The Upper Tenryu Reach
1.Hydro-geologic features of the upper Tenryu reach from a geo-tectonic
viewpoint: how the river was formed (“kawanari”)
1-1.Hydro-Geology

opposed to oceanic crust creation on divergent

The Japanese Archipelago was generated fromboundaries.

relative motions of four interacting tectonic

colliding plates brought trench subductions andplates drifting with different velocities andthe corresponding uplifts in the continental

directions, namely, Pacific Plate, Philippine

plates.

Plate, Eurasian Plate, and North American Plate,water, so to speak, for the Eurasian sea coaston the east coast of the Eurasian Continent.

against tsunamis induced by dip-slip faulting in

Its geology was made complex by diverse

sea trench subduction zones of the Pacificsea-floor sediment deposits piled up andOcean.

surcharged at the continental plate boundary ofJapanese inlands by hot magma plumes fromthe archipelago as exotic terranes by oceanic

deep spots of subduction zones, as it was notplates in a colliding tectonic convergence

the boundary of inter-continental convergence.

process through which plates are subducted, asVolcanoes caused additional active lifting andNorth American
Plate(Okhotsk Plate)Eurasian Plate

The relative motion of the

The Japanese islands stand as a break

Volcanic arcs were formed in the

Kamaguchi
Gate

Chishima Trench

Lake Suwa

MainchannelJapan Deep
Pacific Plate
Nankai TroughSagamiTrough Izu-Ogasawara
TrenchRyukyu Islands
TroughPhilippine Plate

Mt. Akadake
Kiso Mountains
Japan Central Alps
Mibu river

Ina Basin(Ina-dani)
Ryusai areawith tagiri

Mt. Senjoh
Ryutoh area

Koshiburiver

MainchannelAkaishi Mountains
Japan Southern Alps
Mt. Akaishi-dake

Tohyama riverFig-1: Formation of
the upper Tenryu Reach

Narrow path
(Stenosis)

1basin called for an exit of water for lack ofMedian Tectonic Line

Mt.Suribachi
Shiojiri Passsufficient evapotranspiration.

Runoff from theLake Suw alake was made possible by its relative height
Mt.Yatsugatake

along the tectonic line.

Mt.Nyugasa

The south western

Ina city

section became its way-out as a result of

Mt.Komaga-take
Komagane city

cumulative tectonic uplift protrusion in its

Mt.Senjoh-gatakeHyakken-Nagisurrounding and a runway blockage on the
Mt.Shiomi-dake

Iida city

south

Mt.Arakaw a-dake
Mt.Akaishi-dake

Mt.Enaeastern

sectionYatsugatake volcanoes.
Mt.Tekari
-dake

by

eruptionsof

Water runs off

Granitesouthwardly into Ina basin, also a tectonic basin,

Fig-2: Geology of the upper Tenryu reach

which is lower than the lake and slanting gently
towards the south.

metamorphic volatilization of the geology. The

The same relative motion of plates folded thegeo-history of north-eastern and south-western

median tectonic line and brought forth aparts of Japan is mostly describable as an

discontinued section in the rising mountaininterplay of two corresponding sets of tectonic

range. The section, a kind of kink, became aplates.

weak line playing a role as a southern water

On the other hand, the geo-history of

the middle part of the Japanese main island

way-out(Honshu) demands the comprehension of theimpoundment the basin as a whole; and thus thein-between interplays of these two sets ofupper Tenryu reach, “Ina-dani,” came into

oceanic and continental plates.

being with a due water outlet into the Pacific

The Japanese median tectonic line turns out toOcean.

be a far wider tectonic topography of Fossa

The relative motions of the plates andMagna in the middle part of Japan that stands

distribution of intra-plate geologic weak lines

between the north-eastern and south-western

caused a series of westward shifts of upliftparts.

The tectonic line is simply runningzones in the basin from one era to the other.

parallel to Philippine-Eurasian plate boundary

As a result, the present trunk channel of thein the south-western part of Japan.

The

upper Tenryu river is situated on the western

western margin of Fossa Magna is calledpart of the basin, along Ina-dani fault line

Itoigawa-Shizuoka tectonic line in particular.

between the Akaishi mountain range (theLake Suwa, a rift lake, was formed at the center

Japanese southern Alps) and the Kiso mountainof the Japanese main island by transformative

range (the Japanese central Alps).

relative motions between two sets of plates,

Long principal tributaries of the river have as

four in total.

The lake region is the highest

their catchments an older north-south tectonic

part along the tectonic line between risinglineament, seen particularly in the eastern

mountain ranges.

“Ryutoh” region.

The rift lake forming Suwa

2

for

Ina

basin

to

prevent

theThese tributaries run

westward to join the main channel of Tenryu

the southern side of the mountains, which areriver

low-rising

still in the uplifting process despite its“Ina-sanchi” hills lying at the western edge of

discontinuity due to the kink of the medianthe lineaments.

tectonic line.

throughpassesdividing

Younger western “Ryusai”

The middle part of Tenryu river,region has not seen sufficient development ofdissecting the upper and lower reach, is annorth-south tectonic lineaments.

antecedent valley in a tectonically uprising

Tributarygorges, therefore, run eastward with steep

mountainous

gradients to hit the main channel straightly.

channel gives superiority to entrenchment,

The gorges entrench rising mountainous ranges

while hardly broadening.

deeply.

range,

where

erosivemain

The western gorges, going down

still-rising Ryusai terraces, have dynamic flows

1-2. Sediment production

and form “Tagiri” (namely incised paddy fields,Bothor literally ‘charged’).

