Geographical locations of the corresponding areas and harbors in Taiwan. 

Contexts in source publication

Context 1

... downcoast. This phenomenon is known as the “groin effect” in coastal engineering practice. However, it appears that most coastal engineers do not understand the link between the bay shape of downcoast and a groin. Detached breakwaters are positioned offshore and aligned roughly parallel to the local shoreline. Detached breakwaters are generally taking the form of a series of units to reduce wave energy and cause sand deposition in the area which they shelter, thus protecting a long stretch of coast. Such breakwaters are termed segmented breakwaters. Numerous researchers (Shinohara & Tsubaki, 1966; Dally & Pope, 1986; Pope & Dean, 1986; Suh & Dalrymple, 1987; Chasten et al., 1993; Ming & Chiew, 2000; Hsu et al., 2003) have used physical experiments to study the key parameters affecting sand deposition behind detached breakwaters. The shoreline can take the form of salients, tombolos, or only limited modifications of the shore configuration in the lee of breakwaters. The key parameters that influence on salient or tombolo formulation include the gap between breakwater segments, breakwater length, offshore distance, and crown height. The detached breakwater has been employed as a primary countermeasure since the 1970s in Japan and the 1980s in Taiwan. Up to now, no design criteria have been developed for an optimal detached breakwater design. Toyoshima (1982) was the main researcher to address designed criteria for the detached breakwaters in Japan. There were 347 units (28 km) of detached breakwaters in Japan in 1965 and 544 units by 1972, which jumped to 3,732 units (347 km) by 1985 and 7,371 units (837 km) by 1996. Notably, 6,827 new units were built within the 24-year period from 1972 to 1996, representing a rate of 285 units per year. However, there are some disadvantages associated with using detached breakwaters to prevent beach erosion. The first disadvantage is that armor blocks accumulated on the detached breakwater can easily slide, roll, or collapse away from the structure and become submerged because of scouring at the toe of the detached breakwater or breaking wave impact on the breakwaters. Figure 9(a) shows an example of the collapse of armor blocks of detached breakwaters built on the Hualien coast. This prevention work causes a higher cost to maintain the coastal structure to continually and repeatedly apply effectiveness to coastal defense. The second disadvantage implies that detached breakwaters have difficulty complying with the nearby coastal environment owing to landscape issues. Because detached breakwaters are commonly built by regular or irregular accumulations of armor blocks, it is very difficult for them to maintain a regular shape under the action of waves and currents in the shallow water region. As shown in Figure 9(b), the third disadvantage implies a strong current causing significant beach erosion at the gap between two segmented breakwaters. Toyoshima (1974) thus conceded that it is impossible to completely prevent most coastal erosion by detached breakwaters because the shoreline immediately beyond the opening between the neighboring two breakwaters tends to retreat, and an alternative plan for shore protection should be further considered. Another practical aspect, from the perspective of swimmers or fishermen, is the difficulty of approaching or bringing a small boat into the leeward side of the breakwaters when a strong rip current exists at the entrance. Despite some disadvantages, detached breakwaters have been implemented almost indiscriminately to prevent beach erosion. Notably, a recent trend in Japan has been to replace old detached breakwater systems with submerged structures or to use artificial reefs for aspects of landscape and ecology. In Taiwan, the first detached breakwaters were built at Redhill coast in Kaohsiung County (Figure 1), southern Taiwan, in 1981. Figure 10(a) presents an example of beach erosion of a sandy bluff on the Redhill coast. Six units of detached breakwaters were constructed near the shoreline to prevent waves from reaching the eroding sandy cliff (Figure 10(b)). Each segment is 80 m long, 3 m wide, 1 m high relative to sea level, and has a 30 m gap distance between two neighboring breakwaters. This prevention work mitigates the serious erosion of the sandy cliffs, which varies from 2 m–6 m. Figure 10(c) shows a successful example of detached breakwaters that have effectively stopped sandy bluff erosion and following grass rebirth on the naked sandy cliff. To date, a total of 184 segments of detached breakwaters have been installed along the southern coast of Taiwan (Table 1). Figure 11 illustrates the temporal variation of the total number of detached breakwaters built along the southern coast of Taiwan from 1987 to 1999. Notably, detached breakwaters have increased rapidly during the past 12 years. Figure 12 shows two examples of detached breakwaters on the Cheding coast in Kaohsiung County and the Wenfeng coast in Pingtung County (Figure 1) according to the design produced by Ou et al. (1984). The figure shows that development of tombolos and formulation of salients in the lee of the breakwater occurred owing to the reduction of wave energy and control of the patterns of wave diffraction and refraction. The modern concept of coastal defense is based on developing compromises among the competing considerations of safety, landscape, ecology, and attraction to the water. Coastal defense should be achieved based on analysis of nearshore hydrodynamics, sediment transport, coastal process, and the natural features of a beach. A beach can be rebuilt by beach nourishment combined with coastal structures that do not disrupt the natural environment, when the sand or gravel is mined at deep-water sites or from some accumulated places in which engineering costs are considerable. However, it is recognized that these new coastal defenses are sustainable and attempts have been made to maintain a beach with a natural appearance to prevent beach erosion. According to Silvester and Hsu (1993), the best means of coastal defense is to reorient the shoreline parallel to the crests of the incoming waves, thus minimizing or eliminating the total sediment transport alongshore. This approach creates a harmony with nature in terms of the ability to sculpt zeta-shaped bays between headlands. The method of headland control with or without sand fill proposed by Hsu et al. (1989) provides a natural method of maintaining beaches that are in dynamic or static equilibrium. This concept has been employed by China Engineering Consultants Incorporation (2004), Taiwan, in the coastal protection of the Hualien coast (Figure 1) located at the middle east of Taiwan (Figure 13). The Hualien coast consists of three subcoasts, namely Beibin, Nanbin, and Huajen coasts, and it is bounded by the Meilum river in the north and the Hualien river in the south (Figure 13(a)). The Beibin coast is close to the western breakwater of Hualien harbor. According to Hsu et al. (2000), the Nanbin shoreline was rapidly retreating in the area approaching the new seawall, while increasing sediment was accumulating on Beibin beach, particularly near the outlet of the Meilum river following the completion of the eastern breakwater, with a length of 800 m, in 1987 (Figure 13(a)). The parabolic bay equation of Hsu and Evans (1989), which has been developed into a more convenient software called MEPBAY (Klein et al., 2003), is applied to predict the static bay shape of the designed fill beach at Beibin coast. Figure 13(b) shows the results obtained using MEPBAY. The curve represents a headland zeta-shaped bay produced by oblique persistent swell in conditions of static equilibrium. In this region the tidal range is approximately 1 m and two mushroom head-type structures are initially located at 6 m and 5 m mean water depth at point B and C, respectively, as indicated in Figure 13(b) This arrangement requires a spacing of 280 m to maintain the greatest indentation of two headlands at the original shoreline. The project will be performed with the aid of beach fill in the form of 370,000 m 3 of sand supplied from the Meilum river. Headland control is a well-known natural defense for erosional coasts and is strongly promoted by Hsu (2002) in Taiwan. The project is mainly designed to provide an expanded recreation beach to replace the area that progressively shrank from points B to C (Figure 13(c)). The widened beach also protects the highly developed beach-front area of Hualien beach against typhoon waves and storm surges. The project also provides the northern headland, which guides river discharge flows out to offshore so as to carry the sands that are deposited at the river mouth to a deep-water region and thus reduce river flooding. The project will be completed in 2008. Figure 13(c) shows the expected shape of the equilibrium beach in the future. Beach nourishment involves placing large quantities of sand or gravel in the littoral zone to advance the shoreline seawards. This method is implemented in coastal engineering to maintain recreational beaches or rebuild the shore to improve the capacity of a beach to protect coastal properties from wave attack and storm surges. Beach nourishment is considered a reasonably soft means of preventing beach erosion. From the perspective of the littoral sediment budget, beach nourishment provides sediment to refill the quantities of sand that are left to the littoral cells. More recently, beach nourishment has become the most cost-effective alternative method for coastal protection. Some successful projects have managed to preserve a wide beach over long periods in the United States (CERC, 1984; Egense & Sonu, 1987; Wiegel, 1992), France (Hallegout & Guilcher, 1990), Great Britain (May, 1990), Spain (Pe na et al., 1992), Japan (Koike, 1990), and elsewhere (Komar, 1998). These projects are called artificial nourishment works and the sand for the fill generally ...

