Potential Longshore Sediment Transport Research Articles

Wave-driven sediment transport potential on a tropical coast: Implications for the northeastern Australian sediment budget

Coastal dynamics are governed by the interface of complex, multidimensional processes that result from the interaction between offshore wave climate and local geomorphology. Nearshore waves are usually the primary driver of sediment transport in the coastal zone. However, nearshore wave processes in sub-tropical to tropical regions are often poorly understood, since deep-water waves are often substantially transformed, via interaction with coral reefs, as they propagate towards the nearshore zone. Here, we produce a suite of nearshore wave conditions using a discrete set of representative deep-water wave parameters to determine the potential for large-scale, wave-driven longshore sediment transport along the sub-tropical to coral reef mediated tropical northeastern coast of Australia (15-28oS). Representative conditions at deep-water source points, determined using a Maximum Dissimilarity Algorithm (MDA), were used as boundary conditions for a coastal wave model. Potential longshore sediment transport is largely dependent on offshore wave direction and the presence (or lack thereof) of the Great Barrier Reef (GBR). There is a decrease in mean, wave-driven transport potential from >500,000 m3/year in southern Queensland to <50,000 m3/year north of Fraser Island and along the section of the coast regulated by wave transformation through the GBR. Seasonal changes in the deep-water wave regime control patterns of sediment transport along the entire coast, even in the low wave energy regions. We also show that there are complex sediment transport pathways on this tropical coast with large variability in both direction (up-coast vs. down-coast transport) and magnitude in the nearshore. Our results provide insights into the potential volumes, pathways, and complexity of sediment transport on tropical and sub-tropical coasts and a methodological approach that can be applied globally to efficiently construct wave-driven sediment flux estimates on tropical coastlines where coral reefs influence nearshore wave processes.

Uncertainties in the Projected Patterns of Wave-Driven Longshore Sediment Transport Along a Non-straight Coastline

This study quantifies the uncertainties in the projected changes in potential longshore sediment transport (LST) rates along a non-straight coastline. Four main sources of uncertainty, including the choice of emission scenarios, Global Circulation Model-driven offshore wave datasets (GCM-Ws), LST models, and their non-linear interactions were addressed through two ensemble modelling frameworks. The first ensemble consisted of the offshore wave forcing conditions without any bias correction (i.e., wave parameters extracted from eight datasets of GCM-Ws for baseline period 1979–2005, and future period 2081–2100 under two emission scenarios), a hybrid wave transformation method, and eight LST models (i.e., four bulk formulae, four process-based models). The differentiating factor of the second ensemble was the application of bias correction to the GCM-Ws, using a hindcast dataset as the reference. All ensemble members were weighted according to their performance to reproduce the reference LST patterns for the baseline period. Additionally, the total uncertainty of the LST projections was decomposed into the main sources and their interactions using the ANOVA method. Finally, the robustness of the LST projections was checked. Comparison of the projected changes in LST rates obtained from two ensembles indicated that the bias correction could relatively reduce the ranges of the uncertainty in the LST projections. On the annual scale, the contribution of emission scenarios, GCM-Ws, LST models and non-linear interactions to the total uncertainty was about 10–20, 35–50, 5–15, and 30–35%, respectively. Overall, the weighted means of the ensembles reported a decrease in net annual mean LST rates (less than 10% under RCP 4.5, a 10–20% under RCP 8.5). However, no robust projected changes in LST rates on annual and seasonal scales were found, questioning any ultimate decision being made using the means of the projected changes.

