HGG12-01

Japan Geoscience Union Meeting 2016

Formation factors of the 2015 Kanto-Tohoku heavy rainfall and its correspondences and NWP
results of the JMA*Teruyuki Kato1, Hiroshige Tsuguti1, Naoko Kitabatake1
1.Meteorological Research InstituteIn the 2015 Kanto-Tohoku heavy rainfall, 48-hourly accumulated rainfall amounts until 21 JST (= 9hours + UTC) on 10 Sep. exceeded 500 mm in the northern part of Tochigi Prefecture, and thatexceeding 300 mm was also observed in the southern part, which caused the collapse of an embankmentof Kinu River in Joso City, Ibaraki Prefecture around 13 JST on 10 Sep. The Japan Meteorological
Agency (JMA) alerted emergency warning at 0020JST on 10 Sep. for whole the region of Tochigi
Prefecture and at 0745JST for Ibaraki Prefecture. For Kinu River, the information of overflowing
occurrence was alerted for Kinu River at 0630JST on 10 Sep. In Tohoku area, 24-hourly accumulated
rainfall amounts until 09 JST on 11 Sep. exceeded 300 mm around Ohsaki City, Miyagi Prefecture,
which caused the collapse of an embankment of Shibui River around 07 JST on 11 Sep. JMA also
alerted emergency warning at 0320JST on 11 Sep. for whole the region of Miyagi Prefecture.
In the heavy rainfall in Kanto area, many band-shaped precipitation systems (BPSs) with the widthof 20~30 km and the length of about 100 km successively formed to organize a huge rainfall areawith the width of 100~200 km that extended over 500 km in a south-north direction. The formationand maintenance factors of the huge extending rainfall area could be that atmospheric conditions
favorable for BPS formation (Kato 2015; 2016) maintained over Kanto area. These conditions were
produced by the continuous inflow of low-level humid air to Kanto area that was initiated from thesurrounding of Typhoon 1517 and was directed northwestward to the low pressure in the Sea of Japanchanged from Severe Tropical Storm 1518. It also influenced the conditions that Kanto area was
located between a deep pressure trough over western Japan and a sharp pressure ridge around
Hokkaido. The heavy rainfall in Miyagi Prefecture was also caused by several BPSs.
The maximum 24-hourly accumulated rainfall amount (R24max) of 605 mm was analyzed in northern Kanto
until 12 JST on 10 Sep. Here, numerical weather predictions (NWP) are evaluated based on thisvalue. The JMA global model (horizontal resolution: 20 km) with initial conditions at 09 JST on 9
Sep. predicted R24max of 165 mm in northern Kanto, but not any extending rainfall area. On theother hand, the JMA mesoscale model (horizontal resolution: 5km) with initial conditions at 12 JST
on 9 Sep. predicted a south-north extending rainfall area in Tochigi Prefecture and R24max of 447
mm close to analyzed rainfall amounts. The location of the extending rainfall area predicted by themesoscale model moved in northern Kanto for different initial conditions, and the predicted Rmax24
ranged between 300 and 500 mm. The mesoscale model, however, predicted the extended rainfall area
between eastern Gunma Prefecture and Tochigi Prefecture before 24 hours (initial: 21 JST on 8
Sep.), and could indicate high potential to BPS formation in northern Kanto before further 12 hours(initial: 12 JST 8 Sep.) that was estimated from atmospheric conditions favorable for BPS formation(Kato 2016).
Keywords: heavy rainfall, band-shaped precipitation system, numerical prediction©2016. Japan Geoscience Union. All Right Reserved.

