Longshore Sediment Transport Rate Research Articles

Wave-driven sediment transport and beach-dune dynamics in a headland bay beach

This paper presents a comprehensive study of wave refraction, wave and wind driven sediment transport, foredune development and Holocene barrier evolution over a variety of time scales at Moçambique Beach, Santa Catarina State, Southern Brazil. The motivation for this study was to examine the relationships between estimated wave driven sediment transport, medium and long term aeolian transport, foredune development, and Holocene barrier volumes and morphology. An analysis of 2years of wave rider data for the region shows two well defined peaks of frequencies: one of swell waves from the south with a period of 12s, and another peak of sea waves from east-northeast with a period of 7s. Longshore sediment transport rates were calculated using high resolution hindcast wave data for the South Atlantic Ocean, which was calibrated by the measured buoy data. The dominant southerly waves drive a longshore gradient in wave energy from south to north, and nearshore/surf zone sediment transport increases from south to north. Beach grain size is fine in both the south and north, and medium in the center. The combination of grain size and wave energy variations creates a marked alongshore variation in surf zone beach types ranging from low energy dissipative in the south, moderate energy intermediate in the central area to moderate to high energy dissipative in the north. Estimates of aeolian sediment transport, volumetric changes in foredune deposition and total Holocene dunefield volumes were also calculated. Results indicate that the morphological behavior of the foredune profiles reflects the gradients of longshore sediment transport and the exposure to wind energy and aeolian sediment delivery, with a maximum of sediment volume and transport towards, and in the central part and northern end of the barrier. Holocene (0–7000years) barrier volumes vary along the embayment, mimicking the trends in both calculated wave and wind driven sediment transport. The Short and Hesp (1982) model was more suitable in predicting the long term (Holocene) barrier evolution than the size and volume of the foredune. The combination of wide beach, high energy dissipation, maximum sediment supply, and high exposure to strong onshore winds is found in the northern end of the embayment where Holocene subaerial barrier volumes are at a maximum. Overall, this study proves that foredune development is closely related to wind exposure, wave energy and gradients of longshore sediment transport, and that dunefield development reflects the increase downdrift in potential sediment supply from the southern to the northern end of the beach, and the change alongshore from low energy dissipative, through intermediate, to high energy dissipative beach-surf zone environments. This paper significantly extends previous models of beach and dune interactions in that it (i) actually determines wave driven sediment transport for various sections of a long embayment, (ii) relates those transport patterns to surf zone/beach morphodynamic types and variations in alongshore sediment patterns, and (iii) correlates foredune volumes and Holocene barrier volumes (which reflect proxy Holocene onshore transport rates) with wave driven sediment transport rates.

Beach Erosion and Recovery

AbstractOur capability for predicting beach and dune erosion has improved in the last three decades, but the recovery of an eroded beach above the mean sea level (MSL) cannot be predicted at present. The cycle of beach erosion and recovery will need to be predicted for the long-term maintenance of a sand beach with a dune for coastal flooding reduction. The cross-shore numerical model (CSHORE) is extended and evaluated using natural beach erosion and recovery data along 16 cross-shore lines spanning 5 km alongshore for the duration of 272 days. The CSHORE predicts beach and dune erosion fairly well, as has been shown in previous comparisons. The bed-load formula used in the CSHORE is adjusted to predict the accreted beach profile with a berm. The computed beach profile evolutions are shown to be affected little by the alongshore gradient of the longshore sediment transport rate along the straight beach. The extended CSHORE predicts both erosion and accretion above MSL within a factor of about 2.

Longshore Sediment Transport—Field Data and Estimations Using Neural Networks, Numerical Model, and Empirical Models

ABSTRACT Ari Guner, H.A.; Yuksel, Y., and C evik, E.O., 2013. Longshore sediment transport—field data and estimations using neural networks, numerical model, and empirical models. This work suggests an alternative approach, namely, the use of an artificial neural network (ANN), for the estimation of longshore sediment transport (LST). The ANN technique provides a powerful utility for input–output mapping if there is sufficient data and can be useful for modeling processes about which adequate knowledge of physics is limited, such as sediment transport. A feed-forward network was developed to predict the LST from a variety of causative variables. The best network was selected after testing many alternatives. The network was validated by experimental and field data. In addition, the ANN method was applied to the case study area (Karaburun, Turkey), located on the SW coast of the Black Sea. The accuracy of the ANN predictions was evaluated against the measured LST rate at Karaburun and compared with two well...

