DSpace at VNU: Effects of climate change on geo-disasters in coastal zones and their adaptation

DSpace at VNU: Effects of climate change on geo-disasters in coastal zones and their adaptation tài liệu, giáo án, bài g...

Geotextiles and Geomembranes 30 (2012) 24e34 Contents lists available at ScienceDirect Geotextiles and Geomembranes journal homepage: www.elsevier.com/locate/geotexmem Effects of climate change on geo-disasters in coastal zones and their adaptation K Yasuhara a, *, H Komine b, S Murakami b, G Chen c, Y Mitani c, D.M Duc d a Institute for Global Change Adaptation Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan Department of Urban and Civil Engineering, Ibaraki University, Hitachi, Ibaraki 316-8511, Japan c Graduate School of Civil Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan d Department of Geotechnics, Hanoi University of Science, Vietnam National University, 334 Nguyen Trai, Thanh Xuan, Hanoi, Viet Nam b a r t i c l e i n f o a b s t r a c t Article history: Received 19 May 2010 Accepted 19 December 2010 Available online February 2011 Results of recent investigations suggest that climate change tends to exacerbate geo-disasters Therefore, it is understood clearly that adaptation to climate change has rapidly become the most important and urgent issue for the future existence of human beings on Earth These inferences form the background of this research In comparison to those examining water disasters, few studies have examined climatechange-induced geo-disasters This study aims at upgrading the methodology for estimating effects on geo-disasters of combined events, e.g., global warming with increased typhoon and rainfall severity or occurrence of great earthquakes Such a methodology is expected to contribute to progress in the fields of natural disaster mitigation and land preservation, particularly near seacoasts and rivers Ó 2011 Elsevier Ltd All rights reserved Keywords: Global warming Climate change Compound disaster Torrential rainfall Great earthquake Adaptation Introduction Coastal zones and riversides are the residential areas that are most likely to be influenced by global warming Especially, seashores will be strongly influenced if global warming induces increased frequency or intensity of typhoons Climate factors might cause disasters that are more severe if smaller disasters were to occur concurrently A disaster that is deemed important and which occurs because of overlapping factors is designated herein as a complex disaster Fig depicts such a complex disaster schematically This figure portrays that complex disasters are roughly classifiable into disasters related to water (water disasters) and disasters related to soil or ground conditions or behaviors (geological hazards) Fig portrays compound disasters as classified into disasters that occur by overlapping of global warming factors, and those by overlapping of factors related to and independent of global warming Large cities in Japan are especially vulnerable to natural threats because they are located in low-lying coastal areas It is therefore important to predict these natural threats and to consider appropriate countermeasures Previous studies have revealed the following (Suzuki et al., 2006; Suzuki, 2007; Suzuki, 2008; Komine, 2007a,b; Yasuhara 2008) * Corresponding author Tel.: ỵ81 294 38 5166; fax: ỵ81 294 38 5268 E-mail address: yasuhara@mx.ibaraki.ac.jp (K Yasuhara) 0266-1144/$ e see front matter Ó 2011 Elsevier Ltd All rights reserved doi:10.1016/j.geotexmem.2011.01.005 a) The risk of flooding by high tides is enhanced in long ago developed reclaimed lands and their periphery in the inner parts of Japan’s Three Major Bays (Tokyo Bay, Ise Bay, and Osaka Bay) when global warming progresses (Suzuki 2007, 2008) b) Sea level rise results from climate change and changes in the frequency and intensity of rains Those influences magnify high risks in areas prone to liquefaction, especially in coastal zones (Yasuhara et al., 2007; Yasuhara , 2008; Yasuhara et al., 2010) c) Great economic merits of sandy beaches and tidal flats will disappear because of a sea level rise (Suzuki, 2008) d) River levees might be degraded and damaged if seawater invades into riverine areas because of a sea level rise This mechanism was clarified, and river levees’ vulnerability to rainfall because of global warming has been clarified on a national level in Japan (Komine, 2007a,b) e) Because of global warming, disaster risks on slopes adjacent to coastal zones are magnified by heavy rains It is therefore necessary to study slope recovery plans using a risk index (Yasuhara, 2008; Yasuhara 2010) Supporting