Tagiri is an incisedsouthern Alps) on the eastern rim and Kiso

riverine terrace with high cliffs between stream

mountains (the Japanese central Alps) on thebeds and tablelands with a trace of debris fanswestern rim of Ina basin are active zones withon it. The western gorges promptly meet the

impressive uprising rates. They have not been

main trunk of strong transport power, which

subject to embrittlement effects of volcanic

itselfalteration, as they are away from the inland

has

entrenched

its

own

course.

Akaishivolcanic zones.

mountains(theJapanese

Located inland, sea trench

earthquakes, strong as they may be, seem tohave had only limited impacts on them.
Abrasive effects were seen in high altitudes
during past glacial periods.

The effects left

only minor impacts as their 3000-m heights
barely reach the southern tip of the Japaneseglacial formation zone since Japanese southerncoastlines are found in warmer fluctuating

Picture: Tagiri in Ryusai area
(Ohtagiri River, Komagane-Miyada)

monsoon belts.
The basin stands in The Japanese Pacific

The south-bound main channel, as it runs

climate region, as opposed to that of Japan Sea

down, sees occasional obstacles of geologic

climate region with much snow.

blocks with high erosion-resistibility andbasinnarrow pass sections of stricture left mostly

precipitation impacts of typhoons and frontal

untouched by wash-out effects of attacking

activities seen in monsoon belts, since it is nottributary streams.

on coastline but in the inland mountain range.

The main channel isrestrained by stenosis sections.

It flows out to

has

been

mostlyfree

However, theofstrongAlso, its major orientation runs north-south,3causing

lessorographic

precipitationAsaconsequence,theself-sustaining

amplification of warm wet air coming from theagricultural productivity and the population

south.

As a result, the basin has not seen

accumulation in Ina basin, in themselves, havemuch erosion and landslide impacts, even after

been limited in spite of thriving traffic ofinterglacial periods of Holocene era.

It keeps

people as a pivotal route from ancient times.

the highest potential of sediment productivity in

Major dams were constructed in the modern era

the Japanese Archipelago, with No.1 sedimentat cross sections of the trunk and the lower

wash-out production rate despite the mere 12th

boundary of Ina basin and at ending narrow

status in terms of catchment area.

The

paths of principal tributaries. In combination

insufficient erosion and slope failure processwith Sakuma dam in the lower reach, theyleft considerable amounts of seabed deposit inenabled hydro-power utilization in the river

shallow layers along the median tectonic line

basin as a whole.

with less metamorphism.

The deposit may

have derived either from the shallow sea on the

1-4. Flood control

eastern edge of the Eurasian Continent or fromThe upper Tenryu reach, with a relatively

oceanic plates transported by their drifts, andindependent rift lake on its upstream catchment,

sometimes accompanied by local accumulation

runs southward in the tectonic basin whoseof mineral substances, for instance, throughlower end is held tightly by stricture sections inleaching.

tectonically rising mountains.

The reachretains high sediment production potential

1-3. Water utilizationcompared to other regions of the Japanese

The upstream catchment of the independent

Archipelago presumably because it has beenbasin of Lake Suwa has another irrigation

mostly intact of volcanic activities and situatedsystem separated from those of the downstream

in the inland part of the Pacific side of Japandespite its juxtaposition as a basin.

Manywhere neither of impacts of glacial abrasion,

farmlands are found on terraces higher than thesnow, nor rainfall have been excessive in theriver channel in Ina basin.

Quaternary Period.

Major intake

Thus, both floodwater andpoints, where large-scale inlet is possible

sediment washout could become overwhelming

through dams and/or dikes, are mostly found inwith peak discharges seen mainly in upstream

eastern principal tributaries of Ryusai.

Thesections of geological stenosis, once drastic

In addition,

precipitation phenomena were to take place,intake points are limited.

Tohyama river, a major southern tributary, runs

although

off at the lowest end of Ina basin.

frequently.

There

they

have

not

been

observed

remain areas relying on rainwater, groundwater,

The fact that irrigation was not universallyand local irrigation both for agricultural andavailable

potable purposes.

development in Ina basin.

4

has

determined

the

land

use

As a result, landuse has been developed so as to adapt to thesenatural conditions, rather than to overcome.
One of the ways is to adopt successive open
leveessuitablechannels

and

for
to

unstablecrop

meandering

while

acceptingoccasional overtopping and retarding along themain trunk of the river.
Daminstallation,

which

was

Picture: Damages in Ohshika Village
in 1961 “Saburoku Disaster”(Koshibu River)promotedbasin-wide in the modern period, changed thecapacity of river discharge in the main channel
as

well

as

in

tributaries,

adversarily

downgrading rapport at narrow sections, forinstance.

