Transverse Bars Research Articles

Changes in surfzone morphodynamics driven by multi-decadal contraction of a large ebb-tidal delta

The impact of multi-decadal, large-scale deflation (76 million m3 of sediment loss) and contraction (~ 1 km) of a 150 km2 ebb-tidal delta on hydrodynamics and sediment transport at adjacent Ocean Beach in San Francisco, CA (USA), is examined using a coupled wave and circulation model. The model is forced with representative wave and tidal conditions using recent (2005) and historic (1956) ebb-tidal delta bathymetry data sets. Comparison of the simulations indicates that along north/south trending Ocean Beach the contraction and deflation of the ebb-tidal delta have resulted in significant differences in the flow and sediment dynamics. Between 1956 and 2005 the transverse bar (the shallow attachment point of the ebb-tidal delta to the shoreline) migrated northward ~ 1 km toward the inlet while a persistent alongshore flow and transport divergence point migrated south by ~ 500 m such that these features now overlap. A reduction in tidal prism and sediment supply over the last century has resulted in a net decrease in offshore tidal current-generated sediment transport at the mouth of San Francisco Bay, and a relative increase in onshore-directed wave-driven transport toward the inlet, accounting for the observed contraction of the ebb-tidal delta. Alongshore migration of the transverse bar and alongshore flow divergence have resulted in an increasing proportion of onshore migrating sediment from the ebb-tidal delta to be transported north along the beach in 2005 versus south in 1956. The northerly migrating sediment is then trapped by Pt. Lobos, a rocky headland at the northern extreme of the beach, consistent with the observed shoreline accretion in this area. Conversely, alongshore migration of the transverse bar and divergence point has decreased the sediment supply to southern Ocean Beach, consistent with the observed erosion of the shoreline in this area. This study illustrates the utility of applying a high-resolution coupled circulation-wave model for understanding coastal response to large-scale bathymetric changes over multi-decadal timescales, common to many coastal systems adjacent to urbanized estuaries and watersheds worldwide.

Formation and migration of transverse bars along a tidal sandy coast deduced from multi-temporal Lidar datasets

A field of long-crested transverse bars was monitored from a 2.5-year series of topographic Lidar surveys in the vicinity of a tidal inlet on the macrotidal (mean spring tidal range = 7 to 12 m) west coast of Cotentin (Normandy, France). The bar field, the alongshore extent of which is about 1.8 km, is composed of a total of 8 bars with lengths varying from 320 m to 1300 m and mean heights comprised between 0.5 m and 2.5 m. Bar cross-sections are variable between bars and for a single bar, and also over time. The surveys show a consistent northward migration of the bars at a mean rate of about 2 m/month, but the rate is larger in winter than in summer. The Lidar observations show that the tidal inlet, located at the southern limit of the bar field where the bars start forming, comprises a large sediment platform that acts as a source of sand for the bars. The ebb jet debouching from the inlet is deflected northward by the ambient strong shore-parallel tidal currents in this large tide-range setting, and this may be the primary mechanism leading to the emplacement of the bars. Smaller wave-formed swash bars that further feed the development of these large transverse bars have also been observed. Monitoring of bar migration in the course of six consecutive spring tides with fair-weather conditions showed that strong spring tidal currents are sufficient to drive bar mobility in the absence of waves. Storm wave resuspension of sand is thus expected to enhance bar mobility rates, as shown by the higher rates of winter bar migration compared to the summer rates. The ebb jet explains the slower bar migration rates at the vicinity of the inlet, these rates increasing with distance northward of the inlet as the tidal currents become unimpeded. The main difference between these macrotidal transverse bars and their counterparts in microtidal settings resides in these strong tidal currents that are the essential driver of bar migration, unlike the wave-driven migration of microtidal bars. The large tidal range, in conjunction with storm wave activity, also induces longshore and seasonal variability in bar morphology. The transverse bars of Normandy appear to be inscribed in a sand circulation system involving the west Cotentin coast, the large ebb tidal delta from which they are formed, and the central Cotentin embayment where they are ultimately incorporated into the nearshore sand pool. Longer-term field hydrodynamic monitoring and modelling will be required in order to further elucidate the mode of formation of these transverse bars.

