?0.12 m/year, with approximately 65% of shoreline segments eroding and 35% advancing. During periods of storm clustering (1994–2015), retreat rates along portions of this Gulf coast barrier accelerated to ??5.49?±?1.4 m/year. Along the northern portion of Merritt Island on Florida’s Atlantic coast, the overall mean rate of change was 0.22?±?0.08 m/year, indicative of a shoreline in a state of relative dynamic equilibrium. In direct contrast with the Gulf coast shoreline segment, the majority of transects (65%) evaluated along the oceanfront of Merritt Island over the long term displayed a seaward advance. Results indicate that episodes of clustered storm activity with fairly quick return intervals generally produce dramatic morphological alteration of the coast and can delay natural beach recovery. Additionally, the data show that tidal inlet dynamics, shoreline orientation, along with engineering projects, act over a variety of spatial and temporal scales to influence shoreline evolution. Further, the trends of shoreline movement observed in this study indicate that nearshore bathymetry—the presence of shoals—wields some influence on the behavior of local segments of the shoreline.  相似文献   

8.
The tropical storm database used in this study was obtained from the National Oceanic and Atmospheric Administration’s (NOAA) Coastal Service Center, using the Historical Hurricane Tracks tool. Queries were used to determine the number of storms of tropical origin that have impacted the State and each of its counties. A total of 76 storms of tropical origin passed over New York State between 1851 and 2005. Of these storms, 14 were classified as hurricanes. The remaining hurricanes passed over New York State as weaker or modified systems—27 tropical storms, 7 tropical depressions, and 28 extratropical storms (ET). Long Island experiences a disproportionate number of hurricanes and tropical storms. The average frequency of hurricanes and storms of tropical origin (all types) is one in every 11 years and one in every 2 years, respectively. September is the month of greatest frequency for storms of tropical origin, although the storms of greatest intensity tend to arrive later in the hurricane season and follow different poleward tracks. While El Nino Southern Oscillation (ENSO) cycles appear to show some influence, the frequency and intensity of storms of tropical origin appear to follow a multidecadal cycle. Storm activity was greatest in both the late 19th and 20th centuries. During periods of increased storm frequency and intensity storms reached New York State at progressively later dates. While the number and timing of storms of tropical origin is likely to increase, this increase appears to be attributed to a multidecadal cycle, as opposed to a trend in global warming.  相似文献   

9.
Pensacola Bay, Florida, was in the strong northeast quadrant of Hurricane Ivan when it made landfall on September 16, 2004 as a category 3 hurricane on the Saffir-Simpson scale. We present data describing the timeline and maximum height of the storm surge, the extent of flooding of coastal land, and the magnitude of the freshwater inflow pulse that followed the storm. We computed the magnitude of tidal flushing associated with the surge using a tidal prism model. We also evaluated hurricane effects on water quality using water quality surveys conducted 20 and 50 d after the storm, which we compared with a survey 14 d before landfall. We evaluated the scale of hurricane effects relative to normal variability using a 5-yr monthly record. Ivan's 3.5 m storm surge inundated 165 km2 of land, increasing the surface area of Pensacola Bay by 50% and its volume by 230%. The model suggests that 60% of the Bay's volume was flushed, initially increasing the average salinity of Bay waters from 23 to 30 and lowering nutrient and chlorophylla concentrations. Additional computations suggest that wind forcing was sufficient to completely mix the water column during the storm. Freshwater discharge from the largest river increased twentyfold during the subsequent 4 d, stimulating a modest phytoplankton bloom (chlorophyll up to 18 μg l−1) and maintaining hypoxia for several months. Although the immediate physical perturbation was extreme, the water quality effects that persisted beyond the first several days were within the normal range of variability for this system. In terms of water quality and phytoplankton productivity effects, this ecosystem appears to be quite resilient in the face of a severe hurricane effect.  相似文献   