- HGG12-01 -HGG12-02

Japan Geoscience Union Meeting 2016

Estimation of Catchment Averaged Extreme Rainfall in Kinu River*Shigenobu Tanaka1
1.Disaster Prevention Research Institute, Kyoto University
The Kinu river, which is a tributary of the Tone river, runs from Tochigi prefecture to Ibaragi
prefecture. The Kinu river basin was devastated by the 2015 Kanto-Tohoku torrential rainfall. Heavyrain continued along narrow area between the typhoon 17 and the extratropical cyclone reduced fromtyphoon 18 and the cumulative rainfall reached 500mm at upstream of the basin. This heavy raincaused a breach at the left bank in Joso city and then devastating inundation. Rescue activities
with helicopters were broadcasted many times.
This paper shows extreme analysis on several durations of catchment averaged rainfall at Ishii
reference point of the Kinu river. While Annual Maximum Series(AMS) analysis has been usuallyemployed so far, the author also uses Peaks Over Threshold(POT) analysis. POT with a thresholdlarge enough can be analyzed with generalized Pareto distribution(GP) which includes Exponential
distribution(Exp) as its special case of shape parameter is equal to zero. Generalized Extreme
Value distribution(GEV) and Gumbel distribution which is a special case of GEV with shape parameteris zero for AMS correspond to GP and Exp for POT. When AMS and POT are compared, the Poissonprocess is assumed for the occurrence of POT.
Rainfall data of 15 rain gages of both Ministry of Land, Infrastructure, Transport and Tourism andJapan Meteorological Agency in and around the Kinu river basin are used to calculate the catchment
averaged hourly rainfall. The data from 1979 to 2015 were collected and processed with Thiessen
poligons. Analyzed rainfall durations are 6, 12, 18, 24, 48, 72 hours and 1, 2, 3 days. In order tocheck stationarity in AMS of all durations, Mann-Kendall test was employed and the result showed
all time series are stationary with significant level of 5% but slightly in increasing trend.
Several methods for selecting threshold have been proposed. One of them is to use Sample Mean
Excess Function(SMEF) which is based on the characteristics that the mean of threshold excess ofExponential distribution is constant for varying threshold. Thus the thresholds of POT of every
duration were set to 48, 64, 75, 80, 85, 98, 67, 80, 94mm respectively with drawing SMEF. The
sample size of POT with these thresholds became 69, 77, 78, 82, 96, 88, 86, 95, 88 and more than
twice of AMS except for 6h. The parameters of the four distributions were estimated with L-moment
method. The estimated Exp and Gumbel have almost same return levels in the extrapolating range
while three parameter distributions such as GEV and GP shows different extreme estimations.
When these four distributions are compared with each other, several points should be noted that
1)POT uses just threshold excess and does not care about smaller data than threshold which may
appear in AMS, 2)three parameter distribution such as GEV and GP uses skewness but two parameter
distribution Gumbel and Exp does not, that is, the former will bend(with upper bound or with thicktail) on Gumbel probability paper but the latter will be in straight line.
The patterns of estimated distributions are classified as 1)for short durations such as 6h and 12h,
Gumbel, Exp and GP have almost same extrapolations but just GEV has upper bound, 2)for 18h and 1
day, Gumble, Exp and GEV are almost same but just GP has thick tail, 3)for other durations, Gumbeland Exp are almost same but GEV and GP have thick tails.
The event of 2015 is the historical record from 1979 in the time series of AMS for each duration
except for 6h and 12h,. However, corresponding plots are located around estimated distributions on
the Gumbel probability paper and not unprecedented, namely “outlier”. Their return periods are
estimated to be 50 to 100 years. Comparing to the result for 1979 to 2014, some of fitted GEVchanged from having upper bound to having thick tail. The 100 year return levels of Gumbel for each©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

durations are about 30mm larger than that of 1979 to 2015.
Keywords: Kinu river, 2015 Kanto-Tohoku Torrential Rain, POT Analysis©2016. Japan Geoscience Union. All Right Reserved.

