Towards continuous long-term measurements of suspended particulate matter (SPM) in turbid coastal waters

The dynamics of sediment transport in the East Frisian Wadden Sea are important for the coastal zone and for ecosystem functioning. The tidal inlets between the East Frisian islands connect the back-barrier intertidal flats to the North Sea. Here, concentrations of suspended particulate matter (SPM) in the water column are highly variable, depending on weather conditions and tides. In order to estimate the nature and quantity of sediment transport, in situ measurements were carried out at a Time Series Station in the tidal inlet between the islands of Spiekeroog and Langeoog. This study shows the suitability of multispectral transmissometry (MST) for obtaining long-term SPM measurements with high resolution. The comparability of this technique to the standard filter method and the laser diffraction method [laser in situ scattering and transmissometry (LISST)] is demonstrated. In addition, the Junge coefficients derived from both MST and LISST measurements are compared. A time series of SPM data covering nearly 4 months is presented. As a major result, the data reveal that a single storm surge can have less impact on SPM dynamics than longer-lasting gales. This high-resolution long-term data set is very valuable for modelling suspended matter flux. It also provides background information for studying the influence of SPM dynamics on coastal sediments.     

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.     

Dynamics of multiple intertidal bars over semi‐diurnal and lunar tidal cycles,North Lincolnshire,England

Multiple intertidal bars are common features of wave‐dominated sandy beaches, yet their short‐term (<1 month) and small‐scale (<1 km) morphology and dynamics remain poorly understood. This study describes the morphodynamics of multiple intertidal bars in North Lincolnshire, England, during single and lunar tidal cycles under two contrasting conditions – first when significant wave height was <0·5 m and second when significant wave height frequently exceeded 1 m. The relative importance of swash, surf and shoaling processes in determining morphological change was examined using detailed field observations and a numerical model. The beach featured four intertidal bars and both cross‐shore and longshore bar morphology evolved during the field investigation, particularly under medium to high wave‐energy conditions. Numerical modelling suggests shoaling processes are most common on the seaward two bars under calm wave conditions (H_s < 0·5 m) and that surf zone processes become more common during neap tides and under more energetic (H_s < 0·5 m) conditions. Surf processes dominate the inner two bars, though swash influence increases in a landward direction. The numerical modelling results combined with low tide survey data and high‐resolution morphological measurements strongly suggest changes in the intertidal bar morphology are accomplished by surf zone processes rather than by shoaling wave or swash processes. This is because shoaling waves do not induce significant sediment transport to have any morphological effect, whereas swash action generally does not have enough scope to act as the swash zone is much narrower than the surf zone. It was found, however, that the absolute rate of morphological change under swash action and surfzone processes are of similar magnitudes and that swash action may induce a significant amount of local morphological change when the high tide mark is located on the upper bar, making this process important for bar morphodynamics. Copyright © 2007 John Wiley & Sons, Ltd.     

Characteristics and dynamics of multiple intertidal bars,north Lincolnshire,England

Multiple intertidal bars and troughs, often referred to as ‘ridges and runnels’, are significant features on many macrotidal sandy beaches. Along the coastline of England and Wales, they are particularly prevalent in the vicinity of estuaries, where the nearshore gradient is gentle and a large surplus of sediment is generally present. This paper examines the dynamics of such bar systems along the north Lincolnshire coast. A digital elevation model of the intertidal morphology obtained using LIDAR demonstrates that three to five intertidal bars are consistently present with a spacing of approximately 100 m. The largest and most pronounced bars (height = 0·5–0·8 m) are found around mean sea level, whereas the least developed bars (height = 0·2–0·5 m) occur in the lower intertidal zone. Annual aerial photographs of the intertidal bar morphology were inspected to try to track individual bars from year to year to derive bar migration rates; however, there is little resemblance between concurrent photographs, and ‘resetting’ of the intertidal profile occurs on an annual basis. Three‐dimensional beach surveys were conducted monthly at three locations along the north Lincolnshire coast over a one‐year period. The intertidal bar morphology responds strongly to the seasonal variation in the forcing conditions, and bars are least numerous and flattest during the more energetic winter months. Morphological changes over the monthly time scale are strongly affected by longshore sediment transport processes and the intertidal bar morphology can migrate along the beach at rates of up to 30 m per month. The behaviour of intertidal bars is complex and varies over a range of spatial and temporal scales in response to a combination of forcing factors (e.g. incident wave energy, different types of wave processes, longshore and cross‐shore sediment transport), relaxation time and morphodynamic feedback. Copyright © 2005 John Wiley & Sons, Ltd.     