evidence of triggering natural disasters Hazards that have been predicted to result from global warming can be either certain or uncertain One highly certain occurrence is a sea level rise, as reported by the IPCC A recent report by the IPCC (2007) describes that the sea level will rise to around 60 cm, on K Yasuhara et al / Geotextiles and Geomembranes 30 (2012) 24e34 25 River levees 3.1 Methodology Fig Disasters caused by overlapping multiple phenomena caused by global warming average, by the end of the 21st century, although several scenarios have been proposed According to early research by Mimura (2006), 70e80% of sandy beaches will disappear if the sea level rise (SLR) reaches 60 cm A sea level rise would also force groundwater levels (GWL) upward, thereby engendering infrastructural instability along coastal zones Low atmospheric pressure, including intensified typhoons, generally brings about locally heavy rainfall, so-called torrential rainfall, as it did in 2004; sometimes it produces “Guerilla” heavy rains, as in 2008 in Japan Fig presents variations of the occurrence frequency of torrential rainfall during the last 30 years Torrents exceeding 50 mm/h are shown there according to data obtained from the Ministry of Land, Infrastructure and Transportation, who summarized data provided by the Japan Meteorological Agency (JMA) Results presented in Fig show the average frequency of torrential rainfall over 100 mm/h as well as over 50 mm/h These strong rains might increase geotechnical damage such as slope failure, and might even magnify it, particularly when great earthquakes strike soon before or after severe local rainfalls Regarding earthquakes, which cannot be related directly to global warming, it is unfortunate that both earthquakes with large and small seismic intensity have been increasing, as portrayed in Fig Special attention must be devoted to the possibility of severe damage to slopes, earth structures, and grounds that must be induced by the combination of torrential rainfall with great earthquakes The climate and weather variations described above show that geo-hazards tend to increase over time Fig Disasters caused by overlapping of the sea level rise and local heavy rains brought about by global warming and a phenomenon unrelated to global warming, such as an earthquake A sea level rise attributable to global warming is expected to cause seawater to move up-river Consequently, brackish water regions in river downstream areas might extend upstream Such an outcome might affect river levees, which are a necessary disaster prevention facility Quantitative assessment of the vulnerability of infrastructure facilities by global warming is a pressing issue Therefore, in addition to investigations directed at securing of river levees, suitable adaptation measures are demanded to mitigate this vulnerability For evaluation of global warming’s impact to river levees, river levees soils were collected nationwide: experiments were conducted to investigate the soil consistency (deformability according to water content) and compressibility (ability of volume change by force) Changes of deformability and compressibility will induce settlement and instability of river levees, engendering the overflow of river water (Komine, 2007b) Results of these experiments clarified mechanisms of river levee degradation and damage when the seawater moves up-river because of the sea level rise Details of the experimental results described above are available for reference in previous reports (Komine, 2007a, 2007b) Moreover, a test was conducted to investigate the water-holding capacity of the soil to evaluate the vulnerability of river levees to rainfall A water-holding property database of earth materials assumed to constitute the river levee of every region was created Results indicated vulnerability of river levees to rainfall, in rough terms, on a Japanese national level Details of the experimental results presented above have already been reported in the literature (Uchida et al., 2007) 3.2 Future estimate of river levee vulnerability An important concern is that the sea level rise and frequent heavy rain occurring because of global warming will magnify the vulnerability of river levees Sea level rises are expected to expand brackish water areas near rivers Moreover, it is expected that frequent heavy rains and increases in river levels will encourage soaking into river levees Experiments were conducted from such a viewpoint assuming the incursion of seawater into a river levee or increased flood volume River levee vulnerability was evaluated (Komine, 2007a, 2007b) Nine soil materials assumed