How do braided river dynamics affect sediment storage?

Braided rivers, with their continuously changing network of channels, are highly dynamic systems. Four mechanisms of channel change and evolution are considered the classic mechanisms of braided river formation: development of central bars, conversion of single transverse bars to midchannel braid bars, formation of chutes, and dissection of multiple‐braid bars. There have been few studies, though, on how each of these braiding mechanisms contributes to changes in sediment storage and to the dynamics of a river. In one of the first field studies on the topic, Wheaton et al. analyzed repeat topographic surveys conducted over a 5‐year period of the River Feshie, an active, braided, gravel bed river in the United Kingdom.

New species ofLigophorus(Monogenea, Ancyrocephalidae), parasite ofLizaspp. (Teleostei, Mugilidae) off the Northwestern African coast

This study of monogenean species of Ligophorus Euzet & Suriano, 1977 from Liza spp. (Mugilidae) from the Northwestern African coast identifies the occurrence of four new species. Ligophorus gabrioni n. sp. on Liza falcipinnis (Valenciennes, 1836) is characterized by a small antero-median protuberance and two lateral and symmetrical expansions on the ventral transverse bar; a tubular accessory piece distally expanded; and a vagina that is not sclerotised (not visible). Ligophorus benhoussai n. sp. on Liza grandisquamis (Valenciennes, 1836) is characterized by a very long sickle-shaped accessory piece, which is wide at the base and tapering at the end, and a α-shaped vagina. Also found on Liza grandisquamis were Ligophorus bazairii n. sp. and Ligophorus hamzati n. sp. The former is characterized by a tubular bottle-opener shaped accessory piece; whereas the latter is characterized by a tubular accessory piece with a bifurcated distal extremity whose branches are also bifurcated. No Monogenea were found on the endemic Liza bandialensis Diouf, 1991. In our opinion, the differences in monogenean species richness that exist among the various hosts may be due to fluctuations of host populations as the result of bottleneck or vicariant events.

A new miniature species of Characidium Reinhardt (Ostariophysi: Characiformes: Crenuchidae) from the headwaters of the rio Araguaia, Brazil.

Characidium inirim is described from the rio das Mortes, rio Araguaia basin in Central Brazil. The new species is distinguished from its congeners by having an incomplete lateral line, a conspicuous dark longitudinal stripe and dark transverse bars not extending ventrally to the lateral line, and by lacking the adipose fin and the dark caudal blotch. A phylogenetic hypothesis based on the available data on the phylogenetic relationships of the subfamily Characidiinae is presented. Results suggest that the new species is closely related to C. bahiensis, C. interruptum, C. lagosantense, C. nupelia, C. lanei, C. laterale, C. occidentale, C. orientale, C. rachovii, C. stigmosun, C. vestigipinne and C. xavante.

Morphodynamic signatures of braiding mechanisms as expressed through change in sediment storage in a gravel‐bed river

AbstractPrevious flume‐based research on braided channels has revealed four classic mechanisms that produce braiding: central bar development, chute cutoff, lobe dissection, and transverse bar conversion. The importance of these braiding mechanisms relative to other morphodynamic mechanisms in shaping braided rivers has not yet been investigated in the field. Here we exploit repeat topographic surveys of the braided River Feshie (UK) to explore the morphodynamic signatures of different mechanisms of change in sediment storage. Our results indicate that, when combined, the four classic braiding mechanisms do indeed account for the majority of volumetric change in storage in the study reach (61% total). Chute cutoff, traditionally thought of as an erosional braiding mechanism, appears to be the most common braiding mechanism in the study river, but was more the result of deposition during the construction of diagonal bars than it was the erosion of the chute. Three of the four classic mechanisms appeared to be largely net aggradational in nature, whereas secondary mechanisms (including bank erosion, channel incision, and bar sculpting) were primarily net erosional. Although the role of readily erodible banks in facilitating braiding is often conceptualized, we show that bank erosion is as or more important a mechanism in changes in sediment storage than most of the braiding mechanisms, and is the most important “secondary” mechanism (17% of total change). The results of this study provide one of the first field tests of the relative importance of braiding mechanisms observed in flume settings.

