IJERD ± International Journal of Environmental and Rural Development (2018) 9-2

Research article
erd

Survey on the Slope Protection Method for Sloped
Farmland Aimed at Conservation of Regional UniqueLandscape
SHOKO NISHIWAKI*Graduate School of Frontier Sciences, The University of Tokyo, Tokyo, Japan
Email: 7063598150@edu.k.u-tokyo.ac.jp

KENJI OKAJIMA
Graduate School & Faculty of Bioresources, Mie University, Mie, Japan

EIJI YAMAJI
Graduate School of Frontier Sciences, The University of Tokyo, Tokyo, Japan
Received 13 January 2018

Accepted 20 October 2018(*Corresponding Author)

Abstract Japan's National land has many steep mountains and few flat lands. We
performed slant ground use for a long time to secure farmland, in Japan. In slope protection
me hod of he loping fa mland, he e a e f ndamen al o pe of lope tamping andone all . The lope p o ec ion me hod of he loping fa mland a e one of he elemencharacterizing a scene including sloping farmland as a thing peculiar to area. In this paper,
we analyzed the type of the slope protection method of sloping farmland in the point of
one h nd ed elec ion of Japane e loping fa mland and he ep e en a i e loping
farmland in Japan using a subsurface geological map drawn on a scale of 1 to 200000. Thegeology in each point of target area was classified into three main groups as volcanic rock,sedimentary rock and metamorphic rock. Three main groups were further classified by rocktypes or geological timescale. We formed clear that rock types or geological timescale ofthe subsurface geology in the point was related to the choice of the slope protection methodof sloping farmland. We conducted a field survey based on this classification. As a result, inregion where two or more subsurface geologies are adjacent, the rock of the subsurface
geology next to each other in domains from the subsurface geological feature border toaround 200m is used as materials of the protection method of sloping farmland.
Keywords sloping farmland, rice terrace, terraced field, stone wall, slope protection method

INTRODUCTION
Japan's National land has many steep mountains and few flat lands. We performed slant ground use
for a long time to secure farmland, in Japan. In Japan, farm village landscapes with rice terrace orterraced fields are cultural landscape. The slope protection methods of the sloping farmland are oneof the elements characterizing a scene including sloping farmland as a thing peculiar to area.
Typical ones in the slope protection method of rice terraces and Terraced fields are stone walls andslope tamping.
In slope protection methods of the sloping farmland, there are fundamental two types oflope tamping and one all . Some e ea ch gge ed ha he pe of he lope p o ec ion
method of sloping farmland depended on the presence or absence of unearthed rocks at the time ofthe paddy field reclamation; however, these are not describe detailed the kind of stones. When theslope protection methods are broken for some reason or to deteriorate over time, we may notchoose appropriate slope protection method or materials. It shows the possibility that a traditionallandscapes fails.

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IJERD ± International Journal of Environmental and Rural Development (2018) 9-2

METHODOLOGY
We performed documents investigation and a field survey. In this paper, we will express Riceterrace and terraced field with sloping farmland.
Documents Investigation
In this paper, we focused on relationship between the rock types of the subsurface geology and theslope protection method and revealed tendency in choosing slope protection method. We basicallyused subsurface geological map drawn on a scale of 1 to 200000 published by AIST Geological
Survey of Japan. In this map, the discontinuous boundaries between neighboring quadrangles wereresolved using a unified legend.
We chose 464 areas registered in a prefecture or country of Japan as the sloping farmland
which represented an area. Fig.1 shows the locations of the 464 areas. In the analysis, we used
information on registered sloping farmland. The black dots in Fig. 1 are the target area. The rockclassification and geologic time classification of the subsurface geology we used are shown in Fig.
2 (Arai et al., 2005; Itoh, 1982; Itoh and Nishiki, 1985).

Fig. 1 Distribution of Documents investigation target area

Fig. 2 Rock classification and geological time classification of subsurface geology
Field Survey
We did a field survey to more quantitatively show the relationship between the subsurface geology
and the choice tendency of the slope protection method. The purpose of the survey is to clarify
what kind of stone were used for stone wall of slope protection method. We grasped the subsurface
geology of the target area by subsurface geological map, and we investigated how far thegeological boundary of the subsurface geology affects the stone used in stone wall.
The boundary between Arita City and Yuasa Town in Wakayama Prefecture of Japan wasselected as a target area where surface geology is changing within the region. We investigated theⒸ ISERD71

