Sediment budgets on a partially sheltered bay subjected to low wave energy in South East Thailand Coast | |
| Author | Somchet Thinaphong |
| Call Number | AIT Thesis no. 751 |
| Subject(s) | Wave mechanics Sedimentation and deposition |
| Note | A thesis submitted in partial fulfillment of the requirements for the Degree of Master of Engineering at the Asian Institute of Technology, Bangkok, Thailand. |
| Publisher | Asian Institute of Technology |
| Abstract | Sediment budgets for a partially sheltered bay along the southeast Thailand coast are determined through comparisons of bottom surveys charted from 1940 to 1973, covering a long term and short term changes of 33 year period. The bay is divided into seven individual cells and differencing of depth values between different surveys permits evaluations of rates of erosion and deposition. In general the deposition rates are found to be in exceedance of those of erosion. The sediment deficit demands an input to the whole bay over the 33 year period at about 1.3 x 10 6 cubic metres. The net long shore drifts from adjoining embayments are not perceived to fill the deficits. Source such as cliff erosion is recognized to be negligible, while the total sediment yield from overland flow to the bay was previously reported to be only 0.12 x 10 6 cubic meters estimated using annual rainfall of 125 centimeters along with effective drainage basin of 36 square kilometers. To make up for the deficit of 1.18 x 10 6 cubic metres, it is envisaged that some unconsolidated relict sediments off shore are being continually transported by current and wave mechanism. Computations basing on different methods applied primarily to unidirectional flow indicate that the maximum sediment discharges of flood tides into the bay exceed those of ebb tides by only about 0ยท.14 x 10 6 cubic meters over this same period. The wave effect on the off-shore bottom sediments is next investigated. Since in this off shore zone the wave energy dissipation is primarily due to bottom friction, the primary quantitative determination required is the on-shore bed load transport rate. On turning to deal with this fundamental aspect of coastal sedimentation, the writer finds no guides that possess eases of application to constitute basis of assessing the bed load transport rate; despite the vast output of present research publications. In response to the need, existing measurements of incipient motion and bed load data previously obtained by a number of researchers are then compiled and re-analyzed. Readily useable forms of expressions for estimating incipient motion of sea-bottom sediments and bed load transport rates under wave action are developed. Only their final forms and their uses are included herein. Al though the accuracy of extrapolating these expressions justifiably to the application to the natural conditions may seem questionable," total sediment contributions by wave for 33 years are computed. using these formulae in conjecture of other techniques. They all lend support to a general conclusion that if wave characteristics in 1974 is a good average value for any other year the wave could contribute about 0.80 x 10 6 cubic meters. It is le~ with an unbalanced quantity of 0.26 x 10 6 m3 representing a combination of possible interpretations. Biogeneous deposition partially accounts for the remaining deficit, since shell fragment and CaC0 3 are found to be considerably large per cent constituents for beach sediments. A number of information of beach profiles and beach samples are processed so that techniques such as considerations of effect of man-made structures, sediment grain size distribution and long term trend of coastline configuration in relation to persistent wave energy, can be later utilized to appraise the characteristics of near shore sediment movement. Finally, decisions related to the maintenance and improvement of the navigation channel in the bay; which are the ultimate objective of this study await more hydraulic/geomorphologic data and critical judgement of more detailed analysis results. |
| Year | 1975 |
| Type | Thesis |
| School | Student Research Before 1980 |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Thesis (Year <=1979) |
| Chairperson(s) | Suphat Vongvisessomjai |
| Scholarship Donor(s) | British Government |
| Degree | Thesis (M. Eng.) - Asian Institute of Technology, 1975 |