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A STUDY ON THE EROSION CONTROL OF THE COASTAL BEACH WITH AN ARTIFICIAL REEF

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Author(s)
문지원
Issued Date
2008
URI
http://dcoll.jejunu.ac.kr/jsp/common/DcLoOrgPer.jsp?sItemId=000000004262
Abstract
Recently, the erosion problem in our coast zone becomes more and more serious because of several artificial activities due to the expansion of city function, industrial complex and harbor facility and so on. To make matter worse, the erosion problem becomes serious more and more because of picking of sea sand that is used to aggregate resources in construction sites, which is major factor of income and outgo of sea sand. Also, environmental and economical importance of the coastal beach zone grows bigger and bigger.
Coastal beach zone is eroded constantly by the waves accompanied with the rising of the water lever by storm surge and high tide. For this reasons, the concern for the coastal beach protection increases more and more. Therefore, it is necessary to study on the erosion control of the coastal beach.
When it comes to the models of the coastal beach erosion, Vellinga (1982, 1983, 1986) calculated the coastal beach change by the time. But Vellinga(1982, 1983, 1986) model for the numerical simulation of the coastal beach erosion has restrictions, which is that it will not timely be able to track the coastal beach change to reappear the sandbar and predicted time is restricted. Also, Krebel Model can calculate the change of the coastal beach and sandbar, but can not express the sandbar, timely. So considering the drawbacks of the incident waves of the Vellinga model, SBEACH model proposed by Larson and Kraus (1989) is applied to calculation of the formation and the erosion behavior of the coastal beach topography in this study, for SBEACH model proposed by Larson and Kraus (1989) is more suitable to this numerical computation.
The calculative order of the two-dimensional SBEACH model is the same with other normal coastal beach models and can be written as follows:
(1) Dally (1980), Dally et al. (1985)'s equation is used to calculation of the wave transformation in this paper.
(2) About the calculation of the cross-shore sediment transport rate in this study, the cross-shore sediment transport rate is basically calculated by energy dissipation per unit day in broken wave zone. And based on the division of the profile applied in near-shore wave dynamics and the physical characteristic of cross-shore sediment transport under various flow conditions, four different zones of transport were introduced as four sections. These zones are pre-breaking zone, breaker transition zone, broken wave zone and swash zone.
(3) The profile change calculation of the coastal beach by continuity equation of sediment is based on sediment transport rate of time level of two.
In this study, an artificial reef is applied to exposed non-erodible bottom, and this study is composed of three sub models. The formation of the coastal cliff and erosion behavior of the coastal beach has been carried out using SBEACH model proposed by Larson and Kraus (1989).
First, the numerical analysis of the coastal beach with and without an artificial reef is carried out in order to investigate erosion control effect by an artificial reef. Form the numerical results, it is shown that the result is more effective for the case with an artificial reef than without an artificial reef in controlling the coastal beach erosion.
From the results of the coastal beach erosion analysis due to the offshore distance of the artificial reef, it is shown that as the offshore distance of the artificial reef is closer to the shoreline, the erosion control ability of the artificial reef is more effective in controlling the coastal beach erosion.
When it comes to the coastal beach erosion analysis due to the height of the artificial reef, it is shown that the higher the height of the artificial reef is, the smaller the coastal beach erosion occurs. And, it is also shown that the scouring phenomenon is occurred at the outside of the artificial reef and sandbar is formed. It is considered because higher the height of the artificial reef is, the weaker the wave force becomes.
From the results of the coastal beach erosion analysis due to the width of the artificial reef, it is shown that the narrower the width of the artificial reef is, the bigger the scouring depth and scouring area by the wave is. This reason is considered because the broader the width of the artificial reef is, the weaker the wave force becomes.
As the optimum conditions of the artificial reef in controlling the coastal beach erosion, it is shown that as the offshore distance of the artificial reef is close to the shoreline, the erosion control of the coastal beach is more effective. And, it is shown that as the height of the artificial reef is high, the erosion control of the coastal beach is more effective. Also, it is shown that as the width of the artificial reef is wide, the erosion control of the coastal beach is more effective than any other condition of the artificial reef. But, the conditions of the height and the width of the artificial reef are not more effective than the condition of offshore distance of the artificial reef in controlling the coastal beach erosion.
