The unprecedented heavy rainfall that occurred in western Japan in 2018 caused flooding, inundation, and sediment disasters extending over a wide area, resulting in various types of damage to lifelines, transport systems, diverse structures and so on, and exposing problems that extend across many sectors. One of the major roles of the Japan Society of Civil Engineers is to compile disaster survey data regarding the frequent occurrence of increasingly severe disasters in recent years and then share this information widely with the public. In order to contribute to the development of disaster prevention technologies and academic fields, this special issue is devoted to a collection of reports and preliminary research papers regarding the 2018 heavy rain event in western Japan. Some of the Japanese papers have been translated into English and posted on the Journal of JSCE.
In this study, we detect the detours of commercial vehicles during heavy rains in western Japan using machine learning technology and then analyze the cause of these detours. Due to heavy rains in 2018 in western Japan, road regulation was implemented over a wide area. GPS-generated probe trajectories revealed the detour routes taken. The necessity of taking detours is one of the traffic failures caused by disasters. To identify these detours, a road administrator must visually check and analyze the probe vehicle trajectory, which requires considerable labor. Therefore, in this study, we detected detours during a disaster by learning the probe vehicle trajectory under normal circumstances using a one-class support vector machine (OCSVM). Results of detour detection for Shikoku revealed that vehicles were using distant detour routes even when nearer detour routes were accessible. An analysis of the cause of these detours showed that the “risk” of the traffic failure was one factor.
This paper explores the variation properties of trip generation, trip attraction, intrazonal trips, and travel time under transport network disruption in Tenno district in July 2018 due to landslides. The empirical results obtained by using multiple passive transport data show that (1) traffic volume per hour on the National Route 31 went down to around 300 vehicles at maximum due to a large number of short-distance trips traveling between the affected area and a disaster response base, (2) recovery of the train line did not really reduce the travel time on the National Route 31, and the average travel time had been 1.5 times longer compared to that before the disaster for more than two months after the disaster, and (3) travel time variability, which could not be explained by day of week and time of day, had been dominant for the first one month after the disaster.
This study presents the characteristics of disaster-related meteorological information and evacuation protocol based on a case study of the heavy-rain event of July 2018. By clarifying their characteristics, this enables us to obtain policy implications for municipalities and residents to respond appropriately to imminent heavy-rain hazards. As a result, it was found that many municipalities did not issue the evacuation preparation protocol. In addition, the proportion of residents who received the evacuation protocol in the order of the evacuation preparation, the advisory, and the order, was less than 50% of the residents targeted by the order. Moreover, the national government recommends that municipalities should associate their issuance of evacuation protocol with the meteorological information; however, there were differences in the utilization of the meteorological information between the municipalities.
Due to heavy rains in July 2018, many sediment disasters occurred in western Japan. Not only were there direct damage caused by debris flows, such as destructed buildings, but some places several kilometers downstream from the landslides and debris flows also experienced flooding that lasted several hours and sediment deposition from the rivers. In this study, we focused on Tennou, Kure City in Hiroshima Prefecture, aimed to study the disaster situation in detail, and applied simulations. In Tennou, debris flows occurred and large boulders moved upstream. Sediment movement occurred but did not cause flooding outside the midstream river. Deposition and flooding occurred outside the downstream river. Downstream, deposition occurred at the upstream side of the box culvert but did not occur downstream; thus, it was assumed that blocking due to sediment occurred at the culvert. In the simulations, we considered the culvert blocking, and also considered sediment runoff continuing for many hours, which was different from short-time debris flow. From the simulation results, the flooding and deposition outside the river first occurred at the blocked culvert point. However, as the runoff continued, the riverbed rising from deposition became larger in the upstream side. Flooding and deposition outside the river also occurred in the upstream area from the culvert.
The heavy rain in July 2018 led to debris flows in mountainous residential areas, causing severe damage in western Japan. In Japan, mountainous streams where debris flows originate from the valley exit are often concealed by culverts upstream of the residential areas. Therefore, during the disasters that occurred in Kobe City and Hiroshima City due to the heavy rain in July 2018, culverts that existed upstream of the residential area were blocked by sediment, and debris flows moved down along the roads connected to the culverts. Furthermore, the slopes of the roads were steep, and debris flow in Kobe showed high mobility owing to the presence of fine sediment from the deposited granite sediment layer. Therefore, sediment extensively encroached into the residential areas. In this study, we aimed to analyze the disaster situation focusing on culverts and roads existing in residential areas based on field surveys. We conducted numerical simulations by applying a high-resolution digital elevation model (DEM) and digital surface model (DSM) to describe the disaster scenario. From simulation results, applying DSM in residential area described the disaster situation better than DEM. Furthermore, we considered disaster mitigation planning and proposed safe landuse in residential areas based on the simulation results.