10.
Though most hurricane evacuation studies have focused on residents, tourists are also a vulnerable population. To assess their perceptions of risk and evacuation likelihood under different hurricane conditions, we surveyed 448 tourists visiting central Florida. Respondents viewed four maps emulating track forecast cones produced by the National Hurricane Center and text information featuring variations of storm intensity, coast of landfall, centerline position relative to the survey site, time until landfall, and event duration. We performed chi-square tests to determine which hurricane conditions, and aspects of tourists such as their demographics and previous hurricane experience, most likely influenced their ratings of risk and evacuation likelihood for respondents located on Pinellas County beaches or inland near Orlando, FL. Highly rated scenarios featured a Category 4 hurricane making landfall along the Gulf Coast with the centerline passing over the sampling site. Overall, tourists that indicated the highest risk and evacuation ratings were not previously affected by a hurricane, had a trip duration of less than 6 days, and had checked for the possibility of a hurricane strike before departure. However, results for other tourist attributes differed between tourists in coastal and inland locations. We found that although somewhat knowledgeable about hurricanes, tourists misinterpreted the track forecast cone and hurricane conditions, which led to a lower perception of risk and subsequent likelihood to evacuate. Tourists, particularly those from outside of Florida, need to be better educated about the risks they face from hurricanes that make landfall.  相似文献   

11.
The internal structure of coastal foredunes from three sites along the north Norfolk coast has been investigated using ground‐penetrating radar (GPR), which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non‐destructive or geophysical technique. Combining geomorphological and geophysical investigations into the structure and morphology of these coastal foredunes has enabled a more accurate determination of their development and evolution. The radar profiles show the internal structures, which include foreslope accretion, trough cut and fill, roll‐over and beach deposits. Foredune ridges contain large sets of low‐angle cross‐stratification from dune foreslope accretion with trough‐shaped structures from cut and fill on the crest and rearslope. Foreslope accretion indicates sand supply from the beach to the foreslope, while troughs on the dune crest and rearslope are attributed to reworking by offshore winds. Bounding surfaces between dunes are clearly resolved and reveal the relative chronology of dune emplacement. Radar sequence boundaries within dunes have been traced below the water‐table passing into beach erosion surfaces. These are believed to result from storm activity, which erodes the upper beach and dunes. In one example, at Brancaster, a dune scarp and erosion surface may be correlated with erosion in the 1950s, possibly the 1953 storm. Results suggest that dune ridge development is intimately linked to changes in the shoreline, with dune development associated with coastal progradation while dunes are eroded during storms and, where beaches are eroding, a stable coast provides more time for dune development, resulting in higher foredune ridges. A model for coastal dune evolution is presented, which illustrates stages of dune development in response to beach evolution and sand supply. In contrast to many other coastal dune fields where the prevailing wind is onshore, on the north Norfolk coast, the prevailing wind is directed along the coast and offshore, which reduces the landward migration of sand dunes.  相似文献   

12.
The morphodynamic behavior of a mesotidal sandy beach was monitored during both calm and energetic conditions. Two years of seasonal surveys were carried out on Charf el Akab, a gently sloped beach in the North Atlantic coast of Morocco. The method of survey consisted of a 3D study of the beach morphological changes and provided 2 cm vertical accuracy. During the surveyed period, Charf el Akab beach underwent very energetic wave conditions, and the breaking wave height was of H b ≥ 1.5 m. The beach is characterized by a nonpermanent swash bar and composed of well-sorted medium sand. The application of environmental parameters revealed a dissipative state with very low beach gradient which did not vary significantly over the studied period. Morphological changes consist of beach erosion and bar decay under high-energy waves, whereas the intertidal bar re-established and the beach recorded an accentuated accretion due to relatively fair weather conditions. The beach volume reveals a seasonal behavior; the sand accumulated during summer is dramatically removed during winter season. The range in beach sand volume from the most accreted to the most eroded conditions observed is about −5,493 m3. The average sand volume flux between surveys reaches −1 and 0.4 m2/day during peak erosion and accretion periods. The relationships between the wave forcing and the sand volume adjustments were examined. The sand volume change was found to be highly correlated (0.91) with the wave energy flux. The highest correspondence (0.95) was found between the sand flux rate and the wave energy flux. The wave forcing is expected to be the main factor governing beach morphodynamics at Charf el Akab site.  相似文献   