Human casualties and economic

damages

of

major

flood

and

sediment

discharges in the order of historic “Saburoku
Saigai (Disaster)” in June, 1961, for example,
Picture: Damages in Takamori town
in 1961 “Saburoku Disaster”(Main channel)

could have been worsened by these and otherfacts such as short-sighted land use with poor
planning.

Basic dimensions of the upper

Tenryu reach are summarized in Table-1 below.

Picture: Damages in Komagane Cityin 1961 “Saburoku Disaster”(Shingu River, Nakazawa district)

Table-1: Basic dimensions of of the upper Tenryu reachCharacteristics
Headwater of the river
Highest point
Drainage area
Stretch of the main channel
Max. design discharge
Coefficient of river regime
River width
Typical Gradient in the maiin channel
Typical Gradient in the tributaries
Typical size of bed material
Precipitation

Dimension
Chino city, Nagano Prefecture
3,120m5090km2
228 km
5,700m3/sec
18-22764 - 546m
0.5%
5% - 20%3-120mm30-300mm
118.0mm
150.0mm
346.3mm
1471.7mm
1072mmNote
Mt. Yatsugatake(Mt. Akadake with the altitude of 2899.2m)
Mt. Akaishidake, Koshibu river
Approximately
Including the portion in Lake Suwa, approximately
At Tenryu valley datum pointAt Miyagase datum point, year 2003-2012.
At high water levelor 1/200
or 1/5 - 1/20
Main channel
Tributaries
Max hourly rainfall, Ushiroyama rain gauge, August 8, 2009
Max 3-hr rainfall, Ushiroyama rain gauge, August 8, 2009
Max daily rainfall, Ichida rain observatory, June 27, 1961
Averaged annual rainfall from 2003-2012, averaged over observatories
12-month total in the worst drought year (1994), averageed over observatories

5

2.Socio-economic environment of the upper Tenryu reach seen from geographic
conditions: broader networks have supported the regional economy
Each period has had different states andeastern edge of the continent in the mid-latitude.

regions with mature culture and prosperous

Its south and southeast coast, facing northward

economic activities.

Whether it is thewarm Kuroshio ocean current, sees much rain

structure of political rule or that of economic

from monsoon climate while the north andproduction, or the combination thereof, that

northwest coasts see much snow by the lake

decides how mature their culture and prosperity

effect of the Japan Sea, a wide and deep

are, is still under discussion.

back-arc basin.

It appears

Fauna and flora of thereasonable to expect that an economy thrives

Japanese

under a less-exploitative ruling regime withtransformation and made a diverse ecosystemwell-balanced distribution of resources andas a variety of biological species had visited thereinvestment to production, in concomitanceislands in the Holocene Period.

with a production structure not only with land,come either through connection by land and of

production capital, and labor but also withthick ice during glacial ages and throughsizable technical innovation.

History seems tomaritime

have provided plenty of counter examples,

periods.

however.

Modern social science is full of

Likewise, in regard to connectedness and tie,

many useful ideas for analyzing dominant

the history on the Japanese Archipelago could

factors and mechanism such as a market based

be better understood by taking note of the factonefficientthat ruling influence of continental civilization

hierarchical organization, significance of wider

has not been unilaterally dominant with thetrade conditions, etc.

presence of a back-arc basin.

well-establishedrules,an

It would be a shorter

Archipelagoconnection

had

seen

duringmuch

They hadinterglacial

The Japan Sea

way to take notice of networks, how regions

was depressed widely by prominent mantle

have been connected and tied, in the first place,plumes from underneath.

for a broader comprehension not only of

been accessible from every direction throughpolitics and economy, but of society andthe sea.

ecosystem as a whole.

In fact, the economy

place in the ancient system of internationalon the Japanese Archipelago, situated to thetribute trading as a peripheral region of theeast of the Eurasian Continent, has been

Chinese civilization which had established its

historically influenced greatly by the Continent

political

and southeast Asia by way of the sea.

Distance between the continent, however, has

The islands has

The islands certainly found their

order

in

the

continental

plain.

enabled the islanders to hold a degree of
The Japanese Archipelago is situated on the

independence.

6

Migration to the archipelago

on the eastern border of the continent has beenand safety of port facilities from typhoons andalmost incessant since as late as the ritsuryo

tsunamis near coastlines are surely to be met.

legal code era(7 A.C.), Heian era(9-12 A.C.),

The economy of The Japanese islands has been

through the modern era, estimated fromblessed with logistical networks much readilyfragmented records at hand so far.

tenable than continental countries.

The reason

Peopleof migration varied presumably from accidental

have had access to sea surface transportation,

shipwreck, exploration, flight from politicalriver transportation mainly up to the medieval

oppression, urge for conquest, on one end, toperiod, and land transportation by rail and thenabduction by ancient Japanese-based pirates

by automobile from the modern period.