In an extreme climate event named “the Heavy Rain Event of July 2018, ” prolonged and widespread heavy rainfall in western Japan caused several debris flows, which led the sediment to flow into rivers, causing further damage from sediment-flood inundation. For the existing landslide alert information, it is important to establish prediction methods that account for the amount of rainfall on individual mountain slopes and the topographic and geological information. The estimation of the probability of debris flow initiation and quantitative risk assessment have been challenging issues. In order to solve this problem, in this paper, the rainfall data of XRAIN with high spatial resolution and the features of the slope failure sites were examined during heavy rainfall events. This paper also discussed the reliability of rainfall index 𝑅' to the heavy rainfall with strong long-term precipitation in July 2018, which is different from previous disasters due to the heavy rainfall with strong short-term precipitation, such as those in August 2014 and June 1999.
The heavy rain in July 2018 caused huge damage in the west Japan area, including Hiroshima, Okayama, Ehime, and Yamaguchi. Noro-gawa River basin in Hiroshima Prefecture was also damaged by the heavy rain. This disaster was typical of complex heavy rain coupled with sedimentation and river flooding, which is peculiar to Hiroshima Prefecture. This paper reports the influence of sedimentations and driftwoods on Noro-gawa dam and on river flooding in the downstream region of Noro-gawa River.
The main results of this paper are summarized as follows: 1) The damage in Noro-gawa dam, Noro-gawa River, and Nakahata-gawa River was enhanced by the accumulation of sedimentations and driftwoods. On the other hand, the river blockage by driftwoods at the bridge in Nakahata-gawa River induced the flooding. 2) The estimated maximum inflow discharge to Noro-gawa dam and outflow discharge from Noro-gawa dam were 179 m3/s and 173 m3/s, respectively. 3) The inflow discharge to Noro-gawa dam was estimated, excluding the influence of sediment discharge and driftwoods. 4) The estimated river discharges during the flooding were 180 m3/s at the downstream side of Noro-gawa dam, 230 m3/s at Fujinami water level observation station, and 430 m3/s behind the connection points of two branch rivers.
This paper presents an analysis of reflection and transmission coefficients as boundary element solutions of guided Lamb wave scattering in a two-dimensional, isotropic, and linear elastic layered plate. A scatterer, defined as a debonding, is located on the interface between layers. The numerical model is formulated based on the boundary element method with elastodynamic traction and displacement fundamental solutions in frequency domain, where the boundary integral equations, including artificial boundaries, are discretized with constant elements. Lamb wave modal functions in each layer can be calculated by using the partial wave technique. Wave fields on the artificial boundaries, which are set long enough from the debonding to neglect near-field evanescent scattering modes, are treated as the superposition of incident wave and possible scattered waves. Then, the traction boundary condition on the artificial boundary can be expressed by unknown total displacement fields. In addition to the artificial boundary condition, the continuity condition of layer interface and the traction-free boundary conditions yield a system of linear equations that can be solved by the efficient indirect solver. The reflection and transmission coefficients are obtained from the total displacement fields after solving the system of linear equations. Various configurations of problems, including materials and length of the debonding are considered. Furthermore, the mode conversion and resonance phenomena of scattering coefficients can be seen directly related to the length of the debonding.
The authors intend to clarify the swimming ability of the natural sweetfish (Plecoglossus altivelis altivelis) fingerlings during the initial period of its upstream river migration in the field. The critical swimming speed (CSS) of the natural sweetfish was measured in a small channel with a rectangular cross section under an average cross-sectional water flow velocity of 9–75 cm/s. The body length of the natural sweetfish fingerlings ranged from 5.9cm to 9.9 cm (the mean body length was 7.5 cm, and the number of fishes was 50). The following results were obtained: (1) The CSS, measured for a duration of 60 min, ranged from 19 to 61 cm/s, and a positive correlation was observed between the CSS and the body length. A regression formula between the 60-min CSS and body length was obtained. (2) The ratio of the CSS and the body length was 3.1–8.0 (that is, the distance travelled per second based on the body length), and the mean ratio of the CSS and the body length was 4.7 times (the standard deviation was 1.1).