Sediment budget of a cuspate shoreline and its influence on spit development—Lagoa dos Patos, Brazil

The coastal sediment budget is an essential tool to understand erosion/accretion patterns along coastlines and to predict future changes. This work is one of the first approaches of a coastal sediment budget study in a cuspate shoreline covering the whole embayment-spit system. Taking this into consideration, this study aims to estimate the main longshore sediment transport patterns and propose a conceptual model of the regional sediment budget of the lagoon cuspate shoreline (Lagoa dos Patos-Brazil), while also analyzing its influence on the spit development. To do so, representative wind conditions (direction and speed) were used to force a validated lagoon wave model utilizing the process-based modeling suite Delft3D. The potential longshore sediment transport was computed along widely distributed cross-sections, based on representative wave cases, and the annual sediment budget was estimated. The results showed a pattern of inter-related source and storage areas along the bay beaches and the occurrence of short-term nodal zones (convergent and divergent), which have an important control on the regional sediment budget of the coast. The central littoral cells of the embayments behave as temporary sediment storage areas, while the southern littoral cells act as sources of sediments to the spits. The findings of this study demonstrate the important control that short-term nodal zones have on the annual coastal sediment budget of complex coastline shapes and, the importance of the budget of the adjacent updrift cell to the sediment supply for the spits.

Numerical modelling of the spatial variation of sediment transport using wave climate schematization method - a case study of west coast of Sri Lanka

This study quantifies the variations in wave characteristics and the resulting variations in potential longshore sediment transport rate along the coastline between Mount Lavinia and Negombo, Sri Lanka. Over the last 25 years, this coastal belt has been subjected to dramatic interventions due to the influence of rapid social-economic development in the country such as construction of the Colombo South Harbor jetty, ongoing Colombo Port City Project and mega sand dreading off Negombo coast. For the wave transformation, SWAN (Simulating Waves Nearshore) numerical model was applied, forced by offshore wave/wind. The Delft3D-FLOW model was used to estimate the longshore sediment transport rates and related morphodynamics using input reduction and morphological acceleration techniques. Results of the alongshore sediment transport capacity computations clearly indicate the variable characteristics of different parts of the study zone. The annual alongshore sediment transport capacity computed in the study area oriented northward, comply very well with the observations. The coastal belt between Mount Lavinia and Colombo, the wave climate, and subsequently the annual alongshore transport reached the highest values indicating a relative dynamic environment and there after decreased with a strong gradient northward. The explanation for these negative steep gradients and the environmental forcing/human interventions that govern the regional sediment transport are discussed in this paper.

Recent Sedimentation of a Mesotidal Wave-Dominated River Mouth: Lach Van, Vietnam

ABSTRACT Chien, N.Q. and Tung, T.T., 2018. Recent sedimentation of a mesotidal wave-dominated river mouth: Lach Van, Vietnam. In: Almar, R.; Almeida, L.P.; Viet, N.T., and Sall, M. (eds.), Tropical Coastal and Estuarine Dynamics. Journal of Coastal Research, Special Issue No. 81, pp. 50–56. Coconut Creek (Florida), ISSN 0749-0208 The sedimentation of a wave-dominated river mouth in Tonkin Gulf, Vietnam, has been investigated for the time period 2005–2017. Deepwater wave statistics and the potential longshore sediment transport (LST) has been determined, which shows a net LST rate of ~105 m3/yr southward. A one-line model is used to estimate the change in local coastline; the model is verified against shoreline position data obtained from satellite images. It is apparent that the accretion occurs on both sides of the river mouth with a rate of ~10 m/yr. Coastline evolution trend is then predicted for the aforementioned time period, and results show evidences that accretion is intensifying in recent years, ...

A Climate Index Optimized for Longshore Sediment Transport Reveals Interannual and Multidecadal Littoral Cell Rotations

AbstractA recent 35‐year endpoint shoreline change analysis revealed significant counterclockwise rotations occurring in north‐central Oregon, USA, littoral cells that extend 10s of kilometers in length. While the potential for severe El Niños to contribute to littoral cell rotations at seasonal to interannual scale was previously recognized, the dynamics resulting in persistent (multidecadal) rotation were unknown, largely due to a lack of historical wave conditions extending back multiple decades and the difficulty of separating the timescales of shoreline variability in a high energy region. This study addresses this question by (1) developing a statistical downscaling framework to characterize wave conditions relevant for longshore sediment transport during data‐poor decades and (2) applying a one‐line shoreline change model to quantitatively assess the potential for such large embayed beaches to rotate. A climate INdex was optimized to capture variability in longshore wave power as a proxy for potential LOngshore Sediment Transport (LOST_IN), and a procedure was developed to simulate many realizations of potential wave conditions from the index. Waves were transformed dynamically with Simulating Waves Nearshore to the nearshore as inputs to a one‐line model that revealed shoreline rotations of embayed beaches at multiple time and spatial scales not previously discernible from infrequent observations. Model results indicate that littoral cells respond to both interannual and multidecadal oscillations, producing comparable shoreline excursions to extreme El Niño winters. The technique quantitatively relates morphodynamic forcing to specific climate patterns and has the potential to better identify and quantify coastal variability on timescales relevant to a changing climate.

