Location and height of intertidal bars on macrotidal ridge and runnel beaches

Previous studies devoted to the morphology and hydrodynamics of ridge and runnel beaches highlight characteristics that deviate from those initially postulated by King and Williams (Geographical Journal, 1949, vol. 113, 70–85) and King (Beaches and Coasts, 1972, Edward Arnold). Disagreements on the morphodynamics of these macrotidal beaches include the position of the ridges relative to the mean neap and spring tide levels, the variation in the height of the ridges across the intertidal profile and, most importantly, whether the ridges are formed by swash or surf zone processes. The morphological characteristics of ridge and runnel beaches from three locations with varying wave, tidal and geomorphic settings were investigated to address these disagreements. Beach profiles from each site were analysed together with water‐level data collected from neighbouring ports. It was found that the ridges occur over the entire intertidal zone. On one site (north Lincolnshire, east England), the ridges are uniformly distributed over the intertidal beach, whereas on the two other sites (Blackpool beach, northwest England, and Leffrinckoucke beach, north France) there is some indication that the ridges appear to occur at preferential locations. Most significantly, the locations of the ridge crests were found to be unrelated to the positions on the intertidal profile where the water level is stationary for the longest time. It was further found that the highest ridges generally occur just above mid‐tide level where tidal non‐stationarity is greatest. These findings argue against the hypothesis that the ridges are formed by swash processes acting at stationary tide levels. It is tentatively suggested that the ridges are the result of a combination of swash and surf zone processes acting across the intertidal zone. Elucidation of the morphodynamic roles of these two types of processes, and other processes such as strong current flows in the runnels, requires further comprehensive field measurements complemented by numerical modelling. Copyright © 2001 John Wiley & Sons, Ltd.     

Aircraft wind measurement considering lift-induced upwash

Flow distortion is a universal consideration in the measurement of wind. Usually the distortion results from deflection of the flow by the support. Instruments mounted on airplanes, however, experience an additional deflection associated with lift, which changes rapidly and continuously during flight. In front of the airplane, this deflection appears as upwash. Characteristic upwash contamination ranges from 0.5 to 2.5 m s^-1, depending on wing loading, flight speed, and forward distance from the wing to the measurement location. On pressure-radome installations the distance from the wing is usually small and the potential for upwash contamination large. Sensors mounted at the end of long probes attached to smaller airplanes with light wing loading are less susceptible to upwash contamination. Since wing loading also depends on the local vertical wind velocity the upwash velocity is directly correlated with vertical wind velocity. Generally, empirical corrections are derived from flight tests. We develop a simple method from principles of aerodynamics which explains these corrections in terms of upwash. The applicability of our approach to moderate upwash is demonstrated with data collected from the NOAA Long-EZ research airplane. More severe upwash conditions require a more sophisticated correction beyond the scope of this paper, but basically derived from the same principles.Oak Ridge Associated Universities, assigned to NOAA/ATDD     

Sediment toxicity in the Hudson-Raritan estuary: Distribution and correlations with chemical contamination

The Hudson-Raritan Estuary is one of several United States coastal areas where chemical data have suggested a potential for contaminant-related biological effects, and multiyear intensive bioeffects surveys have been conducted by the National Oceanic and Atmospheric Administration. The severity and spatial patterns in sediment toxicity were determined in an estuary-wide survey during spring 1991 using amphipods, bivalve larvae, and luminescent bacteria as test organisms. Spatial patterns in toxicity corresponded to the distributions of a number of toxic chemicals in the sediments. Areas that exhibited the greatest sediment toxicity included the upper East River, Arthur Kill, Newark Bay, and Sandy Hook Bay. The lower Hudson River adjacent to Manhattan Island, upper New York Harbor, lower New York Harbor off Staten Island, and parts of western Raritan Bay generally showed lower toxicity. Supporting chemical analyses of the sediments, including acid-volatile sulfide and simultaneously-extracted metals, suggested that metals were generally not the cause of the observed toxicity, with the possible exception of mercury. Among all contaminants analyzed, toxicity was most strongly associated with polynuclear aromatic hydrocarbons, which were substantially more concentrated in toxic samples than in nontoxic samples, and which frequently exceeded sediment quality criteria.     