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.

Modeling Regional-Scale Sediment Transport and Medium-Term Morphology Change at a Dual-Inlet System Examined with the Coastal Modeling System (CMS): A Case Study at Johns Pass and Blind Pass, West-Central Florida

The Coastal Modeling System (CMS), developed by the US Army Engineer Research and Development Center's (ERDC) Coastal Inlets Research Program (CIRP), is applied to model morphology change at a dual-inlet system, the Johns Pass and Blind Pass system in West-Central Florida. The CMS combines computation of current, wave, and sediment transport, leading to the prediction of morphology change at tidal inlets and the surrounding beaches. Medium-term CMS runs, with simulated times of 1.2 to 1.6 years, were completed and compared with extensive field data. Stronger tidal flow through the dominating Johns Pass and weaker flow through the secondary Blind Pass were calculated, indicating that the model reproduced an essential aspect of this interactive two-inlet system. The complicated wave refraction and breaking over the ebb tidal deltas and along the adjacent shorelines were accurately modeled, leading to a realistic representation of the wave-current interaction. Wave-breaking induced elevated sediment suspension and transport were described by the model. The predicted morphology change agreed well with field data. The CMS captured several key spatial trends of morphology change, e.g., erosion along the downdrift beach and accretion at the attachment point. The computed 32,000 m3/yr sedimentation volume in the dredge pit at the updrift side of Blind Pass matched the measured value of 35,000 m3/yr with a similar spatial distribution pattern, suggesting that the calculated net longshore sediment transport rates are accurate. The computed sedimentation rate of 60,000 m3/yr at a designed dredge pit on Johns Pass ebb-delta agrees with the generally accepted gross longshore transport rate. Rapid and large morphology change in response to high wave-energy events is predicted and is consistent with field observations.

Application of neural networks and fuzzy logic models to long-shore sediment transport

Predictions of long-shore sediment transport rate (LSTR) are a vital task for coastal engineers in the determination of erosion or accretion along coasts. Many scientists have tried to find empirical method for the estimation of LSTR in the past decades. However, due to the influence of significant number of parameters and randomness of the data, the existing empirical methods provide quite different results and have limited applications. In this paper, an alternative approach, fuzzy logic and neural network, is proposed to estimate LSTR. Six dominant variables on LSTR are considered in the present models, including wave breaking height ( H bs ), wave period ( T), wave breaking angle ( α bs ), beach slope ( m), grain size ( D) and sediment mass flow rate along shore ( Q s ). A comprehensive comparison between both neural networks and fuzzy logic models and the existing empirical formulae will be presented to demonstrate capacity of fuzzy logic and artificial neural network.

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.

Storm response and beach rotation on a gravel beach, Slapton Sands, U.K.