13.
Following the catastrophic and devastating Atlantic Hurricane seasons in 2004 and 2005, there has been increased interest in formulating planning directives and policy aimed at minimizing the societal impacts of future storms. Not all populations will evacuate an area forecast to be affected by a hurricane, so emergency managers must plan for these people who remain behind. Such planning includes making food, water, ice, and other provisions available at strategic locations throughout an affected area. Recent research has tackled problems related to humanitarian and relief goods distribution with respect to hurricanes. Experience shows that the torrential rains and heavy winds associated with hurricanes can severely damage transportation network infrastructure rendering it unusable. Scanning the literature on hurricane disaster relief provision, there are no studies that expressly consider the potential damage that may be caused to a transportation network by strong storms. This paper examines the impacts of simulated network failures on hurricane disaster relief planning strategies, using a smaller Florida City as an example. A relief distribution protocol is assumed where goods distribution points are set up in pre-determined locations following the passage of a storm. Simulation results reveal that modest disruptions to the transportation network produce marked changes in the number and spatial configuration of relief facilities. At the same time, the transportation network appears to be robust and is able to support relief service provision even at elevated levels of hypothesized disruption.  相似文献   

14.
We examined nekton community-level responses to Hurricanes Frances and Jeanne, which made landfall 20 d apart in the St. Lucie estuary in southeastern Florida in 2004. The passage of these storms contributed to large freshwater discharges that exceeded 150 m3 s−1, as well as estuary-wide reductions in salinity and near-hypoxic conditions in the North Fork of the estuary that persisted for several months. Although such environmental variations are not uncommon, seasonal patterns of community structure were disturbed throughout much of the estuary, likely in response to uncharacteristically-rapid reductions in salinity. Immediately following the hurricanes, abundances of several freshwater and oligohaline taxa (i.e., blue crabCallinectes sapidus, shadDorosoma spp., and ladyfishElops saurus) increased markedly in the inner estuary, while abundances of several other fishes (i.e., striped mulletMugil cephalus, white mulletM. curema, lookdownSelene vomer, pigfishOrthopristis chrysoptera, and pinfishLagodon rhomboides) declined. Nekton communities recovered quickly, and by spring, community structure throughout much of the estuary was indistinguishable from pre-hurricane conditions. Although nekton communities were resilient to hurricane-related disturbances, projected increases in Atlantic hurricane activity and associated freshwater discharges over the coming decades may test the resilience of estuarine communities in Florida.  相似文献   

15.
The nearshore parameters, viz., wave runup, wave setup, and wave energy have been estimated during storm and normal conditions of SW monsoon (June–September) and NE monsoon (November–February) by empirical parameterization along Visakhapatnam coast. These results were compared with the field observations during three storms of SW monsoon season in the year 2007. The higher nearshore wave energies were observed at R.K. Beach, Jodugullapalem beach, and Sagarnagar beach during both the seasons. During storm events, the higher wave energies associated with higher wave runups cause severe erosion along the wave convergence zones. The storm wave runups (SWRUs) were higher at R.K. Beach, Palm beach, Jodugullapalem beach, and Sagarnagar Beach. The yearly low wave energy was observed at Lawson’s Bay with lowest wave runup, considered as safest zone. R.K. Beach, Palm beach, and Jodugullapalem beach are identified as vulnerable zones of wave attack. It is noteworthy that in addition to wave energies, wave runups and wave setups also play a vital role in endangering the coast.  相似文献   

