京都大学防災研究所年報 第 56 号 B 平成 25 年 6 月

Annuals of Disas. Prev. Res. Inst., Kyoto Univ., No. 56 B, 2013࣮ࣞࢲ㞵㔞ࢆ⏝࠸ࡓὶฟࢩ࣑࣮ࣗࣞࢩࣙࣥ࡜ᱜᓥ࡟࠾ࡅࡿᅵ▼ὶⓎ⏕῱ὶ࡬ࡢ㐺⏝
Application of X-band Radar and Runoff Model to Debris Flow Frequently Occurred Creeks inSakurajima Islandᐑ⏣⚽௓࣭⸨⏣ṇ἞Shusuke MIYATA, Masaharu FUJITA


Synopsis To examine effects of spatial distributions of rainfall on local occurrence of debris
flow and flash flood, we observed stream discharge by interval cameras and conductedhydrological simulations with X-band rainfall radar data in four catchments in
Sakurajima Island. Hydrological processes were simulated for two rainfall data; rainfall
data in downstream areas (Case 1) and upstream areas (Case 2) of each catchment wasapplied for whole area of the catchments. Debris flows generally occurred when verystrong rainfall intensity was observed in upstream areas of the study catchments.
Simulated stream discharges of Case 2 were more consistent with occurrence of debris
flows than those of Case 1. The simulation results also suggested that concentrations ofoverland flow into gullies were essential for occurrences of debris flow.
࣮࣮࢟࣡ࢻᅵ▼ὶ㸪ⅆᒣ⅊㸪㝆㞵ศᕸ㸪ὶฟࣔࢹࣝ

Keywords: debris flow, volcanic ash, rainfall distribution, hydrological model ࡣࡌࡵ࡟ ࠸ࡿ㸦஭ཱྀ㸪2012㸧㸬2009ᖺ௨㝆ࡢᖺ㛫ⅆᒣ⅊ᨺฟ㔞ࡣ400୓ࢺࣥ௨ୖ࡛࠶ࡾ㸪ⅆᒣ⅊࡛ᒣ⭡ࡀそࢃࢀࡿᅵ▼ὶ࡞࡝ࡢᅵ◁⅏ᐖࡸࣇࣛࢵࢩࣗࣇࣛࢵࢻ࡟ࡼ

ࡇ࡜࡛ᾐ㏱⬟ࡀపୗࡋ㸪୙Ᏻᐃ࡞ᄇⅆሁ✚≀ࡀከࡃࡿ⅏ᐖࡣ㸪῱ὶࡈ࡜࡟Ⓨ⏕࣭㠀Ⓨ⏕ࡀࡣࡗࡁࡾ࡜ศὶᇦෆ࡟Ꮡᅾࡍࡿࡓࡵᅵ▼ὶࡀ㢖Ⓨࡋ࡚࠸ࡿ㸬ᱜᓥ࠿ࢀࡿ⌧㇟࡛࠶ࡿ㸬ᆅୖ㞵㔞ィ࡟ࡼࡿほⅆᒣࡢୖ✵ࢆ┘どࡍࡿࡇ࡜ࢆ┠ⓗ࡜ࡋ࡚㸪ᱜᓥ඲ᓥ⥙࡛ࡣ㸪᭱ࡶ㔜せ࡞ධຊ࡛࠶ࡿ㝆㞵㔞ࢆ῱ὶࡈ࡜ṇ☜࡟ᢕᥱࢆほࡍࡿࡇ࡜ࡣ㞴ࡋ࠸㸬ࡑࡢࡓࡵ㸪ᚑ᮶ࡢほࢀ࡚࠸ࡿ㸬ࡑࡇ࡛㸪ᮏ◊✲࡛ࡣᒣᆅ῱ὶ㝆㞵㸫ὶฟࢹ࣮ࢱࡢ⠊ᅖ࡟ྵࡴࡼ࠺࡟XࣂࣥࢻMP࣮ࣞࢲࡀ㓄ഛࡉࡳ࡛ࡣ㸪Ⓨ⏕⣲㐣⛬ࡢゎ᫂ࡸⓎ⏕࡟ᐤ୚ࡍࡿせᅉࡢࣔࢹࣝ࡟XࣂࣥࢻMP࣮ࣞࢲࡢほᢳฟ࡞࡝ࡣᅔ㞴࡛࠶ࡿ㸬ࡇ࡜࡛㸪㮵ඣᓥ┴ᱜᓥࡢᅵ▼ὶ㢖Ⓨ῱ὶࡢὶฟ㐣⛬㏆ᖺ㸪ᅜᅵ஺㏻┬ࡸẼ㇟ᗇ࡞࡝࡟ࡼࡾ࣮ࣞࢲ㞵㔞ほ⥙ࡀᩚഛࡉࢀࡘࡘ࠶ࡿ㸬≉࡟XࣂࣥࢻMP࣮ࣞࢲࡣ✵㛫ศゎ⬟250m㸪᫬㛫ศゎ⬟1ศ࡜᫬✵㛫ⓗ࡟㠀ࢹ࣮ࢱࢆ㐺⏝ࡍࡿ࡟࠾ࡅࡿ㝆㞵ศᕸࡢᐤ୚ࢆ᳨ウࡍࡿࡇ࡜ࢆヨࡳࡓ㸬ᑐ㇟ὶᇦࡢᴫせ࠾ࡼࡧほ㡯┠ ᖖ࡟⣽࠿࠸ࢹ࣮ࢱࢆᚓࡿࡇ࡜ࡀ࡛ࡁࡿ㸬XࣂࣥࢻMP࣮ࣞࢲࡢࢹ࣮ࢱࢆ⏝࠸ࡿࡇ࡜࡛㸪῱ὶࡈ࡜ࡢᅵ▼ὶᱜᓥࡢᅵ▼ὶࡀ㢖Ⓨࡍࡿ῱ὶࢆᑐ㇟࡜ࡋ࡚⌧ᆅほⓎ⏕࡟ཬࡰࡍ㝆㞵ࡢ✵㛫ศᕸ࡟ࡘ࠸᳨࡚ウࡍࡿࡇ࡜࠾ࡼࡧᩘ್ࢩ࣑࣮ࣗࣞࢩࣙࣥࢆ⾜ࡗࡓ㸬ᱜᓥࡣ୰ᚰ㒊࡟ⅆᒣࡀ఩⨨ࡋ࡚࠾ࡾ㸪ᱜᓥⅆᒣࢆ※ὶ࡜ࡍࡿࡀ࡛ࡁࡿ࡜⪃࠼ࡽࢀࡿ㸬㮵ඣᓥ┴ࡢᱜᓥⅆᒣࡣ༡ᓅᒣ㡬ⅆཱྀ࡟ᘬࡁ⥆ࡁ༡

