Longshore sediment transport in the surf zone based on different formulae: a case study along the central west coast of India

Understanding longshore sediment transport (LST) is a prerequisite for designing an effective coastal zone management strategy. The present study estimates the LST along the central west coast of India based on four bulk LST formulae: (1) the Coastal Engineering Research Center (CERC) formula, (2) the Walton and Bruno formula, (3) the Kamphuis formula and (4) the Komar formula. The Delft3D–wave module is used for estimating nearshore waves with measured directional wave data at a water depth of 9 m as the input parameter. Wave data for the validation of the nearshore wave transformation model is measured using the InterOcean S4DW wave gauge. The model results show that waves approach from the south 90 % of the time in a year and that they generate predominantly northerly longshore currents. Upon comparison with the measured data, the findings show that the estimates based on the Kamphuis formula agree with the field data. A high ratio (~1) of the monthly net and gross transport rates indicates that the LST is dominating in one direction in all months except February and July. The study shows that a slight change in the angle of the wave approach during the Asian summer monsoon period (JJAS) can significantly alter the direction and magnitude of the LST. Inter-annual variations in the LST based on the data for 2009 and 2011 show that the variations in the annual net and gross LST rates in different years are less than 7 %.     

Towards an effective framework for coastal zone management: the Egyptian experience

Coastal areas are among the most highly populated, most exploited areas and vulnerable ecosystems in the world. How these interface areas between terrestrial and marine environments can effectively planned and managed has proved to be extremely challenging. Integrated Coastal Zone Management (ICZM) has been promoted as a potential panacea for the effective planning and management of these areas. However achieving such goals for ICZM is complex because of the many human activities and diverse regulatory regimes in coastal areas requires effective integration along many dimensions. Within the context of the developing world, which is often characterised by highly centralised governance systems combined with a lack of effective public and stakeholder participation in planning delivering an effective ICZM, which is drawn from collaborative planning ideas has proved particularly problematic. Furthermore within these countries there have been few critical and analytical evaluations of why ICZM experiments have failed. This paper seeks to begin to address this gap by suggesting that Actor Network Theory (ANT) is an appropriate analytical framework to critically evaluate why ICZM initiatives in Egypt, at both the national and local level, have been relatively unsuccessful. The critical evaluation leads to some practical recommendations that could help to enhance the implementation of ICZM in Egypt.     

Restoration and sequestration of carbon and nitrogen in the degraded northern coastal area in Nile Delta,Egypt for climate change mitigation

Most of coastal area in Nile Delta, Egypt, is salt-affected soils and have low carbon (C) and nitrogen (N) inputs as a result of declining vegetation growth and low net primary production. Therefore, this study amid to compare between C and N pools in degraded (uncultivated and salt-affected soil) and restored (cultivated and reclaimed 20 years ago) locations in North Nile Delta. and to examine the impact of cultivation on sequestering C and N pools in this area as one of the most important methods for mitigating climate change impacts. C and N pools increased significantly in surface soil from 2.99 and 0.43 Mgh^?1 in uncultivated sites to 19.26 and 1.66 Mgh^?1 in cultivated ones as salinity was reduced and net primary production was increased due to leaching and reclamation. Particulate (associated with sand) and nonparticulate (associated with clay +silt) soil organic C or N was significantly higher cultivated sites. In addition, nonparticulate organic C or N was lower than particulate part indicating and supporting the strong relationship between organic matter and clay. The sequestration rate (in approximately 1 m profile) was 1.69 and 0.14 Mgh^?1 yr.^?1 C and N pools respectively. Although the cultivation is leading to loss of organic matter in some areas; C and N in this coastal area are partially restored and stored. Therefore, restoration and appropriate management practices will lead to mitigate the negative impacts of climate change in this area.     