Estimation of the Probability of Exceedance of Contaminant Concentrations

Several alternative probability distributions for estimating the probability of exceedance of contaminant concentrations are examined for their appropriateness for developing inputs to risk assessments. The rationale is provided for using the log Pearson Type III distribution, a three-parameter model, for estimation of the exceedance probabilities.     

Floodplain development based on selective preservation of sediments, Squamish River, British Columbia

In the conventional model of floodplain sediment accumulation, mechanisms of floodplain growth are differentiated into lateral and vertical accretion processes, in which within-channel deposits are capped by overbank deposits. In the high-energy, gravel-based Squamish River, sediments laid down on bar surfaces are composed of trough and planar crossbedded coarse sands. These sequences contrast incongruously with adjacent floodplain deposits which are composed in large part of vertically accreted fine sands atop coarse alluvial gravels. Using element analysis it is inferred that bar platform sediments are stripped away by chute channels, which are subsequently infilled with lower-energy deposits. From this, a model of floodplain growth based on selective preservation of bar platform sands and prefrential preservation of vertically accreted deposits is proposed. This mechanism of sediment replacement occurs independent of channel planform type.     

Holocene Environmental Change and River-Mouth Sedimentation in the Baie des Anges, French Riviera

River mouths on the steep, high-relief coast of the French Riviera exhibit thick sequences of Holocene marine, estuarine, deltaic, and river channel-floodplain sediments that overlie basal fluvial Pleistocene gravel. Gravel is uncommon in most of the early to middle Holocene aggradational-progradational marine, estuarine, deltaic sediments, despite an ample supply from rock units in the steep adjoining uplands. River-mouth gravel is common only in late Holocene river channels and in barrier beaches perched on finer-grained nearshore sediments. Neither downslope grain-size fining on alluvial fans nor sediment stacking patterns during sea-level (base-level) rise readily account for the lack of early to middle Holocene gravel in the river-mouth sediment wedges. Holocene sea-level rise led to the storage of fine-grained sediments in shallow marine, estuarine, and deltaic environments in the present coastal zone. We infer that humid temperate conditions, a dense forest cover, landscape stabilization, and a regular quiescent river flow regime associated with the Atlantic climatic optimum limited gravel supply in the adjoining catchments and gravel entrainment downstream during the early Holocene. Sea-level stabilization in the middle and late Holocene coincided with a marked change in bioclimatic conditions toward the present Mediterranean-type regime, which is characterized by a less dense forest cover, soil erosion, and episodic catastrophic floods. The late Holocene was thus a time of downstream bedload channel aggradation, fine-grained floodplain and paludal sedimentation, and seaward flushing of clasts leading to the formation and consolidation of the gravel barrier beaches that bound the rivermouths and embayments.     

Th-228/Th-232 and Pb-210 geochronologies in marine and lake sediments

Two dating techniques, applicable to coastal marine and lacustrine sediments over periods ranging from years to a century, evolve from the natural radioactive series: Th-228/ Th-232 from the Th-232 series and Pb-210 from the U-238 series.There is an excess of Th-228 over and above that supported by the parents Th-232 or Ra-228 in such deposits. The amounts of Th-232-supported and Ra-228-supported Th-228 are similar, indicating that both radium and thorium isotopes are removed from solution in these coastal zones quite rapidly after introduction or formation. The radium isotopes are probably transferred from the overlying waters to the sediments via phytoplankton, where they are reportedly enriched. In the surface levels of the deposits analyzed, there is nearly an order of magnitude more unsupported than supported Th-228. This excess Th-228 can be used both for dating purposes over time periods of the order of a decade and as permissive evidence that the uppermost levels of the deposit were obtained during the coring operation. Preliminary results from several lakes indicate the possibility that Th-228/Th-232 geochronologies are held by their sediments.Average rates of accumulation of lake sediments have been obtained from decreases in Pb-210 activity as a function of depth, although surface layers of the deposits may not have been recovered in the coring operation. Finally, Pb-210 geochronologies have been extended from varved to unvarved marine sediments.     

Noble gases in eleven H-chondrites

He, Ne, Ar and Xe were measured in aliquots of 11 H-chondrites, to complement trace element studies on the same meteorites (Laulet al., 1972). Bielokrynitschie, Charsonville, Pultusk and Supuhee have lost radiogenic gases before cosmic-ray exposure and Doroninsk, during exposure.