Context 2

... a beach with a natural appearance to prevent beach erosion. According to Silvester and Hsu (1993), the best means of coastal defense is to reorient the shoreline parallel to the crests of the incoming waves, thus minimizing or eliminating the total sediment transport alongshore. This approach creates a harmony with nature in terms of the ability to sculpt zeta-shaped bays between headlands. The method of headland control with or without sand fill proposed by Hsu et al. (1989) provides a natural method of maintaining beaches that are in dynamic or static equilibrium. This concept has been employed by China Engineering Consultants Incorporation (2004), Taiwan, in the coastal protection of the Hualien coast (Figure 1) located at the middle east of Taiwan (Figure 13). The Hualien coast consists of three subcoasts, namely Beibin, Nanbin, and Huajen coasts, and it is bounded by the Meilum river in the north and the Hualien river in the south (Figure 13(a)). The Beibin coast is close to the western breakwater of Hualien harbor. According to Hsu et al. (2000), the Nanbin shoreline was rapidly retreating in the area approaching the new seawall, while increasing sediment was accumulating on Beibin beach, particularly near the outlet of the Meilum river following the completion of the eastern breakwater, with a length of 800 m, in 1987 (Figure 13(a)). The parabolic bay equation of Hsu and Evans (1989), which has been developed into a more convenient software called MEPBAY (Klein et al., 2003), is applied to predict the static bay shape of the designed fill beach at Beibin coast. Figure 13(b) shows the results obtained using MEPBAY. The curve represents a headland zeta-shaped bay produced by oblique persistent swell in conditions of static equilibrium. In this region the tidal range is approximately 1 m and two mushroom head-type structures are initially located at 6 m and 5 m mean water depth at point B and C, respectively, as indicated in Figure 13(b) This arrangement requires a spacing of 280 m to maintain the greatest indentation of two headlands at the original shoreline. The project will be performed with the aid of beach fill in the form of 370,000 m 3 of sand supplied from the Meilum river. Headland control is a well-known natural defense for erosional coasts and is strongly promoted by Hsu (2002) in Taiwan. The project is mainly designed to provide an expanded recreation beach to replace the area that progressively shrank from points B to C (Figure 13(c)). The widened beach also protects the highly developed beach-front area of Hualien beach against typhoon waves and storm surges. The project also provides the northern headland, which guides river discharge flows out to offshore so as to carry the sands that are deposited at the river mouth to a deep-water region and thus reduce river flooding. The project will be completed in 2008. Figure 13(c) shows the expected shape of the equilibrium beach in the future. Beach nourishment involves placing large quantities of sand or gravel in the littoral zone to advance the shoreline seawards. This method is implemented in coastal engineering to maintain recreational beaches or rebuild the shore to improve the capacity of a beach to protect coastal properties from wave attack and storm surges. Beach nourishment is considered a reasonably soft means of preventing beach erosion. From the perspective of the littoral sediment budget, beach nourishment provides sediment to refill the quantities of sand that are left to the littoral cells. More recently, beach nourishment has become the most cost-effective alternative method for coastal protection. Some successful projects have managed to preserve a wide beach over long periods in the United States (CERC, 1984; Egense & Sonu, 1987; Wiegel, 1992), France (Hallegout & Guilcher, 1990), Great Britain (May, 1990), Spain (Pe na et al., 1992), Japan (Koike, 1990), and elsewhere (Komar, 1998). These projects are called artificial nourishment works and the sand for the fill generally comes from offshore dredging or mining from the river and land. The use of beach nourishment is rare in Taiwan, not only because of the high expense involved but also because the new sand is prone to disappearing during typhoon events. However, some projects have been successfully carried out outside Taiwan that are designed to provide a wide beach that will last for a number of years, for example Miami beach in the United States (Komar, 1998). Furthermore, beach nourishment with segmented breakwaters has been implemented on the Mediterranean coast of Spain and the Shirarahama coast in Japan (Komar, 1998; Van der Salm & Unal, 2003; Tsuchiya et al., 1992). The experience of these cases has encouraged coastal engineers in Taiwan to use a conceptually different approach, namely a soft solution, to protect beaches naturally. A more typical beach nourishment project was conducted by Hsiao (2004) at the Yenliao and Fulong coasts in northeastern Taiwan (Figure 1). Both coasts extend for 5 km from north to south (Figure 14(a)). Moreover, beaches attract thousands of visitors who use them for various recreational activities such as swimming, surfing, sunbathing, walking, fishing, and singing and dancing at music festivals. Twenty years ago, there was a wide sandy beach and sand dune on the Yenliao and Fulong coasts, providing a natural buffer zone between the ocean and land. In winter, longshore sediment is mainly transported southwards by waves coming from the north. During the summer season, storm waves develop in the South Pacific Ocean and attack the beach, producing the offshore transport of sand in the form of a bar, and the sand bar then migrates onshore and becomes a berm rebuilt by a following swell. To meet the growing energy needs associated with the rapid economic growth of Taiwan, the fourth nuclear power plant was constructed at Yenliao coast. Figure 14(a) shows that two breakwaters of a heavy machine harbor were built on the Yenliao coast from 1999. The inlet harbor basin also provides an intake to dispose of cooling water for nuclear machine operations. The breakwater was demonstrated by Yang and Hsu (2004) to interrupt the longshore transport and again resulted in accretion along its updrift side and erosion on its downdrift side. After the extension of the eastern breakwater at Hualien harbor, sand accumulated to the south of the breakwater, moved along the arm of the breakwater, and finally deposited into the quiet water of the harbor. To keep the harbor open, dredging was initiated in 2003. The main aim of the project is to provide a wider recreational sand dune area and beach in response to the shrinkage that had occurred over the years. The filled beach also protects the sand dune and beach front area from typhoon waves and storm surges. Figure 14(b) illustrates that the beach fill of the shore line is approximately 760 m long and 0.6 m high, and the width is from mean water level to the toe of the sand dune. The project was completed in 2005 and added 25,000 cubic meters of natural sands for storm wave protection, placing the sand in the front of erosional dunes as a raised berm to the mean water depth. It is of particular interest to this project because a thorough monitoring program was undertaken during and following the beach fill, including the collection of changes of beach profiles from the dune to the offshore of profile changes. Since completion of the project the beach has experienced a series of typhoons. Although typhoon waves and storm surge removed sand from the berm and cut into new nourished dunes back to offshore, the eroded material from the exposed beach has remained within the littoral system; that is, it has not moved offshore beyond the closure depth, and much of the sand subsequently has been transported onshore back to the subaerial beach during heavy swell situations. The changes in beach fill profiles following the placement of the nourishment are shown in Figures 14(b) and Figures 14(c). In Figure 14(b) the migrated shoreline shows offshore shift of the nourished sand in response to typhoon waves, whereas Figure 14(c) illustrates the return of the filled sand to the subaerial beach profile recovered by following a coming swell. The project currently is considered a success, with the nourished beach and dunes having acted to protect beach erosion during typhoon events. Various countermeasures exist for protecting the shore from beach erosion and possible destruction of coastal properties. This article first addressed the causes of beach erosion resulting in various coastal impacts. Typical examples of coastal defenses on the Taiwanese coast were presented to review their functions during typhoon events. Countermeasures ranging from hardening the coast by constructing seawalls, revetments, groins, and detached breakwaters, to soft methods such as building zeta-bay shaped beaches via headland control and beach buffer zones as part of nourishment projects were discussed for their effectiveness. This study suggests that different situations require different responses. Any response must be based on analyses of the physical processes of waves, nearshore currents, and sediment transports. Countermeasures must be selected from within the overall framework of coastal zone management because such an approach can maintain a broad perspective regarding long-term coastal evolution and the associated natural hazards. Notably, hard structures designed only for minor storms might fail during large storm events. Even when a property is protected by a seawall, the adjacent shoreline can erode and retreat. The seawall thus may be destroyed by the deepened surf zone in situations where there is no fronting beach, and can create a barrier to the longshore movement of beach sediment. This study concludes that the soft solutions produce outcomes that cause less disruption to the coastal environment, and that reasonable ...

Context 3

... Like seawalls, groins have been widely used since World War II to mitigate coastal erosion. Taking Japan as an example, the total number of groins in Japan was 6,781 units (273 km) in 1965; 10,043 units in 1981; and 9,387 units (384 km) in 1996 (Kawata & Shibayama, 1998). Despite a slight reduction in the number of groins in Japan recently, groins are still widely utilized in developing and developed countries. Based on the concept of headland control, beach platforms downcoast from a long groin can appear to be curved concave indented in the shoreline, which is termed as a zeta-shape bay in coastal engineering. As stated by Komar (1998), nearshore current frequently prevents groins from achieving their objective of trapping sand to create a protective beach. According to the field survey of WRA, groins can deflect longshore currents and effectively create a rip current adjacent to the groin that can scour away impounded sand and transport it offshore or to the downdrift side of the groin. Hsu and Evans (1989) proposed that the longer a groin or the steeper its incline out of the sea is, the larger the bay that can potentially form downcoast. This phenomenon is known as the “groin effect” in coastal engineering practice. However, it appears that most coastal engineers do not understand the link between the bay shape of downcoast and a groin. Detached breakwaters are positioned offshore and aligned roughly parallel to the local shoreline. Detached breakwaters are generally taking the form of a series of units to reduce wave energy and cause sand deposition in the area which they shelter, thus protecting a long stretch of coast. Such breakwaters are termed segmented breakwaters. Numerous researchers (Shinohara & Tsubaki, 1966; Dally & Pope, 1986; Pope & Dean, 1986; Suh & Dalrymple, 1987; Chasten et al., 1993; Ming & Chiew, 2000; Hsu et al., 2003) have used physical experiments to study the key parameters affecting sand deposition behind detached breakwaters. The shoreline can take the form of salients, tombolos, or only limited modifications of the shore configuration in the lee of breakwaters. The key parameters that influence on salient or tombolo formulation include the gap between breakwater segments, breakwater length, offshore distance, and crown height. The detached breakwater has been employed as a primary countermeasure since the 1970s in Japan and the 1980s in Taiwan. Up to now, no design criteria have been developed for an optimal detached breakwater design. Toyoshima (1982) was the main researcher to address designed criteria for the detached breakwaters in Japan. There were 347 units (28 km) of detached breakwaters in Japan in 1965 and 544 units by 1972, which jumped to 3,732 units (347 km) by 1985 and 7,371 units (837 km) by 1996. Notably, 6,827 new units were built within the 24-year period from 1972 to 1996, representing a rate of 285 units per year. However, there are some disadvantages associated with using detached breakwaters to prevent beach erosion. The first disadvantage is that armor blocks accumulated on the detached breakwater can easily slide, roll, or collapse away from the structure and become submerged because of scouring at the toe of the detached breakwater or breaking wave impact on the breakwaters. Figure 9(a) shows an example of the collapse of armor blocks of detached breakwaters built on the Hualien coast. This prevention work causes a higher cost to maintain the coastal structure to continually and repeatedly apply effectiveness to coastal defense. The second disadvantage implies that detached breakwaters have difficulty complying with the nearby coastal environment owing to landscape issues. Because detached breakwaters are commonly built by regular or irregular accumulations of armor blocks, it is very difficult for them to maintain a regular shape under the action of waves and currents in the shallow water region. As shown in Figure 9(b), the third disadvantage implies a strong current causing significant beach erosion at the gap between two segmented breakwaters. Toyoshima (1974) thus conceded that it is impossible to completely prevent most coastal erosion by detached breakwaters because the shoreline immediately beyond the opening between the neighboring two breakwaters tends to retreat, and an alternative plan for shore protection should be further considered. Another practical aspect, from the perspective of swimmers or fishermen, is the difficulty of approaching or bringing a small boat into the leeward side of the breakwaters when a strong rip current exists at the entrance. Despite some disadvantages, detached breakwaters have been implemented almost indiscriminately to prevent beach erosion. Notably, a recent trend in Japan has been to replace old detached breakwater systems with submerged structures or to use artificial reefs for aspects of landscape and ecology. In Taiwan, the first detached breakwaters were built at Redhill coast in Kaohsiung County (Figure 1), southern Taiwan, in 1981. Figure 10(a) presents an example of beach erosion of a sandy bluff on the Redhill coast. Six units of detached breakwaters were constructed near the shoreline to prevent waves from reaching the eroding sandy cliff (Figure 10(b)). Each segment is 80 m long, 3 m wide, 1 m high relative to sea level, and has a 30 m gap distance between two neighboring breakwaters. This prevention work mitigates the serious erosion of the sandy cliffs, which varies from 2 m–6 m. Figure 10(c) shows a successful example of detached breakwaters that have effectively stopped sandy bluff erosion and following grass rebirth on the naked sandy cliff. To date, a total of 184 segments of detached breakwaters have been installed along the southern coast of Taiwan (Table 1). Figure 11 illustrates the temporal variation of the total number of detached breakwaters built along the southern coast of Taiwan from 1987 to 1999. Notably, detached breakwaters have increased rapidly during the past 12 years. Figure 12 shows two examples of detached breakwaters on the Cheding coast in Kaohsiung County and the Wenfeng coast in Pingtung County (Figure 1) according to the design produced by Ou et al. (1984). The figure shows that development of tombolos and formulation of salients in the lee of the breakwater occurred owing to the reduction of wave energy and control of the patterns of wave diffraction and refraction. The modern concept of coastal defense is based on developing compromises among the competing considerations of safety, landscape, ecology, and attraction to the water. Coastal defense should be achieved based on analysis of nearshore hydrodynamics, sediment transport, coastal process, and the natural features of a beach. A beach can be rebuilt by beach nourishment combined with coastal structures that do not disrupt the natural environment, when the sand or gravel is mined at deep-water sites or from some accumulated places in which engineering costs are considerable. However, it is recognized that these new coastal defenses are sustainable and attempts have been made to maintain a beach with a natural appearance to prevent beach erosion. According to Silvester and Hsu (1993), the best means of coastal defense is to reorient the shoreline parallel to the crests of the incoming waves, thus minimizing or eliminating the total sediment transport alongshore. This approach creates a harmony with nature in terms of the ability to sculpt zeta-shaped bays between headlands. The method of headland control with or without sand fill proposed by Hsu et al. (1989) provides a natural method of maintaining beaches that are in dynamic or static equilibrium. This concept has been employed by China Engineering Consultants Incorporation (2004), Taiwan, in the coastal protection of the Hualien coast (Figure 1) located at the middle east of Taiwan (Figure 13). The Hualien coast consists of three subcoasts, namely Beibin, Nanbin, and Huajen coasts, and it is bounded by the Meilum river in the north and the Hualien river in the south (Figure 13(a)). The Beibin coast is close to the western breakwater of Hualien harbor. According to Hsu et al. (2000), the Nanbin shoreline was rapidly retreating in the area approaching the new seawall, while increasing sediment was accumulating on Beibin beach, particularly near the outlet of the Meilum river following the completion of the eastern breakwater, with a length of 800 m, in 1987 (Figure 13(a)). The parabolic bay equation of Hsu and Evans (1989), which has been developed into a more convenient software called MEPBAY (Klein et al., 2003), is applied to predict the static bay shape of the designed fill beach at Beibin coast. Figure 13(b) shows the results obtained using MEPBAY. The curve represents a headland zeta-shaped bay produced by oblique persistent swell in conditions of static equilibrium. In this region the tidal range is approximately 1 m and two mushroom head-type structures are initially located at 6 m and 5 m mean water depth at point B and C, respectively, as indicated in Figure 13(b) This arrangement requires a spacing of 280 m to maintain the greatest indentation of two headlands at the original shoreline. The project will be performed with the aid of beach fill in the form of 370,000 m 3 of sand supplied from the Meilum river. Headland control is a well-known natural defense for erosional coasts and is strongly promoted by Hsu (2002) in Taiwan. The project is mainly designed to provide an expanded recreation beach to replace the area that progressively shrank from points B to C (Figure 13(c)). The widened beach also protects the highly developed beach-front area of Hualien beach against typhoon waves and storm surges. The project also provides the northern headland, which guides river discharge flows out to offshore so as to carry the sands that are deposited at the river mouth to a deep-water region and thus reduce river flooding. The project will be completed ...

