The Ministry of Land, Infrastructure, Transport and Tourism(MLIT) implements a variety of flood control projects to protect life and property from floods. To drain flood waters safely and efficiently, the MLIT improves river channels and constructs floodways and retarding basins. In urban areas, comprehensive MLIT flood protection measures improve the water-retaining and retarding functions of river basins. MLIT projects also improve and construct river channels, regulating basins, and underground rivers. MLIT projects also use dams for flood mitigation.
River Channel Improvement
River channel improvement includes channel widening, levee construction and reinforcement, and riverbed dredging so that flooding of less than the design flood can be discharged without inundating lands along the river.
Floodway
A floodway is a canal constructed to lead flood waters from the middle and lower reaches of a river to another river or directly to the sea.
A floodway is constructed when channel improvement is insufficient to carry the design flood.
Retarding Basin and Control Basin
Retarding basins and control basins mitigate flooding in the lower reaches. In case of flood part or most of the floodwaters flow into the basins. The water stored in basins can also be used as a water resources.
City Inundation Countermeasures
Inundation can cause great damage in cities. In addition to active improvement of city rivers in order to diminish inundation, construction of underground discharge channels, water reservoirs, and storm sewers are carried out.
Protection against Tsunami and Storm Surges
To protect vulnerable coastal areas from storm surges caused by typhoons and tsunami caused by earthquakes, various structures, such as sea walls, tide gates, and drainage pump stations, are constructed along seashores and at the mouths of rivers that have suffered major damage in the past.
High-Standard Embankments (Super Levees)
A "super levee" is a thick embankment created by applying a layer of fill material over a conventional embankment. Super Levee are designed to prevent catastrophic flood damage which could result from urban levee breaks caused by overflowing of banks, seepage, and earthquakes. They also enhance urban spaces with water and greenery.
Comprensive Flood Control Measures
River basins that are being rapidly urbanized are losing their natural water-retaining and retarding functions. At the same time, concentration of population and property in these urban river basins contributes to increasing "damage potential" (maximum amount of damage that could potentially result from a disaster).
These problems are being dealt with through MLIT "Comprehensive Flood Control Measures", which consolidate the combined use of facilities to maintain the water-retaining and retarding functions of river basins, the creation of incentives to use land safely and to build flood-resistant buildings, and the establishment of flood warning and evacuation systems.
Comprehensive flood control measures are implemented through the establishment of Council for Comprehensive Flood Control Measures for individual river basins and through the formulation of basin development plans that include improvement of the environment.
Securing the Water Resources that Support a Rich Lifestyle
The MLIT implements diverse projects, including construction of multipurpose dams, to ensure an adequate water supply that will satisfy people's daily requirements.
Dam Construction
A multipurpose dam, constructed to temporarily store rainwater that falls upstream, can provide flood protection, maintain normal running water functions, store municipal and irrigation water, and create electric power.
As of 1994, the MLIT had completed 358 dams and is currently working on 326 more.
Various other water resources development projects are also underway. These projects include development in connection with lakes and ponds, as well as construction of channels for river flow adjustment, estuary barrages, and reservoirs to compensate for periods of low water flow.
Lake Development
Weirs, which control the discharge of rivers that flow from lakes or marshes, and surrounding dikes are constructed in order to diminish flooding of the lower reaches and the lake and marsh areas. Water resources development is also executed.
Estuary Barrage
The purpose of estuary barrages is not to store flood waters but to safely run them off by ensuring an adequate flow area.
Estuary barrages also help to ensure a stable water supply by storing river water or preventing salinization of river water by sea water.
Channels for Adjusting of the Flow of River
River flow can be adjusted by diverting water from rivers with abundant flow to those with insufficient flow. Water thus diverted is used to develop new water resources and to replenish general-use water supplies.
River flow adjustment also helps to mitigate flood damage by contributing to drainage of the inner basin.