A new equation to predict the total potential longshore sediment transport rate in the beach ocean area

This paper proposes a novel predictive formula for the estimation of the total longshore sediment transport rate (TLSTR) using the incomplete selfsimilarity (ISS) and sediment transport physics principles with the assumption that sediments are mobilised by breaking waves. The key factor in this study is the use of dimensional analysis and self-similarity concepts based on a number of independent variables to develop an integrated classical formula for the noncohesive TLSTR in marine coastal regions. To assess the prediction capability of the proposed formula, high-quality sediment transport and hydrodynamics datasets were gathered and six well-known formulae were employed for both the field and laboratory test conditions. Results show that the novel formula agrees well with both the flume and field data and it is quite suitable both for practical applications in coastal regions and for the numerical modelling of sediment transport and nearshore variations.

A new equation to predict the total potential longshore sediment transport rate in the beach ocean area

A new equation to predict the total potential longshore sediment transport rate in the beach ocean area

Variations in the Wave Climate and Sediment Transport Due to Climate Change along the Coast of Vietnam

This study quantifies the climate change (CC)-driven variations in wave characteristics and the resulting variations in potential longshore sediment transport rate along the ~2000 km mainland coast of Vietnam. Wind fields derived from global circulation models (GCM) for current and future (2041–2060 and 2081–2100) climate conditions are used to force a numerical wave model (MIKE21 SW) to derive the deep water wave climate. The offshore wave climate is translated to nearshore wave conditions using another numerical model (Simulating WAves Nearshore—SWAN) and finally, a sediment transport model (GENEralized model for Simulating Shoreline Change—GENESIS) is used to estimate potential sediment transport for current and future climate conditions. Results indicate that CC effects are substantially different in the northern, central and southern parts of the coast of Vietnam. The 2081–2100 mean significant wave height along the northern coast is estimated to be up to 8 cm lower (relative to 1981–2000), while projections for central and southern coasts of Vietnam indicate slightly higher (increases of up to 5 cm and 7 cm respectively). Wave direction along the northern coast of Vietnam is projected to shift by up to 4° towards the south (clockwise) by 2081–2100 (relative to 1981–2000), up to 6° clockwise along the central coast and by up to 8° anti-clockwise (to the north) along the southern coast. The projected potential longshore sediment transport rates show very substantial and spatially variable future changes in net transport rates along the coast of Vietnam, with increases of up to 0.5 million m3/year at some locations (by 2081–2100 relative to 1981–2000), implying major changes in future coastline position and/or orientation. The vicinity of the highly developed city of Da Nang is likely to be particularly subject to coastline changes, with potentially an additional 875,000 m3 of sand being transported away from the area per year by the turn of the 21st century.

Experimental study on dynamic equilibrium of headland-bay beaches

A dynamic equilibrium bay (DEB) is an embayment with continuous sediment supply and its shoreline planform can remain stable over a long period of time without erosion or accretion. For coastal conservation of sandy headland-bay beaches (HBB), the concept of using a static equilibrium bay (SEB) is well known, but that for DEB has received little attention. Moreover, an empirical equation for the stability of a DEB is not yet available. Experiments on DEB shape that aim to derive new coefficients in the parabolic bay shape equation (PBSE) for DEB are now being conducted in the laboratory. The work commences from an initial artificial HBB in static equilibrium with sediment supply source from the lee of an upcoast headland. A final equilibrium planform is obtained for the condition with a specific wave obliquity and sediment supply rate until no further shoreline change is found. In order to fit the PBSE for a DEB, a new parameter called SSR (sediment supply ratio) that represents the ratio of sediment supply rate from the source and the potential longshore sediment transport rate is introduced to quantify the balance of sediment to the bay. Alternative C coefficients in the PBSE for DEB, which include wave obliquity and the SSR, are then calculated. These new coefficients for DEB can now be used to evaluate the influence of sediment supply from a riverine source on a DEB and to classify its equilibrium status for planning sediment management strategies in coastal conservation.