The fender is part of the ancillary equipment of mooring facilities and plays an important role in safe vessel berthing and smooth cargo handling. If fenders are damaged, economic loss will occur due to the suspension of service or restriction of operation of the mooring facility, and the operation and maintenance of the entire facility may be affected. Since fenders are used for a long time, it is necessary to ensure their durability. In 2002, the International Navigation Association (PIANC) published the “Guidelines for the Design of Fender System” and proposed a new method for confirming the durability of rubber fenders. In Japan, in 2010, consistent with the PIANC guidelines, a description of the durability of rubber fenders was added to the Standard Specifications for Port and Harbour Works of the Ports and Harbours Bureau of the Ministry of Land, Infrastructure, Transport and Tourism. In this study, the data of durability tests conducted by rubber fender manufacturers were statistically analyzed. From the results of the durability tests, a longterm performance criterion for rubber fenders was proposed.
Wigner and Choi-Williams distributions produce increased time-frequency resolution and are applied to obtain the time-frequency distributions for tsunamis. In this study, a chirp signal was analyzed to examine the performance of the Wigner distribution. The Choi-Williams distribution, which suppresses the cross terms, was applied to estimate the time-frequency distributions for tsunamis. The distribution for the tsunami waveform observed at Susaki, Kochi Prefecture showed that variations in the natural time periods at Susaki Bay were predominant and the maximum peak of the time-varying spectrum appeared about 80 minutes after the first tsunami wave arrived. The decay relation of the tsunamis was theoretically estimated using a wave energy equation with the rate of dissipation due to bottom friction and turbulence. A Talbot formula was obtained as the relationship of tsunami decay with time and its applicability was verified.
Information of surface water is necessary for flood disaster mitigation and the hydrological cycle studies. Normalized Differential Frequency Index (NDFI) was calculated by multiple microwave radiometers GMI and AMSR2 to produce a daily and 0.1-degree global surface water map for five years (2013–2017). Diurnal variation and bias between sensors in NDFI were adjusted. The basic performance of the surface water map was tested with global datasets. The five-year average NDFI and inundation ratio by Global Surface Water showed very high correlation around Japan. Monthly variation in NDFI and inundation ratio by Yesterday’s Earth at EORC showed positive correlation along some large river channels. NDFI showed a sudden increase at daily scale in some dry areas where daily variation in NDFI and antecedent precipitation index had positive correlation. These indicate that the increase in NDFI could be caused by inland water inundation rather than flood inundation.
In Japan, great damage to abutment backfills caused by large-scale floods occurs every year. It is necessary to examine the fundamental collapse mechanism on as close to full scale as possible, in order to achieve a sufficient effect of the similarity laws in geotechnical engineering, river engineering, and bridge engineering. In this study, geotechnical evaluations were carried out, such as observation of pore water pressure behavior in an embankment, settlement of an embankment crest, and applicability of a reinforced soil wall as a countermeasure construction, under conditions affected by flowing water. The results show that the collapse behavior of an embankment surface differs depending on the soil properties of the embankment material. The erosion of the river bed progressed even in the footing lower surface of the abutment foundation and in the upstream side of the abutment, where the flow velocity was locally large and changes in the flow direction were confirmed. In addition, when a gabion-reinforced earth wall with water permeability was used for the wall surface construction as a countermeasure, washout of the embankment in the abutment to the extent that a pavement surface above would collapse did not occur, thereby confirming the gabion’s usefulness as a countermeasure.
The Partial Floating Sheet-pile (PFS) method is a method used to install sheet-piles near the toe of an embankment to inhibit the settling of the embankment built on soft clay ground. This method combines partially floating sheet-piles and end-bearing sheet-piles. Originally, the PFS method was developed as an anti-subsidence countermeasure by the weight of a river embankment built on soft clay ground in a residential area. The PFS method could be effective against soil deformation caused by consolidation and liquefaction during the 2016 Kumamoto earthquake. However, quantitative discussions are still needed to clarify its effectiveness against liquefaction. Therefore, the authors carried out numerical analyses using LIQCA3D17 to evaluate the effectiveness of the PFS method quantitatively. As a result, the interval between the end-bearing sheet-piles was found to be an important factor for embankment settlement, and the installation of the end-bearing sheet-piles alternately could be reasonable.
The author proposed a city model for Burmese capital cities based on the analysis of the spatial structure of Mandalay, the last capital city of the Burmese kingdom1). This paper discusses the applicability of the Burmese city model to other historical capital cities of the Burmese kingdom.
This research first examines and discusses the spatial structure of the historical capital cities of the Burmese kingdom from documents, maps, and satellite imagery in terms of shape, orientation, size, land use, and disposition of important devices. The historical capital cities dealt with, from the oldest to the newest are: 1) Sri Ksetra, 2) Bagan, 3) Toungoo, 4) Pegu, 5) Shwebo, 6) Inwa (Ava), 7) Amarapura, and 8) Mandalay. Most of the capital cities were rectangular- or square-shaped with a moat; in most cases they were aligned to the four directions; and that the size of the walled city ranged between 1 to a little less than 2 km on each side.