to be used for river levees were collected from various locations in Japan, as presented in Fig Several experiments using the “test method for liquid limit and plastic limit of soils (JIS A 1205:1999)”, the “test method for onedimensional consolidation properties of soils using constant rate of strain loading (JIS A 1227:2000)” and the “The Japanese Geotechnical Society Standard the Method of water retentivity test of soil (JGS 0151-2000)” were conducted to elucidate physical properties that are useful for estimating river embankment vulnerability to erosion by floods Effects on levee embankment materials of the extension of river brackish water regions attributable to sea level rise are estimated as presented in Table The future cannot be designated as a definite period in this estimate Fig portrays maps of vulnerability assessment produced based on the results presented in Table Estimates and measures used to assess river levee embankment materials’ vulnerability to rainfall are shown in Table (Uchida et al., 2007) In relation to these estimates, the future cannot be designated as a definite period Fig displays a map of the vulnerability assessment obtained according to the results in Table and respective measures River 26 K Yasuhara et al / Geotextiles and Geomembranes 30 (2012) 24e34 Fig Recent situation of rainfall in Japan (data from JMA, 2006) levee vulnerability is known to be influenced by boundary conditions such as the levee size, and by external conditions such as the rainfall intensity However, these conditions vary widely, making it difficult to evaluate river levees’ vulnerability from the perspective of levees’ boundary and external conditions In this study, levee vulnerability is evaluated according to mechanical properties of the soil materials used for river levees Variation of liquefaction risk 4.1 Methodology The earth is in an “age of ground disturbance” now; presumably, events resulting from abnormal weather caused by global warming will overlap with other events and trends However, short-term and long-term factors can engender different variations of groundwater levels For example, the groundwater level rises temporarily according to local heavy rain Fig Frequency of recent earthquakes in Japan (data from JMA, 2006) Alternatively, groundwater levels can rise slowly over many hours, as in a recent case in which underground structures of Ueno and Tokyo Stations were lifted When local heavy rains increase because of global warming, the groundwater level rises abruptly Accordingly, the possibility of liquefaction might increase not only in coastal zones, but in inland areas also Consequently, global warming presents the risk of exacerbating disasters The following issues are pointed out for foundations and earth structures of coastal land areas that are influenced by a sea level rise attributable to global warming Increased risk to foundations of liquefaction caused by earthquakes is likely Coastal structures’ instability will affect levees, shore protection, and breakwaters Problems resulting from a rising groundwater level, such as diffusion by submersion of soil pollutants that had existed above the groundwater level, and groundwater salinationeegroundwater of high salinity extending inlandeeis likely to occur For that reason, the fluctuation of groundwater levels in coastal zones caused by a sea level rise or climate-change-induced rainfall should be predicted A diagnostic technique of local disaster prevention capabilities must be established considering the fluctuation of groundwater levels Such an impact evaluation of climate change to liquefaction risks in the case of an earthquake has been done for the Tokyo Bay coastal zone Fig Map showing expansion of river brackish water regions on levee embankment materials (Komine, 2007a, b) K Yasuhara et al / Geotextiles and Geomembranes 30 (2012) 24e34 Table Effects on levee embankment materials of the extension of river brackish water regions attributable to sea level rise Region and district Predicted impact on levee embankment materials Hokkaido Strength reduction, increased compression, and enhanced permeability of levee embankment materials are anticipated The main dyke break pattern is expected to include seepage and overtopping failure Kanto and Shin-etsu Deterioration of water permeability of embankment districts materials is expected The main dyke break pattern is expected to include levee body breakage caused by residual water pressure after water seepage into the levee Chugoku district Strength reduction, increased compression, and enhanced permeability of levee embankment materials are expected Seepage