10th Asian Regional Conference of IAEG (2015)

Evaluation of Micro-Topographies in Riverside Areas to Estimate High Flood Disaster
Potential by Using DEM Data
Takahito KUROKI(1) and Nozomi ISO(2)(1) Fukuoka University of Education, Japan
E-mail: kuroki0@fukuoka-edu.ac.jp(2) Seinan Gakuin University, Japan
Abstract
In this study, the Mikasa River in Fukuoka City and the Ooyodo River in Miyazaki City
are selected in flood plains. We want to show variable background of flood disasters indrainage areas of both rivers by using free downloadable geographic information of Japan.
We made relief maps by GIS using 5m DEM and classified several micro-topographies
concern to overflow and/or inundation. The topographies are dike, slope of dike, river side,
water area, lowland, natural levee and others. Average elevation of the topography is
calculated in each section of the river. Relative elevation to a referenced topography wascalculated and longitudinal profiles on each of the topography were made by Excel. We
confirmed the areal relation between the convex curves of the longitudinal profiles and theriver conditions of existence some barriers such as weirs, bridges, confluence of tributaries,
flection of the rivers and bottleneck sections. We also confirmed the relation between theconvex curves of the profiles and previous flood conditions, where overflow points and/or
inner water flooding areas existed. Consequently, we clarified that it is easy to recognize thevulnerable section or area for natural disaster of inundation from the analysis of geomorphic
quantities on micro-topographies.
Keywords: micro-topography, 5m DEM, longitudinal profile, the Mikasa River, the Ooyodo
River
1.

Introduction

5m DEM. We clarified the characteristics of theelevation change on each of the topography in thelongitudinal profile and yielded factors of the change
at where the flood damage is likely to occur. Then we
discussed the evaluation method to define weak areasfor natural disaster such as overflow or inundation byflood using the characteristics of the change.

In Japan of the humid monsoon region, thedisasters by flood and storm surge induced by rainyseason and typhoons are likely to occur every year.
Residential and cultivation areas are damaged by theflood that develop micro-topographies such as natural
levee and back marsh by the overflowed sediments.
Newer residential area has developed at the backmarsh with lower grand elevation by urbanization in
Japan. Such area is often to suffer damage induced byinundation in flooding.
Because it is believed that we can predict thecharacteristics of flood damage from the distribution
and topography of micro-topography, researchers
tried to classify the topographies qualitatively using
by aerial photographs (Ohkura et al., 1989) orsatellite images (Oya, 1975). The classification on
micro-topography is used in making disaster maps.
Usually there is a damage size difference in the same
topography areas because of the ground elevationdifference. In this study, we evaluated each
topography class quantitatively by GIS analysis using

2.

Research Methods

2.1 Case Study Areas
We selected the Mikasa River as a small example
and the Ooyodo River as a large example of Japaneseriver (Fig.1).
The Mikasa River is a class B river flowing
through the northern part of Fukuoka Prefecture. Its
stream length is approximately 21km and its
catchmentarea
isapproximately
90km2.
Approximately 12km length upstream from the rivermouth is selected as our study area. We set 119
analysis sections for the river. Each size isapproximately 150m wide and 100m length. Large
areas were inundated by the river water and a large

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10th Asian Regional Conference of IAEG (2015)

amount of sediment was deposited in the Mikasa
River basin by the flood induced by the heavy rain of
rainy season in July 2003 (Kuroki et al., 2012).
Mountains and hills of granite are distributed upperstream area of the river.
The Ooyodo River is a class A river flowing
through the southern part of Miyazaki Prefecture. Its
stream length is approximately 107km and its
catchment area is approximately 2,230km2.
Approximately 29km length upstream from the rivermouth is selected as our study area. We set 116
analysis sections for the river. Each size isapproximately 1,000m wide and 250m length. Large
areas were inundated inside the levee and a large
amount of sediment was deposited in the downstreamof the Ooyodo River basin by the flood induced by
the heavy rain due to the typhoon no.0514 in
September 2005 (Iso et al., 2006). The Ooyodo Riveris flowing through the valley bottom plain or coastal
plain. They are surrounded by the mountains and hills
consisting of Neogene and pyroclastic flow plateau
consisting of Ito pyroclastic flow.

profile by the elevation on each of the topography
was made by Excel. On the Mikasa River, we
confirmed the areal relation between the existence ofweirs and bridges and the forms of longitudinal
profiles, and between the forms and overflow
sections. On the Ooyodo River, we confirmed theareal relation between the river conditions such asconfluence of tributaries, flection of the rivers andbottleneck sections and the forms of longitudinal
profiles, and between the forms and inundated
sections inside the levee. Then we discussed how
vulnerable sections to the inundation should beclarified from the longitudinal profiles made by theground elevation data on micro-topographies.

Fig.2 Topography classification of the Ooyodo River
3.