It can be seen from the analysis that the city model proposed for Mandalay may be applicable to the capital cities of Inwa and Amarapura in several aspects, including the square or rectangular shape of the capital city surrounded by a moat, and basically three gates on each side and the eastward orientation. In close scrutiny of Burmese historical capital cities, there is yet another model with five gates on each side instead of the three on each side as in Mandalay. The proposed Burma models are to be positioned as subsidiary models of the ancient India model.
The authors have investigated the soundness evaluation of existing reinforced concrete (RC) slabs supported by girders using deflection at a loading point and an integrated deflection area through falling weight deflectometer (FWD) tests. In FWD tests, an asphalt concrete layer deforms locally around a loading point under an impact load. The deflection of RC slabs thus needs to be determined with an appropriate correction method. This study proposes an equation to determine the average temperature of asphalt concrete layer using a regression analysis with measured results. The results show that the proposed equation can accurately predict the average temperature by incorporating a one-hour difference in asphalt concrete surface temperature. Furthermore, the correction method of deflection using the average temperature during FWD tests proposed was analytically verified for asphalt concrete layers with temperature gradients throughout the depth. The influence of temperature gradients in correcting the deflection was also noted to be small and the previously proposed correction method was applicable to determine the deflection of RC slabs in FWD tests.
Two types of transformants with different drug resistance were developed from the phenol-oxidizing bacterium, Cupriavidus sp. KN1. The first transformant is Cupriavidus sp. KN1-TGF that has green fluorescence and tetracycline resistance. The second transformant is Cupriavidus sp. KN1-KRF that has red fluorescence and kanamycin resistance. These two strains can be selectively colonized with antibioticcontaining media, and they can be also distinguished by fluorescent color. First, Cupriavidus sp. KN1-TGF cells remaining after predation with the flagellate, Spumella sp. TGKK2, were mixed with Cupriavidus sp. KN1-KRF that did not contact with the flagellate TGKK2 to investigate the change in characteristics for the protistan predation. As a result, Cupriavidus sp. KN1-KRF was preferentially predated. On the other hand, Cupriavidus sp. KN1-TGF in the same tube was relatively resistant to predation. Similar phenomena were observed when the conditions of these two strains were reversed. Next, two complete mixing reactors connected in series were operated. Bacteria were cultured in the first reactor, and the protistan predation was made in the second reactor. Two runs were operated, one with Cupriavidus sp. KN1-TGF and the other with Cupriavidus sp. KN1-KRF. Then the first reactor effluent that contains Cupriavidus sp. KN1-KRF was mixed with the second reactor effluent that contains residual Cupriavidus sp. KN1-TGF and the flagellate TGKK2 in a tube. The cells of Cupriavidus sp. KN1-KRF not in contact with the protist were preferentially predated. This phenomenon was similarly confirmed by combinatorial inversion that Cupriavidus sp. KN1-TGF from the first reactor was mixed with Cupriavidus sp. KN1-KRF from the second reactor.
Activated sludge method is a wastewater treatment technique used for removing organic matter from sewage using biological floc. It is a widely used low-cost and environmentally friendly method for sewage treatment. However, this method is not suitable for treating high-concentration wastewater since it is often necessary to perform physicochemical pretreatment, such as dilution with water, pressure floatation treatment, or chemical treatment. This study aims to biologically treat high-concentration wastewater using a suitably selected soil bacteria. The soil bacteria adopted in this study were separated and cultured from the soil collected in Okinawa Prefecture in 2012. The base sequence was then determined, and the homology search was performed by the Basic Local Alignment Search Tool of the DNA Data Base of Japan. It was found to be a soil bacterium called Agrobacterium Tumefaciens by 99% homology. When Agrobacterium Tumefaciens was directly used to treat high-concentration wastewater, it caused sludge bulking, and its treatment capacity was low and the chemical oxygen demand value found using chemiluminescence detection of permanganate index (CODMn) was unstable. However, there was no outflow of bacteria from the inside of the inclusion when Agrobacterium Tumefaciens were inclusively immobilized by the sodium alginate-acrylamide method, which suggested that the sludge volume could be reduced. The CODMn concentration of the artificial sewage added was 1500 mg/L, which was exponentially attenuated, and a high removal rate of 96% was observed 12 hours after the start of treatment. Furthermore, the allowable design value for the volumetric load is 3CODMn-kg/m3 per day, and thus the compactification of wastewater treatment facility should be possible. These findings have proved the significance of the treatment method proposed in this article in the field of excluded facilities for the purpose of high-concentration wastewater treatment owing to its cost reduction and downscaled treatment facility advantages.