Beach morphodynamics and types of foredune erosion generated by storms along the Emilia-Romagna coastline, Italy

The objectives of this study are to examine the response of a dune and beach system on the Adriatic coastline in northern Italy to the arrival of storms, compare it with seasonal (months) and medium-term (3-year) morphodynamic change, and evaluate results predicted by the numerical model XBeach. The studied coastline stretches 4km from the Bevano River mouth to the north of the site to the township of Lido di Classe to the south, where the beach is protected by coastal structures. Fieldwork consisted of topographic profile surveys using RTK-DGPS technology (7 times over an approx. 3-year period). 103 samples of surface sediment were collected along 20 of the cross-shore profiles at 6 distinct cross-shore positions, selected on the basis of morphological beach characteristics. Data analyses of dune and beach slopes enabled the study area to be divided into 6 separate morphological zones using the spatial (longshore and cross-shore) variation of morphologies located on the backshore and intertidal beach observed in a preliminary survey of the area. Other criteria were a spatial consistency in beach slopes and/or presence/absence of intertidal morphologies identified in the aerial photographs and Lidar data. The swash zone slope did not show any significant variability for the entire area. A weak seasonal trend in the variability of the mean foredune slope was observed, with steeper slopes typically during winter and flatter slopes during summer. Analysis of grain size revealed that the beach sediment is well-sorted fine sand tending to medium, with a decreasing trend in size from the Bevano River mouth southwards towards Lido di Classe. According to the Masselink and Short (1993) classification, the natural part of the study site has an Intermediate Barred Beach (IBB) and following the Short (1999) classification, results in a modally LBT (longshore bar-trough) or LTT (low tide terrace) with a small section being TBR (transverse bar and rip). Storms are considered the main factor controlling changes in the beach and dune slope. The most significant storm was recorded in March 2010 with a peak significant wave height of 3.91m. Contrary to the seasonal dune trend, several foredune slopes were observed to flatten following this event, which can be attributed to the action of dune slumping from the already weakened dune state. Modelling of foredune erosion, using a process-based model (XBeach), reproduced the erosion of the upper beach and dune toe reasonably well, but is currently limited by the acceptable slope value for dune stability, which does not account for biotic factors (e.g. plant roots). The comparison between the storm impact categories of Sallenger (2000) and the DSF (Dune Stability Factor) of Armaroli et al. (2012) shows a very good correspondence between the effects of the winter 2008–2009 storms and the vulnerability of the dune system predicted using both classifications.

Nearshore circulation over transverse bar and rip morphology with oblique wave forcing

ABSTRACTThere is a paucity of field data to describe the transition in nearshore circulation between alongshore, meandering and rip current systems. A combination of in‐situ current meters and surf zone drifters are used to characterize the nearshore circulation over a transverse bar and rip morphology at Pensacola Beach, Florida in the presence of relatively low energy oblique waves. Current speeds vary in response to the relative wave height ratio (Hs/h), which defines the degree and extent of breaking over the shoal. In the absence of wave breaking the nearshore circulation was dominated by an alongshore current driven by the oblique waves. As waves begin to break across the shoal (0.2<Hs/ h<0.5) the nearshore circulation is characterized by a meandering alongshore current. As conditions became more dissipative (Hs/h>0.5), the meandering current is replaced by an unsteady rip circulation that moves offshore between the shoals before turning alongshore in the direction of wave advance outside the surf zone. The increase in wave dissipation is associated with an increase in very low frequency (VLF) variations in the current speed across the shoal and in the rip channel that caused the circulation to oscillate between an offshore and an alongshore flow. The unsteady nature of the nearshore circulation is responsible for 55% of all surf zone exits under these more dissipative conditions. In contrast, only 29% of the drifters released from the shoal exited the surf zone and bypassed the adjacent shoal with the alongshore‐meandering current. While the currents had a low velocity (maximum of ~0.4 m s‐1) and would not pose a significant hazard to the average swimmer, the results of this study suggest that the transverse bar and rip morphology is sufficient to create an alongshore variation in wave dissipation that forces alongshore meandering and low‐energy rip circulation systems under oblique wave forcing. Copyright © 2013 John Wiley & Sons, Ltd.