19῱ὶࡀᾏ࡟ὶୗࡋ࡚࠸ࡿ㸬ᮏ◊✲࡛ࡣᅵ▼ὶࡀ㢖ᓅᮾᒣ⭡ࡢ᫛࿴ⅆཱྀ࡟࠾ࡅࡿᄇⅆάືࡀάⓎ໬ࡋ࡚

Ⓨࡍࡿࡇ࡜࡛▱ࡽࢀࡿ㔝ᑼᕝ㸪ᣢᮌᕝ㸪➨஧ྂ㔛ᕝ㸪― 457 ―

᭷ᮧᕝࡢ4ὶᇦࢆᑐ㇟࡜ࡋࡓ㸦Fig. 1㸧㸬ᅜᅵ஺㏻┬
኱㝮Ἑᕝᅜ㐨஦ົᡤ࡟ࡼࡗ࡚㞟ィࡉࢀࡓ㔝ᑼᕝ㸪ᣢᮌᕝ㸪➨஧ྂ㔛ᕝ㸪᭷ᮧᕝ࡟࠾ࡅࡿ2002㹼2011ᖺࡢ
ᅵ▼ὶⓎ⏕ᅇᩘࡣࡑࢀࡒࢀ78㸪24㸪2㸪27ᅇ࡛࠶ࡾ㸪㠀ᖖ࡟Ⓨ⏕㢖ᗘࡀ㧗࠸Ἑᕝ࡛࠶ࡿ㸬 㝆㞵࡟ᑐࡍࡿὶฟ࠾ࡼࡧᅵ▼ὶⓎ⏕ࢆほࡍࡿࡓࡵ࡟㸪ྛὶᇦࡢୗὶ㒊࡟࠾࠸࡚࢖ࣥࢱ࣮ࣂ࣓ࣝ࢝ࣛࢆタ⨨ࡋࡓ㸦Fig. 1㸧㸬࢖ࣥࢱ࣮ࣂ࣓ࣝ࢝ࣛ࡟ࡼࡿ᧜ᙳࡣ◁㜵ࢲ࣒ࡸὶ㊰ᕤ࡞࡝ࢆྵࡴࡇ࡜࡛㸪ὶୗ᩿㠃ࢆᐜ᫆࡟ㄞࡳྲྀࢀࡿࡼ࠺࡟ࡋࡓ㸬᧜ᙳࡣ2ศ㛫㝸࡟࡚㔝ᑼᕝ⾜ࡗࡓ㸬࢖ࣥࢱ࣮ࣂ࣓࡛ࣝ࢝ࣛࡣኪ㛫ࡣ᫂░࡞⏬ീᣢᮌᕝ᭷ᮧᕝ➨஧ྂ㔛ᕝࡀ᧜ᙳ࡛ࡁ࡞࠿ࡗࡓ㸬ࡑࡇ࡛㸪ᅜᅵ஺㏻┬኱㝮Ἑᕝᅜ㐨஦ົᡤⓎ⾲ࡢᅵ▼ὶⓎ⏕࡟㛵ࡍࡿ㈨ᩱࢆ⏝࠸ࡿࡇ࡜࡛㸪ほᮇ㛫୰ࡢྛἙᕝ࡟࠾ࡅࡿᅵ▼ὶⓎ⏕ࢆ

Fig. 1 Map of study catchments in Sakurajima Island,Kagoshima.

⿵᏶ࡋࡓ㸬 㝆㞵ࡢ✵㛫ศᕸࡀὶฟ࡟ཬࡰࡍᙳ㡪ࢆ᳨ウࡍࡿࡓࡵ࡟㸪XࣂࣥࢻMP࣮ࣞࢲ࡟ࡼࡿ㞵㔞ほ⤖ᯝ㸦௨ୗ㸪࣮ࣞࢲ㞵㔞࡜ࡍࡿ㸧ࢆ⏝࠸ࡓ㸬㞵㔞ほࡢ✵㛫ศゎ㞵㔞ほⅬ⬟ࡣ250m㸦Fig. 2㸧㸪᫬㛫ศゎ⬟ࡣ1ศ࡛࠶ࡿ㸬ᅵ▼ὶⓎ⏕※࡛࠶ࡿୖὶᇦ࠾ࡼࡧ࢖ࣥࢱ࣮ࣂ࣓ࣝ࢝ࣛ࡟ࡼࡿほࢆ ⾜ࡗࡓୗ ὶᇦ࡟ ࠾ࡅࡿ௦⾲ Ⅼࢆ㑅ᐃࡋ
NU

㸦Fig. 2㸧㸪᫬⣔ิ㞵㔞ࢹ࣮ࢱࢆゎᯒ࡟⏝࠸ࡓ㸬

AUMU

ὶฟࣔࢹࣝࡢᴫせ࠾ࡼࡧィ⟬᮲௳

NDFUMDFDADὶฟ㐣⛬࡟࠾ࡅࡿ㝆㞵ศᕸࡢᐤ୚ࢆ᳨ウࡍࡿࡓࡵ࡟ศᕸᆺࡢ㝆㞵㸫ὶฟࣔࢹࣝࢆ⏝࠸࡚ᑐ㇟ὶᇦࡢὶฟゎᯒࢆ⾜ࡗࡓ㸬ᮏࣔࢹࣝࡣ㸪ὶᇦࢆᩳ㠃㒊࡜Ἑ㐨

Fig. 2 Rainfall observation mesh of X-band MP radar㒊࡟ศ๭ࡋ㸪㝆㞵ࢆධຊࢹ࣮ࢱ࡜ࡋ࡚ᩳ㠃㒊ࡢゎᯒ

and representative meshes of upstream and downstreamࢆ⾜࠸㸪ᩳ㠃㒊ᮎ➃࠿ࡽࡢὶฟࢆἙ㐨㒊ࡢධຊࢹ࣮reaches in the four study catchments.