PERFORMANCE EVALUATION OF SUBMERGENCE RATIO OF A RECTANGULAR SUBMERGED VANE WITH A COLLAR

1 INTRODUCTION Odgaard and Kennedy (1983) suggested that for values of angle of attack, α greater than or equal to approximately 20o, a persistent scour hole is produced near the upstream end of a vane. As α was reduced the number of vanes producing obj…     

DIKE FORMATION WITH SUBMERGED VANE

1 INTRODUCTION Increasing capital costs, emerging environmental concerns and rising maintenance expenses of conventional river training works around the world have led to the development of submerged vanes in practice. Submerged vanes are being favoured f…     

Morphodynamics and sediment dynamics on intertidal mudflats in China (1961–1994)

This paper presents an overview of the significant research on morphodynamics and sediment dynamics on intertidal mudflats in China (1961–1994), particularly in the past 15 years (1980–1994). Development of intertidal mudflats has long been regarded as the response of the intertidal profile to tides, waves and storms. It has been found that there were long-term and short-term cyclic developments of intertidal mudflats in China. Three sedimentological zones have generally been identified from land to sea within the intertidal zone: high mudflat, middle mudflat and low mudflat. In addition, the sediments in the middle mudflat are relatively coarser than those in the high mudflat and low mudflat. Storms have great impacts on the intertidal morphology, sediment textures and sedimentary structures. Based on field investigations of intertidal sedimentary processes, many researchers have found that “settling and scour lags” were only applicable to intertidal cohesive sediment transport during periods of weak waves, but not during storms. In fact, flood fronts, waves, storm surges and longshore drift play important roles in suspended sediment transport on open intertidal mudflats in China. Despite of these extensive studies in the past several decades, there is still a need for an improved understanding of fundamental physical and biological processes governing erosion and deposition of cohesive fine sediment within the intertidal zone in China.     

Short‐term intertidal bar mobility on a ridge‐and‐runnel beach,Merlimont, northern France

Digital elevation models and topographic pro?les of a beach with intertidal bar and trough (ridge‐and‐runnel) morphology in Merlimont, northern France, were analysed in order to assess patterns of cross‐shore and longshore intertidal bar mobility. The beach exhibited a pronounced dual bar–trough system that showed cross‐shore stationarity. The bars and troughs were, however, characterized by signi?cant longshore advection of sand under the in?uence of suspension by waves and transport by strong tide‐ and wind‐driven longshore currents. Pro?le changes were due in part to the longshore migration of medium‐sized bedforms. The potential for cross‐shore bar migration appears to be mitigated by the large size of the two bars relative to incident wave energy, which is modulated by high vertical tidal excursion rates on this beach due to the large tidal range (mean spring tidal range = 8·3 m). Cross‐shore bar migration is also probably hindered by the well‐entrenched troughs which are maintained by channelled high‐energy intertidal ?ows generated by swash bores and by tidal discharge and drainage. The longshore migration of intertidal bars affecting Merlimont beach is embedded in a regional coastal sand transport pathway involving tidal and wind‐forced northward residual ?ows affecting the rectilinear northern French coast in the eastern English Channel. Copyright © 2004 John Wiley & Sons, Ltd.     

Burying response of an intertidal gastropod to freshwater and copper contamination

The effects of sublethal concentrations of freshwater and copper on the burying responses of the intertidal marine gastropod, Polinices incei, are presented. Such responses are inhibited by both pollutants and the two also act additively. Behavioural responses obtained in a 30 min assay were found to be good predictors of the results of 96 h lethal assays. The results are discussed in light of previous work.     