and overtopping failure will cause dyke failure Kyushu district Permeability rise and decline and compression increase and decrease might be observed depending on embankment materials Major dyke break patterns are expected to include seepage and overtopping failure and levee body breakage by residual water pressure after water seepage into the levee Impact evaluation was performed as follows: the ground structure was modeled using the soil information database in the object region Then the rise of the groundwater level in coastal zone foundations caused by sea level rise or climate change was predicted using the 2-D unconfined groundwater flow analysis method (Murakami et al., 2005) with finite element method (FEM) Vulnerability assessment was performed using this method in the event of an earthquake for a coastal zone ground affected by the sea level rise Variation of liquefaction risk was computed before and after the sea level rise and climate change A climate unification scenario produced by the Meteorological Agency, RCM20, was used for the assumed rainfall 27 Table Estimates and measures used to assess river levee embankment materials’ vulnerability to rainfall Region and district Predicted impact on levee embankment materials Hokkaido After penetrating into a levee body by rainfall, water drains, creating the possibility of abruptly decreased levee embankment material strength, possibly causing sudden slope failure Devices in drained areas can be regarded as countermeasures Kanto and Shin-etsu After penetrating into a levee body by rainfall, water districts drains The volume considerable shrinkage of river levee embankment materials might decrease the freeboard Additional banking is among the candidate countermeasures Chugoku district The water retention capacity of levee embankment materials is low This low holding capacity renders levees vulnerable to rainfall, thereby engendering their sudden collapse and volumetric shrinkage of slope faces Possible measures include sealing Deterioration of water-holding capacity and strength are especially rapid in the Kagoshima area, where remarkable volumetric shrinkage might occur; it is expected that synthetic measures are especially necessary there Kyushu district The water-holding capacity of levee embankment materials is low This low holding capacity renders levees vulnerable to rainfall, thereby engendering their sudden collapse and volumetric shrinkage of slope faces Possible measures include sealing A rise in ocean water levels raises the groundwater level not only at coastlines but at riversides as well Consequently, the liquefaction risk attributable to the sea level rise increases concomitantly with a site’s proximity to coastal zones and riversides Variation of rainfall resulting from climate change raises groundwater levels in inland regions, where rainfall increases Consequently, liquefaction risk posed by rising groundwater levels increases in inland regions where local heavy rains increase Ground liquefaction caused by earthquakes is a factor increasing the building collapse risk and damage, such as a collapse of building foundations or bridges and ground subsidence, accompanied by the lifting of underground structures such as sewer pipes or a lateral flow of soil Assessment of the grade of effects of climate change on this liquefaction risk is important to elucidate the geological hazards posed by earthquakes in an area Among areas where increased rainfall is expected because of climate change, the areas of Kawasaki and Yokohama between the Tsurumi and Tama Rivers on the Tokyo Bay coastal zone were Fig Assessment of river levee embankment materials’ vulnerability to rainfall (Komine, 2007a, b) Fig Assessment of river levee embankment materials’ vulnerability to rainfall (Komine, 2007a, b) 4.2 Evaluation of variation of liquefaction risk 28 K Yasuhara et al / Geotextiles and Geomembranes 30 (2012) 24e34 weight and fine content of soil, the N-value and GWL Furthermore, L, the seismic shear stress ratio generated during earthquakes, is determined by the seismic intensity, which depends on the ground classification and the earthquake type, and the same information as R Liquefaction occurs when FL, given by Eq (1), is less than 1.0 Evaluation of possible liquefaction through depth in an objective location can be performed by integration of the liquefaction potential, PL, with depth as follows: Table Rank of liquefaction hazard PL PL value Rank < PL < 5 < PL < 15 15 < PL < 25 25 < PL Rank Rank Rank Rank selected as our study object Geological structure modeling was performed for the object region using a ground information database