Beach Drift and Swash The longshore current is part of the longshore transport that moves sand and sediment down the coastline, but there is also another process that contributes to the longshore transport called beach drift, or longshore drift. There is also an ecological aspect to consider when discussing hardening of North Carolina's coastline. Beaches In relatively quiet areas along a shore, waves may deposit sand. As with the Waimataitai lagoon the , which currently lies to the north of the Timaru port is undergoing erosion and may eventually breach causing loss of another lagoon environment. Bays are sheltered, low energy zones that form in bands of weak geology, e.
You can see a spit in Figure. How does it help protect the shoreline? Seawalls are commonly very massive rock, sometimes reinforced cement structures, designed to withstand waves, including large, storm-generated waves. Sediment transport along the and surf zone is influenced by the swash occurs in the direction of prevailing wind , which moves the pebble up the beach at the angle of the waves, and moves the pebble back down the beach due to the influence of. This video shows how longshore drift works. The structuring of tidal inlets is also important for longshore drift as if an inlet is unstructured sediment may by pass the inlet and form bars at the down-drift part of the coast. As a result of wave refraction, destructive waves concentrate their energy on all three sides of the headland and so it slowly erodes overtime.
This page will discuss the process of longshore transport, and how it relates to shoreline erosion, a process that affects all development located on the coastline. This is superbly animated below. Many a time as a child this caused me great stress. The starting point to discussing depositional features is with swash and drift aligned beaches. This results in deposits of sediment all along the coast.
Individual particles are moved along the beach in a zig zag pattern. The sediment moves straight down the beach with it. You will also notice that the features caused by glacial erosionare a lot cruder than those from rivers: compare the Grand Canyonand any glacial trough, the one I know best is Nant Ffrancon inSnowdonia, though I'm sure there's another near you. Formulas Used in Calculating Longshore Drift There are about six formulas that are used in calculating the factors that are considered to cause longshore drift. Natural features This section consists of features of long shore drift that occur on a coast where long shore drift occurs uninterrupted by man-made structures. As well as dominant drift direction, spits are affected by the strength of wave driven , wave and the height of incoming waves.
Coasts of erosion form as a result of high energy waves, large fetch, high exposure and limited deposition. The system underwent further changes c. Firstly, the roots bind the sand together, and secondly the above ground vegetation traps particles of sand as they are blown over the surface. While flood deltas are likely to expand the availability of space in a lagoon system or bay, ebb-deltas are most likely to become stunted when in smaller spaces or highly exposed shores. Erosion is a process of geological denudation, which involves the breakdown and transport of rock materials. Sediment will again commonly accumulate on the updrift side of the jetty, and erode on the downdrift side of the jetty.
They consist of more resistant rock, e. On approaching the shorline waves will curve in to beaches and reducer the liklihood of drift. Longshore, tidal, and fluvial currents construct submerged bars in shallow water coastal environments. Both ports and harbors pose a short-term threat to longshore drift. In this way you nnot only have to identofy varying rates within headland and bays, but you should also be thinking of ocean fetch, exposure, geoology and sub-aerial processes. Over time, they erode the shore. In brief, dunes begin to form beyond the strandline of the beach where dry sediment is transported by wind through saltation and suspension.
This is called longshore drift. It's unclear how cusps form but once they do they are a self sustaining formation. The accretion of this sediment to the south, therefore meant a lack of sediment being deposited on the coast near the Waimataitai lagoon to the north of the port , which led to the loss of the barrier enclosing the lagoon in the 1930s and then shortly after, the loss of the lagoon itself. Breakwater: A breakwater is similar to a seawall in that it is built parallel to the shoreline, but it is located offshore at some distance away from the beach. The diagram to the right shows the process of longshore drift and longshore currents. Cuspate forelands can be described as triangular beaches.
Groins Longshore drift can erode the sediment from a beach. In order to accommodate drawdown in storm conditions detached breakwaters have no connection to the shoreline, which lets currents and sediment pass between the and the shore. Tidal inlets can act as sinks and sources for large amounts of material, which therefore impacts on adjacent parts of the coastline. As vegetation stabilizes the dunes, fore dunes and yellow dunes develop. Nant Ffrancon, on the otherhand it just a simple trough - a U-shaped valley. The second diagram shows a Post 16 model example.