Sexually dimorphic melanin-based colour polymorphism, feather melanin content, and wing feather structure in the barn owl (Tyto alba)

Feathers confer protection against biophysical agents and determine flying ability. The geometry and arrangement of the barbs, together with the keratin and pigments deposited in the feathers, determine the mechanical stability of the vane, and its stiffness and resistance to abrasive agents. In colour-polymorphic species, individuals display alternative colour morphs, which can be associated with different foraging strategies. Each morph may therefore require specific flying abilities, and their feathers may be exposed to different abrasive agents. Feathers of differently coloured individuals may thus have a specific structure, and colour pigments may help resist abrasive agents and improve stiffness. We examined these predictions in the barn owl (Tyto alba), a species for which the ventral body side varies from white to dark reddish pheomelanic, and in the number and size of black spots located at the tip of the feathers. White and reddish birds show different foraging strategies, and the size of black feather spots is associated with several phenotypic attributes. We found that birds displaying a darker reddish coloration on the ventral body side deposit more melanin pigments in their remiges, which also have fewer barbs. This suggests that wear resistance increases with darkness, whereas feathers of lighter coloured birds may bend less easily. Accordingly, individuals displaying a lighter reddish coloration on the ventral body side, and those displaying larger black spots, displayed more black transverse bars on their remiges: as larger-spotted individuals are heavier and longer-winged birds also have more transverse bars, these bars may reduce feather bending when flying. We conclude that differently coloured individuals produce wing feathers of different strengths to adopt alternative behavioural and life history strategies. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 562‐573.

Functional dynamics observations of haptoral armature in Mizelleus indicus (Jain 1957) Pandey et al. 2003.

The negative effect of monogenea on piscine host may vary in the host species. Genus Mizelleus (Monogenea: Ancyrocephalidae) was reported for the first time from the freshwater shark, Wallago attu (Bl. and Schn.) at Lucknow by Jain (1957). Haptor or opisthohaptor of monogenea which is more or less discoid muscular structure situated posteriorly, is the chief adhesive organ. It is usually provided with anchors and marginal hooklets. Anchors, ventral transverse bar, together with the additional supporting dorsal bars (patches) are active elements of haptor while, marginal hooklets serve as secondary supportive participants, whereas, the dorsal transverse bar can be treated as an inactive element in the whole organ of attachment. Functional dynamics detail of haptoral armature is almost unattended. The anchors in case of M. indicus (Jain 1957) Pandey et al. (2003) are disposed one against the other and used to act like four lobed grapnel like a spreader. All components of haptoral armature contribute in one way or another in the process of functional process. Interestingly the worms do not follow the same pattern of sequences during their movements. Various elements and factors are involved in the process. The authors tried to pinpoint the changes in the activity of one major element i.e., dorsal anchor. The movement and change in position/orientation of various elements with reference to dorsal anchors were observed and summarized. Present paper is rare effort in unexplored aspect in monogenea biology.

Performance of large circular reinforced concrete columns under compression

Six sets of large-scale circular reinforced concrete column sections were tested under monotonically axial compression. The primary variables were the transverse reinforcement class (spiral or circular tie), splice type and crossties. The equivalent volumetric ratio of transverse steel bar for two crosstie types is proposed and findings for practical design are outlined in this paper.

Redescription of Parapercis macrophthalma (Pietschmann, 1911) and description of a new species of Parapercis (Pisces: Pinguipedidae) from Taiwan.

Parapercis macrophthalina is confirmed as a valid species and redescribed on the basis of the holotype and other specimens collected from the type locality, Taiwan, and Japan. It is morphologically similar to P. muronis Tanaka, 1918, but differs in having five vertical transverse bars that extend well below the lateral line versus five oblique transverse bars, with the third to fifth bars ending on or above the lateral line. A new species is also described on the basis of a specimen collected from southwestern Taiwan. It is distinct in having numerous pores interconnected by canals on the head, forming 10 vertical or oblique rows on the cheek and opercular apparatus, predorsal scales extending to the level of the posterior margin of the eye, four dorsal-fin spines, six oblique bars laterally on the body, and a combination of other characters. A key to species of Parapercis with narrow transverse bars on the upper body is provided.