(wakoh) or coercive immigration by invading

Solely favorable as this condition may appear,forces to the Korean peninsula to the other end.

it has its own caveat as having induced declines

Multiple sources convince us to conclude that,ofother than officially-recognized diplomatic andhorticulture, fishery, and mineral resource

trade channels with Min dynasty (and Chin

mining, to name a few.

dynasty after the transition) and with the

been harmful to national land conservation of

Netherland, exchange contacts in terms of

the Japanese Archipelago in a sense that thepeople and goods were not totally suppressed.

land outside urbanized areas has been left

They were, for example, through illegal trades

uncared after much disruption due to overuse

northward in the Japan Sea and through transit

for a long time.

trades southward via Ryukyu kingdom eventhe condition is favorable in giving competitive

during the so-called national isolation (Sakoku)

advantages to many manufacturing sectors.

period from the 17 through the mid-19 century.

The accessibility is critical to how the map ofThis historic background is compelling enoughcooperation and competition among regions isto think of the Japanese Archipelago as based

drawn in the long run.

on the exchanging two-way networks of people

Generaland goods, whether it might be regarded as acooperation and competition may suggest thatstate or a region, especially after modernization

the Japanese Archipelago is not inferior to other

with

the

development

transportation.

Large

of

domestic

industries

asagriculture,

To that extent, it has

It goes without saying that

discussiononinternational

means

of

regions.

portionsof

we turn our eyes on how Japanese domestic

The case is, however, different whensocio-economic activities on the Japaneseregions have been connected and tied.

Archipelago are properly understood as an

The Japanese Archipelago saw the emergence

entity on the global network of human andof the system of centralized administration,material exchange, particularly given thepatterned formally after ruling structures in thepresent form of cross-bordered economic

continental plains, later than other countries.

activities.

Preconditions such as security on

It had also experienced the longer period ofand around international navigational channels

distributed and self-sustaining forms of the7economy in each region.

It is widely acceptedfacts lead us to hold that the political andand normal to ascribe these causes to theeconomic connection and ties on the Japanesedistribution of steep mountain ranges, blocking

Archipelago have been so developed, against

rapid

The

the blocking, but not complete, terrestrial

hypothesis is adequate for the explanation oflandforms, that the human society of collecteddifficulty of militarily and politically uniting

wills, under self-adaptation, has brought forth

the islands in an authoritative and uniform way

economic regions which are cooperative in one

by large armies.

sectorlong-distancetransportation.

It can also explain thewhilecompetitive

in

the

others.

difficulty of the establishment of an exchange

Networks of many kinds, rather than of a kind,marketdaily

were weaved out for many layers with

It is not, however, suitable forinteraction, as a consequence of relatively

forcommodities.
the

bulk

explanation

goods

of

including

human

and

cultural

distributed and self-sustaining development of

exchanges among regions that have beeneach local economy.

accomplished despite time and economic

thought to have a central function in one area,burden needed for transportation nor for theand a marginal function, or a mere path, for

explanation of exchanges of such goods as

another.

highly symbolic or of high value added, noble

As the east and the west of the world havemetals and of specialties, though limited inbeen separated and divided by traffic andterms of quantities.

Many illustrative tracestransportation cost, including those of time foraround the islands reveal that people have madepassengers and goods, so have been those ofcultural, religious, and economic exchanges

the Japanese Archipelago by the mountains ofamong the same trades between and among

Chubu (literally, “central part,” of the Japanesesurprisingly far regions through routes andmaincorridors, not excluding mountains.

transportation

Mountain ranges and rapid streams, which do

This geographical obstacle of mountains,

not easily allow people to go upstream, arehowever,

widely seen all over The Japanese islands.

unsurmountable.

The collection of goods by way of going down

or conditions of each period, it has behaved as

rivers, nevertheless, was within their reach.

semi-permeable membrane, obstacles in a caseAs a result, rice and trees which had

and passages in another, and even provided

well-sorted qualities for smooth trade among

stages for active intercourse and exchange.

daily commodities, were collected to politicalIna basin, or Ina-dani, as the south part ofand economic center(s), firstly but not limited

Chubu

to the capitol (Miyako), from greater regions inreligious-cultural obstacle during the medieval

the medieval period and from around theperiod.

country in the early modern period.

itself, between Tendai sect of Buddhism on its

These

8

island,has

Each locality was

Honshu)that

rendergeographically

not

been

land

challenging.

absolutely

Depending on trade fields,

mountains,

did

not

act

as

It provided a division line, withinsouth with Kouzenji an abri for Hieizan

and Imperial prince Munenaga (or Muneyoshi),

Enryakuji temple of Kyoto, and Sino-Japanese

disfavored by the political tide, of the Southernesoteric Buddhism on its north, in the process

Dynastyof spreading through a conciliatory relationship

Dynasties Period (1336-1392 A.C.) found theirwith much-influential Suwa great shrine to thedestination in deep eastern mountainsides ofnorth of the basin.

Ina basin.

The former was advocatedduringNorthernandSouthern

The region might be taken as aby Saicho of Enryakuji temple, the latter by

place of refuge at the period.

Kukai of Kouyasan.

Ina basin has been underbasin provided a path for a march advance attheagricultural

production.

the beginning and a graveyard at the end when

Willing or forced, religious donation is

Shingen Takeda, reputed as one of the mostdependent on production surplus.