ࢱ࡜ࡋ࡚ࢩ࣑࣮ࣗࣞࢩࣙࣥࢆ⾜࠺ࡶࡢ࡛࠶ࡿ㸬ᮏ◊✲࡛ࡣ㸪ᅜᅵᆅ⌮㝔࡟ࡼࡾබ⾲ࡉࢀ࡚࠸ࡿ10m࣓ࢵr

ࢩࣗᶆ㧗ࢹ࣮ࢱ࠿ࡽGISࢆ⏝࠸࡚ᑐ㇟ὶᇦࢆᩳ㠃㒊࡜Ἑ㐨㒊࡟ศ๭ࡋࡓ㸬ᩳ㠃㒊ࡣ1010m࣓ࢵࢩࣗ࡟

Qva_in1ⅆᒣ⅊ᒙศ๭ࡋ㸪ྛ࣓ࢵࢩࣗࡀ⾲ᒙࡢⅆᒣ⅊ᒙ࡜ᅵᒙ࠿ࡽ࡞ࡿᅵሢ࡜⪃࠼㸪ᇶᮏせ⣲࡜ࡍࡿ㸦Fig. 3㸧㸬ྛせ⣲࡟hva౪⤥ࡉࢀࡓ㝆㞵ࡣ㸪ⅆᒣ⅊ᒙ࠾ࡼࡧᅵᒙࡢ㣬࿴Ỉᖏ

Qva_in2
Qva_out
Isoilࢆࡓࡔࡕ࡟ኚ໬ࡉࡏࡿ࡜௬ᐃࡋ㸪୙㣬࿴ᾐ㏱࠾ࡼࡧᅵᒙ୙㣬࿴ഃ᪉ὶ࡟ࡘ࠸࡚ࡣ⪃៖ࡋ࡚࠸࡞࠸㸬ⅆᒣ⅊ᒙ
࡬ࡢᾐ㏱⬟࠾ࡼࡧⅆᒣ⅊ᒙ࠿ࡽᅵᒙ࡬ࡢ㖄┤ᾐ㏱㏿ᗘࡣ㸪ᐃᩘ࡜ࡋࡓ㸦Table 1㸧㸬hsoil

ྛせ⣲ࡢⅆᒣ⅊ᒙ࠾ࡼࡧᅵᒙ࠿ࡽࡢഃ᪉ὶฟQsࡣ

Qsoil_in2
Qsoil_outࡑࢀࡒࢀୗࡢࢲࣝࢩ࣮๎࡟ࡼࡾồࡵࡓ㸬

Qs

Qsoil_in1

Ibedrock

WhK cosT sin T         㸦㸯㸧Fig. 3 Schematic illustration of hydrological simulation
at a mesh of slope segment.

― 458 ―Table 1 Parameters used in simulation of slope segment
Parameter
dt

Value

1Time step in slope segment

2.0secva

Thickness of volcanic ash layer

0.15m

Thickness of soil layer

1.5m

ߣva

Porosity of volcanic ash layer

0.5-

ߣs

Porosity of soil layer

0.4-

K

Saturated hydraulic conductivity of volcanic ash layer

3.6mm/h360.0mm/h

3.6mm/h

DDsva

K

s

Saturated hydraulic conductivity of soil layervaInfiltration rate into volcanic ash layer

Is

Infiltration rate into soil layer

360.0mm/hbInfiltration rate into deep layer

1.0mm/hn

Manning’s roughness coefficient (slope)

0.7mII

1

Table 2 Parameters used in simulation of stream segment
Parameter

dt2
n2
ߙ

Unit

Time step in a streamsegment
Manning’s roughness
coefficient (stream)
Coefficient of artificial
viscosity

Value

Unit

0.5

sec

0.08 m-1/3

wA wQ
wt wxs

Qin             㸦㸱㸧wQ wUQwz
 gAwtwx
wx

s-1/3

 gAW   㸦㸲㸧UgR

ࡇࡇ࡛㸪A㸸ὶỈ᩿㠃✚㸪Q㸸ὶ㔞㸪Qin㸸ᩳ㠃࠿ࡽࡢ

0.2ഃ᪉ὶධ㸪U㸸᩿㠃ᖹᆒὶ㏿㸪g㸸㔜ຊຍ㏿ᗘ㸪z㸸ᇶ‽㠃࠿ࡽࡢỈ఩㸪 ߬㸸Ἑᗋ㠃࡟స⏝ࡍࡿࡏࢇ᩿ᛂຊ㸪ߩ㸸Ỉࡢᐦᗘ㸪R㸸ᚄ῝࡛࠶ࡿ㸬ᗏ㠃ࡏࢇ᩿ᛂຊ࡟ࡘࡇࡇ࡛㸪W㸸せ⣲ࡢ1㎶ࡢ㛗ࡉ㸪h㸸㣬࿴ᖏỈ῝㸪K㸸࠸࡚ࡣ࣐ࢽࣥࢢ๎ࢆ⏝࠸ࡓ㸬ⅆᒣ⅊ᒙࡶࡋࡃࡣᅵᒙࡢ㣬࿴㏱Ỉಀᩘ㸪ߠ㸸ὶୗ᪉ྥࡢᩳ㠃໙㓄࡛࠶ࡿ㸬ⅆᒣ⅊ᒙࡢ㣬࿴ᖏỈ఩ࡀᆅ⾲㠃

