All wave components from south to west will yield northward littoral drift contributions, and all wave components from west to north will yield southward littoral drift contributions. The sum of the northward drift components is called the northward littoral drift , and similarly is the sum of the southward drift components referred to as the southward littoral drift.
The difference between the northward and the southward littoral drifts is called the net littoral drift , which is associated with a net littoral drift direction. The sum of the northward and the southward drift rates is called the gross littoral drift , which has no direction. Littoral drift budgets can be made for any period relevant for the site under study as long as there are sufficient data. An overview of the magnitude of littoral drift is provided in the following table as a function of the following parameters:. An important parameter in relation to the littoral drift conditions is the variation of the net transport with varying orientation of the coastline.
This means that the sand will accrete upstream of the groyne forming a coastline with the orientation, which gives zero transport. The efficiency of the groyne depends very much on the angle between the present orientation of the coastline and the orientation of net zero transport. If this angle is small, the groyne will be efficient, as it will be able to hold a long sand filet. If the angle is large, which is the case with a very oblique wave exposure, the groyne will only be able to hold a very short sand filet, which means that a groyne will not be an applicable type of coast protection in this case.
When discussing the littoral transport along a coastline in general, it is always the net littoral drift that is referred to unless otherwise specified. Gradients in the net littoral drift along a section of coast lead to coastline erosion or accretion. The littoral drift also depends on the sea current, although to a much smaller extent than it depends on the longshore current. This means that the most important hydraulic parameter for the littoral transport is the wave conditions. The water-level mainly determines where in the coastal profile the transport will take place, but the water-level only influences the magnitude of the littoral drift to a lesser extent.
However, the tide may have significant influence on the transport conditions for macro-tidal environments.
Northern Gulf of Mexico: Spatial Analysis of Mississippi Delta
Positive or negative correlation between the waves and the water-level variations may be of importance for sedimentation patterns near large structures. At many locations there is a considerable variation in the grain size depending on the distance from the coastline. Typically the sediments become finer with increasing distance from the coastline.
This will, to some extent, blur the picture of the littoral drift given above. The fine cohesive sediments , which may be present in the outer part of the profile, will be in suspension over the entire water column and will also tend to spread over the entire coastal profile during strong wave exposure. The transport which this gives rise to is normally not considered a part of the littoral drift, as this only takes the non-cohesive sediments into consideration.
The transport of the cohesive sediments thus only plays an indirect role in the stability of the coastal profile. The existence of this transport of fine suspended sediments will, however, be of importance in relation to sedimentation in ports and in trenches. Even when the sand is in suspension it is still relatively close to the seabed because of the relatively high fall velocity of sand grains. This means that any change in the hydrodynamics or bathymetric conditions will "immediately" result in a corresponding change in the transport capacity and therefore also in the morphology.
It is not possible to guide the sand between the coastal breakwater and the shoreline if the breakwater has a length of more than around 0.
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If the length of the breakwater is more than approximately 0. This immediate morphological response to even small changes in the littoral transport is also the reason why many attempts to construct island-ports with zero impact on the shoreline have failed. Most of them have been connected to land by tombolo formations. Varying wave conditions result in varying onshore and offshore transports over the coastal profile.
These transports are, to some extent, reversible and therefore non critical in terms of long term coastal stability. However, extreme storm surge and wave exposure result in coastal erosion. When the coastal profile is exposed to non extreme waves and storm surge, the sediments near the shoreline will be transported offshore and typically be deposited in a bar resulting in an overall flattening of the slope of the shoreface.
However, the inner part of the shoreface as well as the foreshore will become steeper in this process, and the shoreline will recede. During the following periods of smaller waves, swell and normal water-level conditions, the bar will travel very slowly towards the coastline again, practically rebuilding the original coastal profile. During such a sequence of profile erosion and rebuilding, certain parts of the coastal profile may experience temporary erosion.
This may not be recorded in profile surveys, because some rebuilding will already have taken place before it is possible to carry out surveys after the storm. It is important to take such temporary profile fluctuations into account when designing structures in the coastal zone. It is particularly important to have a sufficiently wide beach so that the temporary beach erosion will not cause erosion of the coast.
This onshore and offshore transport is closely related to the form of the coastal profile.
Several investigations have revealed that a coastal profile possesses an average, characteristic form, which is referred to as the theoretical equilibrium profile. The equilibrium profile has been defined as "a statistical average profile, which maintains its form apart from small fluctuations, including seasonal fluctuations".
The depth d [meters] in the equilibrium profile increases exponentially with the distance x from the shoreline according to the equation . It is seen that the equilibrium profile does not depend on the wave height.
Tidal hydrodynamics and sediment transport processes in ‘de Slufter’, the Netherlands
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Hydrodynamics and Sediment Dynamics of Tidal Inlets
This second edition offers a comprehensive overview of the physiological functions of vertebrate kidneys from This second edition offers a comprehensive overview of the physiological functions of vertebrate kidneys from a comparative viewpoint, with particular emphasis on nonmammalian vertebrates. The topics covered include renal structure;glomerular ultrafiltration; tubular transport of inorganic ions, organic In order to answer the research question field measurements were carried out in and around the mouth of the Slufter, in September and October Measured fluxes are quite equal for both inflow and outflow stages, but calculated sediment fluxes clearly indicate an export of sediment during spring tidal conditions.
This difference can partly attributed to high measured suspended sediment concentrations during flood. During neap tide, both computed and measured sediment fluxes indicate an import of sediment. The flood dominance is a direct result of the external tide, which emerges in longer ebb durations resulting in higher maximum landward directed flow velocities. Measured and calculated fluxes clearly indicate an export of sediment during spring tidal conditions. Tidal flow asymmetry in the Slufter is mainly controlled by the geometry of the inletsbasin, rather than a differentiation between duration of the ebb and flood currents.
During storm conditions the total basin of the Slufter is inundated, and both current field and suspended sediment concentration SSC greatly differ from calm condition. During storms sediment fluxes in the main channel are significantly larger than during non-flooding conditions.
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