Marsh surface sediment deposition and the role of tidal creeks: Implications for created and managed coastal marshes

The need to understand the processes contributing to marsh sedimentation has become more urgent with the recent recognition of the role of tidal marshes as sea defences, as well as the many restoration efforts currently under way. This study was designed to build upon previous sedimentation work at Scolt Head Island by Combining techniques for measuring short-term sedimentation, with detailed assessment of hydroperiod, previously used only in comparison with longer-term accretion measurements or in micro-tidal systems. Measurements of water level, sediment deposition (at various distances from the creek margin) and suspended sediment concentration (SSC) (creek margin and an interior site) were made at Hut Marsh over three sequential over-marsh tides during May 1994. Sediment trap data show a significant trend of declining sediment deposition away from the creek when data from all three tides are combined. All tides show higher SSC on the flood tide than on the ebb tide at the creek margin location. There is little difference in flood and ebb SSCs at the interior site. An order of magnitude decrease in sediment deposition within 20 m on the creek shows the rapidity with which sediment is deposited on these marshes. Higher tides influence both the magnitude and pattern of marsh surface sediment deposition. Increased creek velocities on higher tides provide more potential for resuspension within the creek and increase the supply of sediment to the marsh surface. This study suggests that the design of tidal creeks may be essential for the development of sustainable coastal marshes in restoration projects.     

Hierarchical modeling of the dilute transport of suspended sediment in open channels

We propose, discuss and validate a theoretical and numerical framework for sediment-laden, open-channel flows which is based on the two-fluid-model (TFM) equations of motion. The framework models involve mass and momentum equations for both phases (sediment and water) including the interactive forces of drag, lift, virtual mass and turbulent dispersion. The developed framework is composed by the complete two-fluid model (CTFM), a partial two-fluid model (PTFM), and a standard sediment-transport model (SSTM). Within the umbrella of the Reynolds-Averaged Navier-Stokes (RANS) equations, we apply K–ε type closures (standard and extended) to account for the turbulence in the carrier phase (water). We present the results of numerical computations undertaken by integrating the differential equations over control volumes. We address several issues of the theoretical models, especially those related to coupling between the two phases, interaction forces, turbulence closure and turbulent diffusivities. We compare simulation results with various recent experimental datasets for mean flow variables of the carrier as well as, for the first time, mean flow of the disperse phase and turbulence statistics. We show that most models analyzed in this paper predict the velocity of the carrier phase and that of the disperse phase within 10% of error. We also show that the PTFM provides better predictions of the distribution of sediment in the wall-normal direction as opposed to the standard Rousean profile, and that the CTFM is by no means superior to the PTFM for dilute mixtures. We additionally report and discuss the values of the Schmidt number found to improve the agreement between predictions of the distribution of suspended sediment and the experimental data.     

Perfluorinated compounds in water and sediment from coastal regions of the northern Bohai Sea,China

Concentrations of perfluorooctanesulfonate (PFOS), perfluorooctanoic acid (PFOA) and other perfluorinated compounds (PFCs) were measured in water and sediment from coastal Bohai Bay and surrounding rivers flowing into the bay. Of the 15 PFCs measured, PFOS and PFOA were detected with the greatest frequency. Concentrations in water ranged from<0.2 to 31 ng·L^?1 and<1.0 to 82 ng·L^?1 for PFOS and PFOA, respectively. Concentrations of PFOS and PFOA in sediments ranged from<0.1 to 2.0 ng·g^?1 dw and<0.1 to 0.5 ng·g^?1 dw, respectively. Concentrations of PFCs in Bohai Bay were less than those observed in other areas in Asia, but greater concentrations of ∑PFCs were observed in the Dalin River with concentrations increasing from upstream to downstream, and the greatest concentrations in sediment were observed in tidal flats. The ratio of ∑PFCs in sediment and water indicated that sediment could serve as a significant sink for PFUnA.     

On force consideration in coupled ISPH framework for sediment transport in presence of free-surface flow

A coupled divergence-free Incompressible Smoothed Particle Hydrodynamics (ISPH) framework for sediment transport is extended for application in generalized free-surface flow situations. The computation of interaction force pair between pure fluid and sediment modules makes the model flexible enough to be applicable for diverse scenarios with variable resolutions. Three scenarios are included to quantify the contribution of individual components in the force pair. First two scenarios with rapid free-surface variation highlight the effect of fluid pressure gradient on granular flow. The third scenario with minimal free-surface variation considers bed movement under a horizontal marine pipeline for a prolonged time period. The framework can simulate sediment transport for generalized problems with slowly/rapidly varying free-surface flow conditions.     

