烟台第一海水浴场沙源匮乏型海滩地貌和表层沉积物粒度特征

在烟台第一海水浴场,利用经纬仪进行2条海滩横剖面形态测量,并在不同地貌单元采集沉积物样品进行粒度分析。测量显示,该海滩仅有小规模沙坝和沟槽体系。后滨上有风成沉积,但滩肩和海岸沙丘发育均不明显。粒度分析结果表明,海滩沉积物以中砂、粗砂为主,杂以砾或细砂,比山东半岛其他海滩沉积物明显要粗。由陆向海沉积物呈带状分布,平均高潮线附近和沙坝迎水坡侵蚀作用均显著。因此认为缺乏沙源供应的基岩岬湾式海岸是导致沙滩地貌发育不典型、海滩侵蚀作用显著的主要原因。     

Theoretical and measured aeolian sand transport on a barrier island, Louisiana, USA

Over the past 100 years, the Isles Dernieres, a low lying barrier island chain along the coast of central Louisiana, Usa , has undergone more than 1 km of northward beach face retreat with the loss of 70% of its surface area. The erosion results from a long term relative sea level rise coupled with day to day wind and wave action that ultimately favours erosion over deposition. At a site in the central Isles Dernieres, 8 days of wind and beach profile measurements during the passage of one winter cold front documented aeolian erosion and deposition patterns under both onshore and offshore winds. For offshore winds, the theoretical erosion rate, based on wind shear velocity, closely matched the measured erosion rate; for onshore winds, the theoretical rate matched the measured rate only after being corrected by a factor that accounted for beach face morphology. In late February 1989, a strong cold front moved into coastal Louisiana. That cold front stalled over the Gulf of Mexico, resulting in 4 days of strong northerly winds at a study site on the Isles Dernieres. During those 4 days, the wind moved sand from the backshore to the upper beach face. When the cold front finally moved out of the area, the wind shifted to the south and decreased in strength. The onshore wind then restored some of the upper beach face sand to the backshore while increased wave activity moved the rest into the nearshore. The theoretical estimate of 1·28 m³ m^?1 for the rate of sand transport by the northerly wind compares well with the measured backshore erosion rate of 1·26 m³ m^?1, which was determined by comparing beach profiles from the start and end of the period of northerly winds. The theoretical estimate of 0·04 m³ m^?1 for the rate of sand transport by the southerly wind, however, is notably less than the measured rate of 0·45 m³ m^?1. The large discrepancy between the two rates can be explained by a difference in the shear velocity of the wind between the beach face, where the erosion occurred, and the backshore, where the wind stress was measured. Using an empirical relationship for the wind shear drag coefficient as a function of coastal environment, the theoretical estimate for the rate of sand transport by the southerly wind becomes 0·44 m³ m^?1     

Hurricanes 2004: An overview of their characteristics and coastal change

Four hurricanes battered the state of Florida during 2004, the most affecting any state since Texas endured four in 1884. Each of the storms changed the coast differently. Average shoreline change within the right front quadrant of hurricane force winds varied from 1 m of shoreline advance to 20 m of retreat, whereas average sand volume change varied from 11 to 66 m³ m⁻¹ of net loss (erosion). These changes did not scale simply with hurricane intensity as described by the Saffir-Simpson Hurricane Scale. The strongest storm of the season, category 4 Hurricane Charley, had the least shoreline retreat. This was likely because of other factors like the storm's rapid forward speed and small size that generated a lower storm surge than expected. Two of the storms, Hurricanes Frances and Jeanne, affected nearly the same area on the Florida east coast just 3 wk apart. The first storm, Frances, although weaker than the second, caused greater shoreline retreat and sand volume erosion. As a consequence, Hurricane Frances may have stripped away protective beach and exposed dunes to direct wave attack during Jeanne, although there was significant dune erosion during both storms. The maximum shoreline change for all four hurricanes occurred during Ivan on the coasts of eastern Alabama and the Florida Panhandle. The net volume change across a barrier island within the Ivan impact zone approached zero because of massive overwash that approximately balanced erosion of the beach. These data from the 2004 hurricane season will prove useful in developing new ways to scale and predict coastal-change effects during hurricanes.     