Sea wave propagation from offshore to Maputo's coast. Application to longshore sediment transport assessment.

This study aims to characterize the wave climate near the coastal region of Maputo (Mozambique), and to provide a first assessment of the sediment transport load in this area. A time-series of 13 years' worth of offshore wave data, obtained from reanalysis products, was propagated to the coast. Wave propagation was performed using Linear Wave theory and the numerical model, Simulating WAves Nearshore (SWAN). Propagations with SWAN were carried out considering different scenarios in order to evaluate the influence of parameters such as wind, tidal level, frequency spectrum and numerical mesh resolution on wave characteristics along the coast. The prevalent waves propagated came from between east and southwest directions. Results from linear propagation were used to estimate the potential longshore sediment transport. The Coastal Engineering Research Center formula was applied for a stretch of beach in the Machangulo Peninsula. A net potential rate of longitudinal sediment transport (of the order of 10(5) m(3)/year, along an extension of the coast of 21 km) was directed northwards, and was consistent with the frequent wave directions.

Longshore Sediment Transport on the Northern Coast of the Yucatan Peninsula

This paper presents a qualitative assessment of coastal processes along the northern coast of the Yucatan Peninsula based on a method used to estimate the potential longshore sediment transport. Despite the deep-water low-energy wave conditions (Hs 5 1 m) in the study area, erosion is critical in many locations, including the urbanized stretches of coast. The waves were characterized using a 12 y (1997‐2009) deep-water wave hindcast data (WAVEWATCH III) as forcing for a spectral wind-wave numerical model (MIKE 21 SW) used to propagate the waves to the coast. Simulated time series of significant wave height, peak period, and direction are compared against in situ measurements at 10 m water depth. Numerical results are further employed for estimation of the nearshore wave climate along the coast. Wave conditions are strongly affected by the wide continental shelf in front of the northern Yucatan Peninsula, with an increase in wave energy at the eastern part of the peninsula where the shelf narrows. The nearshore wave climate is employed for the qualitative assessment of potential longshore sediment transport (LITDRIFT model) in the study area. The sediment transport calculations are consistent with both volume impoundment estimations at a groin and dredging estimates at a harbor (235,000 m 3 /y). A net westward potential longshore sediment transport is found along the entire coast, ranging between 220,000 and 280,000 m 3 /y, except west of Holbox, where longshore transport direction is inverted. Based on sediment transport gradients, potential erosion and deposition areas are identified. Erosion/accretion patterns at nonurbanized areas are consistent with field observations. This dominant westward longshore transport suggests an extremely sensitive shoreline to littoral barriers, as supported by observations in the most urbanized areas. These areas show no gradients on longshore sediment transport, whereas beach erosion is a common feature enhanced by littoral barriers. Shore protection should then be oriented toward sediment management strategies.

Effects of climate change and wave direction on longshore sediment transport patterns in Southern California