16.
Three sequential hurricanes made landfall over the South Florida peninsula in August and September 2004. The storm systems passed north of the Everglades wetlands and northeastern Florida Bay, but indirect storm effects associated with changes in freshwater discharge during an otherwise drought year occurred across the wetland–estuary transition area. To assess the impacts of the 2004 hurricane series on hydrology, nutrients, and microbial communities in the Everglades wetlands to Florida Bay transition area, results are presented in the context of a seasonal cycle without hurricane activity (2003). Tropical activity in 2004 increased rainfall over South Florida and the study area, thereby temporarily relieving drought conditions. Not so much actual rainfall levels at the study site but more so water management practices in preparation of the hurricane threats, which include draining of an extensive freshwater canal system into the coastal ocean to mitigate inland flooding, rapidly reversed hypersalinity in the wetlands-estuary study area. Although annual discharge was comparable in both years, freshwater discharge in 2004 occurred predominantly during the late wet season, whereas discharge was distributed evenly over the 2003 wet season. Total organic carbon (TOC), ammonium ( \operatornameNH + 4 \operatorname{NH} ^{ + }_{4} ), and soluble reactive phosphorus (SRP) concentrations increased during the hurricane series to concentrations two to five times higher than long-term median concentrations in eastern Florida Bay. Spatiotemporal patterns in these resource enrichments suggest that TOC and SRP originated from the Everglades mangrove ecotone, while \operatornameNH + 4 \operatorname{NH} ^{ + }_{4} originated from the bay. Phytoplankton biomass in the bay increased significantly during storm-related freshwater discharge, but declined at the same time in the wetland mangrove ecotone from bloom conditions during the preceding drought. In the bay, these changes were associated with increased nanophytoplankton and decreased picophytoplankton biomass. Heterotrophic bacterial production increased in response to freshwater discharge, whereas bacterial abundance decreased. Hydrochemical and microbial changes were short-lived, and the wetland–bay transition area reverted to more typical oligotrophic conditions within 3 months after the hurricanes. These results suggest that changes in freshwater discharge after drought conditions and during the hurricane series forced the productivity and P-enriched characteristics of the wetland’s mangrove ecotone, although only briefly, to the south into Florida Bay.  相似文献   

17.
Alongshore variation in the rip current hazard at Pensacola Beach, Florida   总被引：2，自引：1，他引：1  
Many drowning and near drownings at Pensacola Beach, Florida are attributed to rip currents, the strong seaward-flowing currents that extend from the shoreline to the line of breakers and sometimes beyond. While surf forecasts assume that the rip hazard is uniform alongshore and that the (erosion) rips are ephemeral features, evidence is presented to suggest that the rip hazard at Pensacola Beach is not uniform alongshore. Rather the rip current “hotspots” develop as a consequence of an alongshore variation in the surf similarity parameter and nearshore state on the order of ~1,450 m. The variation is forced by transverse ridges on the inner shelf that force wave refraction and focusing at the ridge crests. This creates a more dissipative, rhythmic bar and beach morphology at the ridges and rougher surf. Between ridges, where wave heights and periods are smaller and the outermost bar is forced closer to the shoreline, the nearshore is in a (more reflective) bar and rip state during red flag conditions. Drownings between 2000 and 2009 are shown to be clustered between transverse ridges and in the years following a hurricane or tropical storm (2000–2003 and 2005–2008) when the bar and rip morphology first develops as the shore face recovers. This continues until the innermost bar attaches to the beach face unless the bar system is reset by another tropical storm or hurricane. It is argued that the rip hazard is dependent on the alongshore covariation of the environmental forcing with the individual and group behavior in both time and space, even on what appears to be a relatively uniform beach environment.  相似文献   