A sand budget for the Alexandria coastal dunefield, South Africa

The sand in the Alexandria coastal dunefield is derived from the sandy beach which forms the seaward boundary of the dunefield. Sand is blown off the beach onto the dunefield by the high-energy onshore-directed dominant wind. The dunefield has been forming over the past 6500 years. Sand transport rates calculated from dune movement rates and wind data range from 15 to 30 m³ m ^-1 yr^-1 in an ENE direction. The sand transport rate decreases with increasing distance from the sea due to a reduction in wind speed resulting from the higher drag imposed upon the wind by the land surface. Aeolian sand movement rates of this order are typical of dunefields around the world. The total volume of sand blown into the dunefield is 375 000 m³ yr^-1. Sand is being lost to the sea by wave erosion along the eastern third of the dunefield at a rate of 45 000 m³ yr ^-1. The dunefield thus gains 330 000 m³ of sand per year. This results in dunefield growth by vertical accretion at about 1.5 mm yr^-1 and landward movement at about 0.25 m yr^-1. The dunefield is a significant sand sink in the coastal sand transport system. The rate of deposition in coastal dunefields can be 10 times as high as rates of deposition in continental sand seas. The higher rate of deposition may result from the abundant sand supply on sandy beaches, and the higher energy of coastal winds. Wind transport is slow and steady compared to fluvial or longshore drift transport of sediment, and catastrophic aeolian events do not seem to be significant in wind-laid deposits.     

Beach erosion under rising sea‐level modulated by coastal geomorphology and sediment availability on carbonate reef‐fringed island coasts

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.     

The impact,control, and mitigation of off-road vehicle activity in Hungry Valley,California

Hungry Valley, and arid basin situated within the Transverse Ranges of Southern California, has been utilized by off-road vehicles (ORVs) since 1971. Loss of vegetation, severe soil erosion and gullying, alluvial fan formation, and increased sediment discharge are the direct results of ORV activity in the valley. These hydrologic-geologic effects have been documented and monitored utilizing sequential aerial photographs, ground surveys, and sediment transport measurements. Despite the increased usage of ORVs on public lands, and the well-documented short-term physical environmental impacts, little data exists on erosion or sediment transport rates in disturbed vs. adjacent undisturbed areas, the ability of natural vegetation to re-establish itself, or the feasibility of site rehabilitation techniques or methods.     

A study of the monsoonal beach processes around Alleppey,Kerala

The responses of a sandy beach to the southwest monsoonal waves are studied based on biweekly observations. The onslaught of the first spell of monsoonal breakers causes maximum erosion in the sub-aerial section of the beach. However, further spells of high breakers do not affect this zone significantly. The erosion in the sub-aerial zone is followed by accretion in the nearshore zone and vice versa. Whereas the sub-aerial zone has a net erosion the total section of the beach including the nearshore zone shows near equilibrium condition. It is concluded that in spite of erosion or accretion of the sub-aerial zone, equilibrium conditions may be found in the total section of the beach.     

Impacts of vehicles on natural terrain at seven sites in the San Francisco Bay area

The impacts of off-road vehicles on vegetation and soil were investigated at seven representative sites in the San Francisco Bay area. Plant cover of grass and chaparral (with shrubs to 4 m tall) have been stripped by the two- and four-wheel vehicles in use. Impacts on loamy soils include increased surface strength (as much as 275 bars), increased bulk density (averaging 18%) to depths of 90 cm or more, reduction of soil moisture by an average 43% to 30 cm depths, greatly reduced infiltration, extension of the diurnal temperature range by as much as 12°C, and reduction of organic carbon by an average 33% in exposed soils. Very sandy soils respond similarly to vehicular use except that moisture is increased and surface strength of beach sand is decreased. These physical and chemical impacts reduce the land's capability of restoring its vegetative cover, which in turn adversely affects animal populations. Both the loss of plant cover and the physical changes caused by vehicles promote erosion. Measured soil and substrate losses from vehicular use zones range from 7 to 1180 kg/m². The estimated erosion rate of the Chabot Park site exceeds the rate of erosion considered a serious problem by a factor 30, it exceeds United States Soil Conservation Service tolerance values by a factor of 46, and it exceeds average San Francisco Bay area erosion rates by a factor of 17. The resulting soil losses are effectively permanent. Neither the increased sediment yield nor the increased runoff is accomodated on the sites of use, and both are causing adverse effects to neighboring properties.     