Context 4

... around 542.4 km long. Currently, most sandy beaches in Taiwan are surrounded by these hard structures to protect human life and property from wave attack. The front faces of seawalls may be vertical or inclined, and both with or without a protective covering of armor units on the surface or placed in front of the toe. If seawalls are built too close to the shoreline, waves have insufficient distance to travel on the beach to dissipate energy. Such seawalls are highly reflective and thus promote strong backward wave energy to remove sand to offshore regions. The seawall began as a very steep earth embankment and then became a rubble mound dike, and generally comprised a simple masonry structure with a concrete face, toe protection, and more recently used a mildly sloping face (1:2–1:6), and even armored blocks a short distance in front of the seawall to dissipate wave energy. Table 1 lists the countermeasures currently used in Taiwan to protect against beach erosion. Figure 5 illustrates a seawall and revetment built on the southern coast in which the foundation was constructed by sand fill from the beach and laid with a thin concrete face for protection. According to the survey of the Water Resources Agency (WRA) of the Ministry of Economic Affair, Taiwan, failure of seawalls or revetments happens not only on the front side, owing to scouring by standing waves or short-crested waves, but also on the back sides, because of excessive pore pressure (Hsu & Chang, 2002). This excessive pore pressure will bring about soil fluidization response inside the seawall and destroying of the seawall. Figure 6 shows two cases of failure of seawall and revetment resulting from scouring and pore pressure on the front and back sides, respectively. An experiment by Homma (1972) indicated that beach erosion occurs immediately in the front of a seawall owing to the increase of reflected wave energy, and thus the rapid movement of longshore sediment transport along the coast without any refill of sand. Such rapid increase of littoral drift causes rapid disappearance of the beach and tempts engineers to extend the seawall or revetment to protect newly eroded areas. Consequently, the total lengths of seawalls or revetments have increased over the years in numerous developing and developed countries all over the world. For example, Japan had 3,743 km of seawall and 2,086 km seadike in length to prevent flooding from wave and storm surge in 1965. These constructions increased to 5,806 km of seawall and 2,836 km of seadike in 1985, with their total lengths 6,005 km and 2,922 km, respectively, in 1966 over a total length of coastline of 34,608 km (Kawata & Shibayama, 1998). Notably, the impact on adjacent properties and the volume of sand impounded both increase with seawall length as explained by Walton and Sensabaugh (1978). Additionally, seawalls or revetments comprised of different shapes of armor blocks that are usually placed in a random manner. Their landscapes and hard structures are not harmonious with coastal environments and influence the attractiveness of a beach to users. Figure 7 shows the seawall and revetment covered with randomly positioned armor units that do not match the natural environment and prevent people from using the beach. A conceptually different approach to strengthen the coast is the use of groins and detached breakwaters. Groins are built approximately perpendicular to the shore to trap a portion of longshore sediment transport for rebuilding the beach. Groins dam the longshore sediment transport so that sand accumulates along the updrift side but generally erodes in the downdrift direction. To prevent damage to adjacent areas, groins can be filled artificially by beach nourishment, or their length can be shortened to enable sand to pass by them. The action of groins produces a combination of upcoast accumulation and downcoast erosion, inspiring the building of more units further downcoast. Groins are not effective if littoral drift is zero or waves are nearly normal approaching the beach. Figure 8 shows two examples of groins on the Yenshui coast in southern Taiwan, specifically at Tainan city, and on the Ilan coast located in the northeast of Taiwan (Figure 1). Presently, the total length of groins around Taiwanese coast is approximately 10.08 km (Table 1). Groins do not provide significant benefits, and some of them were destroyed during typhoon events, while others appear to accumulate sand and help rebuild beaches. Numerous works have investigated the effectiveness of groins (Nersesian et al., 1992; Kraus et al., 1994; Coastal Engineering Research Center [CERC], 2002; Taborda et al., 2005). Like seawalls, groins have been widely used since World War II to mitigate coastal erosion. Taking Japan as an example, the total number of groins in Japan was 6,781 units (273 km) in 1965; 10,043 units in 1981; and 9,387 units (384 km) in 1996 (Kawata & Shibayama, 1998). Despite a slight reduction in the number of groins in Japan recently, groins are still widely utilized in developing and developed countries. Based on the concept of headland control, beach platforms downcoast from a long groin can appear to be curved concave indented in the shoreline, which is termed as a zeta-shape bay in coastal engineering. As stated by Komar (1998), nearshore current frequently prevents groins from achieving their objective of trapping sand to create a protective beach. According to the field survey of WRA, groins can deflect longshore currents and effectively create a rip current adjacent to the groin that can scour away impounded sand and transport it offshore or to the downdrift side of the groin. Hsu and Evans (1989) proposed that the longer a groin or the steeper its incline out of the sea is, the larger the bay that can potentially form downcoast. This phenomenon is known as the “groin effect” in coastal engineering practice. However, it appears that most coastal engineers do not understand the link between the bay shape of downcoast and a groin. Detached breakwaters are positioned offshore and aligned roughly parallel to the local shoreline. Detached breakwaters are generally taking the form of a series of units to reduce wave energy and cause sand deposition in the area which they shelter, thus protecting a long stretch of coast. Such breakwaters are termed segmented breakwaters. Numerous researchers (Shinohara & Tsubaki, 1966; Dally & Pope, 1986; Pope & Dean, 1986; Suh & Dalrymple, 1987; Chasten et al., 1993; Ming & Chiew, 2000; Hsu et al., 2003) have used physical experiments to study the key parameters affecting sand deposition behind detached breakwaters. The shoreline can take the form of salients, tombolos, or only limited modifications of the shore configuration in the lee of breakwaters. The key parameters that influence on salient or tombolo formulation include the gap between breakwater segments, breakwater length, offshore distance, and crown height. The detached breakwater has been employed as a primary countermeasure since the 1970s in Japan and the 1980s in Taiwan. Up to now, no design criteria have been developed for an optimal detached breakwater design. Toyoshima (1982) was the main researcher to address designed criteria for the detached breakwaters in Japan. There were 347 units (28 km) of detached breakwaters in Japan in 1965 and 544 units by 1972, which jumped to 3,732 units (347 km) by 1985 and 7,371 units (837 km) by 1996. Notably, 6,827 new units were built within the 24-year period from 1972 to 1996, representing a rate of 285 units per year. However, there are some disadvantages associated with using detached breakwaters to prevent beach erosion. The first disadvantage is that armor blocks accumulated on the detached breakwater can easily slide, roll, or collapse away from the structure and become submerged because of scouring at the toe of the detached breakwater or breaking wave impact on the breakwaters. Figure 9(a) shows an example of the collapse of armor blocks of detached breakwaters built on the Hualien coast. This prevention work causes a higher cost to maintain the coastal structure to continually and repeatedly apply effectiveness to coastal defense. The second disadvantage implies that detached breakwaters have difficulty complying with the nearby coastal environment owing to landscape issues. Because detached breakwaters are commonly built by regular or irregular accumulations of armor blocks, it is very difficult for them to maintain a regular shape under the action of waves and currents in the shallow water region. As shown in Figure 9(b), the third disadvantage implies a strong current causing significant beach erosion at the gap between two segmented breakwaters. Toyoshima (1974) thus conceded that it is impossible to completely prevent most coastal erosion by detached breakwaters because the shoreline immediately beyond the opening between the neighboring two breakwaters tends to retreat, and an alternative plan for shore protection should be further considered. Another practical aspect, from the perspective of swimmers or fishermen, is the difficulty of approaching or bringing a small boat into the leeward side of the ...