The fact

capable military commander at the end of thethat the number of Buddhism temples andmedieval period, made his final advancing

Shinto shrines, including other sects, is not

campaign to the west in 1572 A.C.

impressive in comparison to other regions may

battlefields were outside of the region, in thebe understood from this limitation.

south, however.

The Chubu mountain range with its highland

central position of control throughout theand hillside has long been a vital region of

medieval as well as the modern period, underranches of military horses together with anotherthe limitation of its population and industry

region of the northeastern (Tohoku) mountainagglomeration.

range.

As a result, during the medieval period,

area, passively divided by Shogun’s demesne

the region acted as a major supply source inwith its magistrate’s Iijima office in the middle

one case and as an epicenter of a rise in arms,of two feudal domains of Takatoh in the northfor example, by Kiso Genji, in the other, from aand Iida in the south.

political and military viewpoint.

Turning our attention to the economic domain,

limitation

Heike

at

the

of

end

of

Remnants of

Heian

Afterward, Ina

The region has never won a

It has rather been a subjected

Period,Picture:River Transportationin the upper Tenryu reach(Main channel)

Picture: Kouzenji Temple(Komagane City)

9

Main

Picture: Misaka Touge Passon the ancient Tosendo(Achi Village, altitude 1569 m)

Picture: Labor-intensive silk industry
in the upper Tenryu reachcourtesy of Okaya Silk Museum

the region used to be a path for sea salt froma modal shift from river transportation tosouthern Pacific coast to northern inland fromrailroad, in which Iida railway was laid initiallythe medieval period.

forSeveral documents

hydropowerindustries

asaprivate

It was not until the late 20th

indicate that Tohyama river basin, in its

investment.

southern part, provided central pillars for Edo

century, when the central (Chuo) expressway

castle tower in the pre-modern period.

Large

was opened initially in 1975 and 2-wayed inamounts of tree logs, too, were transported out

1985, that Ina basin came to have a full accessof the basin by rafts through Tenryu river to thetosouth.

During the ancient through theJapanese national economy was so integrated

medieval period, Tosendo, which runs throughby policy that Tokaido line on southern PacificIna basin, was crowned as the major route fromcoast,

eastern regions to Kyoto and Nara capitols.

Shinkansen

Itnational

later

expressway

network.

complemented
bullet

train

by

The

Tokaidoexclusively

forwas, however, replaced by Nakasendo during

passengers, was chosen as the backbone overthe Edo period, which won the position of a

Chuo line that penetrates Chubu mountainnational corridor between east and west.

region.

The

As a result, Ina basin has sufferedshift put Ina basin out of the main corridor andfrom disadvantaged passenger traffic andmade it less accessible, to its disadvantage.

material

The Meiji and Taisho period saw the rise of theeconomic regions such as Greater Tokyo

silk industry in Suwa basin, with easy access to(Kanto) and Greater Nagoya (Chukyo), to thehydropower in the basin, which contributed

detriment of its economic integration.

greatly to national economy.

Ina basin

Japanese military regime in the first part of the

supplied plenty of raw materials and fuels of

20th century prepared aborted works of its lastcharcoal as its southern hinterland.

The

confinement fortress in the area, such as themodern Japanese history of transportation saw

army airbase in Ina village and the army

10transportation

cost

from

main

The

Noborito research institute of special covert
operations in Nakazawa village (later integrated
to Komagane), etc.

The region was not,however, chosen as a site of large-scale
munition factories most likely because of its
remoteisolation

agglomeration.

from

major

industrial

The latter half of the 20th

century saw the rise of the Japanese automobile
industry as the centerpiece of the Japaneseindustry agglomeration. They are Mitsubishi

Picture: Sakuma Dam
the largest hydro-electric power damin the entire basin of Tenryu rivergroup with its origin from pre-WWII period
and Toyota group from post-WWII period bothin Greater Nagoya Chubu region, Nissan groupwith its root in southern Greater Tokyo Kanto

frequency conversion station is found in the site

region, and Honda group originated initially inof Sakuma dam in the river basin with other 2

Shizuoka Prefecture whose present production

facilities closely arranged at Shin-Shinano tocenters spread from northern Kanto andthe right north and at Higashi-Shimizu to thesouthern Tohoku region to central Kyushu

right south of the basin.

region.

voltage power transmission networks that

Few automobile parts for the industry

are supplied from Ina basin.

Principal hyper

combine the stations run through the upper

One of the noted

exceptions may be that of Tamagawa Seiki in

TenryuIida city, supplying idiosyncratic angle sensors

Chubu mountains themselves constitute a vast

for all the hybrid vehicles.

The region is not,mountain range which have hindered the entire

by and large, integrated into the major supply

transportation over the Japanese Archipelago.

chain for the automobile industry.