Influence of vegetation on aeolian sand transport rate from a backshore to a foredune at Hasaki, Japan

The influence of vegetation on aeolian sediment transport rate in the region from a backshore to a foredune was investigated at the Hasaki Coast in Japan, where an onshore wind was predominant and the creeping beach grasses Carex kobomugi and Calystegia soldanella were major species. The comparison of cross-shore distributions of the cross-shore component of aeolian sand transport rate with and without vegetation, which were estimated on the basis of the beach profile changes and a mass conservation equation, showed that the creeping grasses influenced the aeolian sand transport rate. The landward aeolian sand transport rate rapidly decreased landward from the seaward limit of vegetation when the grasses grew. The aeolian sand transport rate reduced by 95% with a vegetation cover of 28%. On the other hand, when the grasses were absent, the landward aeolian sand transport rate did not decrease near the seaward vegetation limit, but near the foot of the foredune.     

Seasonal changes and morphodynamic behavior of a high-energy mesotidal beach: case study of Charf el Akab beach on the North Atlantic coast of Morocco

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.     

Coarse‐sand beach ridges at Cowley Beach,north‐eastern Australia: Their formative processes and potential as records of tropical cyclone history

Storm surges generated by tropical cyclones have been considered a primary process for building coarse‐sand beach ridges along the north‐eastern Queensland coast, Australia. This interpretation has led to the development of palaeotempestology based on the beach ridges. To better identify the sedimentary processes responsible for these ridges, a high‐resolution chronostratigraphic analysis of a series of ridges was carried out at Cowley Beach, Queensland, a meso‐tidal beach system with a >3 m tide range. Optically stimulated luminescence ages indicate that 10 ridges accreted seaward over the last 2500 to 2700 years. The ridge crests sit +3·5 to 5·1 m above Australian Height Datum (ca mean sea‐level). A ground‐penetrating radar profile shows two distinct radar facies, both of which are dissected by truncation surfaces. Hummocky structures in the upper facies indicate that the nucleus of the beach ridge forms as a berm at +2·5 m Australian Height Datum, equivalent to the fair‐weather swash limit during high tide. The lower facies comprises a sequence of seaward‐dipping reflections. Beach progradation thus occurs via fair‐weather‐wave accretion of sand, with erosion by storm waves resulting in a sporadic sedimentary record. The ridge deposits above the fair‐weather swash limit are primarily composed of coarse and medium sands with pumice gravels and are largely emplaced during surge events. Inundation of the ridges is more likely to occur in relation to a cyclone passing during high tide. The ridges may also include an aeolian component as cyclonic winds can transport beach sand inland, especially during low tide, and some layers above +2·5 m Australian Height Datum are finer than aeolian ripples found on the backshore. Coarse‐sand ridges at Cowley Beach are thus products of fair‐weather swash and cyclone inundation modulated by tides. Knowledge of this composite depositional process can better inform the development of robust palaeoenvironmental reconstructions from the ridges.     

Evaluation of aeolian sand transport equations using intertidal zone measurements, Saunton Sands, England

Sand transport rates were measured using a vertical sand trap along the intertidal zone of a beach in North Devon, England, together with simultaneous monitoring of the wind speed on the beach and moisture levels in the surface layers of sand. The results of 88 sand trap samples in a wide range of wind speeds showed that moisture levels up to 14%, in the top 1–2 mm of the beach sand, have no discernible effect on the transport rates. Transport rates measured from areas of the beach where the moisture was below this level are compared with the rates predicted by seven expressions based on theoretical and wind tunnel research together with the empirical results of other published research. Measured transport rates range from 0.0001 to 0.22 kg m^-1 s^-1. The results indicate that expressions based on a power relation between the wind speed and the transport rate, and which include a threshold velocity term, provide the best estimates of the observed transport rates.     