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... the 24-year period from 1972 to 1996, representing a rate of 285 units per year. However, there are some disadvantages associated with using detached breakwaters to prevent beach erosion. The first disadvantage is that armor blocks accumulated on the detached breakwater can easily slide, roll, or collapse away from the structure and become submerged because of scouring at the toe of the detached breakwater or breaking wave impact on the breakwaters. Figure 9(a) shows an example of the collapse of armor blocks of detached breakwaters built on the Hualien coast. This prevention work causes a higher cost to maintain the coastal structure to continually and repeatedly apply effectiveness to coastal defense. The second disadvantage implies that detached breakwaters have difficulty complying with the nearby coastal environment owing to landscape issues. Because detached breakwaters are commonly built by regular or irregular accumulations of armor blocks, it is very difficult for them to maintain a regular shape under the action of waves and currents in the shallow water region. As shown in Figure 9(b), the third disadvantage implies a strong current causing significant beach erosion at the gap between two segmented breakwaters. Toyoshima (1974) thus conceded that it is impossible to completely prevent most coastal erosion by detached breakwaters because the shoreline immediately beyond the opening between the neighboring two breakwaters tends to retreat, and an alternative plan for shore protection should be further considered. Another practical aspect, from the perspective of swimmers or fishermen, is the difficulty of approaching or bringing a small boat into the leeward side of the breakwaters when a strong rip current exists at the entrance. Despite some disadvantages, detached breakwaters have been implemented almost indiscriminately to prevent beach erosion. Notably, a recent trend in Japan has been to replace old detached breakwater systems with submerged structures or to use artificial reefs for aspects of landscape and ecology. In Taiwan, the first detached breakwaters were built at Redhill coast in Kaohsiung County (Figure 1), southern Taiwan, in 1981. Figure 10(a) presents an example of beach erosion of a sandy bluff on the Redhill coast. Six units of detached breakwaters were constructed near the shoreline to prevent waves from reaching the eroding sandy cliff (Figure 10(b)). Each segment is 80 m long, 3 m wide, 1 m high relative to sea level, and has a 30 m gap distance between two neighboring breakwaters. This prevention work mitigates the serious erosion of the sandy cliffs, which varies from 2 m–6 m. Figure 10(c) shows a successful example of detached breakwaters that have effectively stopped sandy bluff erosion and following grass rebirth on the naked sandy cliff. To date, a total of 184 segments of detached breakwaters have been installed along the southern coast of Taiwan (Table 1). Figure 11 illustrates the temporal variation of the total number of detached breakwaters built along the southern coast of Taiwan from 1987 to 1999. Notably, detached breakwaters have increased rapidly during the past 12 years. Figure 12 shows two examples of detached breakwaters on the Cheding coast in Kaohsiung County and the Wenfeng coast in Pingtung County (Figure 1) according to the design produced by Ou et al. (1984). The figure shows that development of tombolos and formulation of salients in the lee of the breakwater occurred owing to the reduction of wave energy and control of the patterns of wave diffraction and refraction. The modern concept of coastal defense is based on developing compromises among the competing considerations of safety, landscape, ecology, and attraction to the water. Coastal defense should be achieved based on analysis of nearshore hydrodynamics, sediment transport, coastal process, and the natural features of a beach. A beach can be rebuilt by beach nourishment combined with coastal structures that do not disrupt the natural environment, when the sand or gravel is mined at deep-water sites or from some accumulated places in which engineering costs are considerable. However, it is recognized that these new coastal defenses are sustainable and attempts have been made to maintain a beach with a natural appearance to prevent beach erosion. According to Silvester and Hsu (1993), the best means of coastal defense is to reorient the shoreline parallel to the crests of the incoming waves, thus minimizing or eliminating the total sediment transport alongshore. This approach creates a harmony with nature in terms of the ability to sculpt zeta-shaped bays between headlands. The method of headland control with or without sand fill proposed by Hsu et al. (1989) provides a natural method of maintaining beaches that are in dynamic or static equilibrium. This concept has been employed by China Engineering Consultants Incorporation (2004), Taiwan, in the coastal protection of the Hualien coast (Figure 1) located at the middle east of Taiwan (Figure 13). The Hualien coast consists of three subcoasts, namely Beibin, Nanbin, and Huajen coasts, and it is bounded by the Meilum river in the north and the Hualien river in the south (Figure 13(a)). The Beibin coast is close to the western breakwater of Hualien harbor. According to Hsu et al. (2000), the Nanbin shoreline was rapidly retreating in the area approaching the new seawall, while increasing sediment was accumulating on Beibin beach, particularly near the outlet of the Meilum river following the completion of the eastern breakwater, with a length of 800 m, in 1987 (Figure 13(a)). The parabolic bay equation of Hsu and Evans (1989), which has been developed into a more convenient software called MEPBAY (Klein et al., 2003), is applied to predict the static bay shape of the designed fill beach at Beibin coast. Figure 13(b) shows the results obtained using MEPBAY. The curve represents a headland zeta-shaped bay produced by oblique persistent swell in conditions of static equilibrium. In this region the tidal range is approximately 1 m and two mushroom head-type structures are initially located at 6 m and 5 m mean water depth at point B and C, respectively, as indicated in Figure 13(b) This arrangement requires a spacing of 280 m to maintain the greatest indentation of two headlands at the original shoreline. The project will be performed with the aid of beach fill in the form of 370,000 m 3 of sand supplied from the Meilum river. Headland control is a well-known natural defense for erosional coasts and is strongly promoted by Hsu (2002) in Taiwan. The project is mainly designed to provide an expanded recreation beach to replace the area that progressively shrank from points B to C (Figure 13(c)). The widened beach also protects the highly developed beach-front area of Hualien beach against typhoon waves and storm surges. The project also provides the northern headland, which guides river discharge flows out to offshore so as to carry the sands that are deposited at the river mouth to a deep-water region and thus reduce river flooding. The project will be completed in 2008. Figure 13(c) shows the expected shape of the equilibrium beach in the future. Beach nourishment involves placing large quantities of sand or gravel in the littoral zone to advance the shoreline seawards. This method is implemented in coastal engineering to maintain recreational beaches or rebuild the shore to improve the capacity of a beach to protect coastal properties from wave attack and storm surges. Beach nourishment is considered a reasonably soft means of preventing beach erosion. From the perspective of the littoral sediment budget, beach nourishment provides sediment to refill the quantities of sand that are left to the littoral cells. More recently, beach nourishment has become the most cost-effective alternative method for coastal protection. Some successful projects have managed to preserve a wide beach over long periods in the United States (CERC, 1984; Egense & Sonu, 1987; Wiegel, 1992), France (Hallegout & Guilcher, 1990), Great Britain (May, 1990), Spain (Pe na et al., 1992), Japan (Koike, 1990), and elsewhere (Komar, 1998). These projects are called artificial nourishment works and the sand for the fill generally comes from offshore dredging or mining from the river and land. The use of beach nourishment is rare in Taiwan, not only because of the high expense involved but also because the new sand is prone to disappearing during typhoon events. However, some projects have been successfully carried out outside Taiwan that are designed to provide a wide beach that will last for a number of years, for example Miami beach in the United States (Komar, 1998). Furthermore, beach nourishment with segmented breakwaters has been implemented on the Mediterranean coast of Spain and the Shirarahama coast in Japan (Komar, 1998; Van der Salm & Unal, 2003; Tsuchiya et al., 1992). The experience of these cases has encouraged coastal engineers in Taiwan to use a conceptually different approach, namely a soft solution, to protect beaches naturally. A more typical beach nourishment project was conducted by Hsiao (2004) at the Yenliao and Fulong coasts in northeastern Taiwan (Figure 1). Both coasts extend for 5 km from north to south (Figure 14(a)). Moreover, beaches attract thousands of visitors who use them for various recreational activities such as swimming, surfing, sunbathing, walking, fishing, and singing and dancing at music festivals. Twenty years ago, there was a wide sandy beach and sand dune on the Yenliao and Fulong coasts, providing a natural buffer zone between the ocean and land. In winter, longshore sediment is mainly transported southwards by waves coming from the north. During the summer season, storm waves develop in the South Pacific Ocean and attack the beach, producing the offshore transport of sand in the form of a bar, and the sand bar then migrates onshore ...

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... growth in coastal areas and increasing with the associated development, beach erosion has become a major human and economic problem from the perspective of land preservation problems. According to Komar (1998), about two-thirds of the world’s population lives within a narrow belt of land close to the ocean, in which 53 percent of the U.S. population lives within 80 km of the shore (Edwards, 1989), 83 percent of Australia population lives near the coast, 25 percent within 3 km, and all its major cities are found on the coast, and 18 percent of the total population in Taiwan lives within the shore (Hsu et al., 2007). Inman and Brush (1973) estimated that if everyone in the world decided to visit the 440,000 km of shoreline in the world, each individual would have less than 13 cm of shore to themselves. This information indicates that population pressure could occur at crowded public beaches and a profileration of seaside condominiums, hotels/motels, recreational-vehicle parks, and reclamation areas for industrial utilization and urban lots, which often destroy the aesthetic values that originally drew people to the coast. Beach erosion frequently causes inherent damage to coastal regions. When typhoon waves associated with storm surges attack the shore, the shoreline migrates landwards, destroying homes built on and properties located too close to the sea. The total length of the coastline around Taiwan island is approximately 1139 km including rocky shore, of which only 542 km is considered secure against sea attack. The areas experiencing coastal erosion in Taiwan are shown in Figure 1. Thus more than half of the sandy beaches in Taiwan are suffering from beach erosion and appropriate countermeasures to protect the coastline are required. Major impacts of beach erosion consist of coastal erosion, coastal flooding, wave overtopping, land subsidence, and ecological degradation. This study explores coastal impacts and examines countermeasures adopted in responses to coastal erosion during the past 35 years in Taiwan. One optimal response to coastal eroded areas is proposed for coastal management programs to limit or prevent construction by considering safety, landscape, ecology, and attraction to water. New ideas for responding to receding shorelines are the focus of this study based on the survey of already protected areas. This work includes the review of the protection of threatened properties and the restoration of eroded beach. The analysis of Hsu et al. (2007) showed that heavy beach erosion on the Taiwanese coast is primarily caused by human activities. Specific causes include: (1) a shortage of materials supply from the river to the shore; (2) improperly constructed coastal structures; (3) over pumping of groundwater causing land subsidence; and (4) over development resulting from industrial utilization of coastal areas. This investigation briefly addresses some typical reasons for human-induced beach erosion. Detailed reasons for beach erosion are referred to Hsu et al. (2007). Sediment discharge to river mouths primarily takes place during the flood season, especially during typhoon or storm events. During the dry season, sediment is re-distributed via a coastal process that forms wide beaches updrift of littoral barriers and dunes at certain locations. Construction of flood channels and dams or reservoirs can impact the sediment budget, reducing the amount of sediment reaching the shore. On natural coasts, waves and currents transport sand alongshore. Consequently, the severe reduction of longshore sediment sources from rivers causes rapid shoreline shift. Hsu et al. (2007) provided two examples of the Waisanding barrier offshore island and offshore barriers located on the west coast of Taiwan (Figure 1). The Waisanding barrier has shrunk up to 6.1 km in length and 3 km in width (measured at the narrowest point) during the past 40 years (1962–2002), representing total area shrinkage of 10.7 km . Construction of a reservoir in the middle reach of Tsengwen river (Figure 1) is the other example that brought about coastal erosion at the river mouth on the neighboring coast of Tainan. A series of offshore barriers were moved landward. Among these barriers, the maximum rate of shoreline retreat of the Dingtoue barrier exceeds 50 m/y. The erosion is largely due to the construction of dams in the upstream area of the river, and overmining of sand material in the river for use in construction materials, thus cutting of the delivery of sand to the beaches. The longshore sediment transport on beaches manifests itself whenever this natural movement is prevented by the construction of jetties, breakwaters, and groins. Such coastal structures act as barriers to sediment movement, causing beach buildup on the updrift side and simultaneous erosion in the downdrift direction. A typical example is the extension of the northern breakwater at Taichung harbor, on the central region of the west coast of Taiwan (Figure 1). The extension of the northern breakwater at Taichung harbor has blocked the southward longshore sediment transport after the 1980s. Notably, the interruption of longshore sediment by the northern breakwater has resulted in accumulation updrift of the northern breakwater and severe coastal erosion in the downdrift area to a distance of approximately 1,500 m from the southern breakwater (Hsu et al., 2007). Beach erosion may result from ground subsidence caused by overpumping of groundwater for use by fish farms on the Taiwanese coast. The pumping of groundwater accelerates settlement owing to subsoil consolidation. Subsidence is usually followed by sea water intrusion and shoreline retreat. The number of aquaculture farms along the Taiwanese coast has steadily increased since the 1970s. Large quantities of groundwater are extracted and mixed with sea water for aquaculture farming. Numerous places suffer from severe subsidence in the central southwestern and southern coast of Taiwan. The over-extraction of groundwater for aquaculture has caused serious land subsidence (5–10 mm/y) in Chiayi, Tainan, and Pingtung counties, located in Taiwan (Figure 1). The utilization of coastal and ocean spaces for human activities has increased because of economic and population growth. The reclamation of Mailiao industrial harbor was implemented in 1994 and completed in 2001, and is located in the center of the southwestern coast of Taiwan (Figure 1). The biggest river, the Choshui river (Figure 2(d)), discharges from the north of the Mailiao reclamation area and into the surrounding coastal waters. To allow movement of large vessels of 200,000 tons, the western breakwater was extended to a water depth of –26 m (Figure 2(a)). A large stockpile of material dredged from the seabed in the region of intermediate water depth located 1.5 km away from the shoreline for Mailiao industrial area is one of the sources of sand supply for reclamation. The planned reclamation area on the Mailiao industrial area and harbor has a length of 7 km from north to south (Figure 2(a)). The bathymetry in the coastal region frequently reaches equilibrium under the action of waves and currents without human intervention. However, concern naturally exists when a substantial quantity of sand is removed from the seabed and the subsequent bathymetry alterations will change the wave and current patterns, with detrimental consequences for the nearby beach. Figure 2 shows that the dredging and construction of breakwaters have caused sand accumulation updrift of the western breakwater of the Mailiao industrial area and harbor, as well as severe coastal erosional downdrift extending for a long distance in industrial area. The construction of Mailiao harbor’s western breakwater has blocked the longshore sediment transport that moves southward. Comparing Figures 2(b) and Figures 2(c), interruption of longshore sediment has caused accumulation of the western breakwater and severe coastal erosion downdrift to a distance about 10 km south. The rate change of volume in the upstream of the western breakwater from 1999 to 2006 is 10 6 m 3 /y. Figure 2(d) presents details of sand accretion of a beach updrift of the western breakwater and beach erosion downdrift. It is sufficient to say that this is a typical example resulting in nearby beach erosion due to over development associated with industrial utilization of coastal areas. The most important human-induced causes of coastal erosion along the Taiwanese coast are (1) a shortage of sediment transport from rivers to the shore and (2) improper constructions on coastal areas. According to Figure 1, it has been estimated about 50% of the eroding coasts is affected by reduction of the sand supply from rivers and 30% of beach erosion is caused by the mechanism of improperly constructed coastal structures. Beach erosion produces four main bio-geophysical impacts in coastal areas: (1) exacer- bation of storm flooding and damage; (2) inundation and displacement of wetlands and lowlands; (3) increased soil salinity and threats to freshwater aquifers; and (4) exacerbated coastal squeeze of ecosystems. The increase in extreme water levels threatens all coastal lowlands, and increased coastal flooding is a precursor to the permanent inundation and submergence of low-lying land (Lin, 1996). Figure 3 illustrates a typical example of coastal flooding during typhoon Herb in 1996 along the western coastal lowlands of Taiwan, and the different zones on Kohu and Madou in southwestern Taiwan at risk of coastal flooding in 1998 and 2005 during typhoons Zeb and Haitang. Beach erosion can cause inundation and subsequent displacement of wetlands and lowlands. For instance, the exposure of mangrove and beefwood to flooding events in large surges and waves has led to the disappearance of wetland vegetation. Figure 4 depicts two typical examples of coastal damage in the form of the death of mangrove and beefwood owing to coastal ...