- HGG12-02 -HGG12-03

Japan Geoscience Union Meeting 2016

The levee-breaching and scoured region characteristics of the Kinugawa River and somerivers in Ibaraki Prefecture at Kanto& Tohoku heavy rain in September 2015
*Norio Tanaka1, Junji Yagisawa1, Yoshiya Igarashi1, Genya Yamagishi1
1.Saitama University
To clarify the levee breaching process at large flood event is very important for flood protection
and mitigation countermeasures. Especially, scoured characteristics at levee toe by overflowing
water from embankment is closely related to the enlargement of the breaching length and total flood
volume to the hinterland. At the breaching point of the Kinugawa River in Kanto& Tohoku heavy rainin September 2015, very complex scoured region was generated. The scouring process is supposed tobe related to the ratio of overflowing water depth and levee height, and breaching length instreamwise direction. The objective of this study is to elucidate the breaching phenomena not only
for the Kinugawa River but other rivers in Ibaraki Pref., Miyato River, Nishinizure River, andHachikenbori River, and relates the breaching length and the depth of the scoured region with thehydraulic parameters.
For the objective, post flood survey and flume experiment were conducted after the September flood.
The characteristics of the breaching is that the overflowing water depth is small compared with thelevee height, and half of the levee is scoured before breaching. The condition was set in a flumewith 1/100 scale with two wooden levee. The levee shape were selected as the full shape and thehalf-scoured levee shape. Clear water scour condition was set at the downstream of the levee, andthe scoured characteristics were measured.
The number of scoured region for the two-type levee condition were around 6, and is similar to theactual situation at the breaching point of the Kinugawa River. The scoured depth for half scoured
levee shape was 1.5-1.8 times larger for full-size embankment case. The breaching widths for
Miyato, Nishinizure, and Hachikenbori River, were relatively small, but was similar to the initialbreaching width of the Kinugawa River. Initial breaching width is assumed to be closely related tothe embankment height, but final breaching width is related to the flood duration, thus it isrelated to the river width.
Keywords: levee breach, scoured region, back water effect©2016. Japan Geoscience Union. All Right Reserved.

- HGG12-03 -HGG12-04

Japan Geoscience Union Meeting 2016

Topographic changes of Kinugawa Lowland caused by the flood in September, 2015, Joso City,
Ibaraki Prefecture*Atsuto Izumida1, Shoichiro Uchiyama2, Toshihiko Sugai1
1.Department of Natural Environmental Studies, Institute of Environmental Studies, Graduate Schoolof Frontier Science, The University of Tokyo, 2.National Research Institute for Earth Science andDisaster Prevention
The banks of the Kinu River were damaged by the 2015 heavy rain, with seven overtopping points andone bank breachment point. In this study, we researched the relationship of topographic changes andflood deposits around the bank breachment point in Misaka town, Joso city, Ibaraki prefecture.
Also, we researched the sediment at an overtopping point in Wakamiyado, 4 km upstream of the Misaka
town to make a comparison.
The Kinu River is one of the major rivers in the Kanto Plain and is a tributary of Tone River now,
but originally was an independent river flowing to the Pacific Ocean. Research areas are located in
the lower part of the present the Kinu River. In this region the Kinu River flows in the westernedge of an alluvial lowland, which is 4 - 5 km wide in east and west, limited by Pleistocene
terraces and is elongated in north and south direction. Misaka town is located on natural levees of
the Kinu River, and river bank dunes are developed at Wakamiyado.
After the flood occurred, surveying of the crevasse topography was conducted using a total station
and GNSS with VRS corrections to draw cross sections. 5 m mesh DEM (served by GSI) was used to draw
ones of original topography, too. In laboratory, grain size distributions were measured withSHIMADZU, SALD-3000S, a laser diffraction particle size analyzer. Particle size analysis was
carried out in both location, but surveying was conducted only in Misaka town.
In bank breachment area, pool rags with more than 2 m depth were formed in the center path of theflood. Over 150 m along the downstream path of the flood erosive process was prior, and theelevation was lowered by 30 –40 cm, although flood sediment was deposited by 5 –30 cm in thickness.
The deposit was generally divided into two parts. The lower part consisted of upward coarsening
muddy fine to very fine sand, and the upper part well sorted medium sand.
The figure shows the relationship between topographic changes and grain sizes of flood deposits inside path. Erosive interval was limited close to the collapsed bank, and topographic changes was
small downstream of its path. The surface sediment in this interval was muddy sand, whilesubsurface sediment was finer, probably containing some field soil. A lobe-shaped depositional
landform which had a sharp edge with 30 –40 cm height was formed halfway in the path. The thicknessof the lobe sand was over 60 cm, and it had parallel or cross lamination. A muddy sand bed existed
between the lobe sand and the original field soil.
General succession of flood deposits, lower muddy fine sand and upper well sorted medium sand, may
reflect transportation order of flood deposits, namely, bank body or original ground of pool rags,
or suspension materials in flood water may be the sources of the early fine particles, and that oflater medium sand may be river bed sand.
At the overtopping point of Wakamiyado, we gathered surface and subsurface (20 cm) flood deposits
and measured their particle size with SALD-3000S. In both depths the median particle size was ca.
500 –800 μm, and they were well sorted. The median size of sand at a sand bar in the river channel
there was ca. 700 μm, so this sand may be transported outside the channel. However, it is possiblethat sand of river bank dunes was redeposited by the flood.
There was a difference in the amount of fine particles between the two regions. It probably is due
to occurrence of bank collapse or forming of pool rags, although investigation of Wakamiyado may be©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