Evaluation of spatiotemporal differences in suspended sediment concentration derived from remote sensing and numerical simulation for coastal waters

Remote sensing and numerical models are often used to monitor the suspended sediment concentration (SSC) in coastal waters; however, the derived SSC varies between the two methods in both space and time. In this study, a method was proposed to assess the spatiotemporal differences in SSC derived from Moderate Resolution Imaging Spectroradiometer (MODIS) images and numerical simulation for coastal waters, using the Bohai Sea in China as an example. An empirical model for SSC retrieval from remote sensed images was initially established. A comparison of the temporal synchronicity over a single day period was performed between the observed data and the numerically simulated results. The range in the SSC at different observation sites was significantly different. Both the SSC values and their daily variation ranges were larger near the estuary of the Yellow River compared with the open area due to the concurrence of tidal flow and the introduction of fresh river water with high turbidity near the estuary. The areas that exhibited spatial differences were defined according to their differences in remotely sensed and numerically simulated SSC distribution patterns. Finally, the reasons for these spatiotemporal differences were discussed. The results provided understanding into the spatiotemporal differences that were introduced when multi-source data were used, thus improving the accuracy of the results when monitoring coastal environments for the management of coastal conservation.     

Application of geographic information system technique and analytical hierarchy process model for land-use suitability analysis on coastal area

Land-use suitability is the ability of a given type of land to support a defined use. GIS is known as a powerful tool for handling spatial data in land-use analysis. Application of this tool alone cannot overcome the lack of consistency in opinions given by experts when trying to assign relative importance to each of the several criteria considered in a suitability analysis. The combination of GIS and Multi-Criteria Decision Analysis (MCDA) is a powerful approach used to assess land suitability. To address this issue, the Analytical Hierarchy Process method is used in combination with the GIS tool. The aim of this study is to demonstrate how GIS tools and AHP model can be used for integrated coastal resource planning and management. Based on the information from final map/suitability map, we can define the best area. The findings indicate that the area 1 (2111 m) from class 3 is the most appropriate one because it has good facilities and wide open areas. This study indicates how the integrated tool is handled effectively in a land use suitability analysis for building hotels in the coastal areas of Terengganu in Malaysia. This research develops a framework for integrating GIS and AHP to incorporate the decision maker’s preferences on a range of factors in finding land areas suitable for coastal development.     

Scales of similarity in soft sediment epibenthic assemblages: implications for marine protected area design

Remote videography was used to investigate relationships between biological similarity and distance in Moreton Bay, Australia at site (1 km) and local (10 km) scales, and for separate biotic groups. Numerical analysis using Mantels tests to compare distance and similarity matrices showed that at both scales there was a negative correlation between similarity and distance, in that sites further apart were less similar than sites close together. The relationship, although significant (p <0.001), was quite weak (R²=5%) at the site-scale, with no significant (ANOVA with Tukeys pairwise comparisons, p >0.05) decline in similarity up to distances of 2.1–2.6 km. At the local-scale, between-site similarity was high (mean Bray-Curtis similarity >30% for 4th root transformed data) at scales of 10 km or less, and declined markedly with increasing distance. Scales of similarity for different broad taxonomic and functional groups within Moreton Bay were broadly consistent between groups and with the complete dataset. There was evidence of patchiness in the distributions of seagrass and anthozoans at scales less than 16 km. In other biotic groups there was an essentially monotonic decline in similarity with distance. The study showed that the spatial classification approach to habitat mapping is valid in this case, and that site spacing of less than 10 km is necessary to capture important components of biological similarity. Site spacing of less than 2.5 km does not appear to be warranted to capture additional components of biological similarity at the scales studied.Communicated by G.F. Humphrey, Sydney     