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... 1139 km including rocky shore, of which only 542 km is considered secure against sea attack. The areas experiencing coastal erosion in Taiwan are shown in Figure 1. Thus more than half of the sandy beaches in Taiwan are suffering from beach erosion and appropriate countermeasures to protect the coastline are required. Major impacts of beach erosion consist of coastal erosion, coastal flooding, wave overtopping, land subsidence, and ecological degradation. This study explores coastal impacts and examines countermeasures adopted in responses to coastal erosion during the past 35 years in Taiwan. One optimal response to coastal eroded areas is proposed for coastal management programs to limit or prevent construction by considering safety, landscape, ecology, and attraction to water. New ideas for responding to receding shorelines are the focus of this study based on the survey of already protected areas. This work includes the review of the protection of threatened properties and the restoration of eroded beach. The analysis of Hsu et al. (2007) showed that heavy beach erosion on the Taiwanese coast is primarily caused by human activities. Specific causes include: (1) a shortage of materials supply from the river to the shore; (2) improperly constructed coastal structures; (3) over pumping of groundwater causing land subsidence; and (4) over development resulting from industrial utilization of coastal areas. This investigation briefly addresses some typical reasons for human-induced beach erosion. Detailed reasons for beach erosion are referred to Hsu et al. (2007). Sediment discharge to river mouths primarily takes place during the flood season, especially during typhoon or storm events. During the dry season, sediment is re-distributed via a coastal process that forms wide beaches updrift of littoral barriers and dunes at certain locations. Construction of flood channels and dams or reservoirs can impact the sediment budget, reducing the amount of sediment reaching the shore. On natural coasts, waves and currents transport sand alongshore. Consequently, the severe reduction of longshore sediment sources from rivers causes rapid shoreline shift. Hsu et al. (2007) provided two examples of the Waisanding barrier offshore island and offshore barriers located on the west coast of Taiwan (Figure 1). The Waisanding barrier has shrunk up to 6.1 km in length and 3 km in width (measured at the narrowest point) during the past 40 years (1962–2002), representing total area shrinkage of 10.7 km . Construction of a reservoir in the middle reach of Tsengwen river (Figure 1) is the other example that brought about coastal erosion at the river mouth on the neighboring coast of Tainan. A series of offshore barriers were moved landward. Among these barriers, the maximum rate of shoreline retreat of the Dingtoue barrier exceeds 50 m/y. The erosion is largely due to the construction of dams in the upstream area of the river, and overmining of sand material in the river for use in construction materials, thus cutting of the delivery of sand to the beaches. The longshore sediment transport on beaches manifests itself whenever this natural movement is prevented by the construction of jetties, breakwaters, and groins. Such coastal structures act as barriers to sediment movement, causing beach buildup on the updrift side and simultaneous erosion in the downdrift direction. A typical example is the extension of the northern breakwater at Taichung harbor, on the central region of the west coast of Taiwan (Figure 1). The extension of the northern breakwater at Taichung harbor has blocked the southward longshore sediment transport after the 1980s. Notably, the interruption of longshore sediment by the northern breakwater has resulted in accumulation updrift of the northern breakwater and severe coastal erosion in the downdrift area to a distance of approximately 1,500 m from the southern breakwater (Hsu et al., 2007). Beach erosion may result from ground subsidence caused by overpumping of groundwater for use by fish farms on the Taiwanese coast. The pumping of groundwater accelerates settlement owing to subsoil consolidation. Subsidence is usually followed by sea water intrusion and shoreline retreat. The number of aquaculture farms along the Taiwanese coast has steadily increased since the 1970s. Large quantities of groundwater are extracted and mixed with sea water for aquaculture farming. Numerous places suffer from severe subsidence in the central southwestern and southern coast of Taiwan. The over-extraction of groundwater for aquaculture has caused serious land subsidence (5–10 mm/y) in Chiayi, Tainan, and Pingtung counties, located in Taiwan (Figure 1). The utilization of coastal and ocean spaces for human activities has increased because of economic and population growth. The reclamation of Mailiao industrial harbor was implemented in 1994 and completed in 2001, and is located in the center of the southwestern coast of Taiwan (Figure 1). The biggest river, the Choshui river (Figure 2(d)), discharges from the north of the Mailiao reclamation area and into the surrounding coastal waters. To allow movement of large vessels of 200,000 tons, the western breakwater was extended to a water depth of –26 m (Figure 2(a)). A large stockpile of material dredged from the seabed in the region of intermediate water depth located 1.5 km away from the shoreline for Mailiao industrial area is one of the sources of sand supply for reclamation. The planned reclamation area on the Mailiao industrial area and harbor has a length of 7 km from north to south (Figure 2(a)). The bathymetry in the coastal region frequently reaches equilibrium under the action of waves and currents without human intervention. However, concern naturally exists when a substantial quantity of sand is removed from the seabed and the subsequent bathymetry alterations will change the wave and current patterns, with detrimental consequences for the nearby beach. Figure 2 shows that the dredging and construction of breakwaters have caused sand accumulation updrift of the western breakwater of the Mailiao industrial area and harbor, as well as severe coastal erosional downdrift extending for a long distance in industrial area. The construction of Mailiao harbor’s western breakwater has blocked the longshore sediment transport that moves southward. Comparing Figures 2(b) and Figures 2(c), interruption of longshore sediment has caused accumulation of the western breakwater and severe coastal erosion downdrift to a distance about 10 km south. The rate change of volume in the upstream of the western breakwater from 1999 to 2006 is 10 6 m 3 /y. Figure 2(d) presents details of sand accretion of a beach updrift of the western breakwater and beach erosion downdrift. It is sufficient to say that this is a typical example resulting in nearby beach erosion due to over development associated with industrial utilization of coastal areas. The most important human-induced causes of coastal erosion along the Taiwanese coast are (1) a shortage of sediment transport from rivers to the shore and (2) improper constructions on coastal areas. According to Figure 1, it has been estimated about 50% of the eroding coasts is affected by reduction of the sand supply from rivers and 30% of beach erosion is caused by the mechanism of improperly constructed coastal structures. Beach erosion produces four main bio-geophysical impacts in coastal areas: (1) exacer- bation of storm flooding and damage; (2) inundation and displacement of wetlands and lowlands; (3) increased soil salinity and threats to freshwater aquifers; and (4) exacerbated coastal squeeze of ecosystems. The increase in extreme water levels threatens all coastal lowlands, and increased coastal flooding is a precursor to the permanent inundation and submergence of low-lying land (Lin, 1996). Figure 3 illustrates a typical example of coastal flooding during typhoon Herb in 1996 along the western coastal lowlands of Taiwan, and the different zones on Kohu and Madou in southwestern Taiwan at risk of coastal flooding in 1998 and 2005 during typhoons Zeb and Haitang. Beach erosion can cause inundation and subsequent displacement of wetlands and lowlands. For instance, the exposure of mangrove and beefwood to flooding events in large surges and waves has led to the disappearance of wetland vegetation. Figure 4 depicts two typical examples of coastal damage in the form of the death of mangrove and beefwood owing to coastal flooding on the Donshu coast in Chiayi County and on the Chigu coast in Tainan County. The sandy beach contains extensive sediment deposits because of fluvial sand outflow along the coast. The erosion is serious as a result of imbalanced longshore sediment transport. Owing to beach erosion, the inundation increases the salinity of soil and fresh groundwater. The effect is greater when the landward side is attacked by the waves and high tides. The fact that a net flow of sea water occurs through the beach face creates large potential for this sea water to enter the aquifer. A hydrological salty area would affect land use and agricultural or fish farm production. Generally, hydrological salty regions generally take a long time to recover to their original state. Beach erosion may also change the ecology of the coastal environment and cause socioeconomic problems. Waves and currents move sand and gravel on sandy beaches. Owing to suspended sediment in the water column, muddy water may cause coral to die as a result of reduced oxygen supply. Coral bleaching often results from high sediment concentrations due to coastal erosion on the southern coast of Taiwan. In Taiwan, beach erosion has been a long-term trend. The seriousness of beach erosion in Taiwan has received considerable attention since the 1960s, following rapid population growth and economic development in the coastal areas. Theoretically, in controlling beach erosion it is ...