insufficient.
It is rare to be able to research original topography formed by the flood. Moreover, this study canhelp consideration on developing processes of floodplain because formation of crevasse splays andcrevasse channels may trigger channel avulsion and formation of natural levee. In other words, thisflood event might be an elementary process of floodplain development.
Keywords: the 2015 heavy rain, Crevasse splay, Inundation by river water©2016. Japan Geoscience Union. All Right Reserved.

- HGG12-04 -HGG12-05

Japan Geoscience Union Meeting 2016

Relationship between flood and landform in Shimotsuma City
*Mamoru Koarai1, Kazuya Yasuhara2, Satoshi Murakami3
1.Earth Science course, College of Science, Ibaraki University, 2.Honorary Professor, Ibaraki
University , 3.Civil Ebginnering, College of Enginner, Ibaraki Univeisity
The disaster research group of Kinu River Flood in 2015 was established in Ibaraki University, andthe authors participate as a member of a Geosphere Environment group of this research group. Aninterim report was up on university web site. In this presentation, the authors introduce therelationship between flood disaster damages and landform classification in Shimotsuma City, Ibaraki
Prefecture.
Keywords: Kinu-River flood, Shimotuma City, landform©2016. Japan Geoscience Union. All Right Reserved.

- HGG12-05 -HGG12-06

Japan Geoscience Union Meeting 2016

Importance of the evacuation plan in a flood -The case for the elderly people facility
devastated by the Kanto and Tohoku heavy rain in 2015*JUNKO KANAI1,2
1.Innovation and Creativity Development Center Faculty of Engineering,Tokushima University,
2.Research Center for Management of Disaster and Environment
In this study, we suggest that the welfare facility should have own evacuation plan to avoid futuredisasters. For the 2011 Kii Peninsula-heavy rain, the 2013 Kyoto-Shiga heavy rain, the 2013
Yamaguchi-Shimane heavy rain and the 11th / 12th typhoons in 2014, we have conducted the fieldsurvey to check their damages in an elderly people facility and interviewed them. We report thesurvey result about the one elderly people facility that declined to name as the ‘C elderly people
facility’ that devastated by the Kanto and Tohoku heavy rain in 2015. We interviewed victims in theelderly people facility with focus on their behaviors and support by other organizations inevacuation. By comparing this case and the past case, we show that the evacuation plan is importantfrom the point of necessity of the local co-operations.
We interviewed people in ‘C elderly people facility’ and their associated organization and we
observed the site in November 26, 2015 and January 14-16, 2016. Some groups; the disastercountermeasures office managed ‘C elderly people facility’, disaster countermeasures office inother office, the welfare department in Ibaraki prefecture and Japan Self-Defense Forces, involved
to help ‘C elderly people facility’. The disaster countermeasures office properly fulfilled theirroles by working as follows; collecting information, the safety confirmation, procurement, callingfor help and requesting acceptable facility of users. The other corporation concludes ‘Fureai
partnership’- agreement with ‘C elderly people facility’. They prepared the supply goods and a carfor ‘C elderly people facility’. The welfare department of Ibaraki Prefecture arranged a helicopterof Japan Self-Defense Forces. In this case,most important point is "multistory cooperation".
Concretely, important point is three co-operations of three organizations as follows; their own
co-operation, other co-operations and the co-operation by Prefecture. Quick refuge was achieved by"3, multistory cooperation". On the other hands, the one facility; ‘S elderly people facility’ atNaka-Cho, Tokushima Prefecture, devastated by the 11th and 12th typhoons in 2014 did not have some
co-operations with other organizations. Therefore, they were confused about making arrangements fortransportation of users. "Cooperation with vicinage's other corporations" is a key point indisaster.
Keywords: Elderly people facility, Evacuation plan, Cooperation©2016. Japan Geoscience Union. All Right Reserved.