The case isIna basin is duly regarded as less integrated toCommodities thatthe networks for economic exchanges withcan compete in the national market are limited

insufficient connection and ties, occupying theto less-weighed and/or high-value goods thatsouthern part of Chubu mountains between the

can

high

Japanese Southern Alps and the Central Alps.

transportation cost, such as agar, half-dry

It is widely hoped, and expected to someconfectionaries,

valueddegree, that transportation of goods between

decorative Japanese cords made from twisted

Shizuoka and Aichi prefecture to the south will

papers.

bethe same for other sectors.

justify

andandovercometheculturally

Ina basin has been detoured by mostreach

improvedwithnorth-south

throughmuch

direction.

tunnelednational networks and put in a secondarySan-en-nanshin Jidoshado (Japan National

position in regard to the economy.

Electric

Route 474) highway by 2020 and thatpower is a rare exception in that the oldest

passenger traffic to Greater Tokyo Kanto region

11and Greater Nagoya Chukyo region through the

not be overestimated optimistically, given thecentral magnetic levitation bullet train by 2027.

entailingThe

transportation costs.

effectoftheimprovementonsocio-economic environment, however, should

12

problemofhightrafficand3. Flood control attempted in the upper Tenryu reachEngineering is a system of technology fordischarges in sabo technology developed in thesolving

Asian/Pacific tectonic zone, most notably onsocialso-called

problems,

notnon-structural

excludinginstitutional

the Japanese Archipelago.

Network theory

approaches. Specifically in this context, civil

implies that the network of flood river water

engineering is to be understood as such aand sediment is directed and prescribed bysystemtopography and the gravity.

oftechnology

asreducingandRiver flood

mitigating socially undesirable time and spacecontrol technology has a focus on thepeak phenomena, be they natural or social.

enhancement of node capacities so that eachSeen from the present network theory, it isand every node may contain the transit flow

expected that civil engineering be conductive towithin its capacity every moment as it is theconstructing and maintaining networks oftechnology to process and to wash out natural

infrastructure needed for economy and society,floods safely downstream.

and to shortly reworking in time of suchon the other hand, has its focus on the reduction

emergency situations as disasters.

Applicationof the number of ties to nodes withoutof the definition to the field of flood control

sufficient capacity as it is the technology toleads to the construction and functional

reduce peak sediment discharges, by keeping

conservation of facilities that withstand chiefly

away rain as well as snowmelt water frompeak water discharges in river flood control

coming into mountain hill slopes, for instance.

Sabo technology,

technology in a strict sense, and peak sedimentFig-3: Ancient open levees in the upper Tenryu reach(Mibu river, early Meiji era)
courtesy of Nagano Prefectural Museum of History

13

Not named

Not named
Not named
Not named

Saburoku DisasterNot named

Not named
Not named
Not named

Flood of September Showa 58

Flood of June Heisei 11

Not named

Heavy rain disaster of July Heisei 18

1953

1957
1959
1959

1961

1965

1968
1970
1982

1983

1999

2004

2006

Major flood of May, 18 the first year of Meiji era and July 2, Dragon year

Major flood of Bird year(Toridoshi)
Not named
Major flood of growing Cow year(Kinotonoushi)

Flood of Boar year(Idoshi)

Bank lost of Boar year(another Idoshi)
Major flood of Dog year(Inudoshi)

Flood of Boar year(Idoshi)

Not named
Failure of Mt. Chausu
Not named
Not named
Not named
Not named
Not named
Not named

Name, if known
Not named
Ikeguchi Failure
Not named
Not named
Not named
Not named
Major flood of Ram year(Hitsujidoshi)
Failure of Mt. Morihira

Year(A.D.)
701
715
1533
1624
1691
1696
1715
1718
1719
1731
1742
1755
1789
1838
1865
1868
1898
1899
1907
1910
1911
1923
1945
1950

Prospective socio-economic development is

14

Table-2: Historic flood and sediment disasters in the upper Tenryu reach

Not summarized for specific events.

Typhoon No.23, etc.

About 558 ha inundated, 1076 houses severely inundated and 1465 partially inundated. Road failure of prefecturally admiministered Nakayama-Matsukura, 1 houses partially damaged.

295 houses damaged, severe damages by sediment discharges in Iida city, etc.

Heavy rain(Total rainfall 218mm, Iijima rain gauge)

Flood(1136m3/sec, Ina observatory, Heavy rain(583mm, Ohtagiri rain gauge, Nagano
MLIT), Sediment disasters
Prefecture)

Sediment disasters
Flood and sediment disasters
Flood and sediment disasters
Flood(741m3/sec、Ina observatory,MLIT), Sediment disasters
Flood(696m3/sec、Ina observatory,MLIT), Sediment disasters
Flood(836m3/sec, Ina observatory,
MLIT)

Typhoon No.10
6 casualties and missings, 15 houses totally damaged and 21 severely damaged in Tenryu village. Landslides in Kamimura, Hodono and Funakubo.
Baiu frontal heavy rain
Debris flows and landsilides, croplands lost in Komagane city etc. Economic damages in the basin amounted to about 3.23 billion yen at the time.
Inundation and debris flows in present Iida city, Takatoh and Hase in present Ina city, and Oshika village. Houses, roads, bridges, and croplands damaged. Economic damages in the basin amounted to about 20.4 billion yen at the time.
Typhoon No.10
Typhoon No.10 and heavy rain(Total rainfall282mm, Iida
6 casualties, 28 injured, and 5203 houses damaged. Damages in the entire river basin.
weather station)

53 houses totally washed out, 90+ severely-damaged houses, Tohyama Junior High school washed out.