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... erosion involves shoreline recession as a result of the action of waves, nearshore currents, and winds. Beach erosion is usually determined by imbalanced littoral drift, namely when the volume of longshore sediment rate flows into the littoral cell is less than that of outward flows. Shorelines can be considered to be at equilibrium over a long term although seasonal changes can take place. As a result of economic growth in coastal areas and increasing with the associated development, beach erosion has become a major human and economic problem from the perspective of land preservation problems. According to Komar (1998), about two-thirds of the world’s population lives within a narrow belt of land close to the ocean, in which 53 percent of the U.S. population lives within 80 km of the shore (Edwards, 1989), 83 percent of Australia population lives near the coast, 25 percent within 3 km, and all its major cities are found on the coast, and 18 percent of the total population in Taiwan lives within the shore (Hsu et al., 2007). Inman and Brush (1973) estimated that if everyone in the world decided to visit the 440,000 km of shoreline in the world, each individual would have less than 13 cm of shore to themselves. This information indicates that population pressure could occur at crowded public beaches and a profileration of seaside condominiums, hotels/motels, recreational-vehicle parks, and reclamation areas for industrial utilization and urban lots, which often destroy the aesthetic values that originally drew people to the coast. Beach erosion frequently causes inherent damage to coastal regions. When typhoon waves associated with storm surges attack the shore, the shoreline migrates landwards, destroying homes built on and properties located too close to the sea. The total length of the coastline around Taiwan island is approximately 1139 km including rocky shore, of which only 542 km is considered secure against sea attack. The areas experiencing coastal erosion in Taiwan are shown in Figure 1. Thus more than half of the sandy beaches in Taiwan are suffering from beach erosion and appropriate countermeasures to protect the coastline are required. Major impacts of beach erosion consist of coastal erosion, coastal flooding, wave overtopping, land subsidence, and ecological degradation. This study explores coastal impacts and examines countermeasures adopted in responses to coastal erosion during the past 35 years in Taiwan. One optimal response to coastal eroded areas is proposed for coastal management programs to limit or prevent construction by considering safety, landscape, ecology, and attraction to water. New ideas for responding to receding shorelines are the focus of this study based on the survey of already protected areas. This work includes the review of the protection of threatened properties and the restoration of eroded beach. The analysis of Hsu et al. (2007) showed that heavy beach erosion on the Taiwanese coast is primarily caused by human activities. Specific causes include: (1) a shortage of materials supply from the river to the shore; (2) improperly constructed coastal structures; (3) over pumping of groundwater causing land subsidence; and (4) over development resulting from industrial utilization of coastal areas. This investigation briefly addresses some typical reasons for human-induced beach erosion. Detailed reasons for beach erosion are referred to Hsu et al. (2007). Sediment discharge to river mouths primarily takes place during the flood season, especially during typhoon or storm events. During the dry season, sediment is re-distributed via a coastal process that forms wide beaches updrift of littoral barriers and dunes at certain locations. Construction of flood channels and dams or reservoirs can impact the sediment budget, reducing the amount of sediment reaching the shore. On natural coasts, waves and currents transport sand alongshore. Consequently, the severe reduction of longshore sediment sources from rivers causes rapid shoreline shift. Hsu et al. (2007) provided two examples of the Waisanding barrier offshore island and offshore barriers located on the west coast of Taiwan (Figure 1). The Waisanding barrier has shrunk up to 6.1 km in length and 3 km in width (measured at the narrowest point) during the past 40 years (1962–2002), representing total area shrinkage of 10.7 km . Construction of a reservoir in the middle reach of Tsengwen river (Figure 1) is the other example that brought about coastal erosion at the river mouth on the neighboring coast of Tainan. A series of offshore barriers were moved landward. Among these barriers, the maximum rate of shoreline retreat of the Dingtoue barrier exceeds 50 m/y. The erosion is largely due to the construction of dams in the upstream area of the river, and overmining of sand material in the river for use in construction materials, thus cutting of the delivery of sand to the beaches. The longshore sediment transport on beaches manifests itself whenever this natural movement is prevented by the construction of jetties, breakwaters, and groins. Such coastal structures act as barriers to sediment movement, causing beach buildup on the updrift side and simultaneous erosion in the downdrift direction. A typical example is the extension of the northern breakwater at Taichung harbor, on the central region of the west coast of Taiwan (Figure 1). The extension of the northern breakwater at Taichung harbor has blocked the southward longshore sediment transport after the 1980s. Notably, the interruption of longshore sediment by the northern breakwater has resulted in accumulation updrift of the northern breakwater and severe coastal erosion in the downdrift area to a distance of approximately 1,500 m from the southern breakwater (Hsu et al., 2007). Beach erosion may result from ground subsidence caused by overpumping of groundwater for use by fish farms on the Taiwanese coast. The pumping of groundwater accelerates settlement owing to subsoil consolidation. Subsidence is usually followed by sea water intrusion and shoreline retreat. The number of aquaculture farms along the Taiwanese coast has steadily increased since the 1970s. Large quantities of groundwater are extracted and mixed with sea water for aquaculture farming. Numerous places suffer from severe subsidence in the central southwestern and southern coast of Taiwan. The over-extraction of groundwater for aquaculture has caused serious land subsidence (5–10 mm/y) in Chiayi, Tainan, and Pingtung counties, located in Taiwan (Figure 1). The utilization of coastal and ocean spaces for human activities has increased because of economic and population growth. The reclamation of Mailiao industrial harbor was implemented in 1994 and completed in 2001, and is located in the center of the southwestern coast of Taiwan (Figure 1). The biggest river, the Choshui river (Figure 2(d)), discharges from the north of the Mailiao reclamation area and into the surrounding coastal waters. To allow movement of large vessels of 200,000 tons, the western breakwater was extended to a water depth of –26 m (Figure 2(a)). A large stockpile of material dredged from the seabed in the region of intermediate water depth located 1.5 km away from the shoreline for Mailiao industrial area is one of the sources of sand supply for reclamation. The planned reclamation area on the Mailiao industrial area and harbor has a length of 7 km from north to south (Figure 2(a)). The bathymetry in the coastal region frequently reaches equilibrium under the action of waves and currents without human intervention. However, concern naturally exists when a substantial quantity of sand is removed from the seabed and the subsequent bathymetry alterations will change the wave and current patterns, with detrimental consequences for the nearby beach. Figure 2 shows that the dredging and construction of breakwaters have caused sand accumulation updrift of the western breakwater of the Mailiao industrial area and harbor, as well as severe coastal erosional downdrift extending for a long distance in industrial area. The construction of Mailiao harbor’s western breakwater has blocked the longshore sediment transport that moves southward. Comparing Figures 2(b) and Figures 2(c), interruption of longshore sediment has caused accumulation of the western breakwater and severe coastal erosion downdrift to a distance about 10 km south. The rate change of volume in the upstream of the western breakwater from 1999 to 2006 is 10 6 m 3 /y. Figure 2(d) presents details of sand accretion of a beach updrift of the western breakwater and beach erosion downdrift. It is sufficient to say that this is a typical example resulting in nearby beach erosion due to over development associated with industrial utilization of coastal areas. The most important human-induced causes of coastal erosion along the Taiwanese coast are (1) a shortage of sediment transport from rivers to the shore and (2) improper constructions on coastal areas. According to Figure 1, it has been estimated about 50% of the eroding coasts is affected by reduction of the sand supply from rivers and 30% of beach erosion is caused by the mechanism of improperly constructed coastal structures. Beach erosion produces four main bio-geophysical impacts in coastal areas: (1) exacer- bation of storm flooding and damage; (2) inundation and displacement of wetlands and ...

Context 9

... provided two examples of the Waisanding barrier offshore island and offshore barriers located on the west coast of Taiwan (Figure 1). The Waisanding barrier has shrunk up to 6.1 km in length and 3 km in width (measured at the narrowest point) during the past 40 years (1962–2002), representing total area shrinkage of 10.7 km . Construction of a reservoir in the middle reach of Tsengwen river (Figure 1) is the other example that brought about coastal erosion at the river mouth on the neighboring coast of Tainan. A series of offshore barriers were moved landward. Among these barriers, the maximum rate of shoreline retreat of the Dingtoue barrier exceeds 50 m/y. The erosion is largely due to the construction of dams in the upstream area of the river, and overmining of sand material in the river for use in construction materials, thus cutting of the delivery of sand to the beaches. The longshore sediment transport on beaches manifests itself whenever this natural movement is prevented by the construction of jetties, breakwaters, and groins. Such coastal structures act as barriers to sediment movement, causing beach buildup on the updrift side and simultaneous erosion in the downdrift direction. A typical example is the extension of the northern breakwater at Taichung harbor, on the central region of the west coast of Taiwan (Figure 1). The extension of the northern breakwater at Taichung harbor has blocked the southward longshore sediment transport after the 1980s. Notably, the interruption of longshore sediment by the northern breakwater has resulted in accumulation updrift of the northern breakwater and severe coastal erosion in the downdrift area to a distance of approximately 1,500 m from the southern breakwater (Hsu et al., 2007). Beach erosion may result from ground subsidence caused by overpumping of groundwater for use by fish farms on the Taiwanese coast. The pumping of groundwater accelerates settlement owing to subsoil consolidation. Subsidence is usually followed by sea water intrusion and shoreline retreat. The number of aquaculture farms along the Taiwanese coast has steadily increased since the 1970s. Large quantities of groundwater are extracted and mixed with sea water for aquaculture farming. Numerous places suffer from severe subsidence in the central southwestern and southern coast of Taiwan. The over-extraction of groundwater for aquaculture has caused serious land subsidence (5–10 mm/y) in Chiayi, Tainan, and Pingtung counties, located in Taiwan (Figure 1). The utilization of coastal and ocean spaces for human activities has increased because of economic and population growth. The reclamation of Mailiao industrial harbor was implemented in 1994 and completed in 2001, and is located in the center of the southwestern coast of Taiwan (Figure 1). The biggest river, the Choshui river (Figure 2(d)), discharges from the north of the Mailiao reclamation area and into the surrounding coastal waters. To allow movement of large vessels of 200,000 tons, the western breakwater was extended to a water depth of –26 m (Figure 2(a)). A large stockpile of material dredged from the seabed in the region of intermediate water depth located 1.5 km away from the shoreline for Mailiao industrial area is one of the sources of sand supply for reclamation. The planned reclamation area on the Mailiao industrial area and harbor has a length of 7 km from north to south (Figure 2(a)). The bathymetry in the coastal region frequently reaches equilibrium under the action of waves and currents without human intervention. However, concern naturally exists when a substantial quantity of sand is removed from the seabed and the subsequent bathymetry alterations will change the wave and current patterns, with detrimental consequences for the nearby beach. Figure 2 shows that the dredging and construction of breakwaters have caused sand accumulation updrift of the western breakwater of the Mailiao industrial area and harbor, as well as severe coastal erosional downdrift extending for a long distance in industrial area. The construction of Mailiao harbor’s western breakwater has blocked the longshore sediment transport that moves southward. Comparing Figures 2(b) and Figures 2(c), interruption of longshore sediment has caused accumulation of the western breakwater and severe coastal erosion downdrift to a distance about 10 km south. The rate change of volume in the upstream of the western breakwater from 1999 to 2006 is 10 6 m 3 /y. Figure 2(d) presents details of sand accretion of a beach updrift of the western breakwater and beach erosion downdrift. It is sufficient to say that this is a typical example resulting in nearby beach erosion due to over development associated with industrial utilization of coastal areas. The most important human-induced causes of coastal erosion along the Taiwanese coast are (1) a shortage of sediment transport from rivers to the shore and (2) improper constructions on coastal areas. According to Figure 1, it has been estimated about 50% of the eroding coasts is affected by reduction of the sand supply from rivers and 30% of beach erosion is caused by the mechanism of improperly constructed coastal structures. Beach erosion produces four main bio-geophysical impacts in coastal areas: (1) exacer- bation of storm flooding and damage; (2) inundation and displacement of wetlands and lowlands; (3) increased soil salinity and threats to freshwater aquifers; and (4) exacerbated coastal squeeze of ecosystems. The increase in extreme water levels threatens all coastal lowlands, and increased coastal flooding is a precursor to the permanent inundation and submergence of low-lying land (Lin, 1996). Figure 3 illustrates a typical example of coastal flooding during typhoon Herb in 1996 along the western coastal lowlands of Taiwan, and the different zones on Kohu and Madou in southwestern Taiwan at risk of coastal flooding in 1998 and 2005 during typhoons Zeb and Haitang. Beach erosion can cause inundation and subsequent displacement of wetlands and lowlands. For instance, the exposure of mangrove and beefwood to flooding events in large surges and waves has led to the disappearance of wetland vegetation. Figure 4 depicts two typical examples of coastal damage in the form of the death of mangrove and beefwood owing to coastal flooding on the Donshu coast in Chiayi County and on the Chigu coast in Tainan County. The sandy beach contains extensive sediment deposits because of fluvial sand outflow along the coast. The erosion is serious as a result of imbalanced longshore sediment transport. Owing to beach erosion, the inundation increases the salinity of soil and fresh groundwater. The effect is greater when the landward side is attacked by the waves and high tides. The fact that a net flow of sea water occurs through the beach face creates large potential for this sea water to enter the aquifer. A hydrological salty area would affect land use and agricultural or fish farm production. Generally, hydrological salty regions generally take a long time to recover to their original state. Beach erosion may also change the ecology of the coastal environment and cause socioeconomic problems. Waves and currents move sand and gravel on sandy beaches. Owing to suspended sediment in the water column, muddy water may cause coral to die as a result of reduced oxygen supply. Coral bleaching often results from high sediment concentrations due to coastal erosion on the southern coast of Taiwan. In Taiwan, beach erosion has been a long-term trend. The seriousness of beach erosion in Taiwan has received considerable attention since the 1960s, following rapid population growth and economic development in the coastal areas. Theoretically, in controlling beach erosion it is necessary to first detect the main reason for such a problem occurring. The elimination of the cause is the best method of solving the problem, but is usually difficult to accomplish. To protect against beach erosion, one response is to establish coastal management programs to limit or prevent construction within dangerous zones. Generally two countermeasures are adopted in response to receding shoreline: the “hard” solution of stabilization structures and the “soft” solution of beach nourishment, combined with headland control, coastal structures, the geotextile tube method, and so on. Initially, the most commonly used structures for shore protection in Taiwanese coast were seawalls and revetments, which were constructed at a distance from and parallel to the shoreline. Such structures were built primarily to protect human life and property from the erosive action of nearshore waves, tides, storm surges, and currents. Despite various construction types and locations in relation to local beach and surf, seawalls and revetments are designed to physically block wave energy and storm surge. In Taiwan, the first seawall was constructed in response to the destruction of the coastline by a typhoon event in 1951. Since then seawalls and revetments around Taiwan have been progressively lengthened ...

