This thesis describes results of a field experiment to examine the effect of wave reflection on suspended sediment transport in front of a seawall. Two instrument rigs were set up on the beach at Teignmouth, South Devon, U.K., in June 1995. One rig (the seawall rig) was attached to a protruding section of seawall, positioning the instruments 1.2m seaward of the wall. The other rig (the beach rig) acted as a control and was positioned 135m downcoast where the seawall is set back so that conditions were those of a natural beach. At each rig high frequency measurements of wave elevation, current velocity and suspended sediment concentrations were made using pressure transducers (PTs), bi-axial electromagnetic current meters (EMCMs) and optical backscatter sensors (OBSs) respectively. Wave heights during the experiment were typically in the range 0.1 <Ho<0.3m in deep water outside the surf zone and incident wave periods were around 4 seconds. Measurements were made in a range of water depths from 0.5m to 2.5m. At the natural beach, the reflection coefficient (R = reflected wave amplitude / incident wave amplitude) was found to be dependent on frequency, with low frequency waves (f<0.08Hz) being preferentially reflected (0.7<R<0.9), while incident waves (O.I<f<0.45Hz) were dissipated (O.1<R<0.2). In front of the seawall the incident wave reflection coefficient was high (0.75<R<0.9), indicating only a small amount of dissipation and thus an effective doubling of energy over the sea bed. This was found to increase the suspended sediment concentrations in the water column. For similar water depths (-0.5m), and instrument heights (~ -0.2m) instantaneous maximum sediment concentrations in front of the wall reached 9kg/m3, compared with only 1.2kg/m3 on the adjacent natural beach, despite similar incident wave conditions. Mean suspended sediment concentrations in front of the wall were also enhanced, ranging from 0.08kg/m3 to 2.8kg/m3, while at the beach rig values were typically in the range 0.08kg/m to 0.8kg/m3. At the seawall, mean and maximum suspended sediment concentrations were found to be dependent on water depth. Suspended sediment concentrations increased with decreasing depth. Guza et al.'s (1984) time domain method for separating incoming and outgoing waves was adapted to allow the incoming and outgoing wave contributions to the cross-shore sediment transport to be analysed. Incoming waves transported sediment onshore in both beach and wall cases, with typical values of the oscillatory transport associated with the incoming waves being 0.0005 < Ujn'Cs'bcach < 0.011 kg/m2/s and 0.0011 < Uin'Cs'u^i < 0.0187kg/m2/s. At the beach this resulted in a net onshore sediment transport by the waves, while in front of the wall offshore sediment transport associated with the reflected (outgoing) waves balanced the onshore sediment transport. Although the net cross-shore transport in front of the wall in this case was therefore reduced by wave reflection, the gross cross-shore transport was increased by a factor of two. Sediment accretion which was observed at the top of the natural beach was not observed in front of the wall, implying that the presence of the wall inhibited beach recovery in these accretionary conditions. Mean cross-shore sediment transport rates were also larger at the wall than at the beach. Typical values were u Cs wall = 0.05kg/m2/s compared with u Cs beach = 0.002kg/m2/s. This was attributed to the larger values of mean sediment concentration at the wall. Mean cross-shore sediment fluxes at the wall were directed onshore at the depth of the instruments, although this did not lead to accretion. It is suggested that sediment was prevented from settling by increased wave stirring, and was transported downcoast by enhanced longshore currents in front of the wall. Both longshore currents and longshore sediment transport rates were found to be increased in front of the wall. Typical values of the mean longshore sediment flux were 0.0167 < v Cs UTIU < 0.320kg/m2/s, while at the beach typical values were 0.0001 < v c^ beach < 0.0142kg/m2/s in 1 m water depth. The enhanced longshore transport in front of the wall resulted in a bar forming downcoast from the end of the wall. The seawall reflects incident waves back over the beach and this results in an increase in sediment suspension. The following were all found to be enhanced by the presence of the seawall: wave reflection, mean and instantaneous maximum suspended sediment concentrations, onshore transport by the incident waves, offshore transport by reflected waves, gross oscillatory cross-shore sediment transport, mean cross-shore sediment transport and mean longshore sediment transport rates.