电缆地层测试器在渗透率各向异性地层中的响应

为正确地设计仪器和解释电缆地层测试器的测量结果,文中建立了渗透率各向异性地层中电缆地层测试器响应的数学模型,并利用三维有限元方法得到其数值,解得到了压力场随时间、距离变化及等压面等的各种结果。     

Nearshore intertidal topography and topographic-forcing mechanisms of an Amazon-derived mud bank in French Guiana

The intertidal topography in the vicinity of the contact zone between a longshore-migrating Amazon-derived mud bank and the muddy terrestrial shoreline in French Guiana was defined from a combination of satellite-based SPOT images, airborne lidar data and high-resolution total station ground surveying of a 75,000 m² plot. The three approaches, at different scales, were carried out at different periods. Digital elevation models generated from these three techniques, however, converge in highlighting the topographic micro-scale (centimetre-scale) variability of the mud bank surface while showing meso- to macro-scale features that reflect the dominance of wave activity in mud bank mobilization and attachment to the terrestrial shoreline. These features are bar-like longshore forms that develop in the intertidal zone from the shoreward drift of gel-like mud that accompanies wave damping. The features progressively become consolidated through mud drying out associated with the formation of cracks that are important in mangrove colonization and ecological changes. Fluid-mud accumulations formed from high concentrations of mud trapped in the troughs behind these linear bar forms generate flat featureless surfaces that tend to mask topographic heterogeneity of the mud bank surface. Dewatering of these lower zones by progressive mud consolidation complements tidal water discharge in providing a mechanism for the formation of the numerous channels that dissect the linear bar features, especially in the upper intertidal contact zone with the terrestrial shoreline. This dissection in the upper intertidal zone generates an intricate topography that replaces the original linear bar forms. The innermost bar forms a ‘suture’ zone with the terrestrial shoreline. Reworking of this bar by high-energy waves may lead to mud dispersal over old terrestrial mangrove substrates, resulting in stifling of mangrove pneumatophores. Mud reworking at the narrow trailing edge of the mud bank in the subtidal and lower intertidal zones leaves behind a flat bed that will eventually be completely eroded by waves in the course of mud bank migration.     

A Comparison of Hyporheic Transport at a Cross‐Vane Structure and Natural Riffle

While restoring hyporheic flowpaths has been cited as a benefit to stream restoration structures, little documentation exists confirming that constructed restoration structures induce comparable hyporheic exchange to natural stream features. This study compares a stream restoration structure (cross‐vane) to a natural feature (riffle) concurrently in the same stream reach using time‐lapsed electrical resistivity (ER) tomography. Using this hydrogeophysical approach, we were able to quantify hyporheic extent and transport beneath the cross‐vane structure and the riffle. We interpret from the geophysical data that the cross‐vane and the natural riffle induced spatially and temporally unique hyporheic extent and transport, and the cross‐vane created both spatially larger and temporally longer hyporheic flowpaths than the natural riffle. Tracer from the 4.67‐h injection was detected along flowpaths for 4.6 h at the cross‐vane and 4.2 h at the riffle. The spatial extent of the hyporheic zone at the cross‐vane was 12% larger than that at the riffle. We compare ER results of this study to vertical fluxes calculated from temperature profiles and conclude significant differences in the interpretation of hyporheic transport from these different field techniques. Results of this study demonstrate a high degree of heterogeneity in transport metrics at both the cross‐vane and the riffle and differences between the hyporheic flowpath networks at the two different features. Our results suggest that restoration structures may be capable of creating sufficient exchange flux and timescales of transport to achieve the same ecological functions as natural features, but engineering of the physical and biogeochemical environment may be necessary to realize these benefits.     

The Gladstone (Australia) oil spill - impacts on intertidal areas: baseline and six months post-spill

In January 2006, 25 tonnes of heavy fuel oil spilled into the Port of Gladstone in Queensland, Australia, from the breached hull of a bulk carrier ship. While approximately 18 tonnes of the oil was recovered, a certain amount of oil was deposited in the intertidal areas of Port Curtis leaving a highly visible, viscous residue. The objectives of this research were to assess the short-term (one month post-spill) and medium-term (six months post-spill) impacts on the intertidal habitat.Sediment polycyclic aromatic hydrocarbons (PAHs) and metal concentrations, mangrove communities and intertidal macroinvertebrates were assessed at oil impacted sites, adjacent sites which were not visibly impacted and reference sites which were located outside the recorded distribution of the oil spill.At one month post-spill, highest PAH concentrations were found at the impacted sites, with concentrations of some PAHs exceeding Australian and New Zealand sediment quality guidelines (SQG) [ANZECC/ARMCANZ, 2000. Sediment Quality Guidelines. Australia and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand]. However, by six months post-spill PAH concentrations had significantly decreased. PAH concentrations tended to be higher in the back (upper) intertidal zone than at the front of the mangrove stand, and sediment cores indicated that PAH contaminants had remained in the top 4 cm of the sediment. These results indicate that the overall decreased PAH concentrations are likely to be due to evaporation, photoxidation and tidal flushing of the residual oil in these impacted sites.During the initial survey, the impact site contained very few or no crabholes in the high intertidal area, indicating a low crab density in comparison to reference sites. However, at six months post-spill mangrove crab communities appeared to be fully recovered with crabhole densities in impact sites similar to reference sites.While little immediate impact was evident on mangrove parameters, significantly higher seedling mortality and defoliation was apparent at six months post-spill, particularly in the upper intertidal zone. Intertidal macrobenthic communities did not appear to be impacted, either immediately or at six months post-spill. Monitoring of these oil impacted intertidal areas will continue to examine the long-term impacts/recovery from the oil spill.     

