Wave-induced Longshore Sediment Transport Research Articles

Comprehensive Study of the Sand Spit Evolution at Tidal Inlets in the Central Coast of Vietnam

Tidal inlets along the central coast of Vietnam are located in a microtidal, wave-dominated coastal environment. In addition, the Vietnam coast is highly influenced by the seasonal monsoon regime, which is characterized by large northeast waves from October to March and calm southeast waves from April to September every year. Consequently, the tidal inlet entrance morphologies often suffer from a dynamic seasonal evolution due to distinct differences in the direction of wave-induced longshore sediment transport (LST) between the two monsoon seasons. The migration or closure of tidal inlets causes a lot of problems for socio-economic development in the region since these are the main reasons leading to an increase in the risk of coastal flooding and the obstruction of navigation. This paper presents a comprehensive study of the morphological evolutions of natural tidal inlets on the central coast of Vietnam using long-term remote sensing data sets and by the Delft3D numerical model. Surprisingly, the estimated LST rates from the former method are in an order of magnitude agreement with the results from the latter one for all of the areas in this study. Based on the conservation equation for sand and comprehensive data collection, a new simple empirical formula for predicting the sand spit elongation rate as a function of the sand spit width is developed. Although the breaching of sand spit might happen during an extreme flood event at some tidal inlets, the growth rate of the spit before and after the breaching is almost unchanged. These findings are very useful information for supporting the local coastal authorities to find better management solutions in terms of sustainable development.

Variability of the local wave regime and the wave-induced sediment transport along the Ganpatipule coast, eastern Arabian Sea

For planning coastal protection measures, information on nearshore waves and the wave-induced sediment transport rates are required. This study examines wave-induced longshore sediment transport (LST) rate considering three widely used bulk transport formulae using measured wave data at 14-m water depth covering six years (2011–2016). The study shows that selection of appropriate formulae for estimation of LST rate is important since the estimates based on different formulae vary from 4–5times larger as compared with Kamphuis equation, which is a reliable formula for estimating LST rates across the eastern Arabian Sea. Meridionally oriented coast presents a predominant north to south LST regime as a result of the wave climate, where the lowest values of significant wave heights (Hs) occur during October–April (< 1.5 m) and highest energy conditions occur in the Indian summer monsoon (June–September) when Hs exceed 2 m. Sedimentary dynamics during the monsoon contributes to 77%–88% of the annual LST due to the high wave energy present during this period. Even though the inter-annual variation in annual mean Hs is 6%, the variations in gross LST is up to 22%. The study shows that a small error (∼1-5°) in the estimation of the wave breaker angle leads to a significant error (10%–90%) in the LST rate. Also, 5%–20% error in the wave height leads to 7%–43% error in the annual LST rate.

Nearshore waves and longshore sediment transport along Rameshwaram Island off the east coast of India

ABSTRACT Wave-induced Longshore Sediment Transport (LST) play an important role in the dynamics of the Dhanushkodi sandspit located southeast of Rameshwaram. The LST along the Dhanushkodi coast is studied based on data collected simultaneously in Gulf of Mannar (GoM) and Palk Bay (PB) using directional waverider buoys. The numerical model REF/DIF1 was used to calculate the nearshore waves and the LST rate was estimated using three different formulae. The model validation was done based on the measured nearshore waves using InterOcean S4DW. Numerical model LITPACK was also used for simulating non-cohesive sediment transport and the LITLINE module was used to study the shoreline evolution over 5 years. Low net annual LST along PB (~0.01 × 106 m3) compared to the GoM region (0.3 × 106 m3) were due to the weak waves. Accretion in the region led to growth of the Dhanushkodi sandspit by 65 m during the period 2010-2015.

Wind wave direction impact on the long-shore sediment transport rate, South East Baltic sea coast

