海岸动力学英文PPT课件Coastal Hydrodynamics_6.2.ppt
《海岸动力学英文PPT课件Coastal Hydrodynamics_6.2.ppt》由会员分享,可在线阅读,更多相关《海岸动力学英文PPT课件Coastal Hydrodynamics_6.2.ppt(41页珍藏版)》请在三一文库上搜索。
1、Coastal Hydrodynamics,Shoreline configuration,6.3 Coastal Changes,2. Coastal changes _ case studies,3. Mechanism of coastal changes,4. Methods to analyze coastal changes,Chapter 6,The 1ongshore sediment transport in the surf zone and the subsequent deposition of sediment in regions sheltered by isle
2、ts or reefs may cause the formation of reefs, spits or bar chains along the coast, such as the Jimudao spit at Longkou.,Chapter 6,When a spit links the mainland to a offshore island it becomes a tombolo. A tombolo may also develop from a cusp-shaped body growing in the lee and eventually connecting
3、with an island.,Chapter 6,A growing spit often deflects the mouth of a river or the entrance to a bay prolonging it in the direction of longshore sediment drift.,Chapter 6,For a given littoral compartment, suppose the rate of sediment drift into the compartment is denoted as Qin, and Qout is the rat
4、e drift out.,1. Shoreline configuration,Chapter 6,If Qin Qout, which denotes deposition within the compartment, and the coastline approaches seaward: beach deposition will occur. If Qin Qout, which denotes a net deficit within the compartment, and the coastline retreats landward, that is to say, the
5、re will be beach erosion.,Chapter 6,When Qin is equal to Qout, which indicates that there is neither erosion nor deposition within the compartment, therefore the coast is stable. The lack of either beach erosion or deposition indicates that a state of equilibrium exists between the sources and losse
6、s.,Chapter 6,An equilibrium beach is a beach whose curvature in plan view and profile are adjusted in such a way that the waves impinging on the shore provide precisely the energy required to transport the load of sediments supplied to the beach. The equilibrium condition is one in which the shoreli
7、ne is everywhere parallel to the crests of the incoming waves.,Chapter 6,This condition is most closely approached by a pocket beach where there is little or no additional sand being supplied to the beach. The development of sand beaches in the Henry Bay is an excellent example of the way in which l
8、ocal beaches orient themselves parallel to the refracted wave crests and develop the same curvature.,Chapter 6,Wave refraction diagram of Henry Bay for a 14s southwesterly swell. Every fifth wave crest is shown as a broken line, and sand beaches are represented by thickened lines.,Chapter 6,With est
9、ablished sediment sources and under a certain wave climate, a beach will tend toward a natural equilibrium where the waves are just capable of redistributing the sands supplied from the sources.When jetties, breakwaters, or other structures are constructed in the coastal zone, the natural equilibriu
10、m will be upset, sometimes will disastrous consequences.,2. Coastal changes_ case studies,Chapter 6,Jetties and breakwaters act as partial or total dams to the littoral drift, blocking the natural sediment movement along the shoreline. That is to say, coastal engineering structures upset the natural
11、 equilibrium between the sources of beach sediment and the littoral drift pattern. In response, the shoreline must change its configuration in an attempt to reach a new equilibrium.,Chapter 6,Interfering with the longshore sand transport,Redirecting wave energy,Chapter 6,Case 1:Madras Harbor, India,
12、 showing accretion on the updrift side of barbor and erosion on the downdrift side.,Chapter 6,The initial construction of the harbor for the port of Madras took place in 1875, the breakwater extending outward about 1000m from the original shoreline. this coast is characterized by a strong littoral s
13、and transport from south to north, so that following the breakwater construction, sand accumulated to the south side of the harbor, the shoeline progressively advancing. In the following 36 years (1876-1912), more than 1.8 million square meters of new land formed.,Chapter 6,Waves to the north of the
14、 harbor continued to transport sand northward; this sand was not replaced, however, because the sand that would have normally been deposited there was trapped behind the breakwater. This resulted in rapid erosion to the shoreline north of the breakwater for a length of 5km along the shore, and it be
15、came necessary to install seawalls to check the destruction.,Chapter 6,Subsequently, to prevent harbor shoaling, the breakwater was extended seaward and a suction dredge installed to pump sand past the harbor. It is seen that the work done in bypassing the harbor by dredging has replaced the natural
16、 transport system due to wave action.,Chapter 6,Case 2:Sand deposition in the protected lee of Santa Monica breakwater, California,Chapter 6,At Santa Monica in 1934 a 600-meter-long detached breakwater was constructed parallel to the shoreline and about 600m offshore. Immediately following its const
17、ruction, sand began to deposit in its protected lee. Up-coast from the breakwater the shoreline advanced, while on the down-drift side the shoreline eroded. Only dredging prevented attachment of the shoreline to the breakwater with a complete closure of the harbor.,Chapter 6,Case 3: Deposition_erosi
18、on pattern around the Santa Barbara breakwater,Chapter 6,Originally the breakwater at Santa Barbara constructed in 1927-28 was detached, but in 1930 it was extended and connected to the shoreline to prevent harbor shoaling. The predominant waves are from a westerly direction, causing a large littora
19、l transport to the northeast, computed to average about 215000 cubic meters per year. The breakwater interrupted this littoral drift and caused deposition on its updrift side.,Chapter 6,Sand accumulated on the west side of the breakwater until the entire area was filled, the sand then moving along t
20、he breakwater arm, swinging around its tip, and depositing in the quiet waters of the harbor as a tongue or spit of sand. Without dredging, the spit would have eventually grown across the entire harbor mouth, attaching to the opposite shoreline and closing off the harbor.,Chapter 6,To prevent this c
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 海岸动力学英文PPT课件Coastal Hydrodynamics_6.2 海岸 动力学 英文 PPT 课件 Coastal Hydrodynamics_6
链接地址:https://www.31doc.com/p-3104724.html