Important Cultural Property /Erosion and Sediment Control Work for the Momijidani River Park

Ropeway

Okumomijidani bridge

Momijidani bridge

Where photo(right) was taken

Momiji bridge

NO.1 Sediment Control Dam

The first civil engineering
facility which wasconstructed after WWII, tobe designated as an"Important CulturalProperty" in JapanThe erosion and sediment control work for the Momijidani
River Park is a 688m-length channel works which wasconstructed in 1948-1950. It was the first civil engineering
work which was constructed after WWII, to be designatedas an "Important Cultural Property" in Japan.
If you take a walk along the channel works, you can see
the groundsels and sediment control dams.
A total of 6 types of "Sabo Cards," commemorating thefacility's designation as an important cultural property,
and showing highlights of the project, are distributed freeof charge at the Mt. Misen Observatory.

©Hiroshima Prefecture Civil Engineering Bureau Sediment Control Division（December, 2020）

Sabo Cards
Distributed from January to February

Distributed from March to April

Distributed from May to June

Distributed from July to AugustDistributed from September to OctoberDistributed from November to December

Commemorative sabo cards of Important Cultural Property designation (normal version)
Distributed from January to February

Distributed from March to April

Distributed from May to June

Distributed from July to AugustDistributed from September to OctoberDistributed from November to December

Commemorative sabo cards of Important Cultural Property designation (limited edition)

6 types of sabo cards that
describe the highlights ofimportant culturalproperties

A total of 6 types of "Sabo Cards" commemorating the facility's designation as an important
cultural property, and showing highlights of the project, are distributed free of charge at Mt.
Misen Observatory.
In addition, to commemorate it's designation as an important cultural property, we will distributethe limited edition Sabo Cards to the first 1,000 visitors.
As soon as the limited edition cards run out, only the normal edition ones will be available, soplease come as soon as possible.
There is a one sabo card per two months limit per person, and you can receive up to six cards intotal.

©Hiroshima Prefecture Civil Engineering Bureau Sediment Control Division（December, 2020）

Erosion and Sediment Control Project in Harmony with the Historical
Scenery of Itsukushima

Downstream from Momiji Bridge

The erosion and sedimentcontrol work was carriedout under the post-WWII
turmoil, throughcollaboration between
national and local
governments and GHQ

The Momijidani River, which flows from Mt. Misen down to behind Itsukushima Shrine, was damaged bydebris flows in the 1945 Makurazaki Typhoon. Resultantly, a disaster rehabilitation project of the riverbegan in 1948 and was completed in 1950 at the "historic site and place of scenic beauty of Itsukushima".
This erosion and sediment control work was created through the collaboration of erosion control andgardening experts. The result is a project which skillfully utilizes boulders deposited by debris flow, andwhich is in harmony with the scenery of Momijidani Park, a famous viewing spot for autumn leaves, and thehistorical scenery of Itsukushima.
This was an important disaster rehabilitation project, carried out through collaboration between thenational and local governments and GHQ under the turmoil just after the WWII.

Damage Caused by the 1945 Makurazaki Typhoon

Damage downstream from Momiiji Bridge（※1）

A typhoon with incredibly
force hit through Japan justafter WWII

The Makurazaki Typhoon made landfall near Makurazaki City, Kagoshima Prefecture, around 14:00 on
September 17, 1945.
After making landfall the typhoon moved northeast. As a result, Hiroshima experienced fierce wind with amaximum speed of 30.2m/s, and a total rainfall of 218.7mm, with a maximum hourly rainfall of 57.1mm.
Shortly after the end of WWII, there was little weather information and disaster prevention systems wereinadequate, causing great damage in various places, especially in Hiroshima Prefecture, where more than
2,000 people were killed or went missing.
On Itsukushima, debris flow disasters occurred at the Momijidani, Shiraito, and Omoto Rivers.
©Hiroshima Prefecture Civil Engineering Bureau Sediment Control Division（December, 2020）

Damage to Itsukushima Shrine

Near Sorihashi Bridge, Tenjin Shrine, and Oguni Shrine [September 1945]（※1）

Itsukushima Shrine wascovered by sediment anddriftwood

The area around the Momijidani River was registered as a designated sediment control area on March 13,1934.
After that sediment control dams were built, but they were insufficient to stop the debris flow generated
by the Makurazaki Typhoon. Huge stones and driftwood flushed through the middle and lower stream andrearched grounds of Itsukushima Shrine.
During the disaster rehabiritation project, 16,000m3 had to be dredged.