Typhoon No.6 in May, frontal rain in July, Typhoon
No.24 in September

Flood and sediment disasters

101 casulaties, 29 missings, 1155 fatally to severely injured, 13953 houses damaged. Mt. Ohnishi major landslide.

Baiu frontal heavy rain(Total rainfall565mm at Iida
weather station)

Flood and sedimentdisasters(465m3/sec, Inatomi
Observatory, MLIT), Mt. Ohnishi
major landslide

Damages by major flood in the entire river basin, 535 houses damaged.
Damages by Typhoon No.7, 71 houses, roads and bridges lost at Hase, present Ina city. 19 casualties by debris flows in Fujimi town.
38 houses totally to severely damaged in present Matsukawa town, 1 casualties and 112 severely-damaged houses in Tenryu village.

Typhoon No.5
Typhoon No.7
Typhoon Ise-bay (No.15)

Principal natural causes
Note
Unknown
Flood downstream of Takatoh District, the first flood recorded in the river basin.
Natural dam(s) formed by landslide(s), came to burst after scores of days. The induced flood brought havoc to present Iwata county, Shizuoka Prefecture, loss of 170+houses and paddy fields.
Earthquake（Tohmi Earthquake、est.M=6.5〜7.5）
Unknown
Major flood around present Higashi-Haruchika, Ina city, etc.
Unknown
Major flood at Tajima village at the time, relocation to tableland of Takatohbara.
Unknown
Flood all around the river basin, specifically around Oshika village etc.
Unknown
Flood after snowfall, in the river basin.
64 houses lost, 33 casualties, nearly handreds parcels of croplands washed at Shimada (present Iida city). Failure induced debris flow at Shimohisakata Kitahara in present Iida city. Lost lives who went to collect flood woods in channels.
Heavy rain(frontal precipitation from june 18-24)
Earthquake（Tohyama Earthquake、M=7.0±1/4）5 casualties, western parts of Mt. Morihira in Wada, failed. 50+ died by burst flood(s) caused by natural dam(s) in Tohyama river.
Unknown
Major flood in the river basin.
Unknown
Flood in the river basin.
Heavy rain(Heavy thunderstorm, not seen for 80 years) Croplands as well as ancient trees lost in present Minowa town etc.
Heavy rain
Flood in the river basin.
Unknown
Flood in the river basin, left present Ohkubo field, Komagane city, ravaged.
Unknown
Flood officials from Edo made a survey around present Ina city.
Unknown
Major flood not seen from 1715.
Unknown
Major flood in the river basin. All the houses inundated, 21 houses and 20+ parcels of croplands washed in Tahara, Higashiharuchika, present Ina city.
Typhoon
12 casualties, and 59 houses washed out in Suwa region.
Unknown
Major flood induced the large-scale failure to Mt. Chausu, blocked Koshibu river. 10 guests died as Koshibu spa washed out.
Unknown
Flood in Koshibu river and in the main channel. 3 casualties in present Iida city.
Heavy rain
Flood damages caused by heavy rain band around the southern part of Nagano Prefecture.
Typhoon9 casualties.
Heavy rain
Inundation in Iida town, houses lost along Matsukawa, and debris flood(s) at Hinata, Nanakubo.
Damages in Ohshika village by sediment washout: 2 casulaties, roads lost, croplands lost and ravaged. 7 casualties and 20 houses washed out in Kamihisakata village (present Iida city).
Typhoon No.10
Heavy rain
Road blocked, houses inundated, and paddy fields lost at Takatoh and Hase, present Ina city.
Typhoon No.2 in June, Depression in July, and Typhoon
Banks and croplands washed out. 7 casualties, 9 missings, 169 injured, 93 houses washed out, and 431 disaster victims.
No.13 in September

Flood
Flood and sediment disasters
Flood and sediment disasters

Flood

Category
Flood
Major landslide(〜9.375×107m3)
Flood
Flood
Flood
Flood
Flood
Major landslide
Flood
Flood
Flood
Flood
Flood
Flood
Flood
Flood
Flood
Major landslide
Flood
Flood
Flood
Flood and sediment disasters
Sediment disasters
Flood and sediment disasters

hardly able to justify novel construction

development of the regional economy.

investment

infrastructural

facilities under the permission of the national

networks serving solely for regional economy

administration, even if extracted only for theof the upper Tenryu reach.

Tokai andmain trunk, amounts to sizable numbers by

Tohnankai earthquakes expected near future in

category: 2 large-scale dam facilities over theTokai and Greater Nagoya Chukyo region,

height of 15m (legal threshold), 20 smaller dam

however, could stymy the logistical and energy

facilities with other water utilization purposes

supply to the regional economy of Ina basin toas hydro-electric power intakes and crop

its devastation.

irrigation, 63 bridges, and 244 various sluiceforlarge-scale

It is, therefore, imperative toRiverlessen expected fatal losses by making an effort

gates installed within the riverbank.

to connect to various existing networks and toup for all the tributaries, the number ofstretch out newly in alliance with otherman-made structures is almost innumerable.