Small Scaled Dam for Domestic Water
Communities in mountainous areas, on peninsulas and on islands, rely on wells and mountain streams for their water supply. These sources of water, however, are not reliable in the event of drought and may also provide less-than-ideal water quality. Since these areas are also vulnerable to floods, high-priority projects have been undertaken to construct small reservoirs in these areas to establish reliable water resources for household use and to provide flool control.
Research and Development
The MLIT's Public Works Research Institute has been studying and developing various new technologies, such as the Roller-Compacted-Concrete Dam Construction Method.
RCD (Roller Compacted Dam-Concrete) Method
This method utilizes vibrating rollers on the surface to compact ultra-hard mixed, non-slump concrete. Unlike conventional methods, which use stick-shaped vibrators to compact soft concrete by vibrating from inside, the RCD method can be mechanized, saving labor, which contributes to shortening of the work period as well as reduction of construction costs.
Erosion Control to Protect the Region from Damage by Sediment Disaster
The soil and rock that washes downstream gradually raises the beds of the rivers that have devastated mountains as their sources. During storms, the rivers flood which can lead to major damage. Various facilities, including sabo dams, work in cohesion to maintain the safety of river basins, all the way from their headwaters to the cities and towns located downstream.
Diverse measures are being taken to mitigate damage resulting from landslides and earth flow connected with typhoons, torrential rains, and volcanic eruptions. These measures include projects to control debris flow (Sabo dams, Mountainside reinforcements, Sabo channels), landslides (water channel improvement, pilings, underground drainage), slope failure (retaining walls, crib works), and flow of volcanic material (training dikes, energy dissipaters).
Debris flow
Debris flow refers to the phenomenon where long or heavy rain causes the soil on hillsides and river beds to be washed downstream all at once. Speed of the debris flow varies, but it is not uncommon for it to reach speeds of 20 - 40 km per hour and destroy houses and fields instantaneously.
Debris Flow Measures
Building sabo dams upstream traps the sediment there and prevents it from eroding and flowing downstream. sabo dams also serve to stop debris flow.
Landslides
Landslides tend to occur on gently slopes with weak geology; stratification, faulting, and poor ground water characteristics. Rainfall, melted snow and earthquakes trigger slides. The soil starting at the weakest layer will completely slide away over a very wide area, destroying everything located on the ground surface and causing much other damage.
Slope Failure
Slope failure occurs on steep slopes that have been weakened by extensive water penetration. The falling or crumbling that characterizes slope failure is usually triggered by rains or earthquakes. As slope failure tends to occur quickly, those dwelling nearby often do not have time to get away, giving rise to a very high mortality rate.
Volcanic Disasters
Volcanic eruptions are accompanied by a variety of associated phenomena which cause a number of related disasters. Volcanoes are very powerful, extremely destructive, and cause extensive damage.
Structural Measures
The destruction caused by volcanic eruptions can be significantly reduced by creating and installing flow control dikes to divert the flow of volcanic mud, pyroclastic flow, and lava generated by eruptions: Energy dissipaters weaken the force of the flow, open-type sabo dams are designed to catch large boulders, and sabo channels guide the flow in other directions.
Non-Structural Measures
Various measures are being taken to enable establishment of a warning and evacuation system. These include creation of evacuation routes and emergency shelters, based on volcanic disaster simulation, and the use of monitoring cameras and sensors to provide early warning of volcanic activity.
Creating Safety and Serenity at the Sea
Various measures are taken to protect coastal communities and land from damage caused by storm surges, tsunami, and inundation by high waves (embankments, wave dissipaters) and by erosion (revetments, groins, detached breakwaters).
Protection against Shoreline Erosion
Seawall, revetments, groins, and detached breakwaters are constructed to protect coastal areas against coastal erosion.
Coastal Community Zone(CCZ)
The project aims at the comprehensive conservation and utilization of coastal areas. The improvement of a coastal community zone under the jurisdiction of the MLIT includes such projects as shore protection, public parks, roads, and sewers. At the same time, private enterprise is actively encouraged to provide vital public facilities and events.