WUࡲ࡛฿㐩ࡋࡓሙྜ࠾ࡼࡧ㝆㞵ᙉᗘࡀᾐ㏱⬟ࢆୖᅇࡗࡓሙྜ࡟ࡣ⾲㠃ὶࡀⓎ⏕ࡍࡿ࡜ࡋࡓ㸬⾲㠃ὶࡣୗࡢ

gn2U U
R1 / 3             㸦㸳㸧࣐ࢽࣥࢢᘧ࡟ࡼࡾ⟬ฟࡋࡓ㸬ࡇࡇ࡛㸪n2㸸Ἑᕝࡢ࣐ࢽࣥࢢࡢ⢒ᗘಀᩘ࡛࠶ࡿ㸬⏝

QOF

Wi
n1

hOF

5/3

࠸ࡓㅖᐃᩘࡢ್ࢆTable 2࡟♧ࡍ㸬ࡇࢀࡽࡢᇶ♏ᘧ࡟          㸦㸰㸧ࡘ࠸࡚㸪ேᕤ⢓ᛶࢆ⪃៖ࡋࡓMacCormackἲ࡟ࡼࡗ࡚
ᕪศ໬ࡋࡓ㸬ᨭὶ࡜ࡢྜὶⅬ࡛ࡣ㸪ᨭὶ࠿ࡽࡢὶධ㔞ࢆᩳ㠃㒊࠿ࡽࡢὶධ࡜ྠᵝ࡟ᶓὶධ࡜ࡋ࡚ᢅࡗࡓ㸬ࡇࡇ࡛㸪i㸸ືỈ໙㓄㸪n1㸸ᩳ㠃㒊ࡢ⢒ᗘಀᩘ㸪h OF㸸ୖὶᇦ࡟࠾ࡅࡿ㝆㞵ࡢ㞟୰ࡀᅵ▼ὶⓎ⏕࠾ࡼࡧὶ⾲㠃ὶỈ῝࡛࠶ࡿ㸬せ⣲࠿ࡽࡢࡇࢀࡽࡢὶฟࡣ㸪᭱ฟ࡟ཬࡰࡍᙳ㡪ࢆ᳨ウࡍࡿࡓࡵ࡟㸪␗࡞ࡿ㝆㞵ࢆ୚ᛴ໙㓄᪉ྥࡢ㞄᥋せ⣲࡟ࡍ࡭࡚ὶୗࡍࡿ࡜ࡋ㸪ྛせ࠼ࡓ㸰᮲௳࡟ࡘ࠸࡚ὶฟࢩ࣑࣮ࣗࣞࢩࣙࣥࢆ⾜ࡗࡓ㸬⣲࣭ᒙࡢὶධ㔞࡜ὶฟ㔞ࡢ཰ᨭ࠿ࡽ㣬࿴ᖏỈ῝ࢆồCase 1ࡣᅵ▼ὶࡢ⿕ᐖࢆཷࡅࡿ⠊ᅖ࡛࠶ࡿୗὶᇦ࡟ࡵࡓ㸬Ἑᕝ㒊࡜㞄᥋ࡍࡿせ⣲࠿ࡽࡢὶฟࡣ㸪Ἑᕝ࡬࠾ࡅࡿ௦⾲ᆅⅬࡢ㝆㞵ࢆὶᇦ඲య࡟୚࠼ࡓ㸬୍⯡ⓗࡢὶධ㔞࡜ࡋ࡚Ἑ㐨㒊ࡢィ⟬࡟ཷࡅΏࡋࡓ㸬ⅆᒣ⅊࡞ᒣᆅ῱ὶ࡛ࡣୗὶᇦࡢࡳ࡛ᆅୖ㞵㔞ࡀほࡢᾐ㏱⬟࠾ࡼࡧ㣬࿴㏱Ỉಀᩘ࡞࡝ࡣᱜᓥ࡟࠾ࡅࡿ᪤࠸ࡿ㸬ᱜᓥ࡟࠾࠸࡚ࡣ༡ᓅᒣ㡬ⅆཱྀ࠾ࡼࡧ᫛࿴ⅆཱྀ ◊✲㸦᫓ᒣࡽ㸪1977㸧ࢆཧ⪃࡟Ỵᐃࡋࡓ㸦Table 1㸧㸬ࡢ༙ᚄ2 kmࡣ❧ࡕධࡾ⚗Ṇ༊ᇦ࡜࡞ࡗ࡚࠸ࡿࡓࡵ㸪Ἑ㐨㒊ࡣ㸪୍ḟඖ୙ᐃὶ࡜ࡋ࡚Ἑᕝὶฟ㔞ࢆィ⟬ࡋࡓ㸬㐃⥆ᘧ࠾ࡼࡧ㐠ື㔞ᘧࡣ௨ୗࡢ㏻ࡾ࡛࠶ࡿ㸬ୖὶᇦ࡟࠾ࡅࡿᆅୖ㞵㔞ࢆほࡉࢀ࡚ࡍࡿࡇ࡜ࡀ࡛ࡁࡎ㸪㞵㔞ィࡣ୰ὶ㹼ୗὶ㒊࡟ࡢࡳᩚഛࡉࢀ࡚࠸ࡿ㸬Case 1― 459 ―Fig. 4 Occurrences of debris flow from Jun to September 2012. Arrows indicate occurrence(s) of debris flow in thestudy catchments.
࡟࠾ࡅࡿࢩ࣑࣮ࣗࣞࢩࣙࣥ⤖ᯝࡣ㸪࣮ࣞࢲ㞵㔞ࡀ౑࠼࡞࠸ሙྜ࡟ධᡭ࡛ࡁࡿ㞵㔞ࢹ࣮ࢱ࠿ࡽண

ࡉࢀࡿἙᕝὶฟ㔞ࢆព࿡ࡍࡿ㸬୍᪉Case 2࡛ࡣ㸪ᅵ▼ὶ㝆㞵๓
2012/7/7 10:00Ⓨ⏕※࡛࠶ࡿୖὶᇦࡢ௦⾲ᆅⅬࡢ㝆㞵ࢆὶᇦ඲య࡟୚࠼ࡓ㸬ィ⟬ᮇ㛫ࡣ2012ᖺ6᭶1᪥㹼7᭶15᪥࡛࠶ࡿ㸬 ⤖ᯝ࡜⪃ᐹ  ᅵ▼ὶࡢⓎ⏕
Fig. 4࡟2012ᖺ6㹼9᭶ࡢ㔝ᑼᕝୗὶ㸦ND㸧࡟࠾ࡅࡿ࣮ࣞࢲ㞵㔞࠾ࡼࡧᅵ▼ὶࡢⓎ⏕࡟ࡘ࠸࡚♧ࡍ㸬ࡲࡓ㸪⌧ᆅほࢆ⾜ࡗࡓ㸲Ἑᕝ࡟࠾ࡅࡿᅵ▼ὶⓎ⏕≧ἣࢆ⾲㸱࡟♧ࡍ㸬㸯ศ㛫㞵㔞ࡀ50 mm/hࢆ㉸࠼ࡿࡼ࠺࡞ᙉ࠸㝆㞵ᙉᗘࡀほࡉࢀࡓ㝿࡟ᅵ▼ὶࡢⓎ⏕ࡀ☜ㄆࡉࢀࡓ㸬ࡓࡔࡋ㸪6᭶12᪥ࡢࡼ࠺࡟ప㝆㞵ᙉỈ఩䝢䞊䜽᫬
2012/7/7 10:44

