Responding Properly to Issues on Water Resources

Efforts for Promoting Sound Hydrological Cycles

What are Hydrological Cycles?
Hydrological cycles refer to the system of water circulation comprising natural water cycles of evaporation, precipitation, storage, percolation, and runoff as well as artificial water flows in water supply systems and sewerage systems. Domestic, industrial and agricultural water uses, etc. are also incorporated herein. The concept of hydrological cycles covers various levels from those on the global to continental scales to those on a basin-wide scale. It is important to understand hydrological cycles on a basin-wide scale because the water for our daily use comes from rivers, lakes, marshes and groundwater, and also because floods occur on the basin scale.
Efforts to promote sound hydrological cycles
Against a background of various developments including the concentration of population and industry in cities, the expansion of urban areas, changes in the nation's industrial structure, decreasing population in rural areas, the rapidly aging society, and the recent climatic changes, the hydrological cycles are changing in the history of water resources utilization, with decreases in river water flowing during normal times, depleted spring water, water pollution from waste water discharges, and increases in the incidences of urban flooding due to the expansion of non-water permeable surfaces. For this reason, it has become very important to promote "Sound Hydrological Cycles."
Efforts Made by the Liaison Committee of the Ministries Concerned
As it was expected to be inefficient for each ministry to promote measures separately in its own field in promoting sound hydrological cycles, the ministries involved in water (Ministry of Health, Labor and Welfare, Ministry of Agriculture, Forestry and Fisheries, Ministry of Economy, Trade and Industry, Ministry of Land, Infrastructure and Transport, and Ministry of Environment) established the "Liaison Committee for the Promotion of Sound Hydrological Cycles" in August 1998, and it compiled an interim report regarding common recognition of basic matters for the promotion of sound hydrological cycles in October 1999. A survey to examine comprehensive measures in four River Systems (Edogawa, Nakagawa, Koazegawa (Arakawa), Sennan, Itoshima) was carried out in Fiscal 2000 and 2001, and after formulation of a revitalization plan in two river systems (Kandagawa, Neyagawa) as an urban revitalization project in Fiscal 2002, the guidelines "On Planning for the Promotion of Sound Hydrological Cycles" were formulated in October 2003 based on the findings made at that time.
Outline of the Guidelines "On Planning for the Promotion of Sound Hydrological Cycles"
  • Purpose
    The guidelines "On Planning for Promotion of Sound Hydrological Cycles" indicate the basic concept concerning the targets and processes a region should adopt in order to plan specific measures for the promotion of sound hydrological cycles.
  • Features
    The guidelines serve as a reference for the planning of regional hydrological cycles, provide clues for how regions can autonomously promote the development of a basin and find solutions to problems on how to recover "tasty water" or "clean water". Specifically, it explains how to support activities of non profit organizations (NPOs), and points out the importance of sharing of roles among parties concerned and building of awareness through planning. It also suggestshow government offices, inhabitants, and service providers should take measures in cooperation with each other torespond to the damage caused by water shortages and floods as well as what their roles should be. In addition, it giveseleven good-practices, in which NPOs or regions have taken a positive lead.
  • Instances
    In the basin of River Ebi, sensitivity analysis was conducted for the cases when some measures were implemented,using a hydrological cycle model.
    As the measures, introduction and maintenance of parks and green areas, regulating reservoirs/ storage of rainwater/ percolation facilities and so on were considered. Figures indicated in the diagram below are for the cases when the measures were and were not implemented (parenthesized), assuming precipitation to be 100. By implementing these measures, surface runoff decreases, and percolation and groundwater runoff increase. At the same time, by making use of treated waste water, the amount of river flow at normal times increases and water quality is improved.