- HGG12-06 -HGG12-P01

Japan Geoscience Union Meeting 2016

Fundamental study on accumulation of pore air pressure in geomaterials due to excessive
supply of water*Masahiko Osada1, Rio Sasaki2
1.Graduate School of Science and Engineering, Saitama University, 2.Faculty of Engineering, Saitama
University
The purpose of this study is to observe and explain the behavior of pore air pressure ingeomaterials due to excessive supply of water. The pore air pressure has a significant effect under
the conditions that there is oversupplied water from heavy rain or the rise of the river waterlevel. In order to reveal the system of infiltration considering the pore air pressure, we didsimple experiments of one-dimensional vertical infiltration. As a result, we deduced that flooding
happens on the surface of a specimen when pore air pressure reached the value caused by capillaryaction. Moreover, besides water pressure head and capillary pressure, weights of saturated portion
contribute increasing pore air pressure. In addition, we recognized the remarkable difference
between Toyoura-sand and Kanto-roam. Then the state of dry or low gaseous phase ratio are likely togenerate higher maximum pore air pressure.
Keywords: geomaterial, excessive supply of water, pore air pressure©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Issues on Hazard Information during 2015 Kanto-Tohoku Heavy Rain Disaster from the View
Point of a Health and Medical Responder*Yasuhiro Ishimine1,2
1.Department of Computational Intelligent and Systems Science, 2.Department of Health Crisis
Management, National Institute of Public Health
The author will talk about the outline of his activities on health and medical assistance in Joso
and Tsukuba city during Kanto-Tohoku heavy rain disaster in 2015, and also provide information on
the workers’ response of Joso health center to the emergency warnings such as the evacuation alertwith the intention of enhancing discussions for better countermeasures. National Institute of
Public Health (NIPH), in which the author works, is a national agency under the Ministry of Health,Labour and Welfare for conducting research that yields evidence-base of public health policies aswell as providing training courses for health center workers. The institute is now discussing thecurriculum of health emergency management to improve countermeasures on public health during
large-scale disasters. The author also takes part in “Enhancement of Societal Resiliency against
Natural Disasters”, one of the topics of “Cross-ministerial Strategic Innovation Promotion (SIP)
Program” of Council for Science, Technology and Innovation and conduct research on the information
sharing among multiple agencies during disasters. The author visited Joso city and Tsukuba healthcenter during Kanto-Tohoku heavy rain disaster in 2015 to reveal issues to be tackled in SIP
program. The author will focus on the initial response of health center workers revealed by theinterview to the director of the health center in his presentation.
Keywords: Kinu river, Joso health center, Information sharing©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Resourcing a disaster response map for the 2015 heavy rain in Joso city
*Shoichiro Uchiyama1
1.National Research Institute for Earth Science and Disaster Prevention
1. Motivation
From September 9th to 11th 2015, an exceptionally heavy rain storm caused the occurrence of theoverflow of the Kinugawa River and landslides in a wide range of areas in the Kanto and Tohoku
districts. One bank of Kinugawa River collapsed causing wide-spread flood damage in and around Joso
city in the Ibaraki Prefecture of Japan. Homes were destroyed and washed away leaving many
residents’ property completely underwater. Gaining a quick understanding of the disaster’smagnitude was critical for effective search and rescue (SAR) response, and decision-making so as tocarry out local government offices’ rehabilitation measures to rescue the residents of thesubmerged town.
2. Approach
In this case, the disaster area was as vast as 100 square kilometers as documented by aerial
photography using a Nikon D810 from a manned helicopter, rather than from any unmanned aerial
vehicles. The flight level was 1,200 m in altitude and course and speed were set to create a 75%
overlap in the photography.
3. Results
About 600 oblique photographs were taken from flight level 1,200 m between 15:30–16:30 hours on
September 11, 2015 to create a digital orthoimage of about 100 square kilometers of the flood
region. In addition to the aerial photographs, ground survey data and the orthoimage were madeavailable to the public within 12 hours on the crisis response website of the NIED. These resources
have been provided under the auspices of the Creative Commons license “CC-BY 4.0 international.”
Subsequently, the map that overlaid the housing map of Zenrin, Inc. was created for September 15,
2015, and the disaster countermeasures office was provided with it. In addition, a missing person's
distribution was estimated from the map and a professional team of private SAR and a NPO Japan
rescue dog association provided search assistance on the same day.
4. ConsiderationsFirst, although a lot of information has been released by each organization, there are someproblems regarding copyright, data size, and reliability. Effective use of such information in apost disaster situation is difficult. In this case, the information was provided as open data,
allowing users access to the information without the difficulty of making an application for
permission. The data was used by the disaster countermeasures office, the volunteer center, and theuniversity investigating the disaster. Second, the high definition photographic map of a disastersite makes it much easier to grasp the full impact of a disaster situation. However, when the user
is not familiar with how to interpret the information provided by such maps, it is difficult toutilize these map resources effectively. Consequently, it is necessary to support local public
entities by also providing directions for how to understand the map information. Finally, althoughphotography was performed from a manned helicopter, 14 or more rescue/reporting helicopters
surveyed the area for only 30 minutes. Though there may be an expectation that unmanned aerial
vehicles may be deployed for information gathering following a disaster, it is difficult to operatesuch aerial vehicles safely in airspace where manned aerial vehicles are operational
simultaneously. Excellent communication and cooperation are necessary during such operations toprotect the safety and integrity of both.