(sub-)regions.

It is not beyond our imagination that these

The upper Tenryu reach has suffered fromfacilities can act as roadblocks against flood

major floods and sediment discharges onceand sediment discharges, whose peak loads

every several decades, though not too often,

ought to be reduced for safe and smooth runoff.

with the worst sediment production rate on the

Historic flood and sediment disasters in theJapanese

Archipelago.

flood

river basin are outlined in Table-2.

discharges

cannaturalwould be entirely free of the anthropogenicbeMaximalworsenedasSummingFew

topographical factors combined with suchinfluence.

anthropogenic factors as dam installation for

has often suffered from inundation damages.

the

of

It comes partly from the fact that discharge out

Adaptationof Lake Suwa cannot be increased without

has been attempted but thought good enoughcausing unbearable damages along the main

only for limited planned patterns under thechannellimited justifiable flood control investment,

discharging capacity at the lower end of Ina

which in turn is capped by the prospectivebasin affects backwardly to the upper most area,socio-economic development.

It makes sensea typical example of river system connectivity,

all the more to plan and work together withwhich is a notable characteristics of the upper

other public/private projects in the region,

Tenryu reach.

which have different purposes, to the extent

Basics for better safety of the river basin,that the direct flood control investment iswithout

constrained financially and fiscally.

reinforcements of river embankment mainly

Both the main trunk and tributaries of thealong the main trunk for safe and sure flood

upper Tenryu reach are already under heavy

runoff on one hand, and installations of sabo

water and river use for the promotion of stable

dam facilities to reduce the rise of main trunk

purposeofwater

utilizationhydro-electric power, and others.

15

The upper most Lake Suwa region

downstream.

downgrading

The

the

gridlockutilization,

of

are

riverbed

andtoconcomitantly

mitigate

inundation at the back of the banks in aoverflowing around tributaries on the other.

southern

The river has seen the installation of several

Many as they are, dam facilities which cut

large-scale flood control facilities, whichacross the river channel are not the panacea inrequires due care to reduce their side effects

reducing flood and sediment discharges and can(Fig-4).

sometimes

Miwa dam in tributary Mibu river,section,have

Kawaji-Tatsue-Tatsuoka.

undesiredeffects

asa

dated its operation back to 1959, Koshibu dam

double-edged sword.

in Koshibu river to 1969, Matsukawa dam in

the upper Tenryu reach is, therefore, dependent

Matsukawa river to 1975 are all conductive toupon the river channel capacity kept at a proper

reduce both flood discharges and the rise oflevel and bank embankments well-maintained,riverbed in the main trunk.

not less than other rivers on the Japanese

Their sediment

The safe protection of

bypass tunnels are going to put into operation

Archipelago.

as early as 2016, which have been planned forpolicy of the upper Tenryu reach.

mitigating dam sedimentation in their own

foremost, a code of sediment discharge

reservoirs. Ground level raising of a notable

management has to be sorted out in working

scale was finished in 2002 in cooperation withrelationship with dam facility managers inprivate sectors, which provides vital protection

order to ameliorate the loss of flood discharge

against not solely river flood, but also

capacity coming from the greatest sediment

There arises the flood control

Source: Brief History of National projects on sabo works

Fig-4: Flood control facilities in the upper Tenryu reach

16

First and

production seen on the Japanese Archipelago.

uncared and/or under poor management for

Second, levee banks have to be protected fromdecades. Complex disasters are to be foreseen

damaging hollowlose caving induced by water

as sediment discharges by heavy rainfall can beseepage as the river basin topography makes

augmented and worsened by plethora of flood

unbearable the amount of ground infiltration towoods.

the banks to its detriment.

Groundwateron precipitation indices have been developed

infiltration, together with the immensity ofnationwide since 2008 for better early warning

related facilities, has pushes up the bankand evacuation.

maintenance expenditure to a considerable

such as a large-scale landslide detection system,

order.

too, is under development which can be put

The safe protection has to be kept even

Sediment-related disaster alerts based

Another kind of warning

under the pressure of public expenditure cut.

into use as early as 2016.

Bank structures have to be improved andsecurity of traffic in heavy rains and/or inrenovated,

mid-night

together

with

other

major

remaina

Evacuation anddaunting

challenge,

undertaking seen in the river basin, into a typehowever, given the lack of safe evacuationof structure needed less maintenance expenses.

shelters and the aging population of the basin.

Third, flood wood disasters have to be

It is, therefore, necessary to be cautious incontained

expecting too much for the effects of the earlypre-cautiously,

especiallyintributaries. Forests in the basin have been left

warning and evacuation.

As of February 2014
Written by Dr. Hiroaki NAKAYA, Director General
Tenryu River Upper Reach Office, Chubu Regional Development Bureau, Ministry of Land,
Infrastructure, Transport and Tourism, JAPANUwabu-minami 7-10, Komagane City, Nagano Prefecture JAPAN 399-4114
http://www.cbr.mlit.go.jp/tenjyo/index.htm
No restriction or condition on copying.
Opinions shown here are strictly personal, and not necessarily confirmed officially.

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