Information Network Protects Lives
A river information system has been developed to promptly and accurately communicate river information that can be used to make sound judgments based on composite conditions in widespread areas. Decisions include not only actions to be taken in case of floods or droughts but also measures for proper day-to-day river management.
River Information System
The system collects data such as that on rainfall and water levels using special data acquisition equipment (radar rain gauges and telemetry devices) positioned along a river or in a river basin. Data is relayed to specified destinations through a dedicated microwave line linking the MLIT and Regional Bureaus.
The Foundation of River & Basin Integrated Communications (FRICS) receives and processes diverse river information from various sources, such as the national government and local public bodies and disseminates it to organizations and individuals in particular river basins on an as needed basis.
Disaster Measures
Education and training provide the knowledge necessary to prevent disasters through the development of watch and evacuation systems, and to prepare people for dealing with emergencies.
Flood History Maps, Flood - Prone Area Maps and Hazard Maps
Flood History Maps and Flood - Prone Area Maps are compiled and distributed to the public in order to encourage more appropriate and safer land use and to disseminate information on evacuation in case of emergency. Hazard Maps are also compiled and distributed to the public in order to concretely show the location of evacuation areas and evacuation routes.
Flood Forecasting and Flood Fighting
The MLIT uses information from the river infomation system to predict floods and issue forecasts and warnings, which the agencies involved can use to organize flood watches, flood-fighting, and evacuation operations in order to prevent or mitigate flood damage.
Disaster Restoration
In case public facilities such as rivers, seacoasts, sabo facilities, roads, bridges, landslide protection or steep slope failure protection facilities are damaged by natural disasters, restoration is begun as early as possible.
Living in a Splendid Water Environment
The MLIT conducts a "National Censuses on River Environments" and various other environmental and land-use surveys for a regular and continuous assessment of the state of the environment of rivers, and of the flora and fauna living in and around them. The results of these surveys are reconciled with the views of the local residents and of academic experts and are used in devising the "Master Plans for River Environment Management" which lay down basic policies for the comprehensive and systematic implementation of projects relating to the conservation and creation of river system environments.
Creation of Rivers Endowed with Diverse Nature
Slack water has been created by groins on large rivers, while the lower water channels of small rivers have been made to meander, in order to create pools and rapids. Also, variation has been given to the water line by willow revetments on the Miomote River. These create diverse river environments, providing habitats for plants and animals, and creating beautiful natural environments through the revival of living environments for animals and plants.
Formation of Communities with Rich Water and Greenery
River administrators and mayors make development plans for symbolic rivers and those river improvements, in keeping with the harmony of the surrounding scenes and regional development, form attractive riversides.
Formation of Beautiful Riverside Scenery
The work implemented for the creation of beautiful riverside scenery that remains in harmony with the surroundings includes the planting of cherry trees along rivers.
Creation of Spaces for Recreation Activities around Dams
Environmental improvements have been made around dams, therefore not only making possible the use of water surface of the dam reservoir but also the rich scenery and natural environment of its surroundings, thus providing an area of diverse recreational activities for the residents.
Creation of Streams Surrounded by Rich Greenery
Works are implemented for the creation of streams surrounded by rich greenery, with consideration given to the surrounding environment and ecosystem and also for creation of places where residents can find peace. These works include construction of channels that are friendly to living creatures.
Creation of Cliff Landscape with Rich Greenery
The cliff failure prevention works play a part in the creation of a landscape in which the remaining urban greenery is used effectively in the designated scenic beauty districts.
Creation of Pleasant and Attractive Coastal Works
Works are implemented for environment improvement of sea coasts, thus taking into account the uses of the coastline and the surrounding areas, so as to conserve and create pleasant and attractive coastal environments.
Revival of Clean Streams in Urban Areas
Polluted Rivers have been rejuvenated by the diversion of water from other rivers to clean them so as to return fish to the rivers.