Continuous Argus video data and fortnightly measurements of subaerial morphology were obtained over a 3-year period from a steep macrotidal gravel beach on the southwest coast of the U.K. Concurrent wave and water-level data were also collected, enabling the correlation of the observed morphological changes to the hydrodynamic forcing. Wave conditions are generally low ( H s ≈ 0.5–1 m), but the beach is affected by frequent storm wave activity (c. 15 storms per year with H s ≈ 2–4 m) with waves either approaching from the south (swell waves) or from the east (wind waves). An assessment of the three-dimensional morphological response of the beach to the two typical storm types was carried out by analysing the impact of 27 storms that occurred from April 2007 to April 2009. Southerly storms cause accretion of the supratidal zone and erosion of the intertidal zone, and a significant loss in overall beach volume. Easterly storms, on the other hand, induce supratidal erosion and intertidal accretion, and a significant gain in overall beach volume. During the intervening calm periods a small supratidal berm is constructed and a modest gain in overall beach volume occurs. Wave modelling indicated that opposing longshore energy fluxes occur for the different storm types with a northerly energy flux during southerly storms and a southerly flux during easterly storms. Weekly shorelines derived from the Argus images revealed that the northern end of the beach widened by c. 30 m and the middle beach receded by c. 40 m over a relatively brief period (a few months). The occurrence of this beach rotation event is attributed to a higher frequency of southerly storms and/or a lower frequency of easterly storms over this period. Thus, the development and stability of the beach on annual time scales depend on the relative contributions of the two storm types, and their sequencing. Longshore sediment transport (LST) rates derived from the data on beach morphological change were compared with several littoral drift formulae previously applied to gravel beaches. The CERC equation, with a proportionality factor k between littoral drift rate I l and longshore wave energy flux P l of k = 0.054, yielded the best results.

Modeling Shoreline Evolution at Hai Hau Beach, Vietnam

Abstract The coastline of Hai Hau District, located on the northeast coast of Vietnam with about 30 km of shoreline, is chronically eroding. Previous studies have tried to highlight the main causes of the erosion along this coastline, and several hypotheses exist. To examine the hypothesis that gradients in the longshore sediment transport rate and cross-shore fine sediment lost offshore are the main causes generating the serius erosion at Hai Hau Beach, a newly developed numerical model of shoreline change based on the one-line theory was applied and compared with data. Sea dike segments, reinforced by stones and mortar, were modeled using a seawall boundary condition, and the sediment continuity equation was modified to take into account the offshore transport of fine-grained sediment. The simulated shorelines agreed well with the measured shorelines, both for the calibration and validation periods. The calculated sediment budget shows that the net sediment transport is in the southward direction and th...

Long Term Change of Terrace Morphology and Longshore Sediment Transport around the Tenryu River Mouth

This study investigates long-term change of terrace morphology and longshore sediment transport around the Tenryu River mouth based on bathymetry data of past 50 years. Based on the sediment budget around the terrace and the assumption of little sediment supply from the river in recent years, CERC formula was calibrated to estimate the longshore sediment transport rates at both east and west boundaries of the focusing area. Obtained boundary conditions then yielded distribution of the longshore sediment transport around the terrace and estimations of sediment supply from the river. These results and additional numerical analysis clearly showed increasing impacts of the detached breakwaters and indicated that the terrace morphology in 1984 may be required for dynamic equilibrium of the sediment budget around the river mouth.

Dependence of Total Longshore Sediment Transport Rates on Incident Wave Parameters and Breaker Type

Abstract Experiments were conducted in the Large-scale Sediment Transport Facility (LSTF) at the U.S. Army Engineer Research and Development Center to investigate the importance of wave height, period, and breaker type (spilling and plunging breakers) on total rate of longshore sediment transport (LST) and the cross-shore distribution of LST. Estimates computed by the CERC formula and Kamphius were compared to the accurately measured total LST rates. Several K-values were used with the CERC formula, including the recommended value of 0.39 and calculated values by Kamphuis and Readshaw, Ozhan, Bailard, and Del Valle et al. The recommended K-value and most of the calculated K-values overpredicted the measured total LST rates, but methods that included parameters to indicate breaker type gave good estimates. The Kamphuis and Readshaw equation, in which K is a function of surf similarity parameter, gave consistent estimates with measurements. The Kamphuis equation, which includes wave period and beach slope t...