滨海盐田建设对周边土壤及植被的影响

随着滨海盐业的迅猛发展,盐田的急剧扩张已经对周边环境产生了影响。通过调查盐田周边植被分布特征,分析与植被带对应的典型样地土壤理化性质的空间异质性,研究了盐田对周边土壤及植被的影响。结果表明：盐田周边的植被分布存在明显的空间异质性,在盐田周边呈带状分布,且距盐田越近,植被盖度、物种丰富度越低。土壤含盐量的空间分布在宏观上表现为距盐田越近,含盐量越高,土壤盐渍化越重。距离盐田20m处土壤含盐量平均值达8.22g·kg-1,距离盐田1000m处,土壤含盐量平均值为1.84g·kg-1,土壤含盐量显著降低,且表层土壤含盐量与采样地距盐田间的距离之间呈显著相关关系。由此可见,盐田的扩建已经显著加重了周边土壤的盐渍化程度。     

The effects of intensive aquaculture on nutrient residence time and transport in a coastal embayment

Aquaculture in many countries around the world has become the biggest source of seafood for human consumption. While it alleviates the pressure on wild capture fisheries, the long-term impacts of large-scale, intensive aquaculture on natural coastal systems need to be better understood. In particular, aquaculture may alter habitat and exceed the carrying capacity of coastal marine ecosystems. In this paper, we develop a high-resolution numerical model for Sanggou Bay, one of the largest kelp and shellfish aquaculture sites in Northern China, to investigate the effects of aquaculture on nutrient transport and residence time in the bay. Drag from aquaculture is parameterized for surface infrastructure, kelp canopies, and bivalve cages. A model for dissolved inorganic nitrogen (DIN) includes transport, vertical turbulent mixing, sediment and bivalve sources, and a sink due to kelp uptake. Test cases show that, due to drag from the dense aquaculture and thus a reduction of horizontal transport, kelp production is limited because DIN from the Yellow Sea is consumed before reaching the interior of the kelp farms. Aquaculture drag also causes an increase in the nutrient residence time from an average of 5 to 10 days in the middle of Sanggou Bay, and from 25 to 40 days in the shallow inner bay. Low exchange rates and a lack of DIN uptake by kelp make these regions more susceptible to phytoplankton blooms due to high nutrient retention. The risk is further increased when DIN concentrations rise due to river inflows.     

Pre- and post-beach response to engineering hard structures using Landsat time-series at the northwestern part of the Nile delta,Egypt

Analyses have been undertaken to examine shoreline positions established from remote sensing data along the northwestern part of the Nile delta from the Abu Qir Bay to Gamasa embayment (∼143 km length). The image data used (MSS, TM and ETM+ sensors) are acquired at unequal intervals between 1972 and 2006, i.e., covering a time span of 34 years. Automated waterline positions extracted from Landsat satellite images during this period of time were computer generated. A digital shoreline analysis software was used to calculate the annual rate of beach changes at 1,432 cross-shore transects prior to (1972–1990) and after protection (1993–2006). On comparison, rates estimated from three statistical approaches (the end point rate, the Jackknife and a weighted linear regression) at corresponding positions are successfully validated with those measured from ground survey. Before protection, results reveal longshore patterns wherein erosion along a coastal stretch gives way to accretion in an adjacent stretch, refining the sub-cells previously identified within the littoral system of the delta. Maximum shoreline retreat occurs along the Rosetta promontory (−138.52 m/year) and along the central bulge of the delta at Burullus headland (−6.07 m/year). In contrast areas of shoreline accretion exist within saddles or embayments between the promontories at west Abu Qir Bay (20.04 m/year), Abu Khashaba saddle (16.17 m/year) and Gamasa embayment (20.68 m/year). These rates of changes have been significantly altered by the construction of intensive shoreline protective structures built from 1990 to combat areas of rapid erosion at both the Rosetta promontory and Burullus–Baltim headland, ∼15-km length in total.     