Cleaning Water by Living Creatures
The rivers, which flow into lakes, have been cleaned through removal of Nitrogen and Phosphorus by aquatic plants such as reeds, while at other works, water is being cleaned by the gravel contact aeration process in which the pollutants are broken down and removed by the microorganisms growing on the surface of the gravel.
Conservation of Lake Water Quality
Water quality conservation measures are implemented to prevent or reduce pollution on dam reservoirs where the progress of urbanization in the catchment areas and devastation of surrounding slopes have led to the prolongation of periods of turbid water and also eutrophication.
International Cooperation of the River Bureau, MLIT
The MLIT provides international assistance in fields which include roads, rivers, housing, and sewer systems. MLIT assistance covers project finding and formation, promotion of development and transfer of technology, promotion of international exchanges, and dispatching of advisory attaches. The MLIT also works with the Japan International Cooperation Agency and other organizations to bring trainees to Japan and send study teams abroad.
The River Bureau is the agency responsible for the aspects of such international cooperation activities that relate to rivers.
Major River Bureau Technical Assistance Accomplishments
- 1
- Republic of Indonesia
Volcanic Sediment Control Technical Center Ciujung-Cidurian Comprehensive Water Resources Development Planning
2
- Malaysia
National Estuary Management Flood Control Planning Comprehensive Muda River Basin Administration Planning
3
- Republic of the Philippines
Flood Protection Planning for Designated Localities Flood and Mud Flow Control Planning for River Basins on the Eastern Slope of Mt.Pinatubo
4
- People's Republic of China
Tai Hu Water Management and Water Resources Conservation Survey Guanyinge Multipurpose Dam Construction Project
5
- Republic of Korea
Environment Maintenance Planning for Minor Rivers in the Han Jiang System
6
- Socialist Republic of Vietnam
Hanoi Sewer and Drainage System Development Project (carried out jointly with City Bureau) Dong-nai River Basin Water Resources Development Project
7
- People's Republic of Bangladesh
Flood Control Project Meghna River Revetment Project
8
- Republic of Maldives
Male Coastal Protection Project
9
- Kingdom of Nepal
Flood Control and Sediment Control Center Upper Narnali and Mahakali Basin Water Resources Development Project
10
- Democratic Socialist Republic of Sri Lanka
Greater Colombo Waterside Environment Improvement Project
11
- Cook Islards
Coastal Protection and Improvement Project
12
- Republic of Turkey
Seyhan River Flood Forecasting and Warning System Project
13
- Republic of Kenya
Marewa Dam Construction Project
14
- Mauritius
Port Louis Landslide Control Project
15
- Republic of Rwanda
Eastern Region Domestic Water Supply Development Project
16
- United Republic of Tanzania
Ruvu River Water Resources Development Project
17
- Federal Republic of Nigeria
National Water Resources Development Project
18
- Republic of Zambia
National Water Resources Development Project
19
- Republic of Honduras
Flood and Sediment Control Project for Branches of the Chamelecon River
20
- Republic of Nicaragua
Masaya City River Improvement and Stormwater Drainage Improvement Project
21
- Republic of Bolivia
Northern Santa Cruz Region Flood Control Project
22
- Federal Republic of Brazil
Guanabara Bay Water Pollution Prevention Project Parana Water Resources Utilization Project
23
- Republic of Chile
Northern Region Water Resources Development
24
- Republic of Ecuador
Chone-Viejo River Basin Comprehensive Water Resources Development in Chone-Viejo River BasinÅiManabi) Chone-Portovieijo River Basin Water Transfer Project
25
- Republic of Peru
Lake Vila Cota Withdrawal Project
26
- Republic of Venezuela
Apure River Improvement Project
Other international assistance and cooperation exchange
Japan-China Conference on River and Dams
Japan-Korea Conference on Technical Cooperation for Rivers, and Water Resources Development
Japan-France Seminar on Water Management for Rivers, Lakes and Marshes International Commission on Large Dams
ESCAP/WMO Typhoon Committee