Evaluation of future land-use planning initiatives to shoreline stability of Egypt’s northern Nile delta

An analysis of beach morphodynamics and relative vulnerability to erosion processes and sea inundation within the Nile delta’s lower coastal plain was performed as a basis for evaluation of future planning initiatives undertaken by the National Centre for Planning State Land Uses (NCPSLU). The conceptual management plans incorporate a variety of land-use plans including residential, recreational, industrial, agricultural, harboring, fish farming, and placer sand mining. Appropriateness of shores fronting the planned land uses is assessed in the present study by applying the Coastal Vulnerability Index (CVI) approach, which depends primarily on a variety of variables that affect beach stability of the proposed plans. These variables are prominent morphologic features, shoreline erosion or accretion rates, sea-level rise, beach type (dissipative, reflective, or rhythmic bar), and oceanographic conditions (tidal range and mean wave height). Results disclosed that not all of the examined delta coastlines are equally vulnerable to beach erosion (ranging from relatively low to highly susceptible). However, the most serious threat is that the relatively stable coastlines lying close to nodal points are likely to be affected by erosion due to net sediment transport reversals heading eastward or westward which eventually may require remedial protection. Future planning of the unprotected highly vulnerable and low-elevated subsiding zones, such as Manzala lagoon barrier, requires effective mitigation measures. Quarrying of Abu Khashaba beach, as an example, for mineral mining placers (at Abu Khashaba) and other fish farming applications (possibly at Burullus lagoon barrier) is considered as a risk and is to be avoided as it accelerates eroding the natural protective barrier that fronts the Burullus lagoon.     

Nourishment of perched sand dunes and the issue of erosion control in the Great Lakes

Although limited in coverage, perched sand dunes situated on high coastal bluffs are considered the most prized of Great Lakes dunes. Grand Sable Dunes on Lake Superior and Sleeping Bear Dunes on Lake Michigan are featured attractions of national lakeshores under National Park Service management. The source of sand for perched dunes is the high bluff along their lakeward edge. As onshore wind crosses the bluff, flow is accelerated upslope, resulting in greatly elevated levels of wind stress over the slope brow. On barren, sandy bluffs, wind erosion is concentrated in the brow zone, and for the Grand Sable Bluff, it averaged 1 m³/yr per linear meter along the highest sections for the period 1973–1983. This mechanism accounts for about 6,500 m³ of sand nourishment to the dunefield annually and clearly has been the predominant mechanism for the long-term development of the dunefield. However, wind erosion and dune nourishment are possible only where the bluff is denuded of plant cover by mass movements and related processes induced by wave erosion. In the Great Lakes, wave erosion and bluff retreat vary with lake levels; the nourishment of perched dunes is favored by high levels. Lake levels have been relatively high for the past 50 years, and shore erosion has become a major environmental issue leading property owners and politicians to support lake-level regulation. Trimming high water levels could reduce geomorphic activity on high bluffs and affect dune nourishment rates. Locally, nourishment also may be influenced by sediment accumulation associated with harbor protection facilities and by planting programs aimed at stabilizing dunes.     

The spatial and temporal variability of sand erosion across a stabilizing coastal dune field