©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Keywords: the 2015 heavy rain, disaster response map, Joso city, SfM-MVS (Structure from Motion andMulti-view Stereo)©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Distribution of floodwater depth and damages of road structures in Joso City, Ibaraki
Prefecture, caused by the Kanto-Tohoku torrential rain in September 2015
*Masafumi Aoyama1
1.Faculty of Education, Gunma University
The torrential rain on September 2015 in Kanto-Tohoku regions caused the collapse and overflow ofembankment along the Kinu River, and floodwaters inundated the widespread area of Joso City,
Ibaraki Prefecture. Flood inundation depth in Joso City was estimated based on the height of flood
marks on buildings and houses. Field reconnaissance in inundation area was conducted to measure theheight of flood marks by using leveling rod. The height of flood marks were obtained at 100 sites
in the inundated area. The height of flood marks in the inundated area were less than 3 m, and mostof these obtained values were similar or below the values that were presented on the flood hazard
map of Joso City. In the inundated area, severe damages of road embankments and structures wereobserved in the back marsh area (paddy fields) between the natural levees along the Kinu River andKokai River.
Keywords: Kanto-Tohoku torrential rain in September 2015, Kinu River, floodwater depth, hazard map,
damage of road structure, Joso City

©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Inundation of the eastern part of Joso city, Ibarki prefecture caused by heavy rainfall
disaster in Kanto and Tohoku area
*Naoko Nagumo1, Miho Ohara1, Hisaya Sawano1
1.International Centre for Water Hazard and Risk Management, Public Works Research InstituteHeavy rainfall of September 2015 in Kanto and Tohoku area caused severe flood in the eastern partof Joso city, Ibaraki prefecture. Kinu River water started to flow over banks at around 6 am at
Wakamiyado district and collapse of Kinu River bank at around 12:50 PM at Kamimisaka district on 10th

September resulted in extensive inundation of Ishige area located on natural levees. Then, flood

moved southward along the Hakkenbori River and inundation of Mitsukaido area started at the nightof 10th September to widely inundate the area nearby at 1 pm on 11th September. The maximum
inundation depth confirmed by authors from the flood marks remained on the building walls are lessthan 1.0 m on natural levees, but it reaches 1.5 m at the maximum in core portion of the flood flow
identified by flood deposits. In the floodplain, deeper inundation occurred than natural levees,
and more than 2.5 m inundation was found at Okishinden and Jyukkamachi Okishinden district. Deeper
inundation was observed in the southern part of the floodplain because higher natural leveesurfaces at Mitsukaido area probably prevented to drain water smoothly. Although inundation of
Ishige area was comparatively short and ended by the morning of 11th September, inundation of
Mitsukaido area prolonged and continued until at least the morning of 13th September in the area
north of Shinhakenbori River, and until 16th along the Hekenbori River. Restoration of destroyed
river bank and roads was prioritized, but cleanings of flood sediments and debris take long timeand still households and offices need a certain time to be fully recovered. Also, some importantfacilities such as hospital and school experienced inundation of more than 1.5 m. Therefore, weneed to record the flood impacts and evaluate them appropriately for the formulation of flood
disaster risk reduction strategies in the area.
Keywords: flood, Joso city, Kinu River, inundation depth©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