Wave Transformation and Longshore Sediment Transport Evaluation for the Egyptian Northern Coast, via Extending Modern Formulae*

Studies and evaluations were carried out for the purpose of analyzing satellite measured data, or carrying out preliminary evaluations for the study area, near Port Said. In this study waves were transformed from the offshore area to the nearshore area, and longshore sediment transport quantities and rates were evaluated by applying and adjusting some of the available modern formulae. This was done by calibrating with the available reference data, as given in the literature. Thus, the applicability of such formulae for that area can be checked. Offshore significant wave heights from altimeter measurements, which can be downloaded at www.waveclimate.com, are used in this research for 2003 through 2005. The study domain dimensions are 50 km long offshore and 25 km wide alongshore. Wave nearshore transformation is carried out by using the mathematical Simulating WAves Nearshore model (SWAN) based on seasonal/directional bases. Four seasons are considered, winter, spring, summer, and autumn, representing the whole year. Three bulk-type modern formulae, Coastal Engineering Research Center, U.S. Army Corps of Engineers (CERC), Kamphuis, and Van Rijn, for longshore transport evaluation are applied in the study area. The reference targets used for comparison are based on the literature. Through calibration with the reference targets and among themselves, the study comes up with some correction factors for both CERC and Van Rijn formulae to give quite realistic evaluations for that area. These extended/corrected formulae can also be applied in places with similar conditions to the Egyptian coast.

Wave Energy and Longshore Sediment Transport Gradients Controlling Barrier Evolution in Rio Grande do Sul, Brazil

Abstract This paper aims to verify how wave energy and longshore sediment transport rates could have influenced the evolution of the Rio Grande do Sul Holocene barriers in the last 5000 y, assuming that wave climate conditions did not change much during the Middle and Late Holocene. Calculations of wave energy based on visual observations and longshore sediment transport show that both wave energy and sediment transport decrease as the coastline becomes concave (embayed) and increase as the coastline becomes convex (projected). These variations alongshore create a positive and negative imbalance, respectively, in the sediment budget. The long-term operation of these processes has produced progradational barriers in embayments and retrogradational barriers along projections. In the transition zones between embayed to convex coastlines, neither depositional nor erosional processes predominate, creating a sediment balance and producing aggradational barriers.

Numerical Model for Cross-shore Distribution of Longshore Sediment Transport Rate Including Suspended and Bed Loads in and outside the Surf Zone

A one-dimensional numerical model for predicting the cross-shore distribution of the longshore sediment transport rate was developed. The model predicts the suspended load due to wave breaking and bed load due to longshore current velocity and velocity skewness and atiltness. The model validity was examined for steady flows and for waves and wave-induced longshore currents. The sediment transport rates for steady flows estimated by the present model agreed with those by Ribberink's formula. The total longshore sediment transport rates estimated by the present model were smaller than those estimated by CERC's formula. However, because CERC's formula was found to overestimate the total longshore sediment transport rate, the present model likely predicts the longshore sediment transport in the field properly.

The Analysis of Sediment Transport of Miyazaki Coast by the Sand Tracer Experiment

The purpose of this study is to analyze the sediment transport of Miyazaki Coast, especially the dominant longshore direction of sand transport, from the results of recent 3 years sand tracer experiment and of the analysis of currents observed by camera systems during the experiment. The dominant direction obtained by accumulation of longshore sediment transport rate estimated by equation of Kraus et al.(1982), which is based on the breaking wave height and nearshore currents, agrees with the direction of motion of the tracer. In addition, it becomes clear that there is a high correlation between the distance of tracer movement and the longshore sediment transport rate. It is also obvious that sediment transport to south is predominant in the experiment period.

Longshore sediment transport estimation using a fuzzy inference system

Accurate prediction of longshore sediment transport in the nearshore zone is essential for control of shoreline erosion and beach evolution. In this paper, a hybrid Adaptive-Network-Based Fuzzy Inference System (ANFIS), Fuzzy Inference System (FIS), CERC, Walton–Bruno (WB) and Van Rijn (VR) formulae are used to predict and model longshore sediment transport in the surf zone. The architecture of ANFIS consisted of three inputs (breaking wave height), (breaking angle), (wave period) and one output (longshore sediment transport rate). For statistical comparison of predicted and measured sediment transport, bias, root mean square error and scatter index are used. The longshore sediment transport rate (LSTR) and wave characteristics at a 4 km-long beach on the central west coast of India are used as case studies. The CERC, WB and VR methods are also applied to the same data. Results indicate that the errors of the ANFIS model in predicting wave parameters are less than those of the empirical formulas. The scatter index of the CERC, WB and VR methods in predicting LSTR is 51.9%, 27.9% and 22.5%, respectively, while the scatter index of the ANFIS model in the prediction of LSTR is 17.32%. A comparison of results reveals that the ANFIS model provides higher accuracy and reliability for LSTR estimation than the other techniques.