Result and Discussion

3.1 The Mikasa River
In the longitudinal profiles on relative elevation
on each of the topography, we can identify someconvex curves caused by increasing of the elevation
toward the downstream. Convex curves constituting
multiple sections are clear in the profiles on relative
elevation to lowland (Fig.3). In the lower part ofFig.3, a table on analysis sections with the weirs andbridges, and the overflowing was attached.
On the relative elevation of riverside, theminimum value is -4.76m and the maximum one is
0.07m. Each convex curve was constituted by over 10
sections. In a convex curve, relative elevation
gradually increases and rapidly decreases toward thedownstream. There are convex curve a (from section
117 to 101), convex curve b (from section 100 to 65),
convex curve c (from section 64 to 46) and convex
curve d (from section45 to 01). Weir 3, 6 and 7 arelocated at the downstream ends of the each convex
curves a, b and c, and the sea is located at thedownstream end of the convex curve d. This meansthat the speed of moving fluid decreases and thesediment accumulates affected by the weir and sea atthe downstream end of the convex curves. In Fig.3,
many
small
convexcurvesconstituting
approximately 500m long of about 5 sections can bealso identified. The extreme value of the curve iseasily recognized in the section with a bridge. Section
96, 80, 42 and 33 having extreme values show clear
correspondence with the bridges and do not close to
the weirs. This fact means that speed of moving fluid

Fig.1 Study areas and Rivers in Kyushu Island
2.2 Classification and Calculation on Topography
The micro-topographies are dike, slope of dike,river side, water area, lowland, natural levee andothers (Fig.2). We made two kinds of relief maps by
GIS calculation using 5m DEM and classified these
topographies by using the maps. Average elevation of
the topography is calculated in each section of theriver. Then relative elevation on the basis of thelowland or water area was calculated and longitudinal2

10th Asian Regional Conference of IAEG (2015)

decreases and sediment accumulates affected by thebridges.
Overflowing sections can be identified area 1(from section 102 to 101), area 2 (from section 92 to63) in upstream, and area 3 (from section 36 to 15) indownstream. Each area is located at the sections withhigher relative elevation in convex curves a, b and c.
Overflow occurred at a lot of small areas including
one section and two sections too. In the upstream ofthe section 60, we can confirm clear correspondenceof the overflowing area 1 to weir 3, and theoverflowing area 2 to weir 4, 5 and 6. In thedownstream of the section 60, we can confirm clear
correspondence of the overflowing sections to bridge
18, 19, 20 and 26. These facts mean that weirs, sea,bridges disturbed river flow, speed of moving fluid
decreased, flood level increased, and finally overflow
was induced.
Therefore, we can identify the depositional
condition outside of the dike by the longitudinal
profiles on relative elevation of river side andestimate the location with easy overflowing.

In Fig.4, convex curves A to G can be identified.
In each convex curve, the relative elevation increases
and then decreases towards the downstream. The
amplitude of the convex curve is the maximum about
10m and its wavelength is longer than 2.5km of 10
sections. The convex curve A indicates that the
sediment deposit easily there by the confluence of theriver to the sea. Since tributaries do not always
concentrated near the sections with extreme values ofother curves, the reason of the development of theconvex curves is not the confluence of tributaries
here. Considering the topography setting, because
flection and bottleneck part of the river are close to
the sections with extreme values of the curves, they
seem to be the forming factors of the profiles. The
higher topography’s extreme value of the curve islarger. The difference value of relative elevations
between the topographies maximizes near the centerand minimizes near the both ends in an extent of theeach curve. The sections with extreme values of the
topographies outside of the dike are locatedapproximately 5 sections downstream than those of

Fig.3 Longitudinal profiles of the Mikasa River and river conditions relating overflow

Fig.4 Longitudinal profiles of the Ooyodo River and river conditions relating inundation
the topographies inside of the dike.
Additionally, many small convex curves withapproximately 1 km length by 4 sections can be
identified. The extreme value of the small curve tends
to appear on the section with the confluence oftributary. This fact means that sediment remarkableaccumulates near the section with the confluence oftributary. On the small curve, the sections withextreme values of the topographies outside of thedike are located 1 or 2 sections downstream thetopographies inside of the dike.

3.2 The Ooyodo River
In the longitudinal profiles on relative elevation
on each of the topography, we can identify someconvex curves caused by increasing of the elevation
toward the downstream. The curves constituting theanalysis sections are clear in the profiles on relative
elevation to water area (Fig.4). In the lower part of
Fig.4, a table on analysis sections with the confluenceof tributaries and the inundation by overland flood
was attached.

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10th Asian Regional Conference of IAEG (2015)

We discussed the estimating method for
those of the topographies inside of the dike.
inundated sections by using the waveform shift in the4) In the graph on the difference values of relative
profiles on relative elevation of the topographies.
elevation between lowland and river side1, it is easy
Fig.5 shows an analyzed result on the Honjo River ofto estimate the inundated sections inside the levee
the Ooyodo River tributary. The difference values offrom the concave curves and not inundated sections
relative elevation between river side1 and river side2,
from the convex curves．
lowland and river side1, and natural
levee and lowland are shown in it. In thegraph on lowland and river side1,
concave curves appear close to theinundated analysis sections 4 and 20. In
other graphs, concave curves do notappear close to them clearly.
Therefore, in the graph on the
difference values of relative elevation
between lowland and river side1, we canestimate the inundated sections inside thelevee from the concave curves and notinundated sections from the convex Fig.5 Difference values of relative elevation of the Honjo River
curves exactly．
Acknowledgements
4. Conclusion
We are grateful to Dr. Kensuke Goto, Mr.
Consequently, we clarified that it is easy to
Tatsuroh Soh and Mr. Keisuke Kuroda forrecognize the vulnerable section and area for natural
cooperation in field survey and discussion. Most ofdisaster induced by flood from the analysis of
this study was financially supported by the JSPS
geomorphic quantities on micro-topographies.
Grant-in-Aid for Scientific Research (C), Project
Results of analysis using the longitudinal profile
Number 23501243.
made by the relative elevation of riverside of theMikasa River are as follows.
References
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Triggerd by Typhoon 0514 with Satellite Imagery
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