The relative height map which visualized the slight topography of the flooding plains byaviation laser data
*Hiroshi Kobayashi1, Hiroyuki Miura1, Hiromi Suzuta1, Takeshi Nakamura1
1.Aero Asahi Corporation
In late years the damage caused by the flood of the small and medium size scale decreases as river
improvement measures of the river advance. However, the development of the flooding plains along
the river advances with this, and companies performing population and economic activities to settle
down in without assuming a flood risk increase.The government works on making, publication of thehazard map and the maintenance of the caution refuge system continuously now. However, it is theevent of the dike over there, and, for inhabitants, a company targeted for many staffs of local
government and refuge, the flood is said to be it when hard to be readily arrested as a realistic
risk since it is invisible. Particularly, the slight topography of the flooding plains that greatly
influence distribution of the inundation depth at the time of a flood is very incomprehensible fora citizen, and understanding is difficult when I do not have a skill to be able to comprehend thespecial drawings such as figures of river improvement topography classification.In late years themaintenance of the highly precise numerical value topography model by the aviation laser
measurement advanced and almost completed the maintenance of the numerical value topography modelof the big river riverside. In addition, I came to be able to photograph a high-resolution aerial
photo relatively easily. I visualize the slight topography such as the flooding plains, at the backdamp ground which I match these techniques and use it, and influences the understanding of theflood risk along the river and the three-dimensional management of river facilities for a citizen
and the administrative person in charge, and a technique to be actualized with a risk attracts
attention.In the case of Kanto, Tohoku heavy rain, large-scale flood damage visualized the slight
topography of flooding plains about Joso-City that occurred in September, 2015 and it was plain
and, in this study, produced "a relative height map" to accuse experimentally.The topography which
a human being usually sees is an irregularity in comparison with the neighborhood namely relative
height, and the relative height is one of the elements which it is big, and influences the big
things and small things of the inundation risk for at the time of floods again."The relative heightmap" sets a datum level to represent level ground of the river rear and makes the thing which I
analyze the relative height with it and expressed with an appropriate color by letting irregularity
information of the ground do an overlay. At this chance it was important that I let you display it
at appropriate gradation and it was plain and was able to express the slight topography of flooding
plains as a result of adjustment to emphasize a little slight topography of flooding plains. In
addition, I was able to regard the slight topography of flooding plains as dike high School
integrally by making "a relative height map" with the ground about the bank of a river separately,
and fitting it.I compare it with overflow water, a rip point and the distribution of the depth of
the inundation that "a relative height map" and Ministry of Land, Infrastructure and Transport andthe research organization others which I made announce and am going to repeat improvement in futureso that it is with "the relative height map" which can read a flood risk more precisely.
Keywords: flooding plains, microtopography, The relative height map, visualization, digital terrain
model©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Crevasse-splay deposits of the 2015 Kanto–Tohoku Torrential Rain Disaster in Kami-Misaka,
Joso City, Ibaraki, Japan*Yoshiki Sato1, Yoshinori Miyachi1, Susumu Tanabe1, Junko Komatsubara1, Tomonori Naya1
1.Research Institute of Geology and Geoinformation, Geological Survey of Japan
Introduction
The 2015 Kanto-Tohoku Torrential Rain (JMA, 2015) caused a severe flood disaster along the middle
reaches of Kinugawa River. Rapid water level rise resulted in a dike break 200 m wide in
Kami-Misaka district in Joso City. The KRDB (2015) reported that overbank flow had been recognizedat 11:00 and dike break began at 12:50. In order to clarify distribution and sedimentologicalfeature of "crevasse-splay deposits (Masuda, 1998)" in this flooding, we conducted small trench
excavation survey in Kami-Misaka district.
Distribution of crevasse-splay deposits
Erosional landforms, including pools and crevasse channel were dug by flood stream near the dikebreak site, which have >1.6 m depth and <60 m width. From that point, crevasse-splay deposits were
distributed westward to southward. At least three sandy lobes elongated downward were found.
Thickness of crevasse-splay deposits was less than 10 cm in the range of 150 to 250 m off the dike
except for behind scattered rubbles. Thick crevasse-splay deposits were found between 250 m and 700
m, which consisted of sandy lobes. We found that thickness reached the maximum (around 80 cm) at~400 m off the dike and decreased gradually downward from there. Only muddy flood deposits were
distributed in southern area from 700 m off the dike.
Sedimentary Facies
Crevasse-splay deposits were suggested to be divided into 3 units, Facies A to C in ascendingorder.
Facies A: This unit was inverse graded sandy deposits from silt or silty fine sand to fine sand.
This covered directly artificial soils of paddy fields with sharp boundary. Some layers of plantdebris such as paddy were found. The thickness reached 25 cm in NW part of the lobe and declined
southward.
Facies B: This unit consisted of fine to medium sand showing normal grading. Lenticular thin medium
sand layers were sometimes found. Upper part showed parallel lamination. Concentrated layers ofplant debris and small rubbles were found. The thickness became the maximum, around 20 cm, in thecenter of transverse section and decreased toward both edges.
Facies C: This unit consisted of well-sorted fine to medium sand with parallel lamination. Upper
part showed ripple lamination. Cross lamination developed at the marginal part of the lobe. Rounded
to sub-rounded granules, ~3 cm in diameter, were found. The thickness increased southward.
Discussion
Facies A to C were suggested to coincide with sedimentary processes during the flood.
It is suggested that the Facies A deposited at the overbank stage. Inverse grading shows thatvelocity of overbank flow and/or coarser sediments supply increased. At the beginning of flood,
washed load was supplied from river, and then coarser sediments were transported by high velocity
flood current (Masuda and Iseya, 1985).
Graded beds indicate that the Facies B was deposited by sediment gravity flow or at decreasingstage of clastic materials supply. It is possible that the sediment gravity flow occur when dike
was broken. Distribution pattern that this facies distribute on the downstream side of the erosion
landforms supports this idea. While, temporal large supply from the river just after the dike break
probably resulted in few sediment supply and fine suspended materials deposition.