Groundwater Use and Ground Subsidence Prevention Measures

Current State of Groundwater Use
Groundwater has characteristics such as good quality, small changes in temperature and no need for large-scale water storage/intake/supply facilities because water is taken from wells. Approximately 12.4 billion m3 of groundwater in total is used in Japan every year, and this accounts for roughly 13% of the nation's total water use.
Problems Concerning Groundwater
of rapid economic growth, problems like land subsidence and groundwater salinization arose and posed a great challenge. Currently in Japan, mainly where groundwater problems have become conspicuous, groundwater preservation measures such as intake restrictions and conversion to river water intake are being introduced based on laws and municipal ordinances.
As a result, intense ground subsidence like that experienced in the past has settled down in recent times. However, since rapid increase in groundwater intake at times of water shortage may cause large ground subsidence, it cannot be said even now that problems surrounding groundwater intake and ground subsidence have been solved.
Groundwater Conservation Measures
Intake of groundwater is regulated for the purpose of preserving groundwater. There are two laws that prescribe designated areas with groundwater problems and restrict groundwater intake: "the Industrial Water Law" to regulate industrial use of groundwater and "the Law concerning the Regulation of Pumping-up of Groundwater for Use in Buildings" for building uses. Local governments have also enacted ordinances to regulate groundwater pumping. In three areas including Northern Kanto Plain, Nobi Plain, and Chikugo-Saga Plain, where extreme subsidence has been seen over a wide area, comprehensive measures have been taken based on "the Land subsidence Prevention Guidelines" decided by the conference of ministers concerned.
Quality of Groundwater and New Problems
In order to preserve water quality, prefectures started constant monitoring of groundwater pollution based on the Water Pollution Control Law from 1989. In 1996, the law was amended to newly accommodate measures to purify contaminated groundwater. In Tokyo, by efforts of regulations on groundwater pumping, the groundwater level has been conspicuously restored by approximately 20m compared to the 1960s. However, this dramatic restoration of the groundwater level is likely to cause new problems; for example, foundations of buildings are unstable in areas where they were constructed during the period when the groundwater level was much lower than today.

Waste Water Reusing

What is Waste Water Reusing?
Waste water reusing is a generic term for water that is used for some domestic activities but is lower in quality than drinking water; for example, water to fl ush toilet, for sprinkling, cooling, car washing, and air-conditioning. For this purpose, treated waste water and rainwater are used. In some cases, the term "general service water" is used in contrast to drinking water and sewage water.
Effects of the Use of Waste Water Reusing
Advance in the use of waste water reusing is expected to reduce the use of tap water, raise awareness of water-saving, and thereby contribute to the wise use of limited water resources as well as to the formation of a society prepared for water shortages. It will also reduce sewage water to be discharged into natural environment, and thus have a good effect on the water environment.
Types of Waste Water Reusing
Waste water reusing is mainly obtained from two resources; ① recycling of waste water, and ② the use of rainwater.
① Recycling of waste water

Waste water recycling systems can be classifi ed as follows:

  1. Individual circulation systems, where waste water is purifi ed and recycled in a single building (for example, Tokyo International Forum);
  2. District circulation systems, where buildings in designated districts jointly operate waste water recycling systems (for example, Yebisu Garden Place); and
  3. Wide-area circulation systems, where effl uents from sewage treatment plants and industrial water are supplied over large areas (for example, Fuji TV Head Offi ce Building).
② Use of rainwater

Rainwater is used in waste water reusing, and this is sometimes combined with waste water recycling systems. You can see both large-scale systems such as Tokyo Dome, and small ones like "rainwater barrels" that are widely installed in individual households in Sumida Ward in Tokyo.

Effective Use of Existing Facilities, etc.

Reconstruction and Renewal of Facilities
As a result of the promotion of the construction of water resources development facilities, the storage capacity of water supply facilities increased, and water supply became more stable than before, extending great benefi ts to the lives of people and industry. Meanwhile, it is getting more important to carry out timely reconstruction and renewal of existing facilities so as to prevent deterioration, water leaks and ruptures to secure stable water supply.
Diversion of Water for other Purposes
With mutual understanding and consent among the parties involved, water has sometimes been diverted for other purposes rather than what was fi rst intended, when local needs varied from those in the beginning due to changes in socioeconomic conditions. In Class A rivers, approximately 64 m3/s of water was diverted from agricultural or industrial use to domestic use between 1965 and 2003. As a result approximately 52 m3/s water was additionally secured for domestic use.
Effective Use of Facilities
Various measures are adopted in order to enhance the ef fects of existing facilities by making better use of them.
Integrated management

When there are multiple dams in a single river system, the storage water in those dams is comprehensively managed to achieve more effective water supply.

Redevelopment of dams

The f lood control func tion and water storage capacit y of dams are improved through levee raising, removal of sediment, and constriction of new water intake/ discharge facilities.

Projects of linking dams with channels

Water stored in existing dams can be used more effectively by linking dams with channels to draw water ineffectively discharged from a dam to another dam to be stored there.

Reorganization on dam groups

The flood control ef fect can be improved through rationalization of water usage by effectively reallocating storage capacity of individual dams that are strong in fl ood control function or water supply function. This can also lead to enhancement of river environment.

Water Saving
It is important that each one has a clear understanding of the importance of water when promoting effective use of water resources. Awareness of water saving has been growing in recent years.

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