On the results of the erosion behavior of the coastal beach due to berm location of the artificial reef, an artificial reef with a left-hand side berm is more effective than any other condition in controlling the coastal beach erosion. And the scoring area in artificial reef with a left-hand side berm is greater than other two cases, but the scouring depth is the most small.
From the numerical results of the erosion behavior of the coastal beach due to the incident wave angle, when the incident wave comes into as , the coastal beach erosion was the greatest. And, it is shown that the smaller (bigger) the incident wave angle is, the larger (smaller) the coastal beach erosion occurs. Also, it is shown that the coastal beach erosion is not seriously affected when the incident wave angle comes into as and .
This numerical analysis can be applied to real coastal beach through numerical simulation model of the coastal beach erosion, including non-erodible and exposed non-erodible bottom. But this study should be improved in the future. The numerical simulation of the coastal beach erosion behavior, including erodible bottom, non-erodible bottom and exposed non-erodible bottom, has carried out in this study. But, it is necessary to study in order to raise accuracy of the numerical analysis.
The compacted effect of sand dune surface, the covering effect by landing treatment, the recovering of erodible area by wind-blown sand, the flow effect by the storm waves or tsunami and the formative factor are should be considered in the future as well as erodible bottom, non-erodible bottom, exposed non-erodible bottom. Also, the difference of the coastal beach erosion behavior by porous and non-porous of the artificial reef should be considered. And, the improvement of the numerical simulation by field surveying is necessary in the future.
Therefore, this numerical method will be broadly used to prevent erosion and protect eco-system in the coastal beach zone in the future. And the results obtained by this erosion analysis will usefully be used to control the erosion process.
Alternative Title
人工리프에 의한 海濱의 侵蝕解析에 관한 硏究
Affiliation
제주대학교 대학원
Department
대학원 토목해양공학과
Advisor
금남형
Awarded Date
2008. 2
Table Of Contents
CHAPTER1: INTRODUCTION = 1
1.1 Background = 1
1.2 Objectives = 2
1.3 Study Contents = 3
1.4 Scope and Organization = 3
CHAPTER 2: MODEL OF THE COASTAL BEACH EROSION = 4
2.1 Schematization of the Equation of the Coastal Beach Profile = 4
2.2 Calculation of the Wave Transformation = 6
2.3 Calculation of the Cross-shore Sediment Transport Rate = 10
2.4 Calculation of the Continuity Equation of Sediment = 15
2.5 Organization of the Numerical Model = 16
2.6 Application of the Artificial Reef = 17
CHAPTER 3: VERIFICATION OF THE COASTAL BEACH EROSION MODEL = 20
3.1 Verification of the Erodible Model = 20
3.2 Verification of the Non-erodible Model = 21
3.3 Verification of the Model Applied to an Artificial Reef = 22
CHAPTER 4: RESULTS AND REMARKS OF THE EROSION ANALYSIS OF THE COASTAL BEACH = 23
4.1 Erosion Analysis of the Coastal Beach with and without an Artificial Reef = 23
4.2 Erosion Analysis of the Costal Beach Due to the Offshore Distance of the Artificial Reef = 30
4.3 Erosion Analysis of the Coastal Beach Due to the Height of the Artificial Reef = 34
4.4 Erosion Analysis of the Coastal Beach Due to the Width of the Artificial Reef = 38
4.5 Erosion Analysis of the Coastal Beach Due to the Berm Location of the Artificial Reef = 42
4.6 Erosion Analysis of the Coastal Beach Due to the Incident Wave Angle = 48
CHAPTER 5: CONCLUSIONS AND FUTURE WORK = 54
5.1 Conclusions = 54
5.2 Future Work = 56
References = 57
Degree
Master
Publisher
제주대학교 대학원
Citation
문지원. (2008). A STUDY ON THE EROSION CONTROL OF THE COASTAL BEACH WITH AN ARTIFICIAL REEF
Type
Dissertation
Appears in Collections:
General Graduate School > Civil and Ocean Engineering
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