Inverse Estimation of Sand Transport Rates on Nourished Delaware Beaches

The Delaware Atlantic coast of 40 km length is suffering from beach erosion. The State of Delaware placed approximately 1,100,0001 m3 sand on its four beaches in 1998. Beach profiles were surveyed along fixed 65 cross-shore lines almost semiannually for 9–11 times until 2005. The measured profiles are analyzed to obtain the shoreline displacement and the area changes in the landward and shoreward zones between the two successive profile surveys. The relations among these profile change parameters indicate that a standard one-line model may not be applicable to these nourished beaches because of the dominant summer and winter profile changes. An inverse method based on a two-line model is developed to estimate the cross-shore sediment transport rate and the gradient of the longshore sediment transport rate. The estimated rates indicate the importance of both cross-shore and longshore sediment transport to predict the evolution of these nourished beaches with large variabilities in time and space.

Measurement of Longshore Sediment Transport Rates in the Surf Zone on Galveston Island, Texas

Longshore sediment transport in the surf zone on Galveston Island, Texas, was studied to develop a new technique involving optical instruments rapidly calibrated in situ and to compare measured transport rates with those predicted by the well-known Coastal Engineering Research Center (CERC) formula. This method used an instrumented sled equipped with a LISST-100 for particle size distribution determination, four optical backscatter sensors (OBSs) for turbidity measurements, and two velocity sensors for longshore current measurements. The sled was pulled across the surf zone, occupying 10 to 15 stations spaced about 10 m apart, for approximately 3 minutes each.The OBS data were calibrated with the LISST-100 particle size distribution data, thereby overcoming the difficulties associated with the use of these sensors in the presence of a mix of sand and fine particles. Subsequently, these data were fit to a logarithmic profile to determine the average vertical distribution of suspended sand concentration, assuming that the fine particles were vertically well mixed at each station. A logarithmic profile of average longshore current was also computed based on the measured velocity data. The longshore sediment transport rate was calculated as the spatial integral of the product of suspended sand concentration and velocity and related to the wave conditions at the point of breaking. Measured rates ranged from 86,000 to 231,000 m3/y, and transport was found to be greatest in the vicinity of the sand bars. The popular CERC formula gave sediment transport rates significantly greater than the observed values, with the difference between the two on the order of 100%. The average CERC transport coefficient, K1, computed from our measurements was determined to be 0.19 ± 0.12.

Numerical Study on the Sediment Transport and Morphologic Change of Intertidal Flats by Tides and Wind Waves

The wave forcing term and a sediment transport model of sands were installed into the cohesive sediment transport model named “WD-POM” in order to calculate the morphologic change of intertidal flats due to tides and wind waves. Current fields and morphologic changes in the back of the offshore breakwater were calculated by using the improved model. Numerical results were agreed qualitatively with other experimental results. The model was also applied to the case of oblique incident waves on the uniformly inclined slope. The longshore sediment transport rate agreed quantitatively with the value estimated by using the longshore sediment transport formula. Furthermore, the improved model was applied to the Shirakawa intertidal flat in the Ariake Sea and current fields and morphologic changes were calculated.

Neural network–genetic programming for sediment transport

The planning, operation, design and maintenance of almost all harbour and coastal engineering facilities call for an estimation of the longshore sediment transport rate. This is currently and popularly done with the help of empirical equations. In this paper an alternative approach based on a combination of two soft computing tools, namely neural networks and genetic programming, is suggested. Such a combination was found to produce better results than the individual use of neural networks or genetic programming. The ability of the neural network to approximate a non-linear function coupled with the efficiency of the genetic programming to make an optimum search over the solution domain seems to result in a better prediction.