Characterization of bedload intermittency near the threshold of motion using a Lagrangian sediment transport model

At the smallest scales of sediment transport in rivers, the coherent structures of the turbulent boundary layer constitute the fundamental mechanisms of bedload transport, locally increasing the instantaneous hydrodynamic forces acting on sediment particles, and mobilizing them downstream. Near the critical threshold for initiating sediment motion, the interactions of the particles with these unsteady coherent structures and with other sediment grains, produce localized transport events with brief episodes of collective motion occurring due to the near-bed velocity fluctuations. Simulations of these flows pose a significant challenge for numerical models aimed at capturing the physical processes and complex non-linear interactions that generate highly intermittent and self-similar bedload transport fluxes. In this investigation we carry out direct numerical simulations of the flow in a rectangular flat-bed channel, at a Reynolds number equal to Re = 3632, coupled with the discrete element method to simulate the dynamics of spherical particles near the bed. We perform two-way coupled Lagrangian simulations of 48,510 sediment particles, with 4851 fixed particles to account for bed roughness. Our simulations consider a total of eight different values of the non-dimensional Shields parameter to study the evolution of transport statistics. From the trajectory and velocity of each sediment particle, we compute the changes in the probability distribution functions of velocities, bed activity, and jump lengths as the Shields number increases. For the lower shear stresses, the intermittency of the global bedload transport flux is described by computing the singularity or multifr actal spectrum of transport, which also characterizes the widespread range of transport event magnitudes. These findings can help to identify the mechanisms of sediment transport at the particle scale. The statistical analysis can also be used as an ingredient to develop larger, upscaled models for predicting mean transport rates, considering the variability of entrainment and deposition that characterizes the transport near the threshold of motion.     

A model diagnostic study of age of river-borne sediment transport in the tidal York River Estuary

As nutrients and organic matters are transported preferentially in an adsorbed state and tend to bind to the sediments, sediment transport plays an important role on eutrophication processes in the estuaries. The timescale of sediment transport is of significance for studying the retention of pollutants and eutrophication processes in the estuaries. Unlike transport of dissolved substances that is mainly controlled by advection and diffusion processes, the sediment transport is significantly affected by the intermittent settling and resuspension processes. A three-dimensional model with suspended sediment transport was utilized to investigate the transport timescale of river-borne sediment in the tidal York River Estuary. The results indicate that river discharge dominantly determines the age of river-borne sediment in the estuary. High river discharge results in a low sediment age compared to that under mean flow. The intermittent effects of settling and resuspension events greatly affect the river-borne sediment age. Both settling velocity and critical shear stress are shown to be key parameters in determining the sediment transport timescale. The sediment age decreases as settling velocity and/or critical shear stress decrease, while it increases with the increase of settling velocity that prevents the sediment to be transported out of the estuary.     

Integrated ecological assessment as the basis for management of a coastal urban protected area: A case study of Xiamen,China

In the process of rapid urbanisation in China, environmental problems have increased, from sewage discharge to climate change. Marine protected areas (MPAs) are widely advocated as a means to comprehensively manage human activities and resources in ocean and coastal areas. However, MPAs only safeguard populations or assemblages within their boundaries and fail to offer any protection from many major threats to marine environments. An increase in environmental threats implies an increase in environmental management and assessment. We propose a methodological framework for integrated ecological assessment using the Xiamen marine protected area as a case study. The integrated ecological assessment framework can be generalised from the dimensions of environment, economy, society and institution. Surveys were undertaken to assess the state of the Xiamen coastal environment, the resources of the reserve, and issues associated with human activities. Stakeholders were interviewed about their attitudes towards issues regarding the management of the reserve. The constraints of the reserve management were identified. The methodological framework is presented as a tool to help identify relative ecological security in order to prioritise actions and assess the ecological implications of management and policy decisions.     

Macrobenthic subtidal communities in relation to sediment pollution: the phylum-level meta-analysis approach in a south-eastern coastal region of South America

The relationships between macrobenthic subtidal community structure and the status of sediment pollution were analysed at 24 sampling stations in the Montevideo coastal zone. In order to judge the status of community perturbation a phylum-level meta-analysis was applied to the production data from the Montevideo coastal zone samples alone and combined with the original training data set from 50 samples collected on the NE European shelf. The community was dominated by the gastropod Heleobia cf. australis. The MDS (multi-dimensional scaling) ordination with abundance data (species-level) and the MDS ordination with production data (phylum level), using only our samples, showed the formation of three groups of stations. Results of the BIO-ENV procedure showed that lead, salinity and polycyclic aromatic hydrocarbons (PAHs) were the variables that best explained the biological pattern observed. However, a clear salinity gradient was observed from the inner stations of Montevideo Bay to the outer coastal stations; the high levels of Pb, PAH and Cr concentrations recorded at stations B, C and D in Montevideo Bay were important in discriminating these locations from the others. The MDS ordination combining the production data from the 24 samples from the Montevideo coastal zone with the original data set showed correct assessment of the pollution status for the 24 samples from Montevideo on a common scale of perturbation. The separation of the Montevideo coastal zone samples seems to be mainly due to the high proportion of molluscs. Our results suggest general applicability of the phylum-level meta-analysis approach, even in such cases as this, with high dominance of only one phylum; however, more studies are still necessary.Communicated by O. Kinne, Oldendorf/Luhe     