ᗘ࡟ࡶ㛵ࢃࡽࡎᅵ▼ὶࡀⓎ⏕ࡋࡓ஦౛ࡸ㸪7᭶1᪥ࡢࡼ࠺࡟ᙉ࠸㝆㞵࡟࠾࠸࡚ࡶᅵ▼ὶࡀⓎ⏕ࡋ࡞࠿ࡗࡓ஦౛ࡶࡳࡽࢀࡓ㸬➨஧ྂ㔛ᕝࢆ㝖࠸ࡓ㸱Ἑᕝ࡟࠾࠸࡚ᅵ▼ὶࡀⓎ⏕ࡋࡓ7᭶7᪥ࡢἙᕝࡢᵝᏊࢆFig. 5-8࡟♧ࡍ㸬࠸ࡎࢀࡢἙᕝ࡟࠾࠸࡚ࡶ㸪ᅵ▼ὶࡣἙᕝෆࢆὶୗࡋ㸪≀ⓗேⓗ࡞⿕ᐖࡣⓎ⏕ࡋ࡚࠸࡞࠸㸬ࡲࡓ㸪࠸ࡎࢀࡢἙᕝࡶ↓㝆㞵ᮇ㛫࡟ࡣἙᕝὶ㔞ࡀ㸮࡛࠶ࡾ㸪㝆㞵࡟కࡗ࡚ᛴ⃭࡟ὶฟ㔞ࡀቑຍࡋࡓ㸬㔝ᑼᕝ࡛ࡣ10:44࡟Ỉ఩ࡀ᭱኱࡜࡞ࡾ㸪⣙0.4m࡛࠶ࡗࡓ㸬␭⏣ࡽ㸦1985㸧
࡞࡝ࡢ㐣ཤࡢほ౛࡜ྠᵝ࡟ὶฟࣆ࣮ࢡࡣ1ᗘ࡛ࡣ

Fig. 5 Stream flow of Nojiri River in July 7, 2012࡞ࡃ㸪ᅵ▼ὶࡢࢧ࣮ࢪ࡜ぢࡽࢀࡿ㛫Ḟⓗ࡞኱ࡁ࡞ὶฟࡀࡳࡽࢀࡓ㸬ᣢᮌᕝ࡛ࡣ㝆㞵࡟క࠺ὶฟࡀⓎ⏕ࡋࡓࡶࡢࡢ㸪ほᆅⅬ࡟࠾࠸࡚ࡣὶ㊰඲ᖜ࡛ὶୗࡍࡿࡀⓎ⏕ࡋ࡚࠸ࡓ㸬᭷ᮧᕝ࡟࠾࠸࡚ࡶ㝆㞵࡟࡜ࡶ࡞ࡗࡲ࡛࡟⮳ࡽ࡞࠿ࡗࡓ㸬➨஧ྂ㔛ᕝ࡛ࡣ㸪ᅵ▼ὶ࡜ࡋ

ࡓὶฟࡀほ࡚ㄆ▱ࡉࢀ࡚࠸࡞࠸ࡶࡢࡢ㸪㝆㞵࡟࡜ࡶ࡞ࡗ࡚ὶฟ࡟఩⨨ࡍࡿ࣡࢖ࣖࢭࣥࢧ࣮࡟ࡼࡗ᳨࡚▱ࡉࢀ࡚࠾ࡾ㸪― 460 ―ࡉࢀࡓ㸬ᅵ▼ὶࡢⓎ⏕ࡣྛἙᕝୖὶ㒊㝆㞵๓
2012/7/7 10:00

㝆㞵๓
2012/7/7 10:00

Ỉ఩䝢䞊䜽᫬
2012/7/7 10:46

Ỉ఩䝢䞊䜽᫬
2012/7/7 10:46

Fig. 6 Stream flow of Mochiki River in July 7, 2012㝆㞵๓
2012/7/7 10:00

Fig. 8 Stream flow of Arimura River in July 7, 2012ᣢᮌᕝ࠾ࡼࡧ᭷ᮧᕝ࡛ࡣ࣡࢖ࣖࢭࣥࢧ࣮ࡼࡾୗὶ
࡟࠾࠸୍࡚㒊ࡢἙᕝỈࡀἙᗋ࡬࡜ᾐ㏱ࡋࡓ࡜⪃࠼ࡽࢀࡿ㸬➨஧ྂ㔛ᕝ࡛ࡣ㸪ほ఩⨨ࡢ┤ୖὶ࡟࣡࢖ࣖࢭࣥࢧ࣮ࡀタ⨨ࡉࢀ࡚࠸ࡿࡀ㸪Ỉ఩ࡀࢭࣥࢧ࣮㧗㸦⣙60cm㸧ࡲ࡛ୖ᪼ࡋ࡞࠿ࡗࡓ࡜⪃࠼ࡽࢀࡿ㸬 㝆㞵ࡢ✵㛫ศᕸ㔝ᑼᕝୗὶ㸦ND㸧࡟࠾࠸࡚50mm/hࢆ㉸࠼ࡿ1ศ㛫Ỉ఩䝢䞊䜽᫬
2012/7/7 10:30