IJERD ± International Journal of Environmental and Rural Development (2018) 9-2

outcrop of the geological indicator as an indicator of the survey site. And the survey point wasdecided by changing the distance from the outcrop. The distance between the survey points was set
within 100 m. We gathered the following data at each survey point. Location data by GPS(GARMIN OREGON 300), stone used for material of stone wall types classified by reference tosubsurface geological map, and photographic data as material of stone wall. From theseinformation, the relationship between distance from outcrop or geological boundary, or elevationdifference and stone used in stone wall was considered.
RESULTS AND DISCUSSION
Documents Investigation
Among the sloping farmlands in 464 areas, 293 areas selected stone wall as slope protection
method, 171 areas selected slope tamping as slope protection method. In the rock classification,
157 areas have volcanic rocks, 45 areas have plutonic rocks, 115 areas have sedimentary rocks, 80
areas have accretionary prism, and 54 areas have metamorphic rocks as subsurface geology.
Fig.3 (a) shows the proportion of rock classification and geologic time classification in thestudy area. The rock classification and geological time classification of 464 areas and thedistribution area ratio of rocks in Japan have the same tendency. Fig.3 (b) shows distribution area
ratio of rocks in Japan.
Fig.4 shows the relationship between the rock classification and the slope protection method thesloping farmlands of the survey target area.

Fig. 3 Rock classification and geological age classification of survey target area andDistribution area ratio of rocks in Japan

Fig. 4 Relationship between rock classification of surveyed area andslope protection method of sloping farmlandⒸ ISERD72IJERD ± International Journal of Environmental and Rural Development (2018) 9-2

Field Survey
Table 1 shows the types of stone used at each survey points. In Table 1, ᬅ to ᬈ and No.1 toNo.29 correspond to numbers in Fig. 5. Fig. 5 shows the subsurface geological map around thesurveyed area. In the Fig. 5, the same type of subsurface geology exists in places where the samenumbers are applied. In Fig. 5, It is believed that sedimentary rocks that were made into theHolocene existed in ᬅ. Likewise, it is supposed that ᬆ in Fig. 5 has the accretionary prism thatwere made into Mesozoic Era, ᬇ the metamorphic rocks of about 230 million to 160 million
years ago, and ᬈ the Mesozoic sandstone and conglomerate. Specifically, the rocks present in ᬆare cherts. It must be sedimentary rock in ᬅ, but because it is somewhat unstable at the geologicalboundary of the surface geological map, it is the reason why the outcrop of chert exists in ᬅ. In
this survey, we considered the chert (ᬆ) as the subsurface geology at the survey points near theoutcrop of the chert. The survey points were set up to traverse three subsurface geologies such as
accretionary prism, metamorphic rock, sandstone and conglomerate.
Table 1 Results of each survey point

①

②No.

North latitude

East longitude

Limestone

No.1
No.2
No.3
No.4
No.5
No.6
No.7
No.8
No.9
No.10-1
No.10-2
No.11
No.12
No.13
No.14
No.15
No.16
No.17
No.18
No.19
No.20
No.21
No.22
No.23
No.24
No.25
No.26
No.27
No.28
No.29

34°4′00.71″
34°03 ′57.5″
34°03′54.6″
34°03′50.6″
34°3′46.7″
34°03′43.6″
34°03′41.9″
34°03′38.5″
34°03′35.9″
34°03′34.7″
34°03′34.0″
34°03′33.6″
34°03′32.7″
34°03′28.8″
34°03′27.2″
34°03′24.4″
34°03′23.9″
34°03′23.6″
34°03′19.6″
34°03′18.3″
34°03′16.2″
34°03′14.3″
34°03′14.4″
34°03′12.3″
34°03′9.6″
34°03′5.2″
34°03′00.9″
34°02′54.7″
34°02′49.7″
34°02′45.7″

135°10′40.56″
135°10′39.5″
135°10′39.6″
135°10′39.7″
135°10′40.6″
135°10′38.6″
135°10′40.4″
135°10′45.8″
135°10′45.6″
135°10′47.7″
135°10′48.6″
135°10′46.7″
135°10′47.5″
135°10′47.9″
135°10′46.6″
135°10′46.5″
135°10′49.0″
135°10′49.0″
135°10′53.0″
135°10′55.1″
135°10′56.8″
135°10′57.0″
135°10′59.3″
135°11′00.4″
135°10′59.7″
135°11′00.9″
135°11′01.6″
135°11′04.0″
135°11′03.9″
135°11′02.3″

0
0
0
1
0
0
0
5
0
0
47
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
000

Crystalline
schist
0001
20
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
000000000Chert
100979792
9798
100
92
95
100
53
100
100
7198
3498
100
100
100
055
81
1005100