Context 10

... erosion involves shoreline recession as a result of the action of waves, nearshore currents, and winds. Beach erosion is usually determined by imbalanced littoral drift, namely when the volume of longshore sediment rate flows into the littoral cell is less than that of outward flows. Shorelines can be considered to be at equilibrium over a long term although seasonal changes can take place. As a result of economic growth in coastal areas and increasing with the associated development, beach erosion has become a major human and economic problem from the perspective of land preservation problems. According to Komar (1998), about two-thirds of the world’s population lives within a narrow belt of land close to the ocean, in which 53 percent of the U.S. population lives within 80 km of the shore (Edwards, 1989), 83 percent of Australia population lives near the coast, 25 percent within 3 km, and all its major cities are found on the coast, and 18 percent of the total population in Taiwan lives within the shore (Hsu et al., 2007). Inman and Brush (1973) estimated that if everyone in the world decided to visit the 440,000 km of shoreline in the world, each individual would have less than 13 cm of shore to themselves. This information indicates that population pressure could occur at crowded public beaches and a profileration of seaside condominiums, hotels/motels, recreational-vehicle parks, and reclamation areas for industrial utilization and urban lots, which often destroy the aesthetic values that originally drew people to the coast. Beach erosion frequently causes inherent damage to coastal regions. When typhoon waves associated with storm surges attack the shore, the shoreline migrates landwards, destroying homes built on and properties located too close to the sea. The total length of the coastline around Taiwan island is approximately 1139 km including rocky shore, of which only 542 km is considered secure against sea attack. The areas experiencing coastal erosion in Taiwan are shown in Figure 1. Thus more than half of the sandy beaches in Taiwan are suffering from beach erosion and appropriate countermeasures to protect the coastline are required. Major impacts of beach erosion consist of coastal erosion, coastal flooding, wave overtopping, land subsidence, and ecological degradation. This study explores coastal impacts and examines countermeasures adopted in responses to coastal erosion during the past 35 years in Taiwan. One optimal response to coastal eroded areas is proposed for coastal management programs to limit or prevent construction by considering safety, landscape, ecology, and attraction to water. New ideas for responding to receding shorelines are the focus of this study based on the survey of already protected areas. This work includes the review of the protection of threatened properties and the restoration of eroded beach. The analysis of Hsu et al. (2007) showed that heavy beach erosion on the Taiwanese coast is primarily caused by human activities. Specific causes include: (1) a shortage of materials supply from the river to the shore; (2) improperly constructed coastal structures; (3) over pumping of groundwater causing land subsidence; and (4) over development resulting from industrial utilization of coastal areas. This investigation briefly addresses some typical reasons for human-induced beach erosion. Detailed reasons for beach erosion are referred to Hsu et al. (2007). Sediment discharge to river mouths primarily takes place during the flood season, especially during typhoon or storm events. During the dry season, sediment is re-distributed via a coastal process that forms wide beaches updrift of littoral barriers and dunes at certain locations. Construction of flood channels and dams or reservoirs can impact the sediment budget, reducing the amount of sediment reaching the shore. On natural coasts, waves and currents transport sand alongshore. Consequently, the severe reduction of longshore sediment sources from rivers causes rapid shoreline shift. Hsu et al. (2007) provided two examples of the Waisanding barrier offshore island and offshore barriers located on the west coast of Taiwan (Figure 1). The Waisanding barrier has shrunk up to 6.1 km in length and 3 km in width (measured at the narrowest point) during the past 40 years (1962–2002), representing total area shrinkage of 10.7 km . Construction of a reservoir in the middle reach of Tsengwen river (Figure 1) is the other example that brought about coastal erosion at the river mouth on the neighboring coast of Tainan. A series of offshore barriers were moved landward. Among these barriers, the maximum rate of shoreline retreat of the Dingtoue barrier exceeds 50 m/y. The erosion is largely due to the construction of dams in the upstream area of the river, and overmining of sand material in the river for use in construction materials, thus cutting of the delivery of sand to the beaches. The longshore sediment transport on beaches manifests itself whenever this natural movement is prevented by the construction of jetties, breakwaters, and groins. Such coastal structures act as barriers to sediment movement, causing beach buildup on the updrift side and simultaneous erosion in the downdrift direction. A typical example is the extension of the northern breakwater at Taichung harbor, on the central region of the west coast of Taiwan (Figure 1). The extension of the northern breakwater at Taichung harbor has blocked the southward longshore sediment transport after the 1980s. Notably, the interruption of longshore sediment by the northern breakwater has resulted in accumulation updrift of the northern breakwater and severe coastal erosion in the downdrift area to a distance of approximately 1,500 m from the southern breakwater (Hsu et al., 2007). Beach erosion may result from ground subsidence caused by overpumping of groundwater for use by fish farms on the Taiwanese coast. The pumping of groundwater accelerates settlement owing to subsoil consolidation. Subsidence is usually followed by sea water intrusion and shoreline retreat. The number of aquaculture farms along the Taiwanese coast has steadily increased since the 1970s. Large quantities of groundwater are extracted and mixed with sea water for aquaculture farming. Numerous places suffer from severe subsidence in the central southwestern and southern coast of Taiwan. The over-extraction of groundwater for aquaculture has caused serious land subsidence (5–10 mm/y) in Chiayi, Tainan, and Pingtung counties, located in Taiwan (Figure 1). The utilization of coastal and ocean spaces for human activities has increased because of economic and population growth. The reclamation of Mailiao industrial harbor was implemented in 1994 and completed in 2001, and is located in the center of the southwestern coast of Taiwan (Figure 1). The biggest river, the Choshui river (Figure 2(d)), discharges from the north of the Mailiao reclamation area and into the surrounding coastal waters. To allow movement of large vessels of 200,000 tons, the western breakwater was extended to a water depth of –26 m (Figure 2(a)). A large stockpile of material dredged from the seabed in the region of intermediate water depth located 1.5 km away from the shoreline for Mailiao industrial area is one of the sources of sand supply for reclamation. The planned reclamation area on the Mailiao industrial area and harbor has a length of 7 km from north to south (Figure 2(a)). The bathymetry in the coastal region frequently reaches equilibrium under the action of waves and currents without human intervention. However, concern naturally exists when a substantial quantity of sand is removed from the seabed and the subsequent bathymetry alterations will change the wave and current patterns, with detrimental consequences for the nearby beach. Figure 2 shows that the dredging and construction of breakwaters have caused sand accumulation updrift of the western breakwater of the Mailiao industrial area and harbor, as well as severe coastal erosional downdrift extending for a long distance in industrial area. The construction of Mailiao harbor’s western breakwater has blocked the longshore sediment transport that moves southward. Comparing Figures 2(b) and Figures 2(c), interruption of longshore sediment has caused accumulation of the western breakwater and severe coastal erosion downdrift to a distance about 10 km south. The rate change of volume in the upstream of the western breakwater from 1999 to 2006 is 10 6 m 3 /y. Figure 2(d) presents details of sand accretion of a beach updrift of the western breakwater and beach erosion downdrift. It is sufficient to say that this is a typical example resulting in nearby beach erosion due to over development associated with industrial utilization of coastal areas. The most important human-induced causes of coastal erosion along the Taiwanese coast are (1) a shortage of sediment transport from rivers to the shore and (2) improper constructions on coastal areas. According to Figure 1, it has been estimated about 50% of the eroding coasts is affected by reduction of the sand supply from rivers and ...

