Case study: Sediment budget in direction of longshore drift on Changi beach, Singapore.

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Chow Keng Ji

Coastal Fieldwork

a case study of the spit on Changi Beach on how the amount of beach material changes in the direction of longshore drift in relation to gradient and length of the beach face

  1. Introduction

Changi Beach is one of the longest natural beaches in the north-eastern part of Singapore. The northern part of the beach is extended as a spit, a landform of coastal deposition. Spits are accumulations of beach material which result from longshore drift. Longshore drift is a process which causes beach material to move in a down-drift direction, due to waves approaching the beach at an oblique angle. This causes the swash to carry material in the direction of longshore drift, the process continuing such that material is transported along the beach. In the case of the spit at Changi Beach, longshore drift occurs in the north-west direction (refer to figure 1 and 2). Figure 3 illustrates the oblique angle at which the waves approach the beach.

This study aims to examine the development of the beach profile, with focus on the amount of beach material along the spit in the direction of longshore drift. While most studies would consider longshore drift along a beach, this study differs slightly as the beach face on the spit itself, as a landform of deposition, is being investigated. The gradient and length of the beach face can be hypothesised to increase in the direction of longshore drift, as the amount of the beach material contributes to a steeper and longer beach face. The increase of beach material along the beach can then be deduced using the gradient and length. According to Bird (2008) on beach budgets, conventional methodology can be used in this way to calculate differences in amount of beach sediment along the beach by looking at the cross sectional area of a beach profile.

This case study investigates the extent at which the hypothesis that the amount of material increases in the direction of longshore drift, is applicable to this spit. There may also be interesting findings on the amount of material in the area of the spit facing the channel leading to Changi Creek Reservoir. Even though such an investigation of how amount of sediment increases in the direction of longshore drift is seemingly tautological, according to Schwartz (2005) on longshore sediment transport, the phenomenon is regarded as “almost impossible to discern directly… and viewing the whole beach face does not provide any clues… only when transport rate changes along the shore, because of a barrier such as groin, does the beach change in a manner that can readily be detected.” As such, since preliminary analysis on-site seems to support the hypothesis that beach material does in fact accumulate in the direction of longshore drift, not only can this research examine the relationship of this concept of increase of beach material in relation to the gradient and length of the beach face, but also bring attention to a possibly unique situation on this particular depositional landform.  

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  1. Methodology

The gradient and length of the beach face was measured at several transects each 20 metres apart along the spit, from the area facing open waters, to the tip of the spit to the area facing the river. For the approximate location of these transects, refer to figure 5. The data was collected within five hours around the time of low tide.

At every two metres from the edge of the berm crest until one meter above the low tide level, the gradient of the slope was measured using two ranging poles and a clinometer (refer to ...

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