Then, the groundwater level rise in coastal zone areas accompanying a sea level rise or climate change was analyzed using the 2-D unconfined groundwater flow analysis method with FEM The applicability of numerical analysis to the objective region was confirmed in a previous study (Suzuki et al., 2006) The effect of climate change was evaluated (Murakami et al., 2005; Yasuhara et al., 2007) The changes of liquefaction risk before and after the sea level rise and climate change were computed using this procedure Vulnerability assessment was conducted in the event of an earthquake in coastal zone grounds because of the sea level rise The liquefaction hazard at each location was calculated using a method proposed by “The Japanese Highway Bridge Code (JHBC; “Dorokyo-shihousho”)” established by the Japan Road Association in 1980 This judgment procedure is based on the liquefaction resistance factor, FL, defined as FL ¼ R L (1) where R is the cyclic strength ratio determined by the cyclic shear strength of soil and the correction coefficient related to earthquake movement The cyclic shear strength is estimated using the unit Z20 PL ¼ FðzÞwðzÞdz (2) Therein, F(z) is a function that is F(z) ¼ À FL when FL < 1.0 and F(z) ¼ when FL > 1.0 In addition, w(z) is the weighting parameter defined as w(z) ¼ 10.0 À 0.5 Â z (z: GL À m) (Iwasaki et al., 1980) The liquefaction hazard increases concomitantly with the increasing PL value Using the PL value, the liquefaction hazard is categorizable into four ranks as presented in Table The PL value computed using the soil condition including groundwater levels was used for estimating the liquefaction risk The climate unified scenario produced by the Meteorological Agency, RCM20, was used for the assumed rainfall The sea level rise was predicted to be 88 cm by 2100 Fig 8(a) portrays a liquefaction hazard map for the present day; Fig 8(b) shows a liquefaction hazard map incorporating the sea level rise The maps collectively reveal that the liquefaction risk near the coastline is enhanced by the accompanying sea level rise, and that the liquefaction risk is exacerbated in areas near rivers This fact suggests that areas in which the coastal zone ground is influenced by the sea level rise are influenced not only near the coastline, but in river downstream areas along the shore, which are Fig Variation of liquefaction risk (Murakami et al., 2005) K Yasuhara et al / Geotextiles and Geomembranes 30 (2012) 24e34 29 Fig Regions in which the liquefaction risks class changed in Fig 8(a)e(d) (Murakami et al., 2005) affected by tidal floating Fig 8(c) shows a liquefaction hazard map incorporating rainfall: compared with the case of sea level rise only, liquefaction risk has increased more inland than in riverside areas Climate change exerts various effects Furthermore, the sea level rise influences seashore and riversides, as does the variation of inland precipitation Variations of rain intensity and frequency increase in areas of high liquefaction risk In practice, climate change simultaneously alters the sea level rise and rain intensity and frequency Accordingly, Fig 8(d), which shows both effects, is considered to represent the situation of the future best Fig portrays regions in which the liquefaction risk rank changes In the object region, variation of the sea level rise and the increase in rain intensity and frequency caused by climate change will expand the areas facing high liquefaction risk Fig 11 Slope disaster risk map with global warming in Fukuoka (Chen et al., 2007) Risk of slope disaster 5.1 Background Climate change exacerbates geological hazards (Yasuhara, 2008) A worst-case scenario of the effect of global warming shows that, when phenomena attributable to global warming and other phenomena, such as earthquakes, occur concurrently, they might cause unprecedented complex disasters Moreover, they will take place more frequently than at present For instance, the Niigata Chuetsu earthquake in 2004, in which a huge earthquake occurred after a long rain that continued for about one month, is a typical example of a complex disaster (Yasuhara et al., 2007) Unusually strong rainfall continued until immediately before the earthquake Fig 10 Local heavy rain and landslide disaster Fig 12 Model of assumed landslide mode (Chen et al., 2007) Fig 13 Slope disaster risk under each condition (Chen et al., 2007) 30 K Yasuhara et al / Geotextiles and Geomembranes 30 (2012) 24e34 Table Possible adaptation to natural disasters occurring in coastal zones Hazard River flood Adaptation Protection Accommodation Additional banking Water protection work Early warning system and