The Lithuanian coast of the south eastern part of the Baltic Sea represents a generic type of more or less straight, high-energy (in the Baltic Sea conditions), actively developing coasts that contain a relatively large amount of finer, mobile sediments, are open to predominating wind directions and are exposed to wave activity for a wide range of wave approach directions. The combination of the angular distribution of winds and the geometry of the coast are such that the wave-induced long-shore sediment transport is, in average, to the north over the entire Curonian spit and the mainland coast of Lithuania. Analysis of the field data performed by the G. Žilinskas (2008) from 1976-2007 revealed that the length of accumulative sections has been considerably reduced. Accordingly, the length of the gradually eroding sectors has increased in the end of the 20th century. In this study were analised potential variations in the long-shore sediment transport rate due changes of the wind wave directions. Sediment transport rate is estimated by the energy flux model, also known as the Coastal Engineering Research Centre (CERC) model. The study area covers the entire coast of Lithuania. Entire coast was divided into 90 grids, about 1 km long beach sectors, at the 3 m depth isobaths. Wave directions calculated every 10 degrees. Most intensive long-shore sediment transport from south to the north was induced by waves from South. Changing wave approaching direction to the SW, long-shore sediment transport rate become smaller. Waves from WSW induce long shore sediment transport from opposite direction, from north to south. Westerly waves already induce maximum sediment transport to the south. It should be noticed that wave direction further shifting to the North induces sediment transport to the north again. DOI: 10.15181/csat.v3i1.225

The Impact of Wave-Induced Longshore Transport On A Delta-Shoreface System

Abstract Wave-induced longshore sediment transport is a major basinal process that reworks fluvial sediment supply along a delta–shoreface depositional system. However, the effects of the variable counterbalance between supply and wave reworking have not been sufficiently acknowledged in understanding paleoshoreline evolution and stratigraphic concepts such as sequence stratigraphy and autostratigraphy. With a numerical shoreline model, we quantify the relation between wave-induced longshore sediment transport and shoreline orientation under conditions of steady sea level. A case study of the Po delta–shoreface system reveals that a decrease in delta progradation rate can in part be considered as an autogenic response to steady wave conditions offshore. Long-term wave-induced transport can be quantified by the volume of sediment redistribution. As such, we propose a revised definition of accommodation space by integrating the effect of wave-induced longshore transport. Wave-induced longshore sediment transport has a significant impact on progradation of deltaic and adjacent shoreface shorelines, and needs to be considered while interpreting shallow-marine stratigraphy.

Evaluating Shoreline Response to Offshore Sand Mining for Beach Nourishment

An analytical approach that incorporates analysis of nearshore wave transformation and wave-induced longshore sediment transport was developed to quantify the significance of potential physical environmental impacts associated with offshore sand mining. Calculation of longshore sediment transport potential for a series of wave cases provided a method for determining the extent and magnitude of alterations to nearshore processes, but the magnitude of change alone did not provide enough information to determine the significance of changes for a particular coastline. This paper documents a method for evaluating the significance of borrow site impacts that incorporates temporal and spatial variations in the incident wave field. Example applications of this method are presented for borrow sites offshore Oregon Inlet, North Carolina; Martin County, Florida; and Corsons Inlet, New Jersey. As a management tool, this methodology holds several advantages over methods previously employed to assess the significance of borrow site impacts, including: 1) a model-independent component (observed shoreline change) is used to verify model results; 2) impacts associated with borrow site excavation can be directly related to their potential influence on observed coastal processes; 3) site-specific temporal variability in wave climate and sediment transport potential is calculated as part of the methodology; and 4) the procedure accounts for spatial and temporal variability in wave climate, as well as provides a means of quantifying significance of impacts relative to site-specific conditions.

Longshore sediment transport near Visakhapatnam Port, India

Wave-induced longshore sediment transport rates near Visakhapatnam Port, India, have been estimated using an energy flux method. Wave data from the breaker zone have been collected through daily observations, and are used for the estimation of sediment transport. The direction of littoral drift is from south to north during the period March to October, when the wave directions are between SE and S, and from north to south during the period November to February when the wave directions are between ENE and E. The net drift is northwards and is by far the most dominant for this coast. The beach and shoreline changes are critically examined in relation to the littoral drift. The distribution of sediment transport across the surf zone, at different stations along the coast, is presented.

Directional wave measurement at Haifa, Israel, and sediment transport along the Nile littoral cell

Results of three years of directional wave measurement at the Eastern Mediterranean coast of Haifa, Israel are presented. The wave-height and energy-flux distributions reveal a moderately high-energy coast with a bimodal annual cycle. The rate of wave-induced longshore sediment transport is estimated from the directional energy flux distributions. It describes an annual cycle with a maximum northward transport of 75 ± 14 × 10 3 m 3/month in midwinter and a southward transport of 26 ± 5 × 10 3 m 3/month in summer. The net annual transport is northward and computed at 110 ± 100 × 10 3 m 3/yr. We show that a wave-induced transport is sufficient in explaining the apparent transport of sediments in the Nile Littoral Cell, from the Nile Delta source to the Haifa Bay sink.