Emergency Erosion Control Work in Kumano District, Kii Mountains

2018.07.31

Project name              :    Emergency Erosion Control Work in Kii Mountains in the Aftermath of Typhoon No. 12 of 2011

Work title                   :     Design and other work for erosion control facilities to deal with a landslide dam in Kumano District in FY 2012

Location                     :     Tanabe city, Wakayama Prefecture

Duration                     :     FY 2012 onwards

Implementing body    :     Kii Mountains Erosion Control Office, Kinki Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism (MLIT)

 

Typhoon No. 12 of 2011 caused large-scale sediment disasters accompanied by river channel clogging in the Kii Mountains. In the Kumano District, a hillside collapsed for a width of 450 m and a length of 650 m, making 4.1 million m3 of collapsed sediment clog the river channel. For this reason, in order to control the outflow of sediment from the slops and prevent surface erosion, surface drainage works were constructed, and emergency measures such as installation of erosion control dams and widening and reinforcement of drainage channels were implemented.

 

In this project, EJEC designed the downstream flow/riverbed consolidation, upstream wood debris capture works and sedimentation works, slope protection works and surface drainage works at the collapsed site and road works on the right, in addition to the main check dams.

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2016.03.31  Work for Clogged River Channel Site due to a Large-scale Slope Failure

 

Work title                   :      Design Work for Erosion Control Facilities to deal with Landslide Dams in the Akadani District

Location                     :      Shimizu area, Ohto Town, Gojo City, Nara Prefecture

Duration                     :      June 15, 2012 to March 29, 2013

Implementing body    :      Kii Mountains Erosion Control Office, Kinki Regional Development Bureau, MLIT

 

Typhoon No. 12 of 2011 caused a number of large-scale slope failures in the Kii Peninsula, causing massive damages. EJEC was involved in the works to control further damage occurrence through on-site surveying and monitoring the clogged river after slope failure.

 

Our work involved the planning and design of check dams to deal with the clogged river channel in the Akadani District.

 

Large-scale slope failure and river channel blockage

 

With a deep-seated landslide, deep ground forms the sliding surface and the resulting large volume of collapsed sediment can clog the river channel, creating a water covered area in the upstream.

 

Large-scale slope failure and clogged river channel site

 

Flooded area due to clogged river channel

 

Akadani No. 2 Check Dam

 

At the clogged river channel site formed by a large volume of collapsed sediment, it was assumed that the accumulated water held in the upstream could overflow, eroding the clogged site and causing a new collapse.

 

For this reason, the Akadani No. 2 Check Dam was planned and designed to anchor the leg section of the clogged river channel for stabilization while preventing erosion by an overflow.

 

Of the three planned check dams, the Akadani No. 2 Check Dam to anchor the leg section of the clogged river channel has been completed (March, 2016).

 

Akadani No. 2 Check Dam

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2010.03.31   Check Dam and Torrent Works with Consideration of the Natural Environment (Saka River, Kyoto Prefecture)

 

Saka River Check Dam and Torrent Works

 

Facility name             :      Saka River tributary check dam and Saka River torrent works

Work title                   :      Ordinary Erosion Control Work for Saka River, a Tributary of Obata River of the Yodo River System

Location                     :      Aou, Nagaokakyo City, Kyoto Prefecture

Duration                     :      [Study and Planning Work ~ Detailed Design Work] FY 2000 ~ FY 2005

Completion                :      March, 2010 (Work began in FY 2004)

Implementing body    :      Otokuni Civil Engineering Office, Kyoto Prefectural Government

 

The site and its surrounding area boast a rich natural environment, including rare species, together with a cultural landscape represented by Komyo-ji Temple and the beautiful natural landscape of mountains and hillsides. A local NPO has been very active in the area to support environmental conservation. In cooperation with local residents and the NPO, the project was conducted to create a safe area where people could live with peace of mind while conducting a careful study and adopting an approach of not causing any negative impacts on the environment the landscape.

 

In our planning and design works, we especially noted the following issues.

 

  • Construction will be done in phases to minimize the negative load on the natural environment
  • Introduction of meandering stream works to avoid the cutting of edible grass, such as Celtis, Quercus aliena,, wwhich are food for rare animals
  • Use of porous blocks and a gently sloping structure for structures to conserve as well as create the habitat for living creatures
  • Introduction of a large culvert for the check dam to ensure normal sediment movement and continuity of the stream

 

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2010.03.31   Fukuyama Port (Development of an International Container Terminal)

 

Fukuyama Port International Container Terminal Development

 

Facility name             :      10 m Berth (Berth No. 2) in Mino-oki Area of Fukuyama Port

Work title                   :      Entrusted Work incidental to the Reconstruction Project for Fukuyama Port, as a Designated Major Port

Location                     :      Mino-oki, Fukuyama City, Hiroshima Prefecture

Duration                     :      FY 2008 and FY 2009 (Completed in March, 2011)

Implementing body    :     Eastern Region Construction Office, Hiroshima Prefectural Government

 

In 2005, the Fukuyama Port International Container Terminal (Berth No. 1) was completed to function as an international logistics base (with China and South Korea) in the eastern part of Hiroshima Prefecture. Berth No. 2 was planned and expanded to the west of Berth No. 1 to further increase the trade handling volume. For this work, EJEC was responsible for the basic as well as detailed design of this berth.

 

  • The main structure is the jacket type which is the first in Hiroshima Prefecture as a mooring facility.
  • The sand compaction pile (SCP) method was used to counter the soft ground.
  • Water granulated slag was used as reclamation soil (obtained from the nearby JFE Steel at low cost).
  • Precast boards were used for the superstructure, contributing to shortening the construction period along with the jacket construction method. The overall construction duration was approximately two years.
  • The employment of the entirely preceding pile method was unique in Japan.
  • In preparation for future development, the feasibility of introducing a simultaneous loading system with two gantry cranes (lifting load of 30.5 tons each) was examined.

 

Many difficulties were experienced during the design work, including the design of the rail foundations for the gantry cranes which required a high level of accuracy and also details of the members for three types of jackets of different sizes in the 3D frame analysis.

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2008.07.31   Nanase River: Two-tiered Waterway

 

Nanase River              :      Two-tiered Waterway

Facility name             :      Urban Infrastructure Development Project for Nanase River, a Two-tiered Waterway

Location                     :      Fushimi Ward, Kyoto City

Duration                     :      [Proposal for Structure ~ Detailed Design] FY1989 to FY2000

Completion: July, 2008 (the project commenced in FY1992)

Implementing body    :      River Improvement Division of the Kyoto Municipal Government

 

Nanase River is an urban river which flows from east to west in the south-eastern part of Kyoto City, joining Higashi Takase River of the Yodo River system. A some 2.9 km long section in the upstream of the confluence with Higashi Takase River is designated as a Class A river. The safety level of flood control for Nanase River was generally low throughout the river, resulting in frequent flood damage. Local residents strongly requested fundamental improvement and the work to create a two-tiered waterway, the second of such type nationwide, took place since FY 1992 as an urban infrastructure and river improvement project.

 

For this Nanase River improvement project, an integrated approach combining the construction of a flood prevention facility and riverfront improvement with town development was adopted to create a safe and charming living environment with rich water and greenery. The two-tiered waterway section stretches some 950 m in the upstream of the confluence with Higashi Takase River. The lower channel is responsible for flood control in the basin, acting as a flood control facility channelling flood water safely. The upper channel provides a greenery-rich waterfront and is used as places for the relaxation, recreation and interaction of local residents.