1,721,035 research outputs found
Discussion of Ford, M.R.; Becker, J.M., and Merrifield, M.A. 2013. Reef Flat Wave Processes and Excavation Pits: Observations and Implications for Majuro Atoll, Marshall Islands.Journal of Coastal Research,29(3), 545–554.
No full textFord, Becker, and Merrifield observed reef flat wave conditions during two deployments over a 41 day period to investigate the impact of reef flat excavation pits on wave processes at Majuro Atoll. They noticed that the shoreline with the excavation pit received wave heights slightly less (?8%) than those recorded at the nearby unmodified cross section. They suggested that this net decrease was the net product of a slight increase in sea and swell (SS) wave energy due to a bottom roughness reduction and a decrease in infragravity (IG) wave energy due to the disruption of the cross-shore quasi-standing modes caused by the excavation pit. We argue that, for this particular experiment, the coupling between the SS and IG energy waves may provide an alternative explanation of the observations, and we suggest that further investigations are needed. Although the coupling between SS and IG waves may be important for assessing the impact of excavation pits on IG-dominated shorelines, we show that these excavation pits in SS-dominated surf zones can lead to events such as the observed destruction of the Cadiz (SW Spain) seawall in 179
Suspended sand transport along pier depression
No full textVelocities and sand concentrations measured along 20 transects at the Field Research Facility (FRF) at Duck, North Carolina during October 16–23, 1997 are analyzed to examine the cross-shore and longshore suspended sand transport in the FRF pier depression. The suspended sand volume Vs per unit bottom area remains large outside the surf zone in the depression. The depth-integrated offshore and longshore suspended sand transport rates are shown to be estimated as a , U¯ Vs and V¯ Vs , respectively, where the empirical parameter a is in the range of 0.1–0.4 in the depression, U¯ is the cross-shore current and V¯ is the longshore current. The offshore suspended sand transport rate at the end of the pier is estimated to be as large as 3.5?m3/h/m at the peak of a storm with an offshore significant wave height of 3.5 m. The sand transported offshore appears to have been supplied by the longshore sand transport toward the pier depression<br/
Cross-shore suspended sand and bed load transport on beaches
No full textSimple formulas are developed to predict the time-averaged rates of cross-shore suspended sand and bed load transport. The net suspended sand transport rate is expressed as the product of the depth-averaged current and the suspended sediment volume per unit bottom area with a reduction factor that accounts for the correlation between the time-varying fluid velocity and sediment concentration. The net bed load transport rate under nonlinear waves is assumed to be onshore and proportional to ?U3 where ?U is the standard deviation of the horizontal velocity. The probabilities of sediment movement and suspension are introduced to account for the initiation of sediment movement and suspension. Simple functions are proposed to account for the effects of a steep bottom slope on the bed load and suspended sediment transport rates. The proposed formulas are found to be in agreement with three data sets within a factor of about 2. The proposed formulas are shown to be consistent with existing simple formulas. The formulas are incorporated into a time-averaged wave model and the continuity equation of bottom sediment to predict the beach profile evolution. The numerical model is compared with seven small-scale tests including berm erosion tests and seven large-scale tests including dune erosion tests. The numerical model predicts the overall beach profile evolution including the berm and dune erosion but does not always predict the fairly subtle profile changes including bar migration accurately
Berm and dune erosion during a storm
No full textThe prediction of berm and dune erosion during a storm is essential for storm damage assessment. Simple and transparent formulas for the cross-shore and longshore transport rates of suspended sediment and bed load on beaches are proposed and incorporated into a combined wave and current model to predict the berm and dune erosion under normally and obliquely incident irregular waves. Two small-scale experiments for two different berm profiles were conducted for the calibration of the developed numerical model. The calibrated numerical model is shown to predict the measured berm and dune erosion in these experiments as well as dune erosion measured in three large-scale tests with errors less than a factor of two. The numerical model is used to examine the effects of the wave period and incident wave angle on the berm and dune erosion. These effects are computed to be within a factor of two<br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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