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This thesis aims to examine how and why a continental-oriented China has shifted its maritime strategic orientation and naval force structure from its coast toward the far seas in an era of interdependent international system. Generally, China is an ancient continental land power with an incomplete oceanic awareness. With the transformation after the Cold War of China’s grand strategy from landward security to seaward security, maritime security interests have gradually become the most essential part of China’s strategic rationale. Undoubtedly, the quest for sea power and sea rights has become Beijing’s main maritime strategic issue. Given China’s escalating maritime politico-economic-military leverage in the Asia-Pacific region, its desire to become a leading sea power embodying global strategic thinking means that it must expand its maritime strategy by developing its navy and preparing for armed confrontation in terms of international relations realism. Conversely, Beijing’s maritime policy leads at the same time towards globalization, which involves multilateralism and strategic coexistence of a more pragmatic kind. / This research analyses Chinese maritime strategy in the Asia-Pacific by asking: ‘Whither the Chinese maritime strategy in the ever changing Asia-Pacific security environment since the PRC was established in 1949?’ In general, contemporary China’s national security strategy is closely connected with its maritime strategy and with its comprehensive security plan for its economy, its energy supplies and its sovereignty. According to China’s view of its security environment, the traditional territorial scramble is changing from control of the land to the control of territorial waters, of maritime strategic resources, and of critical sea lanes. As a result, maritime economic competition has become a key focus for many nations. Given this, it is understandable that China’s maritime expansion from the coast to the high seas is part of its strategic approach. As a consequence, this study asks: ‘In order to shape a Sinocentric maritime security environment for China’s rising sea power, how has Beijing’s approach to maritime strategic expansion shifted from one of military antagonism toward one of strategic coexistence in the region.’ / In recent years, Beijing has, purposefully, changed its maritime strategic thinking from Maoist-style coastal defence activities to offshore defence and ultimately a far sea defence. Importantly, this strategic aspiration is clear in China’s recent national defence white papers. According to the 2004 Defence White Paper of China, Beijing clearly acknowledges a shift from China’s traditional land power to a maritime power and its priority apropos the building of the People’s Liberation Army Navy (PLAN) for winning command of the high sea and for conducting strategic counter-strikes. Meanwhile, according to China’s 2006 Defence White Paper, Beijing clearly states that China’s security concerns energy, resources, finance, information and international shipping routes are mounting. To achieve a comprehensive maritime capacity, the PLAN’s mission is urgent. It is to extend China’s offshore capabilities and to increase its maritime strategic depth. In the recent 2008 Defence White Paper, Beijing emphasizes that struggles for strategic resources, strategic locations, and strategic dominance have intensified. This implies that the PLA has shifted the focus of ground force operations from regional defence toward trans-regional mobility. This infers that the direction of maritime strategy must shift from offshore defence to far sea defence / In a few words, maritime strategy is a grand-strategic opportunity, only littoral states are fortunate enough to have. China is one such state. With China’s politico-economic-military use of the sea growing in recent years, the natural expansion of its maritime strategic ambitions and long-range power projection capabilities have generated much concern. Regarding the maritime security dilemma in the Asia-Pacific, undeniably, the crux of the problem is whether an emerging maritime China can play the role of a responsible stakeholder there.

La défense sur terre est l’affaire de l’armée ; la défense sur mer est celle de la marine. Entre les deux se situe la côte. Confiée au Bas Moyen-Age à l’amiral de France, la défense des côtes françaises va devenir une pierre d’achoppement entre les départements de la guerre et de la marine, la première y voyant une frontière maritime à garantir, la seconde y trouvant d’abord la base d’opérations des flottes commerciales et militaires. Largement écartée de la défense des côtes après la guerre de Sept Ans, la marine va progressivement y recouvrer durant le XIXe siècle un rôle prédominant par l’entremise des préfets maritimes, alors que le dispositif se concentre par économie autour des grands ports. Après la Première Guerre mondiale, elle en reprend la responsabilité nominale, même si un partage coopératif des tâches se dessine de plus en plus avec l’armée de terre, puis également la jeune armée de l’air, jusqu’à ce qu’un type de commandement supérieur, interarmées, n’émerge pendant la Seconde Guerre mondiale. Après un dernier sursaut d’activité durant les débuts de l’OTAN, le dispositif côtier est abandonné une quinzaine d’années plus tard, lors de l’avènement de la dissuasion nucléaire, laissant cependant en place une organisation interministérielle d’action de l’Etat en mer, comprenant un volet de défense. Au travers de la défense des côtes, c’est donc la fusion des deux puis trois logiques d’armées vers une logique interarmées qui est étudiée sur le plan des institutions militaires, des organisations locales et des nécessités techniques ou tactiques, sur la période s’étendant de 1815 à 1973. / Defence on land is the business of the Army ; defence at sea is that of the Navy.. The frontier is on the coastline. Managed during the Late Middle-Age by the Admiral of France, French coastal defence will become a stumbling block between the War and Navy departments, the former seeing a naval border to be guaranteed, the latter first considering operational bases for both the merchant and military fleets. Discarded during the Seven Year War, the Navy increasingly comes back into coastal defence throughout the XIXth Century, especially with the maritime prefects, as those defences now mainly concern the strategic harbour areas. After WWI, the Navy recovers its initial responsibilities, even if a sort of burden sharing is organised with the Army and then the Air Force, until a joint command is organised during WWII. After some renewal during the first years of NATO, the coastal defence disappears some fifteen years later, with the advent of nuclear deterrence, but is transformed into an interagency organisation for the action of the State at sea.. Thus, through coastal defence, we will study how two, then three single service organisations merged into a joint one, considering military institutions, regional organisations, technical and tactical requirements, from 1815 to 1973.