The landslide phenomenon is a natural disaster directly affected the development of mountainous areas in general to the traffic and transportation sector particularly. However, it can easily recognize that the responding in face to this dangerous phenomenon current in Vietnam seems to be quite passive. One of reason is materials for detailed instruction or specific regulation of complicated caught up with the world technology development. National Standard namely “The landslide prevention engineering on road-Requirements for investigation and design”, code TCVN9861:2013 issued in 2013 has been the only National Standard for instruction and legally compulsion on survey and design research of landslide prevention works in Vietnam so far. This Standard has been developed for landslide research under corridor along transport arteries, on the other hand, it is also considered as general application material for landslide prevention research in Vietnam. This paper focuses on summarizing content in National Standard namely “The Landslide prevention engineering on road-Requirements for investigation and design”, assessment some limited and proposing some approaches to build up and complete guideline and standard system for more efficient and effective landslide risk prevention works in Vietnam.

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In Vietnam, landslide disasters frequently occur in connection with rapid infrastructure construction. However, few research reports have discussed landslides in Vietnam to date. Particularly, very few if any studies address Vietnam comprehensively. This deficit has hindered sufficient responses to landslide disasters, has delayed development construction, has increased economic liability, and has even affected people’s safety. This report extracts common causes of numerous landslide disasters and discusses landslide mechanisms based on landslide sur veys in various parts of Vietnam. Consequently, landslide activities in landslide disasters in Vietnam are classified according to geological features, geology, and weathering. Moreover, the relation between construction works and landslide occurrence is discussed with respect to a mechanism.

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Along the Ho Chi Minh Road of the Laotian border at the central zone of Vietnam, traffic activities stop by the disasters of many landslides in wet season. A degree of risk evaluation and the construction of the preventive measures are necessary to prevent these landslide disasters. It is necessary to execute pattern recognition of different type classification of landslides having a various moving style, but the analysis of this type classification is affected by various factors having fuzzy natures such as geological feature conditions. Therefore, we examine the analysis method of landslide type classification in consideration of the fuzzy natures. We show that weathering of the ground, a geological feature and landslide scale are important factors through this analysis and the proposed method is the high technique of analysis precision and the field application.

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Landslide is considered as one of the hazardous phenomenon that often occurs in the mountainous region of center area of Vietnam. The prediction of land sliding sensitivty for mitigation should be requireed by fact. This paper focuses on the spatial analysis of landslide susceptibility in this area. For analyse landslide related causative factor maps are derived such as slope angle, type of rock, fault density, distance to the road, land use and precipitation. Landslide causative factor maps were created using GIS, in which each one was alocated in to classes. An analytical hierarchical process is used to combine these maps for landslide susceptibility mapping. As the results, a landslide susceptibility zonation map with 4 landslide susceptibility classes, i.e low, moderate, high and very high susceptibility for potential landslid, is derived based on the inventory map of observed landslide since 2006 to 2013. The landslide susceptibility map indicates that 82.66% total number of occurred landslides, which have been reported fall into highly and very highly susceptible zone. Even there was limited matter concerning relevant, scale and available data, the landslide susceptibility map of this study for corridor along this road is credible for landslide mitigation.

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In the central provinces of Vietnam, the frequency and severity of landslide events are apparently rising. The events cause substantial property damage, traffic disruption, fatalities along transport arteries and severely affect living conditions. However, in spite of the severe hazardous conditions no potential database of landslide exists. First, the authors clarified the distribution of landslide related phenomena by aerial photographic interpretation. Secondly, the authors’ field investigations revealed characteristics and tendencies of landslide movement with special reference to geologic types. Thirdly, the authors assessed the possibility of risk assessment using landslide mapping. The 685 large-scale landslide topographies were identified in six topographical map areas on a scale of 1:25,000. The data was transferred to GIS to create an inventory. The movement types and the spatial distribution of the landslide topographic area are related clearly to their geology, geological structure, and weathering features. Risk evaluation using an AHP approach also applies to each landslide unit. However, some limits of application were apparent there.

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In order to reduce the landslide disaster which occurs in the area along the artery such as national roads, it is important to clarify distribution of landslide topographic feature. However, is too small, or the accuracy of a topographical map is not sometimes necessarily suitable. Moreover, when taking an aerial photo newly, very big cost may start. There are never many countries which an aerial photo is taken repeatedly and it can purchase freely and cheaply at a rate once in ten years like Japan. From last year, based on the picture of millions of sheets which ALOS photoed, 5m mesh DSM (ALOS W3Ddata) and ortho data in the world are fixed, and it can purchase now. Then, for the National Route 7 of central Vietnam, the contour line was created from the DSM data and the topographical map was created. We decided to find out landslide topographic features by deciphering the contour line of this topographical map. As a result, 1000 or more landslide topographic features were able to be checked. It will be evaluated what kind of potential disaster vulnerability this landslide feature will have from now on.

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The author likes to try to think how estimates the slip plane structure in 3 dimensional image without borings. The contents of this paper are summarized as follows. (1) A landslide is a three-dimensional phenomenon. It is therefore important to read aerial photographs and topographic maps, imagining their three-dimensional appearance. (2) A slip plane is assumed to be present at the landslide body boundary in the landslide topography. This assists deduction of a slip-plane structure to some extent from a landslide body boundary. For example, the contour of a cliff can be understood as the extension of a slip plane. (3) Various phenomena such as cracks tend to occur at places where relative displacement - relative displacement rate varies, such as at a landslide body boundary. Places where a slip plane lies shallow are candidates for cracks because the relative displacement rate varies easily there. (4) Various phenomena such as cracks, depressions, and lift ups, are also apt to occur at places where the traveling speed of a slide varies (the uneven part of a slip plane).

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We obtained digital surface models (DSMs) and orthophotos for two periods, 1978 and 2015, from the lower reaches of the Nakama River in Iriomote Island, Taketomicho, Yaeyama District, Okinawa Prefecture, Japan, by processing aerial photographs captured from an aircraft or small unmanned aerial systems (sUASs) with the Structure from Motion–Multiview Stereo (SfM-MVS) program. From the data, we extracted the range of the mangrove forests that were considered to have been destroyed and felled by typhoons in 2006 and 2007. Furthermore, we verified the existence of a wide area in which the growth of mangrove forests as well as their crowns had declined during a 37- year period beginning in 1978. A high-definition DSM could be obtained for any period at a low cost through the preparation of DSMs using SfM–MVS and sUASs. It was therefore possible to elucidate a change in ground surface conditions between the two periods.

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