evacuation system Construction of shelter Hazard map Appropriate land use Regulation of land use in hazardous area Insurance Liquefaction Monitoring of GWL Lowering of GWL Additional banking Soil improvement and reinforcement Slope failure Protective pile Geosynthetics reinforcement Early warning system and evacuation system Coastal erosion Seawater protection work Conservation and replanting mangrove forest Early warning system of extreme weather events and evacuation system Evacuation Restriction of development Evacuation from dangerous area Public support for evacuation Hazard map Restriction of Appropriate land land use use Evacuation Regulation of from land use in dangerous hazardous area area Insurance Public support for evacuation Hazard map Restriction of Risk map land use Regulation of Evacuation land use in from hazardous area dangerous Insurance area Public support for evacuation Hazard map Restriction of Risk map wetland use Regulation of Evacuation land use in from hazardous area dangerous Integrated coastal area zone Public management support for Insurance evacuation For that reason, water had accumulated on the slopes of hills and mountains, causing them to collapse easily because of the earthquake’s vibration Then the large earthquake struck, causing landslides in about 4000 locations Fig 10 portrays the increase in the frequency of landslide disasters 5.2 Methodology Abnormal weather resulting from global warming might include increased intensity of typhoons and frequent heavy rains Typhoons and heavy rains engender severe damage to humans and social property (direct economic loss) Heavy rains also cause landslides and economic loss through the effects of slope disasters (indirect economic loss) Predicting these economic losses and proposing measures to investigate the effects of global warming are important Correlation between the magnitude (intensity) of a typhoon and the economic loss ratio (loss/assets) were analyzed An inference-based model of economic loss with respect to the magnitude of a typhoon was established using past data to evaluate the risk of increased economic loss through intensification of typhoons as a result of global warming Moreover, a typhoon-riskcurve preparation method using a Monte Carlo simulation was established based on statistical characteristics of typhoon magnitude The typhoon-risk-curve was inferred, assuming typhoon intensification resulting from global warming It was then compared with the present risk curve An increased risk of economic loss was demonstrated Assessment of the risk of slope disaster by heavy rains because of global warming was done methodically using a process developed by the authors The proposed assessment method of the risk of slope disaster includes a local-range method and a wide-range method according to the range of the assessment object (Chen et al., 2006, 2007, Chen, 2008; Misumi et al., 2008) The localrange method determines the risk of slope disaster considering the compound effect of heavy rains and earthquakes on the object slope For assessment of the risks of landslide disaster nationwide, the wide-range method, the risk of a landslide disaster over a wide area was estimated using a geographic information system (GIS) according to the following procedures a) A hazard map was created to show the landslide probability using a probabilistic landslide estimation method based on rainfall in the fourth mesh of digital national land information b) The economic loss of property because of landslides was evaluated using the estimation method of the asset distribution in the fourth mesh c) The slope disaster risk was computed as the product of the landslide probability and economic loss attributable to the landslide d) Slope disaster risk maps were created in the present climatic conditions and in the assumed climatic conditions of global warming in 2050, 2100, and thereafter The effects of global warming on slope disasters were inferred from a comparison of risk maps before and after global warming The risk of slope disaster and its increase by global warming in Fukuoka in 2050 was inferred based on this method Fig 14 Modified geosynthetic revetments used against rising sea levels, presently used as permeable “wet” structures K Yasuhara et al / Geotextiles and Geomembranes 30 (2012) 24e34 31 Fig 15 Geotextile Wrap around Revetment in Sylt Island, Germany (Courtesy Dr Dette LWI) 5.3 Analytical results for slope disaster risk Analytical results presented in Fig 11 from the above-described example for compound slope disasters in Fukuoka, Japan indicate the following: a) Fig 11 presents the slope disaster risk (product of the collapse probability of a slope and economic loss by collapse) attributable to global warming for Fukuoka Trial calculations were performed for Fukuoka based on these risk data The following results were obtained 1) Slope disaster risk in the present rainfall condition e loss of 36 billion yen/year - Slope disaster risk in the rainfall condition attributable to global warming in 2050 loss of 61.43 billion yen/year - Consequently, the increase in slope disaster risk in Fukuoka posed by global warming is 70.6% - This case study shows that global warming enhances the risk of slope disaster, which underscores the importance of producing a slope recovery plan with a risk index b) An assessment method of slope disaster risk incorporating the compound effect of heavy rains and earthquakes was developed It was then applied to risk evaluation of a collapsed slope in Shikanoshima by the Fukuoka Seihou-oki earthquake in 2005 This earthquake produced a cave-in geography with large deformation in the upper part of a slope The possibility of Fig 16 Example of GWRs constructed in Fiji 32 K Yasuhara et al / Geotextiles and Geomembranes 30 (2012) 24e34 Geotextile tube Local soil fill 6.1 General comments Water forces causing erosion Soil to be protected Scour apron (optional) a Revetments - exposed or submerged Ocean waves Waves break across breakwater Geotextile tube Calm water breakwater Seabed Scour apron b Offshore breakwaters Flood level or storm water level Geotextile tube dyke core c Adaptation against natural disasters in coastal zones What should be done to reduce the geo-disasters described above? Or what can we do? Can we protect ourselves completely from natural disasters? These questions have been addressed to us, engineers, academia and policymakers, since the Great Hanshin earthquake in 1995 severely altered so many human lives and the functions of the infrastructure, particularly in Kobe The concrete answers to them are difficult because we must consider many aspects of the problem to answer these questions Therefore, in this paper, we present only the following general comments: 1) Along with the influences of global environmental issues, including global warming, adaptation strategies against climate change-related natural disasters are classifiable, mainly from the geotechnical point of view, into three categories: protection, accommodation, and evacuation Their contents are presented in Table 2) We must also develop geotechnical engineering techniques that simultaneously satisfy aspects of mitigation of environmental impacts and reduction of geo-disaster severity (Yasuhara, 2007) 6.2 Possibility of application of geosynthetics Developments to be protected Sand covering Scour apron Protection dykes Fig 17 Example of the use of geotubes for protecting the coastal zones (Lawson, 2006) large-scale landslides occurring with future earthquakes and heavy rains is of great concern The magnitudes of potential collapsed slopes were classified for the three cases presented in Fig 12 Expenditures for measures vary widelyeefrom hundreds of millions of yen to billions of yeneebecause of the assumed collapse magnitude Therefore, risk analyses were conducted for the three cases Results are depicted in Fig 13 - The results suggest the following: 1) In the event of an earthquake, rainfall, and an earthquake after rainfall, the risks of surface sliding and mid-depth middlescale sliding become high, but the risk of deep large-scale sliding is slight 2) When rainfall and an earthquake are combined, the risk of mid-depth middle-scale sliding and surface sliding becomes high too, but that of depths of large-scale sliding does not become so high - Therefore, the following were inferred 1) The risk of deep large-scale sliding in Case C is small 2) The risks of surface sliding in Case A and mid-depth middle-scale sliding of Case B are comparable 3) If countermeasure costs are considered, measures against surface sliding, considering a partial mid-depth slide, are the most cost-beneficial This proposal has been adopted for the recovery plan of Fukuoka city Although the severity of the threat varies regionally, rising sea levels’ currently projected magnitude is expected to have great effects on the economic and social development of many countries (IPCC, 2006) Geosynthetic structures are used primarily as shore protection, indicating that the structures will be useful only in the event of a storm or related phenomena Because of their high permeability (geosynthetic and sand), they are not the most convenient option for use in permanent “wet” situations However, modification of geosynthetic structures