During the onslaught of a storm on the coasts of Taiwan in summer and autumn, large waves and storm surge have often caused beach erosion. In order to mitigate coastal disasters and erosion, soft-options have been promoted in recent years, to fulfill the purpose of shore protection, as well as to meet the new requirements of landscape, ecology and recreation. Consequently, semi-natural approaches have been adopted in stead of the conventional hard-structures. This thesis aims to report a study on the effects of detached submerged breakwater layouts and storm wave types on beach profile changes and berm retreat.
In order to establish a practical procedure to assist the assessment of beach profile changes with submerged breakwaters during storm, we first collect and analyze the beach profile change data performed in large wave tanks (CE from the US and PI from Japan), and apply the well known SBEACH model to derive regression relationship between the two key parameters ( and ) in this model against the non-dimensional fall velocity ( ). The suggestion of Larson and Kraus (2000) to include hard bottom option in SBEACH with a set of modified and values, which may be different from that originally developed for a sandy beach environment, is then carried out using the beach profile changes results conducted experimentally with submerged breakwaters (Risio and Lisi, 2010). Consequently, we have conducted the numerical experiments systematically to study the beach profile changes using submerged breakwaters under various environmental combinations (with 10 different offshore distances, 10 breakwater heights, 10 crown widths and 4 types of storm wave conditions derived from storm return periods), from which a new set of and values are derived and used in SBEACH for the investigation of installing submerged breakwaters to mitigate potential beach erosion.
Our numerical investigations using SBEACH for a beach with submerged breakwater reveal that: (1) Beach profile changes in erosion (0 m line and berm) and accretion (0 m line) due to regular waves are more significant than that of irregular waves. (2) Storm waves with a long return period cause more erosion to the shoreline (0 m line) and berm, while that with short return period may produce accretion to the shoreline. (3) The further a submerged breakwater away offshore, the more sediment transportation offshore and severe beach and berm erosion. (4).An increase of submerged breakwater height would result in accretion near the 0 line; except during a violent storm event, when an increase of berm height could reduce berm erosion. (5) An increase to the crown width of a submerged breakwater could only become effective to reduce wave energy and berm erosion, if an appropriate breakwater height is used; otherwise, a mere increase in width with insufficient height would increase wave height and berm erosion.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0913112-113518 |
| Date | 13 September 2012 |
| Creators | Hsu, Che-Chang |
| Contributors | Wen-Juinn Chen, Rong-Chung Hsu, Tai-Wen Hsu |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0913112-113518 |
| Rights | unrestricted, Copyright information available at source archive |
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