This study aimed at quantifying the temporal and spatial variability in sand erosion and deposition over a coastal dune field in Israel. These were measured monthly over 2 years using 315 erosion pins over four transects that were placed perpendicular to the coastline. Vegetation cover was estimated based on aerial photographs and Landsat satellite images, whereas the relative height was based on a digital elevation model. These variables were calculated for the area upwind (south west) of the erosion pins, at various lengths, ranging from 15 to 400 m. Nine geomorphologic units were defined, five related to active units, and four to stabilized units. In active units at least 65% of the temporal variance in the annual absolute changes in sand level was explained by the index of Resultant Drift Potential, with most of the sand movement occurring during winter storms. Local rainfall had no apparent impact on sand mobility, due to the low coincidence of sand carrying winds and rainfall in Israel during the passage of frontal cyclones. As for the spatial variables, only a weak correlation was found between sand mobility with the distance from the coastline (R² = 18%). Rather, sand erosion and deposition were influenced by vegetation cover and the relative height of an area of 100–200 m upwind. The values of Soil Adjusted Vegetation Index were significantly negatively correlated with annual absolute changes (R² = 40%), whereas the relative height was significantly positively correlated (R² = 36%). Applying a multiple regression model, 68% of the spatial variability in sand mobility was explained. The resulting map of sand activity clearly shows that at this stage of the stabilization process, most of the dunes are now disconnected, and movement of sand grains from the beach or between the dunes, is very limited. These methods can be applied into spatial and temporal models of sand mobility, thus assessing the impact of different management practices on coastal dunes.     

Environmental impacts of Baltim and Ras El Bar shore-parallel breakwater systems on the Nile delta littoral zone,Egypt

This study evaluates the impacts resulting from the construction of two large-scale detached breakwater systems on the Nile delta coast of Egypt at Baltim and Ras El Bar beaches (~18.3 km shoreline length). The two protective systems were installed in a water depth of between 3 and 4 m and consist of 17 units in total (each ~250 m long). A comprehensive monitoring program spanning the years 1990 to 2002 was implemented and included beach-nearshore profiles, grain size distribution of seabed sand and information related to the background coastal processes. Evaluation of these systems concentrates on the physical impacts on coastal morphodynamics, mitigation and their design implications. The beach and nearshore sedimentation (erosion/accretion patterns) and grain texture of seabed sediment in the study areas have been substantially disrupted due to the interruption of longshore transport by the shore-parallel detached breakwaters. Rate of shoreline and seabed changes as well as alongshore sediment volume have been substantially affected, resulting in accretion in the breakwater landward sides (tombolo or salient) followed by downdrift erosion. The preconstruction beach erosion at Baltim (–5 m/year) and at Ras El Bar (–6 m/year) has been replaced, respectively, by the formation of sand tombolo (35 m/year) and salient (9 m/year). On the other hand, beach erosion has been substantially increased in the downdrift sides of these protective systems, being –20 m/year at Baltim and –9 m/year at Ras El Bar. Further seaward, the two protective systems at Baltim and Ras El Bar have accumulated seabed sand at maximum rates of 30 and 20 cm/year and associated with downdrift erosion of –45 and –20 cm/year, respectively. Strong gyres and eddies formed in the breakwater gabs have drastically affected swimmers and subsequently caused a significant number of drownings each summer, averaging 35 and 67 victims/year at Baltim and Ras El Bar beaches, respectively. This study provides baseline information needed to help implement mitigation measures for these breakwater systems.     

Mechanisms of berm development and resulting beach growth along a barrier spit complex

Weekly topographic profile measurements across a southward migrating recurved-spit complex throughout a summer period have revealed three different mechanisms of berm development, each reflected by a distinctive sedimentary sequence. Each mechanism dominates berm widening along certain sections of the active spit with transition zones separating each one. Along the straight beach sections where a net longshore transport is well developed, sand accumulates at the distal high-tide swash mark during neap tide. These sandy accumulations are neap berms which are later redistributed over the main berm by swash occurring at spring high water. The main berm grows vertically and horizontally as a result. To the south, along the middle portion of the recurved spit, swash bars or ridge-and-runnel systems actively develop, migrate, and weld onto the established berms. This is the second method of berm widening and results from an excess of sand carried into this portion of the spit due to the steadily decreasing transport of the longshore current system. Berm-ridges develop along the southernmost portion of the active recurved spit and represent the third and most rapid form of beach progradation. Wide, broad swash bars build nearly up to the spring high tide level. At neap high tide, the swash cannot extend over this feature. Wave energy is expended on the seaward margin of the swash bar initially developing a low-angle beach face. Rapidly, this beach face steepens and a new berm (beach face and berm top) is developed on top of the swash bar. This berm structure still retains much of its swash bar or ridge appearance, hence the term‘berm-ridge'. Numerous trenches dug into the beach provide data to model the distribution of primary sedimentary structures in recurved spits. Berm-ridges are the most important features along rapidly accreting spits, and structures associated with these features are volumetrically the most significant. Berm-ridges also develop arcuate, vegetated ridges separated by low lying, marsh-infilled swales. These features are commonly seen within barrier islands and designate former inlets.     