to produce impermeable structures can be performed In such cases, geosynthetic revetments can provide a countermeasure against rising sea levels Notwithstanding, some modified structures have been used as permanent “wet” structures One example is the “Blue Water Retail and Leisure destination” (Dixon, 1998) (Fig 14) where the GWR was constructed normally, but behind it an impermeable geomembrane was installed to create an impermeable structure Similar structures have been constructed near Shanghai, China (Yan, 1988) Considering the information above, it can be stated that normally used geosynthetic revetments not constitute the best countermeasure against rising sea levels However, if modifications to their structure to transform them into impermeable structures (without reducing their stability) were accomplished, geosynthetic revetments would be a feasible countermeasure against rising sea levels Detailed study and research on this subject is urgently necessary, although fundamental research into the availability of wrap around revetments has already been conducted by Yasuhara and Recio (Yasuhara and Recio-Molina, 2007) Revetments made with geosynthetics offer proven resistance capability according to expected wave conditions that are associated with storms On the island of Sylt, a GWR structure has resisted strong wave conditions and has reduced cliff erosion by more than 10 m compared to coasts that are not protected by GWR installations (Nickels and Heerten, 1996) (Fig 15) Other GWRs constructed in Fiji have performed according to expectations, as presented in Fig 16 As presented in Fig 17 by Lawson (2006), another possible adaptation using geosynthetics is to adopt geotubes for use in protection of coastal zones As presented in Fig 18 by Nickels and K Yasuhara et al / Geotextiles and Geomembranes 30 (2012) 24e34 33 Fig 18 Geotube application against coastal cliffs (Nickels and Heerten, 1996) Fig 19 Geotube used against sandy erosion (Phu Thuan, Thua Thien-Hue, Vietnam) Heerten (1996), geotubes are available for protecting coastal cliffs from erosion Geotubes are also effective for use against erosion of sand beaches in Vietnam(Fig 19) Conclusions Based on the data presented and the subsequent discussions, the following conclusions can be made: 1) Sea level rise caused by global warming expands brackish river water regions, thereby degrading the levee strength 2) Sea level rise and anomalous rainfall raise the groundwater level and expand areas that suffer geotechnical hazards through liquefaction in the event of an earthquake 3) When rainfall and an earthquake are combined, the risk of middepth middle-scale sliding and surface sliding increase too, but the risk of deep large-scale slides does not become so high If countermeasure costs are considered, measures against surface sliding, considering a partial mid-depth slide, are the most cost-beneficial This proposal has been adopted in the recovery plan of Fukuoka city 4) Among possible adaptation measures against climate-changeinduced geo-disasters, geosynthetics are and will be more 34 K Yasuhara et al / Geotextiles and Geomembranes 30 (2012) 24e34 powerful options in the near future for protection of coastal zones Acknowledgement This paper presents a summary of some studies of the Influence of Climate Change on Coastal Infrastructure, which is included in the interim report of the research subject entitled “Comprehensive assessment of climate change impacts to determine the dangerous level of global warming and to determine appropriate stabilization target of atmospheric GHG concentration” (FY2005eFY2009), Ministry of the Environment, Japan The author is deeply indebted to all researchers who have enthusiastically contributed to the progress of this joint research project References Chen G., Zen K., Moriyama S., 2006 Risk analysis of slope disasters in a large area using the GIS Platform In: Proceedings of Recent Development of Geotechnical and Geo-environmental Engineering in Asia, 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Estimation of economic loss from climate- changeinduced natural disasters using GIS Platform In: Proceedings of International Symposium on Mitigation and Adaptation of Climate- change- induced Natural... Soil water characteristic curve and one-dimensional deformation of riverbank soils in Japan In: VietnameJapan Symposium on Mitigation and Adaptation of Climate- ChangeInduced Proceedings of Natural... variation of inland precipitation Variations of rain intensity and frequency increase in areas of high liquefaction risk In practice, climate change simultaneously alters the sea level rise and