Bilateral lobar lung transplantation and size mismatch by pTLC-ratio

tionale for our recently proposed technique [1]. When many different procedures are described for the treatment of the same disease, it is clear that the ideal technique has not been identified yet. In our opinion, the method devised by Actis Dato et al. [2] has a valid theoretical basis and has, in their hands, proved to be safe and effective. Furthermore, the authors have such a considerable experience in this field that their opinion has to be taken into the utmost consideration by the scientific community. In conceiving our technique, we aimed to avoid some drawbacks associated with the use of metallic retrosternal bars while trying to maintain similar long-term results. In fact, a transverse posterior bar limits the thoracic compliance, causes exposures to serious damage in the case of trauma, can be painful and requires a second operation for removal. We think that such disadvantages may justify the research on novel methods. The use of new titanium plates specifically built for sternal stabilization avoids the need for a posterior support, while ensuring the same solidity of the reconstructed sternum. These results can be achieved thanks to the highest strength-to-weight ratio of titanium: the Synthes struts (Synthes, Canada Ltd.) modelled on the anatomical sternal shape are so thin and light that their removal is not required. As correctly noted by Actis Dato et al., the procedure is relatively expensive [3]. This disadvantage is undoubtedly more than offset by the avoidance of a second surgery for the bar removal. Finally, the economic impact of the procedure is limited, as it is indicated in a carefully selected group of patients, with a condition difficult to correct such as the severe asymmetric pectus excavatum.

Reply to Actis Dato et al.

We thank the editor for the opportunity to explain better the rationale for our recently proposed technique [1]. When many different procedures are described for the treatment of the same disease, it is clear that the ideal technique has not been identified yet. In our opinion, the method devised by Actis Dato et al. [2] has a valid theoretical basis and has, in their hands, proved to be safe and effective. Furthermore, the authors have such a considerable experience in this field that their opinion has to be taken into the utmost consideration by the scientific community. In conceiving our technique, we aimed to avoid some drawbacks associated with the use of metallic retrosternal bars while trying to maintain similar long-term results. In fact, a transverse posterior bar limits the thoracic compliance, causes exposures to serious damage in the case of trauma, can be painful and requires a second operation for removal. We think that such disadvantages may justify the research on novel methods. The use of new titanium plates specifically built for sternal stabilization avoids the need for a posterior support, while ensuring the same solidity of the reconstructed sternum. These results can be achieved thanks to the highest strength-to-weight ratio of titanium: the Synthes struts (Synthes, Canada Ltd.) modelled on the anatomical sternal shape are so thin and light that their removal is not required. As correctly noted by Actis Dato et al., the procedure is relatively expensive [3]. This disadvantage is undoubtedly more than offset by the avoidance of a second surgery for the bar removal. Finally, the economic impact of the procedure is limited, as it is indicated in a carefully selected group of patients, with a condition difficult to correct such as the severe asymmetric pectus excavatum.

Numerical Simulation Analysis on Seismic Behavior of a New Type Prefabricated Slab

In previous earthquakes, masonry structures, especially those masonry structures with prefabricated slab was damaged severely, and caused heavy casualty and property losses. In order to improve the seismic behavior of prefabricated slab, a new type of prefabricated slab with longitudinal and transverse joint steel bar was designed. By employing a numerical simulation procedure, LS-DYNY3D, models were established, and their seismic behaviors were analyzed .The results show that, the masonry structure of new type prefabricated slab with longitudinal and transverse joint steel bar is better than the structure with traditional prefabricated slab in structural integrity and stability. That is to say, its seismic behavior is better than the masonry structure with traditional prefabricated slab.

Pullout Resistance Factors for Inextensible Mechanically Stabilized Earth Reinforcements in Sandy Backfill