Changes in deep-water wave climate drive coastal morphologic change according to unique shoaling transformation patterns of waves over local shelf bathymetry. The Southern California Bight has a particularly complex shelf configuration, of tectonic origin, which poses a challenge to predictions of wave driven, morphologic coastal change. Northward shifts in cyclonic activity in the central Pacific Ocean, which may arise due to global climate change, will significantly alter the heights, periods, and directions of waves approaching the California coasts. In this paper, we present the results of a series of numerical experiments that explore the sensitivity of longshore sediment transport patterns to changes in deep water wave direction, for several wave height and period scenarios. We outline a numerical modeling procedure, which links a spectral wave transformation model (SWAN) with a calculation of gradients in potential longshore sediment transport rate (CGEM), to project magnitudes of potential coastal erosion and accretion, under proscribed deep water wave conditions. The sediment transport model employs two significant assumptions: (1) quantity of sediment movement is calculated for the transport-limited case, as opposed to supply-limited case, and (2) nearshore wave conditions used to evaluate transport are calculated at the 5-meter isobath, as opposed to the wave break point. To illustrate the sensitivity of the sedimentary system to changes in deep-water wave direction, we apply this modeling procedure to two sites that represent two different coastal exposures and bathymetric configurations. The Santa Barbara site, oriented with a roughly west-to-east trending coastline, provides an example where the behavior of the coastal erosional/accretional character is exacerbated by deep-water wave climate intensification. Where sheltered, an increase in wave height enhances accretion, and where exposed, increases in wave height and period enhance erosion. In contrast, all simulations run for the Torrey Pines site, oriented with a north-to-south trending coastline, resulted in erosion, the magnitude of which was strongly influenced by wave height and less so by wave period. At both sites, the absolute value of coastal accretion or erosion strongly increases with a shift from northwesterly to westerly waves. These results provide some examples of the potential outcomes, which may result from increases in cyclonic activity, El Nino frequency, or other changes in ocean storminess that may accompany global climate change.

Verification of Longshore Sediment Transport Formulas at Some of the Southern Coastlines of Iran

A correct estimation of the sediment transport rate and the amount of sedimentation is among the important and effective factors to be considered in the design of ports and coastal structures. Although many research efforts are now conducted on the influencing parameters of the sediment transport to quantify the transport rate, the approximate and relatively simple formulas are still routinely used. CERC and Kamphuis are among the well-known formulas for the calculation of the potential longshore sediment transport (LST) rate. However, the accuracy of predictions of transport rates, based on the applications of these formulas at different locations of the world, has not been similar. In present paper, using a limited number of data related to local waves and characteristics of grain size distributions, the longshore sediment transport rates at some of the southern coastlines of Iran have been calculated and the results have been compared with the actual sediment impoundments at breakwaters and groins. The volumes of sedimentation are derived from the comparisons of hydrographic surveys. Verification of these formulas at southern coasts of the country reveals the higher accuracy of Kamphuis formula in comparison to CERC formula. A relationship was also presented for the calculation of K parameter of CERC formula as a function of the surf similarity parameter.

Wave forecasting and longshore sediment transport gradients along a transgressive barrier island: Chandeleur Islands, Louisiana

Louisiana barrier islands, such as the chain surrounding the southeast region of the state, are experiencing rapid loss of land area, shoreline erosion, and landward migration due to transgression and in-place drowning, and the landfall of several major hurricanes in the last decade. Observations of migration rates and overall impacts to these barrier islands are poorly understood since they do not respond in a traditional way, such as barrier rollover. This paper aims to verify how wave energy and potential longshore sediment transport trends have influenced the recent evolution of the Chandeleur Islands, by direct comparison with recent observations of migration and erosion trends. The Chandeleur Islands are characterized by a bidirectional transport system, with material moving from the central arc to the flanks. The longshore sediment transport along the barrier islands was calculated after propagation and transformation of waves to breaking (generated using observed winds), and through the use of a common longshore sediment transport formula. Seasonal variations in wind climate produced changes in the transport trends and gradients that agree with migration and rotation patterns observed for this barrier island system. Results suggest that wind dominance produces seasonal oscillations that cause an imbalance in the resulting transport gradients that over time are responsible for higher rates of transport in the northward direction. These results and data from other works verify the evolutionary model previously suggested, and qualitatively confirm the recent observations in asymmetric shoreline erosion.