Near Tenjinsha on the east side of Sorihashi Bridge [January 1946]（※1）©Hiroshima Prefecture Civil Engineering Bureau Sediment Control Division（December, 2020）

Rehabilitation Plan From the Debris Flow Disaster（left）Member of the Itsukushima Disaster Rehabilitation Committee, taken on 12th Aug 1948（※2）（right）The report of disaster rehabilitation projects at the historical site and scenic beauty of Itsukushima, 15th Mar 1951（※2）

Establishment of theDisaster Rehabiritation
Committee to plancountermeasures anddetails of Rehabioritation
Project

The "Itsukushima Disaster Rehabiritation Committee" was established on Aug 1948, during the rehabiritation
work of Momijidani River and Shiraito River, using construction methods suitable for the historical site andscenic beauty spot.
In the rehabiritation work, it was decided that the stones at the site would be moved without using heavymachinery. In addition, without any prior manufacturing or processing, the stones would be used to cover
the concrete surface of the structure, and gardeners would be worked for the contruction.

Erosion and Sediment Control Works at the Momijidani River

Ropeway

Okumomijidani bridge

Momijidani bridge

Momiji bridge

Where photo(right) was taken

Upstream from the Momiji Bridge

Erosion and Sediment Control Works in Momijidani River were constructed by using the boulders
and outcrops of the bedrock which were carried down by the debris flow to create steps and slow
down the flow.
These steps reduce the momentum of the river when it rains heavily, and suppresses erosion of theProtecting Itsukushima from riverbed and riverbanks.
In the rehabilitation work carried out from 1948 to 1950, a 820m-length channel works and 7 sedimentdebris flow disasters

control dams and 4 groundsels were constructed.
Currently, the 688m-length channel works and 5 sediment control dams are remaining and working same as
before. Therefore, the historical site and the scenic beauty of Itsukushima is still being protected fromsediment-related disasters.
©Hiroshima Prefecture Civil Engineering Bureau Sediment Control Division（December, 2020）

Transportation of Stones

Construction status of the channel works upstream from Momiji Bridge（※1）

Carrying stones using the The method called "kagurasan", wooden tripod with a chain block, was used to move the boulders.
"kagurasan (wooden tripod)" The gardeners move the already present megaliths and gravel, without prior processing, a stone stealer, ormallet.
methodPlacement of Concrete

Construction status of the No.5 dam in 1949（※1）

Current No.5 dam

Construction of sedimentcontrol dam using concrete(under the stones)

Wooden rulers as the marks were placed, concrete was mixed at the field to counstruct dam, and the dam
surface was covered with local quarry stone. So that concrete is not exposed.

©Hiroshima Prefecture Civil Engineering Bureau Sediment Control Division（December, 2020）

Designed related 86 Documents

Part of the attachment（※3）

Foundation for Important
Cultural Properties

The dimensions of the sediment control dams are confirmed in the "Design of Disaster Rehabilitation
Project at the historic site and place of scenic beauty of Itsukushima (Hiroshima Pref, 1949) and theattached figures".
Related precious 86 documents (reports, figures) which have been owned by Hiroshima Prefecture aredisignated※3 to understand Erosion and Sediment Control Works for the Momijidani River Park.

【References】※1※2※3

Photobook of Erosion Control Disaster in 1945 (Hiroshima Prefecture, Civil Engineering Department, Sabo Division, March 1998)
The report of disaster rehabilitation projects at the historical site and scenic beauty of Itsukushima （Hiroshima Prefecture, March 1951）
Designated documents for certify the value of important cultural properties and the foundations for them by agency for Cultural Affairs.

©Hiroshima Prefecture Civil Engineering Bureau Sediment Control Division（December, 2020）