㞵㔞ࡀほࡉࢀࡓ࡟ࡶ㛵ࢃࡽࡎᅵ▼ὶࡀⓎ⏕ࡋ࡞࠿ࡗࡓ7᭶1᪥ࡢ㝆㞵࢖࣋ࣥࢺ࡟ࡘ࠸࡚㝆㞵ศᕸࢆ
Fig. 9࡟♧ࡍ㸬㝆㞵࢖࣋ࣥࢺࢆ㏻ࡌ࡚㸪ྛἙᕝࡢୖὶᇦࡼࡾࡶୗὶᇦ࡟࠾࠸࡚㝆㞵ᙉᗘࡀᙉ࠸ഴྥࡀぢࡽࢀࡓ㸬ྛἙᕝࡢୖὶᇦ࡛ࡣ㸪1ศ㛫㝆㞵ᙉᗘࡀ
᭱኱50 mm/h⛬ᗘ࡛࠶ࡗࡓ㸬 ᅵ▼ὶࡀⓎ⏕ࡋࡓ7᭶12᪥ࡢ㝆㞵࢖࣋ࣥࢺ࡟࠾ࡅࡿ㝆㞵ศᕸࢆFig. 10࡟♧ࡍ㸬㔝ᑼᕝ࡛ࡣ7᭶1᪥18:35
࡟ᅵ▼ὶⓎ⏕ࡀ᳨▱ࡉࢀࡓࡀ㸪ࡑࡢ┤๓࡟100 mm/hࢆ㉸࠼ࡿ㝆㞵ࡢ㞵ᇦࡀ㔝ᑼᕝୖὶᇦ࡟㞟୰ࡋ࡚࠸ࡓ㸬ྠᵝ࡟㸪ᣢᮌᕝ㸪➨஧ྂ㔛ᕝ㸪᭷ᮧᕝ࡟࠾࠸࡚

Fig. 7 Stream flow ofFurusato River in July 7, 2012ࡶୖὶᇦ࡟࠾࠸࡚㠀ᖖ࡟ᙉ࠸㝆㞵ࡀほ― 461 ―ࡉࢀࡓ㸬2012/7/1 7:26

2012/7/12 18:30

2012/7/1 18:16

2012/7/12 18:35

2012/7/2 2:25

2012/7/12 19:00

Fig. 9 Spatial distribution of rainfall in July 1-2, 2012

Fig. 10 Spatial distribution of rainfall in July 12, 2012 㝆㞵ࡢ೫ᅾࡀὶฟ࡟୚࠼ࡿᙳ㡪࠸ࡓ㸦㣬࿴ᖏỈ఩ࡀప࠸㸧ࡓࡵ࡛࠶ࡾ㸪ᮏࢩ࣑ࣗࣞ㔝ᑼᕝ㸪ᣢᮌᕝ㸪➨஧ྂ㔛ᕝ㸪᭷ᮧᕝ࡟࠾ࡅࡿἙ࣮ࢩࣙࣥࡣὶᇦࡢ≧ែࢆࡼࡃ෌⌧ࡋ࡚࠸ࡿ࡜⪃࠼ࡽᕝὶฟ㔞ࡢࢩ࣑࣮ࣗࣞࢩࣙࣥ⤖ᯝࢆFig. 11-14࡟♧ࡍ㸬ࢀࡓ㸬ࡓࡔࡋ㸪➨஧ྂ㔛ᕝࡣ㞟Ỉ㠃✚ࡀᑠࡉ࠸ࡓࡵ㔝ᑼᕝ㸪ᣢᮌᕝ㸪᭷ᮧᕝ࡛ࡣᅵ▼ὶࡀⓎ⏕ࡋࡓ࢖࣋࡟Ἑᕝὶฟ㔞ࡀᑠࡉࡃ㸪Ἑᕝὶฟ㔞ࡢ෌⌧ᛶࡀࡼࡃࣥࢺ࡟࠾࠸࡚ࣆ࣮ࢡὶฟ㔞ࡀ኱ࡁ࠸ഴྥ࡜࡞ࡾ㸪ὶ࡞࠿ࡗࡓ㸬ฟ⌧㇟ࢆᐃᛶⓗ࡟ࡣ෌⌧࡛ࡁ࡚࠸ࡿ࡜⪃࠼ࡽࢀࡿ㸬୍⯡ⓗ࡟ᆅୖ㞵㔞ィࡀタ⨨ࡉࢀࡿୗὶᇦ࡟࠾ࡅࡿࡲࡓ㸪㝆㞵ᙉᗘࡢ኱ࡁ࠸࡟ࡶ㛵ࢃࡽࡎᅵ▼ὶࡀⓎ⏕㞵㔞ࢆὶᇦ඲య࡟㐺⏝ࡋࡓCase 1࡟ẚ࡭࡚ୖὶᇦࡢ

ࡋ࡞࠿ࡗࡓ7᭶1᪥࡟࠾࠸࡚㸪Ἑᕝὶฟ㔞ࡢィ⟬್ࡣ௦⾲ᆅⅬࡢ㝆㞵ࢆ㐺⏝ࡋࡓCase 2࡛ࡣ㸪Ἑᕝὶฟ㔞ࡢᑠࡉ࠿ࡗࡓ㸬ࡇࢀࡣ㝆㞵๓࡟ᩳ㠃ᅵᒙෆࡀ஝⇱ࡋ࡚ኚືࡀᅵ▼ὶⓎ⏕࣭㠀Ⓨ⏕࡜ࡼࡾㄪ࿴ⓗ࡛࠶ࡗࡓ㸬― 462 ―

Fig. 11 Simulation results of stream discharge at thedownstream end of Nojiri River. Arrows indicate observed

Fig. 13 Simulation results of stream discharge at thedownstream end of Furusato River. Arrows indicateobserved time of debris flow.

time of debris flow.

Fig. 12 Simulation results of stream discharge at thedownstream end of Mochiki River. Arrows indicate

Fig. 14 Simulation results of stream discharge at thedownstream end of Arimura River. Arrows indicate observed
time of debris flow.

observed time of debris flow.