18.
This study addresses gaps in understanding the relative roles of sea‐level change, coastal geomorphology and sediment availability in driving beach erosion at the scale of individual beaches. Patterns of historical shoreline change are examined for spatial relationships to geomorphology and for temporal relationships to late‐Holocene and modern sea‐level change. The study area shoreline on the north‐east coast of Oahu, Hawaii, is characterized by a series of kilometre‐long beaches with repeated headland‐embayed morphology fronted by a carbonate fringing reef. The beaches are the seaward edge of a carbonate sand‐rich coastal strand plain, a common morphological setting in tectonically stable tropical island coasts. Multiple lines of geological evidence indicate that the strand plain prograded atop a fringing reef platform during a period of late‐Holocene sea‐level fall. Analysis of historical shoreline changes indicates an overall trend of erosion (shoreline recession) along headland sections of beach and an overall trend of stable to accreting beaches along adjoining embayed sections. Eighty‐eight per cent of headland beaches eroded over the past century at an average rate of ?0·12 ± 0·03 m yr?1. In contrast, 56% of embayed beaches accreted at an average rate of 0·04 ± 0·03 m yr?1. Given over a century of global (and local) sea‐level rise, the data indicate that embayed beaches are showing remarkable resiliency. The pattern of headland beach erosion and stable to accreting embayments suggests a shift from accretion to erosion particular to the headland beaches with the initiation of modern sea‐level rise. These results emphasize the need to account for localized variations in beach erosion related to geomorphology and alongshore sediment transport in attempting to forecast future shoreline change under increasing sea‐level rise.  相似文献   

19.
The variation during 15 years in the shoreline along the North Sinai coast has been determined by analysing TM and ETM true colour Landsat images from 1986 to 2001. The analyses identified erosion and accretion patterns along the coast. The shoreline has advanced west of El Bardawil inlet1, El Bardawil inlet2, and El Arish Harbour, where the wave-induced littoral transport has been halted by jetty construction and beach growth rates are 20,681, 69,855 and 20,160 m2/year, respectively. On the downdrift side of the constructed jetties to the east, the shoreline is retreating and beaches erode at rates of −71,710, −69,968, and −11,760 m2/year, respectively. Sedimentological analyses of beach sediment samples have indicated selective transport of heavy minerals according to their densities and grain sizes. A general correspondence has been found between variation in grain size, sorting and heavy-mineral content of beach sand and the patterns of shoreline changes.  相似文献   

20.
Hydrodynamic Response of Northeastern Gulf of Mexico to Hurricanes   总被引：1，自引：0，他引：1  
The northeastern Gulf of Mexico in the USA is extremely susceptible to the impacts of tropical cyclones because of its unique geometric and topographic features. Focusing on Hurricanes Ivan (2004) and Katrina (2005), this paper has addressed four scientific questions on this area’s response to hurricanes: (1) How does the shallow, abandoned Mississippi delta contribute to the storm surge? (2) What was the controlling factor that caused the record-high storm surge of Hurricane Katrina? (3) Why are the responses of an estuary to Hurricanes Ivan and Katrina so different from the corresponding surges on the open coast? (4) How would the storm surge differ if Hurricane Katrina had taken a different course? Guided by field observations of winds, waves, water levels, and currents, two state-of-the-art numerical models for storm surges and wind waves have been coupled to hindcast the relevant hydrodynamic conditions, including storm surges, surface waves, and depth-averaged currents. Fairly good agreement between the modeled and measured surge hydrographs was found. The quantitative numerical simulations and simple qualitative analysis have revealed that the record-high storm surge of Hurricane Katrina was caused by the interaction of the surge with the extremely shallow, ancient deltaic lobe of Mississippi River. A hypothetical scenario formed by shifting the path of Hurricane Katrina to the observed path of Hurricane Frederic (1979) resulted in a much smaller surge than that observed in coastal Mississippi and Louisiana. However, this scenario did still result in a high surge near the head of Mobile Bay. One of the important lessons learned from Hurricane Katrina is that the Saffir–Simpson scale should be systematically revised to reflect the topographic and geometric features of a complex, heterogeneous coast, including the possible surge amplification in an estuary or a submerged river delta.  相似文献   

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