Vessel-wave induced potential longshore sediment transport at Aegna Island, Tallinn Bay

The potential impact of high-speed vessel wakes on the longshore drift of semi-sheltered, medium-energy beaches is evaluated based on recent studies in almost tideless Tallinn Bay, the Baltic Sea. Energy flux and wave propagation direction of vessel wakes is estimated based on high- resolution water surface profiling in summer 2008. The wind-wave time series in 1981-2008 is modelled on the basis of a simplified scheme for a long-term wave hindcast with the use of a triple- nested version of the WAM model. Longshore drift, created by wind waves and by vessel wakes, is estimated by the energy flux model, also known as the Coastal Engineering Research Centre (CERC) model. Vessel wakes cause longshore drift that in 2007-2008, as compared to the drift produced by wind waves on the SW coast of the Aegna Island at the entrance to Tallinn Bay, had a magnitude about 75% less and the opposite direction.

A study of the deltaic coast morphometry of river Pinios in relation to its hydro- &amp; sediment dynamics

This paper refers to the study of the morphodynamic processes, on a seasonal basis, in the river delta of Pinios (Greece) with the application of the discharge effectiveness index (Ef) -which associates the water discharge (D) with the wave power (PJ- and the estimation of the potential longshore sediment transport (Ql). The delta is characterised according to the classification proposed by Galloway (1975) and revised by Briggs et al (1997), as wave/fluvial dominated type of delta, having a cuspate shape like the deltas of San Francisco and Rhone. Wave processes are dominant during summer-autumn period (low values ofEf) and river processes are important in winter and spring (high values ofEf). The total potential longshore sediment transport is northwards and more intensive in the region to the south of its current mouth.

Coastline changes in relation to longshore sediment transport and human impact, along the shoreline of Kato Achaia (NW Peloponnese, Greece)

Coastal configuration depends upon the equilibrium between available sediment budget and prevailing nearshore wave and current conditions. Human activities often disturb this natural equilibrium by altering the sources of beach material and littoral drift pattern. In the coastal zone of NW Peloponnese, an essentially tideless environment, the oblique approach of wind-induced waves implies an overall longshore drift from east to west. On an annual basis, the potential longshore sediment transport rates at the different sections of the study area (Kato Achaia) is estimated to vary between 0.02 10-3 m3/s and 5 103 m3/s and to fluctuate seasonally. The construction of a port and the extraction of aggregates from the R. Peiros have changed significantly the pattern of sediment transport inducing dramatic changes on coastline configuration; thus, the part of the coastline west to the port had retreated as much as 70 m eliminating a touristic beach, while the entrance of the port was silted inhibiting navigation. Coastal engineering measures, such as modification of port-breakwaters and construction of groins have had only minimal contribution in beach recovery. Hence, coastal management plans should consider this dynamic equilibrium and protect the natural coastal system from the arbitrary human activities.

A Comment on the Paper: “Wave Climate and Potential Longshore Sediment Transport Patterns, Nottawasaga Bay, Ontario” by Robin G.D. Davidson-Arnott and Wayne H. Pollard

A Comment on the Paper: “Wave Climate and Potential Longshore Sediment Transport Patterns, Nottawasaga Bay, Ontario” by Robin G.D. Davidson-Arnott and Wayne H. Pollard

Wave Climate and Potential Longshore Sediment Transport Patterns, Nottawasaga Bay, Ontario

A storm wave climate for Nottawasaga Bay, Ontario, is hindcast, using the SMB technique, from wind records at Cove Island for the period 1966-1970. Thirteen wave classes, defined on the basis of significant wave height, period, and direction, are identified and these are used as inputs into a computer model of wave refraction within the bay. The total and longshore component of wave energy flux are determined for each wave class. The total annual energy flux P 1 and the net longshore component P 1 are determined for 55 points spaced at one kilometre intervals by multiplying the value of energy flux at each point by the mean annual frequency for that wave class and summing the values for all relevant waves. A simple model of potential erosion, transport, and deposition patterns within the bay is then developed from the variation in the net P 1 values. The predicted model is compared with geomorphological evidence of sediment transport patterns visible in vertical aerial photographs and with measurements of erosion and accretion at selected points. It is concluded that the continued eastward growth of the Wasaga spit results primarily from deposition of sediments from the Nottawasaga River rather than littoral transport.