Characterisation and sediment–source linkages of intertidal sediment of the UK’s north Sefton Coast using magnetic and textural properties: findings and limitations

Sediment pathways and links to offshore processes are considered in the textural and magnetic characteristics of sediments of the intertidal flats and salt marshes of the north Sefton Coast, UK. In addition, sediment from a range of intertidal, marine and fluvial locations within the northwest region has similarly been characterised. Subsequently, the characteristics of these regional sediments, using a multivariate statistical approach of R- and Q-mode factor analyses, have been used to investigate the sediment transport pathways of the north Sefton Coast sediment. The benefits of fractionating sediment samples have been observed, and by using combinations of textural and isothermal remanent magnetic measurements, specific environments within the research have been successfully differentiated and characterised. Linkages between potential sediment source areas have also been established on a particle size-related basis.     

Spatial heterogeneity in estuarine mud dynamics

The fate of mud in an estuary over an entire year was unravelled using complementary, independent, spatially explicit techniques. Sequential ERS-2 SAR and Envisat MERIS-FR data were used to derive synoptic changes in intertidal bottom mud and suspended particulate matter (SPM) in the top of the water column, respectively. These satellite data were combined with in situ measurements and with a high resolution three-dimensional cohesive sediment model, simulating mud transport, resuspension, settling and deposition under the influence of tides, wind, waves and freshwater discharge. The spatial distribution of both bottom mud and SPM as observed by in situ and satellite techniques was largely explained by modelled estuarine circulation, tidal and wind-induced variations in vertical mixing and horizontal advection. The three data sources also showed similar spring-neap and seasonal variations in SPM (all factor 1.5 to 2), but semi-diurnal tidal variations were underestimated by the model. Satellite data revealed that changes in intertidal bottom mud were spatially heterogeneous, but on average mud content doubled during summer, which was confirmed by in situ data. The model did not show such seasonal variation in bed sediment, suggesting that seasonal dynamics are not well explained by the physical factors presently implemented in the model, but may be largely attributed to other (internal) factors, including increased floc size in summer, temporal stabilisation of the sediment by microphytobenthos and a substantially lower roughness of the intertidal bed in summer as observed by the satellite. The effects of such factors on estuarine mud dynamics were evaluated.     

Temporal and spatial behaviour of rip channels in a multiple‐barred coastal system

A 15‐month data set of daily time‐averaged video images (Argus) has been analyzed to describe the spatial and temporal variability of the rip channels on a multiple‐barred coast at Noordwijk aan Zee, The Netherlands. The landward boundary of the intertidal bars and a proxy of the subtidal bar crest, defined as the intertidal and subtidal bar lines respectively, were derived from the Argus images. Local seaward‐directed deviations of the bar lines represent the cross‐shore and alongshore locations of the rip channels. The average intertidal rip spacing ( ) was 243 m, but the rips were not spaced regularly (σ_λ/ = 0.47). Some intertidal rips were observed to fill up during falling tide, but the majority remained open. The filled intertidal rip channels had more landward positions and migrated more slowly (2.4 versus 4.6 m/day) in the alongshore direction than the open intertidal rip channels. The number and the alongshore migration rate of open intertidal rip channels increased with the preceding wave heights (r = 0.26, p < 0.01) and alongshore component of the offshore wave power (r = 0.25, p < 0.01), respectively. The shape of the intertidal bar lines was similar to the subtidal bar line shape, suggesting that the intertidal morphology is coupled to the subtidal alongshore variability. The phase of two bar lines could vary from in phase (0°) to out of phase (180°). The phase changes gradually, due to different alongshore migration rates of the intertidal and subtidal bar lines. Copyright © 2009 John Wiley & Sons, Ltd.     