Sandstone Conglomerate Mudstone
03361203
5000016232000100
35
1199
100
100
88
99
40
80

000000000000000
2000001
8000
70
16
20

000000000000000000000000000020Total
100
100
100
100
100
100
100
100
100
100
100
100
100
87
100
39100
100
10010010091100
100
100
100100100
58100In Fig. 5, it is considered that the time of sedimentation is new and it is thought that ᬅ is not
sufficiently consolidated as rocks, but the rocks of ᬆ, ᬇ, ᬈ is considered to be used as thematerial of stone wall. Through on the field survey, the outcrops of the chert at the subsurface
geology of ᬅ and ᬆ was confirmed (triangle dots in Fig. 5), ᬇ and ᬈ confirmed sandstone
outcrops (white triangle dots in Fig. 5 ). It must be sedimentary rock in ᬅ, but because it issomewhat unstable at the geological boundary of the surface geological map, it is the reason why
the outcrop of chert exists in ᬅ. In this survey, we considered the chert (ᬆ) as the subsurface
geology at the survey points near the outcrop of the chert.
At the 20 survey points in ᬅ and ᬆ, the chert was used as material of stone wall at a rate of
53 to 100%. Also, at all the survey points in ᬈ, over 90% of the material rocks of stone wall wereⒸ ISERD73

IJERD ± International Journal of Environmental and Rural Development (2018) 9-2

sandstone and conglomerate. In addition, both stone materials were used at the three survey pointsof the survey spot (within ᬇ) within 200 m from the geological boundary of ᬆ and ᬈ.

Fig. 5 Subsurface geological map around survey area and survey spot
CONCLUSION
From the above results, the following can be considered. As a result of documents investigation,
when the subsurface geology is plutonic rocks, accretionary prism, or metamorphic rocks, the stone
wall is strongly selected as slope protection methods. On the other hand, when the subsurface
geology is volcanic rocks, slope tamping were selected in nearly half of the sloping farmland and in
the case of sedimentary rocks the stone walls are selected in nearly 30% of the sloping farmland. Inaddition, the area where the subsurface geology is pyroclastic flow deposit among volcanic rocks
selects slope tamping as slope protection methods.
Among districts where the subsurface geology is a pyroclastic flow deposit, there is atendency to select slope tamping when the pyroclastic flow is formed in the Holocene or Neogene
period. Sloping farmlands where older pyroclastic flows are located in the subsurface geology tend
to select stone walls. Moreover, in the area that consolidated volcanic rocks are there to thesubsurface geology, the area where the former geologic formations of the Miocene volcanic rocks
where the Green Tuff is formed will tend to select the slope tamping as slope protection methods
for Regardless of its composition. Among mafic volcanic rocks, there is a tendency to select slope
tamping as slope protection method if the subsurface geological districts were made in theQuaternary Period, otherwise it seems to choose stone walls.
When the subsurface geology is plutonic rocks, we found out the following. When theplutonic rocks of the subsurface geology were felsic, stone walls were chosen in general, although
the slope tamping was selected with 27% of the slope farm depending on the weathering degree ofrocks.
Districts where sedimentary rocks in the Quaternary or New Tertiary are located in thesubsurface geology select the slope tamping, but in the area with rocks consolidated where thealtitude in higher than the sloping farmland, there possibility to choose stone walls. It was foundfrom the field survey in the other area that there is a possibility of choosing stone wall as a slope
protection method even if consolidated rocks located in a place where the altitude is high andsloping farmland are separated by a horizontal distance of 500 m or more.
When the surface geology is an accretionary prism, the slope tamping concentrate in thesubsurface geological areas formed in the middle or late Jurassic centers called the Mino - Tanba Ⓒ ISERD74

IJERD ± International Journal of Environmental and Rural Development (2018) 9-2Ashio Belt. In the sloping farmland where the subsurface geology is an accretionary prism andexists outside the Mino - Tanba - Ashio Belt, there is a tendency to choose stone wall as a slope
protection method.
In sloping farmland whose subsurface geology is metamorphic rocks, it turned out that in mostcases would choose stone wall.
In the field survey, basically we could actually confirm that stones of subsurface geology areused on the ground. Furthermore, within about 200 m of the geological boundary of the subsurface
geology, it is possible that adjacent rocks will be used as materials for stone walls. In other words,
in sloping farmland where several subsurface geologies are located nearby, not only the rocks of
the just below subsurface geological structure but also the rocks of adjacent subsurface geology areused.
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