Context 11

... erosion involves shoreline recession as a result of the action of waves, nearshore currents, and winds. Beach erosion is usually determined by imbalanced littoral drift, namely when the volume of longshore sediment rate flows into the littoral cell is less than that of outward flows. Shorelines can be considered to be at equilibrium over a long term although seasonal changes can take place. As a result of economic growth in coastal areas and increasing with the associated development, beach erosion has become a major human and economic problem from the perspective of land preservation problems. According to Komar (1998), about two-thirds of the world’s population lives within a narrow belt of land close to the ocean, in which 53 percent of the U.S. population lives within 80 km of the shore (Edwards, 1989), 83 percent of Australia population lives near the coast, 25 percent within 3 km, and all its major cities are found on the coast, and 18 percent of the total population in Taiwan lives within the shore (Hsu et al., 2007). Inman and Brush (1973) estimated that if everyone in the world decided to visit the 440,000 km of shoreline in the world, each individual would have less than 13 cm of shore to themselves. This information indicates that population pressure could occur at crowded public beaches and a profileration of seaside condominiums, hotels/motels, recreational-vehicle parks, and reclamation areas for industrial utilization and urban lots, which often destroy the aesthetic values that originally drew people to the coast. Beach erosion frequently causes inherent damage to coastal regions. When typhoon waves associated with storm surges attack the shore, the shoreline migrates landwards, destroying homes built on and properties located too close to the sea. The total length of the coastline around Taiwan island is approximately 1139 km including rocky shore, of which only 542 km is considered secure against sea attack. The areas experiencing coastal erosion in Taiwan are shown in Figure 1. Thus more than half of the sandy beaches in Taiwan are suffering from beach erosion and appropriate countermeasures to protect the coastline are required. Major impacts of beach erosion consist of coastal erosion, coastal flooding, wave overtopping, land subsidence, and ecological degradation. This study explores coastal impacts and examines countermeasures adopted in responses to coastal erosion during the past 35 years in Taiwan. One optimal response to coastal eroded areas is proposed for coastal management programs to limit or prevent construction by considering safety, landscape, ecology, and attraction to water. New ideas for responding to receding shorelines are the focus of this study based on the survey of already protected areas. This work includes the review of the protection of threatened properties and the restoration of eroded beach. The analysis of Hsu et al. (2007) showed that heavy beach erosion on the Taiwanese coast is primarily caused by human activities. Specific causes include: (1) a shortage of materials supply from the river to the shore; (2) improperly constructed coastal structures; (3) over pumping of groundwater causing land subsidence; and (4) over development resulting from industrial utilization of coastal areas. This investigation briefly addresses some typical reasons for human-induced beach erosion. Detailed reasons for beach erosion are referred to Hsu et al. (2007). Sediment discharge to river mouths primarily takes place during the flood season, especially during typhoon or storm events. During the dry season, sediment is re-distributed via a coastal process that forms wide beaches updrift of littoral barriers and dunes at certain locations. Construction of flood channels and dams or reservoirs can impact the sediment budget, reducing the amount of sediment reaching the shore. On natural coasts, waves and currents transport sand alongshore. Consequently, the severe reduction of longshore sediment sources from rivers causes rapid shoreline shift. Hsu et al. (2007) provided two examples of the Waisanding barrier offshore island and offshore barriers located on the west coast of Taiwan (Figure 1). The Waisanding barrier has shrunk up to 6.1 km in length and 3 km in width (measured at the narrowest point) during the past 40 years (1962–2002), representing total area shrinkage of 10.7 km . Construction of a reservoir in the middle reach of Tsengwen river (Figure 1) is the other example that brought about coastal erosion at the river mouth on the neighboring coast of Tainan. A series of offshore barriers were moved landward. Among these barriers, the maximum rate of shoreline retreat of the Dingtoue barrier exceeds 50 m/y. The erosion is largely due to the construction of dams in the upstream area of the river, and overmining of sand material in the river for use in construction materials, thus cutting of the delivery of sand to the beaches. The longshore sediment transport on beaches manifests itself whenever this natural movement is prevented by the construction of jetties, breakwaters, and groins. Such coastal structures act as barriers to sediment movement, causing beach buildup on the updrift side and simultaneous erosion in the downdrift direction. A typical example is the extension of the northern breakwater at Taichung harbor, on the central region of the west coast of Taiwan (Figure 1). The extension of the northern breakwater at Taichung harbor has blocked the southward longshore sediment transport after the 1980s. Notably, the interruption of longshore sediment by the northern breakwater has resulted in accumulation updrift of the northern breakwater and severe coastal erosion in the downdrift area to a distance of approximately 1,500 m from the southern breakwater (Hsu et al., 2007). Beach erosion may result from ground subsidence caused by overpumping of groundwater for use by fish farms on the Taiwanese coast. The pumping of groundwater accelerates settlement owing to subsoil consolidation. Subsidence is usually followed by sea water intrusion and shoreline retreat. The number of aquaculture farms along the Taiwanese coast has steadily increased since the 1970s. Large quantities of groundwater are extracted and mixed with sea water for aquaculture farming. Numerous places suffer from severe subsidence in the central southwestern and southern coast of Taiwan. The over-extraction of groundwater for aquaculture has caused serious land subsidence (5–10 mm/y) in Chiayi, Tainan, and Pingtung counties, located in Taiwan (Figure 1). The utilization of coastal and ocean spaces for human activities has increased because of economic and population growth. The reclamation of Mailiao industrial harbor was implemented in 1994 and completed in 2001, and is located in the center of the southwestern coast of Taiwan (Figure 1). The biggest river, the Choshui river (Figure 2(d)), discharges from the north of the Mailiao reclamation area and into the surrounding ...

Context 12

... causes inherent damage to coastal regions. When typhoon waves associated with storm surges attack the shore, the shoreline migrates landwards, destroying homes built on and properties located too close to the sea. The total length of the coastline around Taiwan island is approximately 1139 km including rocky shore, of which only 542 km is considered secure against sea attack. The areas experiencing coastal erosion in Taiwan are shown in Figure 1. Thus more than half of the sandy beaches in Taiwan are suffering from beach erosion and appropriate countermeasures to protect the coastline are required. Major impacts of beach erosion consist of coastal erosion, coastal flooding, wave overtopping, land subsidence, and ecological degradation. This study explores coastal impacts and examines countermeasures adopted in responses to coastal erosion during the past 35 years in Taiwan. One optimal response to coastal eroded areas is proposed for coastal management programs to limit or prevent construction by considering safety, landscape, ecology, and attraction to water. New ideas for responding to receding shorelines are the focus of this study based on the survey of already protected areas. This work includes the review of the protection of threatened properties and the restoration of eroded beach. The analysis of Hsu et al. (2007) showed that heavy beach erosion on the Taiwanese coast is primarily caused by human activities. Specific causes include: (1) a shortage of materials supply from the river to the shore; (2) improperly constructed coastal structures; (3) over pumping of groundwater causing land subsidence; and (4) over development resulting from industrial utilization of coastal areas. This investigation briefly addresses some typical reasons for human-induced beach erosion. Detailed reasons for beach erosion are referred to Hsu et al. (2007). Sediment discharge to river mouths primarily takes place during the flood season, especially during typhoon or storm events. During the dry season, sediment is re-distributed via a coastal process that forms wide beaches updrift of littoral barriers and dunes at certain locations. Construction of flood channels and dams or reservoirs can impact the sediment budget, reducing the amount of sediment reaching the shore. On natural coasts, waves and currents transport sand alongshore. Consequently, the severe reduction of longshore sediment sources from rivers causes rapid shoreline shift. Hsu et al. (2007) provided two examples of the Waisanding barrier offshore island and offshore barriers located on the west coast of Taiwan (Figure 1). The Waisanding barrier has shrunk up to 6.1 km in length and 3 km in width (measured at the narrowest point) during the past 40 years (1962–2002), representing total area shrinkage of 10.7 km . Construction of a reservoir in the middle reach of Tsengwen river (Figure 1) is the other example that brought about coastal erosion at the river mouth on the neighboring coast of Tainan. A series of offshore barriers were moved landward. Among these barriers, the maximum rate of shoreline retreat of the Dingtoue barrier exceeds 50 m/y. The erosion is largely due to the construction of dams in the upstream area of the river, and overmining of sand material in the river for use in construction materials, thus cutting of the delivery of sand to the beaches. The longshore sediment transport on beaches manifests itself whenever this natural movement is prevented by the construction of jetties, breakwaters, and groins. Such coastal structures act as barriers to sediment movement, causing beach buildup on the updrift side and simultaneous erosion in the downdrift direction. A typical example is the extension of the northern breakwater at Taichung harbor, on the central region of the west coast of Taiwan (Figure 1). The extension of the northern breakwater at Taichung harbor has blocked the southward longshore sediment transport after the 1980s. Notably, the interruption of longshore sediment by the northern breakwater has resulted in accumulation updrift of the northern breakwater and severe coastal erosion in the downdrift area to a distance of approximately 1,500 m from the southern breakwater (Hsu et al., 2007). Beach erosion may result from ground subsidence caused by overpumping of groundwater for use by fish farms on the Taiwanese coast. The pumping of groundwater accelerates settlement owing to subsoil consolidation. Subsidence is usually followed by sea water intrusion and shoreline retreat. The number of aquaculture farms along the Taiwanese coast has steadily increased since the 1970s. Large quantities of groundwater are extracted and mixed with sea water for aquaculture farming. Numerous places suffer from severe subsidence in the central southwestern and southern coast of Taiwan. The over-extraction of groundwater for aquaculture has caused serious land subsidence (5–10 mm/y) in Chiayi, Tainan, and Pingtung counties, located in Taiwan (Figure 1). The utilization of coastal and ocean spaces for human activities has increased because of economic and population growth. The reclamation of Mailiao industrial harbor was implemented in 1994 and completed in 2001, and is located in the center of the southwestern coast of Taiwan (Figure 1). The biggest river, the Choshui river (Figure 2(d)), discharges from the north of the Mailiao reclamation area and into the surrounding coastal waters. To allow movement of large vessels of 200,000 tons, the western breakwater was extended to a water depth of –26 m (Figure 2(a)). A large stockpile of material dredged from the seabed in the region of intermediate water depth located 1.5 km away from the shoreline for Mailiao industrial area is one of the sources of sand supply for reclamation. The planned reclamation area on the Mailiao industrial area and harbor has a length of 7 km from north to south (Figure 2(a)). The bathymetry in the coastal region frequently reaches equilibrium under the action of waves and currents without human intervention. However, concern naturally exists when a substantial quantity of sand is removed from the seabed and the subsequent bathymetry alterations will change the wave and current patterns, with detrimental consequences for the nearby beach. Figure 2 shows that the dredging and construction of breakwaters have caused sand accumulation updrift of the western breakwater of the Mailiao industrial area and harbor, as well as severe coastal erosional downdrift extending for a long distance in industrial area. The construction of Mailiao harbor’s western breakwater has blocked the longshore sediment transport that moves southward. Comparing Figures 2(b) and Figures 2(c), interruption of longshore sediment has caused accumulation of the western breakwater and severe coastal erosion downdrift to a distance about 10 km south. The rate change of volume in the upstream of the western breakwater from 1999 to 2006 is 10 6 m 3 /y. Figure 2(d) presents details of sand accretion of a beach updrift of the western breakwater and beach erosion downdrift. It is sufficient to say that this is a typical example resulting in nearby beach erosion due to over development associated with industrial utilization of coastal areas. The most important human-induced causes of coastal erosion along the Taiwanese coast are (1) a shortage of sediment transport from rivers to the shore and (2) improper constructions on coastal areas. According to Figure 1, it has been estimated about 50% of the eroding coasts is affected by reduction of the sand supply from rivers and 30% of beach erosion is caused by the mechanism of improperly constructed coastal structures. Beach erosion produces four main bio-geophysical impacts in coastal areas: (1) exacer- bation of storm flooding and damage; (2) inundation and displacement of wetlands and lowlands; (3) increased soil salinity and threats to freshwater aquifers; and (4) exacerbated coastal squeeze of ecosystems. The increase in extreme water levels threatens all coastal lowlands, and increased coastal flooding is a precursor to the permanent inundation and submergence of low-lying land (Lin, 1996). Figure 3 illustrates a typical example of coastal flooding during typhoon Herb in 1996 along the western coastal lowlands of Taiwan, and the different zones on Kohu and Madou in southwestern Taiwan at risk of coastal flooding in 1998 and 2005 during typhoons Zeb and Haitang. Beach erosion can cause inundation and subsequent displacement of wetlands and lowlands. For instance, the exposure of mangrove and beefwood to flooding events in large surges and waves has led to the disappearance of wetland vegetation. Figure 4 depicts two typical examples of coastal damage in the form of the death of mangrove and beefwood owing to coastal flooding on the Donshu coast in Chiayi County and on the Chigu coast in Tainan County. The sandy beach contains extensive sediment deposits because of fluvial sand outflow along the coast. The erosion is serious as a result of imbalanced longshore sediment transport. Owing to beach erosion, the inundation increases the salinity of soil and fresh groundwater. The effect is greater when the landward side is attacked by the waves and high tides. The fact that a net flow of sea water occurs through the beach face creates large potential for this sea water to enter the aquifer. A hydrological salty area would affect land use and agricultural or fish farm production. Generally, hydrological salty regions generally take a long time to recover to their original state. Beach erosion may also change the ecology of the coastal environment and cause socioeconomic problems. Waves and currents move sand and gravel on sandy beaches. Owing to suspended sediment in the water column, muddy water may cause coral to die as a result of reduced oxygen supply. Coral bleaching often results from high sediment concentrations due to coastal erosion on the southern coast of ...