౛࠼ࡤ㸪㔝ᑼᕝ࡟࠾࠸࡚6᭶16᪥࡟ᅵ▼ὶࡀ᳨▱ࡉࢀ

㔞10.3 m3/sࡼࡾࡶᑠࡉࡃồࡵࡽࢀࡓ㸬ࡇࡢࡼ࠺࡟㸪࡞࠿ࡗࡓࡀ㸪Case 1࡛ࡣࣆ࣮ࢡὶฟ㔞ࡀ8.7 m3/s࡜๓ᅵ▼ὶࡢⓎ⏕※ࡢ㞵㔞ࢆ㐺⏝ࡍࡿࡇ࡜࡛㸪ᅵ▼ὶࡢ᪥࡟ᅵ▼ὶࡀ᳨▱ࡉࢀࡓ㝿ࡢὶฟ㔞ࡼࡾࡶ኱ࡁࡃ࡞

Ⓨ⏕࡟㛵ࢃࡿἙᕝὶฟ㔞ࢆ㐺ษ࡟⾲⌧࡛ࡁࡿ࡜⪃࠼ࡗࡓ㸬୍᪉㸪Case 2࡛ࡣ㸪6᭶16᪥ࡢࣆ࣮ࢡὶฟ㔞ࡣࡽࢀࡓ㸬

4.2 m3/s࡛࠶ࡾ㸪ᅵ▼ὶࡀⓎ⏕ࡋࡓ๓᪥ࡢࣆ࣮ࢡὶฟ

6᭶27᪥ࡣ࠸ࡎࢀࡢἙᕝ࡟࠾࠸࡚ࡶᅵ▼ὶࡀⓎ⏕― 463 ―ࡋ࡞࠿ࡗࡓࡀ㸪Case 1࠾ࡼࡧCase 2࡜ࡶ࡟ࣆ࣮ࢡὶฟ

July 1, 2012㔞ࡀ኱ࡁࡃィ⟬ࡉࢀࡓ㸬཯ᑐ࡟㸪6᭶12᪥࡟ࡣ㔝ᑼᕝ
࡟࠾࠸࡚4 m3/s௨ୗࡢẚ㍑ⓗᑠࡉ࠸ὶ㔞࡜ぢ✚ࡶࡽࢀࡓ࡟ࡶ㛵ࢃࡽࡎ㸪ᐇ㝿࡟ࡣᅵ▼ὶࡀⓎ⏕ࡋࡓ㸬6᭶12᪥ࡢᅵ▼ὶࡣ⣙2࠿᭶ࡪࡾࡢⓎ⏕஦౛࡛࠶ࡾ㸪Ⓨ⏕※࡟୙Ᏻᐃᅵ◁࡛࠶ࡿᄇⅆሁ✚≀ࡀከࡃሁ✚ࡋ࡚࠸ࡓ࡜⪃࠼ࡽࢀࡿ㸬ࡶࡋࡃࡣཌࡃሁ✚ࡋࡓⅆᒣ⅊࡟
ࡼࡿᾐ㏱⬟ࡢపୗࡀ㢧ⴭ࡛࠶ࡗࡓྍ⬟ᛶࡶ࠶ࡿ㸬ࡇࡢࡼ࠺࡟㸪ᅵ▼ὶࡢⓎ⏕࡟ࡣὶฟ㔞ࡢ኱ᑠࡔࡅ࡛࡞
ࡃ㸪ᄇⅆሁ✚≀ࡢሁ✚≧ἣࡶ㔜せ࡛࠶ࡿ࡜⪃࠼ࡽࢀࡿ㸬 ᅵ▼ὶⓎ⏕࡟ᐤ୚ࡍࡿᩳ㠃࠿ࡽࡢὶฟᅵ▼ὶ㠀Ⓨ⏕࢖࣋ࣥࢺ࡛࠶ࡿ7᭶1᪥࠾ࡼࡧᅵ▼ὶ

July 7, 2012ࡀⓎ⏕ࡋࡓ7᭶7᪥࡟࠾ࡅࡿὶฟࣆ࣮ࢡ᫬ࡢ⾲㠃ὶỈ῝ศᕸࢆFig. 15࡟♧ࡍ㸬ᅵ▼ὶⓎ⏕࠾ࡼࡧ㠀Ⓨ⏕᫬ࡢὶᇦෆࡢὶฟ࡟ࡘ࠸࡚ẚ㍑ࡍࡿ࡜㸪ᅵ▼ὶࡀ㠀Ⓨ⏕ࡢ7᭶1᪥࡛ࡣ⾲㠃ὶࡀⓎ⏕ࡋ࡚࠸ࡓࡀ㸪ࡑࡢỈ῝
ࡣ0.05 m௨ୗ࡛࠶ࡾ㸪Ⓨ⏕ሙᡤࡶὶᇦෆࡢ୍㒊࡟㝈ࡽࢀ࡚࠸ࡓ㸬୍᪉㸪ᅵ▼ὶࡀⓎ⏕ࡋࡓ7᭶7᪥ࡢ࢖࣋ࣥࢺ࡛ࡣὶᇦࡢ඲ᇦ࡛⾲㠃ὶࡀⓎ⏕ࡋ㸪Ἑᕝ㒊࡟᥋⥆ࡍࡿ㇂ᆅᙧ㸦࢞ࣜ㸧࡟࠾࠸࡚⾲㠃ὶࡀ㞟୰ࡋ࡚࠸ࡓ㸬ࡇࡢࡼ࠺࡟㸪⾲㠃ὶࡀᩳ㠃㒊ࡔࡅ࡛࡞ࡃ㇂ᆅᙧࡲ࡛㐃⥆ࡍࡿࡇ࡜ࡀ㸪ᅵ▼ὶࢆⓎ⏕ࡉࡏࡿࡼ࠺࡞኱

Fig. 15 Simulation results of water heights of overland flowࡁ࡞Ἑᕝὶฟ㔞࡟ᐤ୚ࡍࡿࡇ࡜ࡀ♧ࡉࢀࡓ㸬

in July 1, 2012 and July 7 2012.