©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Parallel lamination and granules suggest that the Facies C deposited at upper flow regime.
Expansion of broken dike had accelerated flood current for a few hours (Tsuneda, 2015). Thissuggests that the Facies C deposited after the dike break event. Ripple lamination indicatesdeclining of flood current.
Reference
JMA (2015) available in: http://www.jma.go.jp/jma/press/1509/18f/20150918_gouumeimei.pdf (publishedin Sep. 18, 2015).
KRDB (2015) available in: http://www.ktr.mlit.go.jp/ktr_content/content/000633805.pdf (published in
Oct. 13, 2015)
Keywords: 2015 Kanto–Tohoku Torrential Rain Disaster, Crevasse-splay deposit, Joso City, Kinugawa
River©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Particle size analysis of natural levee deposit and flood sediment around the dike-broken
site, Kinugawa River*Hiroshi, P. Sato1
1.College of Humanities and Sciences, Nihon University
The flood on 10 Sep 2015 broke the dike in Kinugawa River, and the protected inland was covered
with huge amount of flood sediment. The inland locates on natural levee, field survey revealed thatnatural levee deposit is finer than this flood sediment in particle size. I sampled both deposit
and sediment, which were sieved and diveded at one-phi interval from -2 phi to less than 4 phi. As
a result, it was found that fine sand of 4 phi notablly exists in natural levee deposit, but medium
sand of 2-3 phi notablly exists in this flood sediments. This infers that contribution of scouringof natural levee is quite low for supplying this flood sediment. This study was supported by
Promotion Grant of Special Study, Grant-in-aid Scientific Research (Grant number: 15H06923;
Principal Researcher: Prof. Shigenobu Tanaka, Kyoto Univ).
Keywords: Flood, Natural levee, Sediment©2016. Japan Geoscience Union. All Right Reserved.

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