Colonization and weathering of engineering materials by marine microorganisms: an SEM study

Microorganisms are a ubiquitous feature of most hard substrata on Earth and their role in the geomorphological alteration of rock and stone is widely recognized. The role of microorganisms in the modification of engineering materials introduced into the intertidal zone through the construction of hard coastal defences is less well understood. Here we use scanning electron microscopy (SEM) to examine microbial colonization and micro‐scale geomorphological features on experimental blocks of limestone, granite and marine concrete after eight months' exposure in the intertidal zone in Cornwall, UK. Significant differences in the occurrence of microbial growth features, and micro‐scale weathering and erosion features were observed between material types (ANOVA p < 0·000). Exposed limestone blocks were characterized by euendolithic borehole erosion (99% occurrence) within the upper 34·0 ± 12·3 µm of the surface. Beneath the zone of boring, inorganic weathering (chemical dissolution and salt action) had occurred to a depth of 125·0 ± 39·0 µm. Boring at the surface of concrete was less common (27% occurrence), while bio‐chemical crusting was abundant (94% occurrence, mean thickness 45·1 ± 27·7 µm). Crusts consisted of biological cells, salts and other chemical precipitates. Evidence of cryptoendolithic growth was also observed in limestone and concrete, beneath the upper zone of weathering. On granite, biological activity was restricted to thin epilithic films (<10 µm thickness) with some limited evidence of mechanical breakdown. Results presented here demonstrate the influence of substratum lithology, hardness and texture on the nature of early micro‐scale colonization, and the susceptibility of different engineering materials to organic weathering and erosion processes in the intertidal zone. The implications of differences in initial biogeomorphic responses of materials for long‐term rock weathering, ecology and engineering durability are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Bio‐geomorphic effects on tidal channel evolution: impact of vegetation establishment and tidal prism change

The long‐term (10–100 years) evolution of tidal channels is generally considered to interact with the bio‐geomorphic evolution of the surrounding intertidal platform. Here we studied how the geometric properties of tidal channels (channel drainage density and channel width) change as (1) vegetation establishes on an initially bare intertidal platform and (2) sediment accretion on the intertidal platform leads to a reduction in the tidal prism (i.e. water volume that during a tidal cycle floods to and drains back from the intertidal platform). Based on a time series of aerial photographs and digital elevation models, we derived the channel geometric properties at different time steps during the evolution from an initially low‐elevated bare tidal flat towards a high‐elevated vegetated marsh. We found that vegetation establishment causes a marked increase in channel drainage density. This is explained as the friction exerted by patches of pioneer vegetation concentrates the flow in between the vegetation patches and promotes there the erosion of channels. Once vegetation has established, continued sediment accretion and tidal prism reduction do not result in significant further changes in channel drainage density and in channel widths. We hypothesize that this is explained by a partitioning of the tidal flow between concentrated channel flow, as long as the vegetation is not submerged, and more homogeneous sheet flow as the vegetation is deeply submerged. Hence, a reduction of the tidal prism due to sediment accretion on the intertidal platform, reduces especially the volume of sheet flow (which does not affect channel geometry), while the concentrated channel flow (i.e. the landscape forming volume of water) is not much affected by the tidal prism reduction. Copyright © 2012 John Wiley & Sons, Ltd.     

Preliminary hydrodynamic results of a field experiment on a barred beach, Truc Vert beach on October 2001

A field experiment conducted on a sandy barred beach, situated on the southern part of the French Atlantic coastline, allowed us to investigate the impact of the intertidal bar on the wave-energy dissipation on the beach face in presence of a high-energy long-incoming swell (significant wave height of about 1.7 to 3.0 m in 56 m water depth and significant wave period about 12 s). Data were collected along three parallel cross-shore transects deployed along an intertidal ridge and runnel system. Wave heights in the inner surf zone are depth-limited, consistent with previous works, and the wave-energy dissipation in the inner surf zone appears to be relatively independent of the offshore energy level. On the other hand, the presence of the bar seems to scatter the data. In models of surf-zone hydrodynamics, wave-energy dissipation is often parameterized in terms of , the ratio of the sea-swell significant wave height to the local mean water depth. The observed values of are not constant along a cross-shore transect, and increase onshore. Furthermore, the observed values observed onshore the intertidal bar are higher than those observed outside the influence of the intertidal bar, and this cannot be fully explained by the different local beach slope.Responsible Editor: Iris Grabemann