 ࡲ࡜ࡵ ࢻMP࣮ࣞࢲ࡟ࡼࡾ㝆ୗⅆᒣ⅊ணᅵ▼ὶ㢖Ⓨ῱ὶࡢὶฟ㐣⛬࡟࠾ࡅࡿ㝆㞵ศᕸࡢᐤ࡟࠾࠸࡚㔜せ࡞ࣃ࣓࣮ࣛࢱ࡛࠶ࡿᄇ↮ᰕ㧗ࡸⅆᒣ⅊⃰ᗘࢆᐃ࡛ࡁ୚ࢆ᳨ウࡍࡿࡇ࡜ࢆ┠ⓗ࡜ࡋ࡚㸪㮵ඣᓥ┴ᱜᓥ࡟࠾ࡿ஦౛ࡀ♧ࡉࢀ࡚࠾ࡾ㸪ࡇࢀࡽࢆྲྀࡾධࢀࡿࡇ࡜࡛㸪࠸࡚⌧ᆅほἙᕝࡈ࡜ࡢᅵ▼ὶⓎ⏕ண㔞ほࢆ⾜࠸㸪ࡉࡽ࡟XࣂࣥࢻMP࣮ࣞࢲࡢ㞵ࢹ࣮ࢱࢆᒣᆅ῱ὶ㝆㞵㸫ὶฟࣔࢹࣝ࡟㐺⏝ࡋ㸪ὶฟࢩ࣑࣮ࣗࣞࢩࣙࣥࢆ⾜ࡗࡓ㸬⌧ᆅほࡼࡾ㸪࠸ࡢ⢭ᗘࡀ኱ࡁࡃྥୖࡍࡿྍ⬟ᛶࡀ࠶ࡿ㸬ࡎࢀࡢἙᕝࡶ↓㝆㞵ᮇ㛫ࡣὶỈࡀ࡞ࡃ㸪㝆㞵࡟కࡗཧ⪃ᩥ⊩࡚㸪ᛴ⃭࡟ὶฟ㔞ࡀቑຍࡋ㸪㝆㞵⤊஢ᚋࡍࡳࡸ࠿࡟

ῶ⾶ࡋ࡚࠸ࡓ㸬࣮ࣞࢲ㞵㔞ほ⤖ᯝࡼࡾ㸪ᅵ▼ὶࡢ஭ཱྀṇே㸦2012㸧㸸ᱜᓥ࡟࠾ࡅࡿⅆᒣ⅊ᨺฟ㔞ணⓎ⏕࣭㠀Ⓨ⏕ࡣྛ῱ὶࡢⓎ⏕※࡛࠶ࡿୖὶᇦ࡟࠾ࡅ࡟㛵ࡍࡿ◊✲㸪ி㒔኱Ꮫ㜵⅏◊✲ᡤᖺሗ㸪Vol. 55B㸪ࡿ㝆㞵ᙉᗘࡀ㠀ᖖ࡟㔜せ࡛࠶ࡿࡇ࡜ࡀ♧ࡉࢀࡓ㸬pp. 169-175 ୍⯡ⓗ࡟ᆅୖ㞵㔞ィࡀタ⨨ࡉࢀࡿୗὶᇦ࡟࠾ࡅࡿ᫓ᒣඖᑑ㸪ୗᕝᝋ㑻㸪஭ୖ฼᫛㸦1977㸧㸸ᱜᓥⅆᒣ㞵㔞ࢆὶᇦ඲య࡟㐺⏝ࡋࡓCase 1࡟࠾ࡅࡿὶฟ㔞ࢩ⅊◁ࡢ≀⌮ⓗㅖᛶ㉁㸪㮵ඣᓥ኱Ꮫ㎰Ꮫ㒊₇⩦ᯘሗ࣑࣮ࣗࣞࢩࣙࣥ⤖ᯝ࡟ẚ࡭࡚㸪ୖὶᇦࡢ௦⾲ᆅⅬࡢ࿌㸪Vol. 5㸪pp. 65-92㝆㞵ࢆ㐺⏝ࡋࡓCase 2࡛ࡢࢩ࣑࣮ࣗࣞࢩࣙࣥ⤖ᯝࡣ␭⏣ㄔ㸪⁀ụ༤ᩥ㸪ᯇᯞಟ἞㸪ᳺᮾ୍㑻㸦1985㸧㸸

ᅵ▼ὶⓎ⏕࢖࣋ࣥࢺ࡛Ἑᕝࣆ࣮ࢡὶฟ㔞ࡀࡼࡾ኱ࡁᅵ▼ὶ࡟࠾ࡅࡿ㌿Ἴิࡢ≉ᛶ㸪➨29 ᅇỈ⌮ㅮ₇఍ࡃ࡞ࡾ㸪㠀Ⓨ⏕࢖࣋ࣥࢺ࡛ࡣࣆ࣮ࢡὶฟ㔞ࡀᑠࡉࡃ㸪ᅵ▼ὶࡢⓎ⏕ண࡞࡝࡟࠾࠸࡚ୖὶᇦࡢ㝆㞵ࢹ࣮ࢱㄽᩥ㞟㸪Vol.29㸪pp.543-548
Ᏻ⏣ᡂኵ㸪Ლ㇂⩏㞝㸪ᅧ཭ඃ㸦2012㸧㸸XࣂࣥࢻMPࢆ⏝࠸ࡿࡇ࡜ࡢ㔜せᛶࡀ♧ࡉࢀࡓ㸬ࡓࡔࡋ㸪㝆㞵࠾࣮ࣞࢲ࡟ࡼࡿᾋ㐟ⅆᒣ⅊ィࡼࡧἙᕝὶฟ㔞ࢩ࣑࣮ࣗࣞࢩࣙࣥ⤖ᯝࡔࡅ࡛ࡣㄝ᫂⅏◊✲ᡤᖺሗ㸪Vol. 55B㸪pp. 1-8

ࡢヨࡳ㸪ி㒔኱Ꮫ㜵࡛ࡁ࡞࠸ᅵ▼ὶⓎ⏕࢖࣋ࣥࢺࡶ࠶ࡾ㸪ⅆᒣ⅊ࡢሁ✚≧ἣ࡞࡝࡟ࡘ࠸࡚⪃៖ࡍࡿᚲせࡀ࠶ࡿ㸬㏆ᖺ㸪Xࣂࣥ

― 464 ―

㸦ㄽᩥཷ⌮᪥㸸ᖺ᭶᪥㸧