Evaluation of criteria for predicting erosion and accretion on an estuarine sand beach, Delaware Bay, Jew Jersey

Predicting erosion and accretion of sand beaches in estuaries is important to managing shoreline development and identifying potential relationships between biological productivity and beach change. Wave, sediment and profile data, gathered over twenty-nine days on an estuarine sand beach in Delaware Bay, New Jersey, were used to evaluate the performance of four criteria that predict beach erosion and accretion due to wave-induced cross-shore sediment movement (Dean 1973; Sunamura and Horikawa 1974; Hattori and Kawamata 1980; Kraus et al. 1991). Each criterion defines a relation, between a wave and sediment parameter, and includes a coefficient that discriminates beach erosion and accretion events. Relations, based on small-scale laboratory and field data, were evaluated for predicting erosion or accretion at the study site. Significant wave heights at the study site, monitored near high water, ranged from 0.08 to 0.52 m with periods of 2.4 to 12.8 s. Median grain sizes of sediments on the beach foreshore, gathered at low water, ranged from 0.33 to 0.73 mm. All four criteria showed a clustering of erosion and accretion events. Relations derived from small-scale laboratory data were better predictors of erosion on the profile at the field site than those derived from field data gathered on exposed ocean environments. The planar profile and dominance of incident waves of low height and short period are similar to laboratory conditions characterized by initial planar beach slopes and monochromatic waves. Decreasing the value of the empirical coefficient to account for the differences in the magnitude of wave energy and grain size increases the performance of the criteria tested to predict erosion of the profile.     

河北省海岸侵蚀动态及成因机制研究

河北省沙质岸滩存在海岸侵蚀现象,对沙滩旅游、海滩工程建设造成严重威胁,制约河北省海洋经济社会发展。海岸侵蚀监测结果显示,区域海滩滩面受波浪、潮流影响较大,时冲时淤,摆动频繁,沙质岸滩整体处于侵蚀状态,各区段蚀淤情况有所差异,高潮线以上有所淤高,海滩坡度开始变陡,呈下蚀状态。海岸侵蚀灾害已引起沙滩沙质粗化、滩肩变窄、滩坡变陡及基岩裸露比率增多等问题。针对这一突出问题,通过定点测量与遥感监测相结合的方式,研究了河北省海岸线动态演变特征,经计算,河北省各侵蚀岸段海岸侵蚀速率达1.0~4.0m/a,单宽体积侵蚀量-1.42~-19.08m~3/m·a。综合分析显示,人类海岸工程建设、区域海洋水文条件及输砂量减少,是河北省发生海岸侵蚀发生的主要原因。     

Natural radioactivity measurements in beach sand along southern coast of Orissa,eastern India

The beach placer deposits in the southern coastal Orissa, India may have significant levels of radiation due to the presence of Th and U bearing minerals such as monazite and zircon. In this study, Gopalpur and Rushikulya beach regions were selected to study the ambient radiation environment. The average activity concentrations of radioactive elements such as ²³²Th, ²³⁸U and ⁴⁰K of beach sand samples were measured by γ-ray spectrometry using a HPGe detector, and found to be much higher than the internationally accepted values. The cross plots of eTh/eU and eTh/K inferred that the sand samples of Gopalpur and Rushikulya beach placer deposit were deposited in leached uranium and an oxidising environment. The absorbed γ dose rate levels of the study areas are similar to other monazite sand-bearing HBRAs of southern and southwestern coastal regions of India and of world. Different radiation hazard indices were estimated for the present study area and were found to be much higher than the internationally accepted values. Hence, Gopalpur and Rushikulya beach placer region can be considered as a high background radiation area and a potential zone for radiogenic heavy mineral exploration.