This paper presents results from a laboratory program of 402 pullout tests of inextensible reinforcements used for walls of mechanically stabilized earth (MSE). Results focus on the evaluation of pullout resistance factors for ribbed-steel strip and welded-steel grid reinforcements embedded in sandy backfill that marginally met AASHTO requirements for select granular fill. This project used Texas Tech University's large-scale MSE test box with dimensions of 12 3 12 3 4 ft and an applied overburden capacity of 40 ft of backfill. This test box facilitated pullout testing at a scale not unlike typical field construction. The research design evaluated pullout resistance factors for both ribbed-strip and welded-grid reinforcements for a variety of independent variables, including overburden pressure, reinforcement length, level of compaction, grid wire size, and grid geometry, such as transverse and longitudinal wire spacing. Appropriate statistical analyses were used to interpret the data within the context of published AASHTO design guidance for inextensible MSE reinforcements. The results show that pullout behaviors of both ribbed strips and welded grids in properly compacted sandy backfill are conservative compared with the default pullout resistance factors provided by AASHTO. The data also suggest that the current AASHTO equations for pullout resistance factors for grid reinforcement do not accurately capture the influence of transverse and longitudinal bar spacings.

Review Of Stiphodon (Gobiidae: Sicydiinae) From Western Sumatra, With Description Of A New Species

Three Stiphodon species are found on the western slope of Sumatra, Indonesia. They include a new species, S. maculidorsalis, distinguished from its congeners by second dorsal- and pectoral-fi n ray counts (usually I, 9 and 15, respectively) and relatively high premaxillary teeth counts, pointed fi rst dorsal fi n of male, scalation on dorsum of head and trunk, black spots scattering dorsally on head and trunk of male and female, broad black bands on distal part of second dorsal fi n and dorsal part of caudal fi n of male, fi ne black spots on pectoral-fi n rays of male, and dusky transverse bars laterally on trunk and tail of female. The other two species are S. ornatus and S. semoni; the latter is fi rst reported from this region, expanding the westernmost limit of the range of this widespread species. These three species appear to form the major components of the Stiphodon gobies in the aquarium trade.

Simulation of Reinforcing Bar Buckling in Circular Reinforced Concrete Columns

The buckling of longitudinal reinforcing bars is a significant damage stage for reinforced concrete (RC) structures subjected to seismic loads. This study is concerned with understanding the critical parameters that control the buckling response of reinforcing bars in typical circular RC columns subjected to lateral loads. A series of nonlinear finite element (FE) simulations of laterally loaded RC columns are first carried out to simulate reinforcing bar buckling behavior. Next, to achieve computational efficiency and enable a large range of simulations for a parametric study, a simplified 'beam-on-springs' model is developed, wherein the longitudinal reinforcing bar in a column is isolated and simulated as a flexural member. The restraining mechanism provided by transverse reinforcement is represented by springs at the location of each transverse bar. The simplified model is validated through comparison of average stress-strain curves with simulations obtained from high-fidelity FE analyses. It is shown that stress-strain response is primarily a function of the ratio of the buckling length to the diameter of the longitudinal bar. Findings from this work provide insight into key factors that influence bar buckling in circular RC columns and provide guidelines for constitutive modeling of the compression behavior of reinforcing bars.

Ductile Structure Framework of Earthquake Resistant of Highrise Building on Exterior Beam-Column Joint with the Partial Prestressed Concrete Beam-Column Reinforced Concrete

Abstract A monolithic exterior beam-column joints without plastic-hinges on the beam is designed as a model structure of the Special Moment brace using a partially prestressed concrete beams with dimension of 250/400 mm, tensile reinforcements of 5 D13 and 3 D13 at the top section and bottom, respectively, and 1(one) Freyssinet tendon with 2 (two) strands of ∅17.7 mm and transverse bars of ∅ 8-75 mm. The column is designed with section dimension of 400/400 mm, with the main reinforcements of 6 D16 + 4D13, and the transverse bars of ∅ 10-50 mm. Experimental studies in laboratory are proposed with lateral load dynamik (pseudo dynamic) applied on the beam, and static load applied on the column as a stabilizer.The goal is to get the level of ductility of the structure of μ = (δ_max/δ_(first yielding)), calculated until the condition of stable structures. The expected results could provide a basis in the development of framework design of earthquake resistant structures.

Two Kinds of Cold Working Steel Performance Contrast Research

In project practice, Anchor ability of coupled steel bars concrete will higher than cold rolling belt rib steel bars. So, more economical steel bars and cement contents. Through comparative trial about on concretes component of coupled steels bars and cold rolling belt rib steel bars in this article. Summarizes that anchor ability of Low-alloy coupled steels are depending transverse steel, well, steel bars and concretes has the better joint work ability.