Time series analysis for the estimation of tidal fluctuation effect on different aquifers in a small coastal area of Saijo plain, Ehime prefecture, Japan

Considering the current poor understanding of the seawater–freshwater (SW–FW) interaction pattern at dynamic hydro-geological boundary of coastal aquifers, this work strives to study tidal effect on groundwater quality using chemical tracers combined with environmental isotopes. In situ measurement data of electrical conductivity and groundwater level along with laboratory measurement data of hydro-chemical species were compared with tidal level data measured by Hydrographic and Oceanographic Department, Saijo City, Japan for time series analysis. Result shows that diurnal tides have significant effect on groundwater level as well as its chemical characteristics; however, the magnitude of effect is different in case of different aquifers. Various scatter diagrams were plotted in order to infer mechanisms responsible for water quality change with tidal phase, and results show that cations exchange, selective movement and local SW–FW mixing were likely to be the main processes responsible for water quality changes. It was also found that geological structure of the aquifers is the most important factor affecting the intensity of tidal effect on water quality.     

Flowering of the seagrass Posidonia oceanica in a north-western Mediterranean coastal area: temporal and spatial variations

Sexual reproduction in Posidonia oceanica (L.) Delile is likely to be highly variable both in space and time. However, there has been little effort to identify at what spatial scale variability exists in the distribution and abundance of reproductive shoots or the magnitude of these variations. Such information is important for elucidating several aspects of the reproductive strategy of this species. Here, by using a reconstructing technique, I estimated the rate at which flowering events occurred over the last decades in three P. oceanica meadows along the coastline of the north-western Mediterranean (Italy). Then, variation in inflorescence frequency (i.e. the percentage of shoots that flowered in a particular year of the total number of shoots present in the sample in that year) was examined on a hierarchy of spatial scales, ranging from a few metres to meadows separated by tens of kilometres over a 3-year period. Separate analyses were also conducted to examine the patterns of spatial variability of several plant characteristics (i.e. shoot age and density of vegetative shoots) that may influence the timing of flowering. In total, ten reconstructed flowering events were recorded during the period 1983–1999. Despite the similar climatic conditions experienced in the three meadows surveyed, no inflorescence scars were found in one meadow. In the other two meadows, the flowering rate fluctuated considerably from year to year (0–26%), and simultaneous flowerings were detected only in 3 years (1993, 1994 and 1995). The pattern of spatial variability in the inflorescence frequency varied among years. An investigation of the flowering events recorded along the north-western Mediterranean coast reveals that in the studied period flowering also occurred across a broad range of meadows. Therefore, flowering could be a far more widespread phenomenon in this sector of the Mediterranean basin than previously thought. Analysis of variance showed significant variation in 1993 at the mean inflorescence frequency on very small scales (metres to tens of metres), whereas variation was not found at any of the scales investigated in 1994 and 1995. Overall, variation in the inflorescence frequency within individual meadows (65–93%) was at least an order of magnitude greater than that among separate meadows (0.5–19%). Patterns of spatial variation in the plant characteristics examined did not reflect those of flowering. It may be hypothesised that internal rhythms of populations, in conjunction with changes in environmental conditions, which are consistent over relatively large spatial (kilometres), are involved in the control of flowering induction. Environmental heterogeneity (in terms of nutrient availability) on a very local scale (metres to tens of metres) and intrinsic factors might affect the distribution of reproductive shoots within P. oceanica meadows.Communicated by R. Cattaneo-Vietti, Genova