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5.5 PROJECTS UNDERTAKEN TO ACHIEVE SUSTAINABLE DEVELOPMENT OF DAM RESERVOIRS IN JAPAN

5.5.1 Introduction to the Japanese reservoir policy

By adjusting natural flow fluctuations, reservoirs have made a large contribution to the prevention or reduction of damage from flooding and to the provision of a stable supply of water resources. This is particularly true in Japan, a country with steep topography and widely fluctuating meteorological and hydrological conditions, where dams have provided superior flood control and water utilization, based on improvements in dam construction technology.

A study of dams in Japan reveals that about 40% of the area of each water­shed is regulated. Although this means that the density of dams in Japan is extremely high compared with the rest of the world, Japan's dams can control only flood water produced by an equivalent rainfall of about 120 mm, and considering the growth of the water demand that must be satisfied, reservoir capacity per capita is still quite low. About 50% of the country's population and 75% of its assets are concentrated on downstream alluvial lowlands. Considering these circumstances, more reservoirs must be constructed and the flood control and water utilization functions of dams have to be improved. For these reasons, dams are indispensable in Japan, and their use must continue.

The construction of a dam submerges land, has significant social and economic impacts on its surrounding communities, and, temporarily harms the natural environment. This means that the consensus building process, which starts with the preparation of an initial plan and concludes with the construction of the dam, is an extremely time-consuming process. On top of this the amount of available land suitable for efficient dam construction has declined. And recently, the public's need to use dam reservoir surroundings for recreational activities has changed, as shown in Fig. 5.11, requiring dam development plans that incorporate measures to improve the surroundings of dam lakes to meet these new needs.

In response to these changes, projects related to "sustainable development of reservoirs" are undertaken in Japan.

5.5.2 Projects related to sustainable development of reservoirs

The projects are as follows:

(1) Legal arrangement for social impacts of dam construction projects. This incorporates measures for obtaining a smooth achievement of public consensus for dam construction and to reduce the socio-economic impacts.

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1955 1965 1975 1985 1990

k i Study: Study of nature,

»*** Î ecology, etc. around dams f »•** i and dam reservoirs y** i (Biotope, Dam)

• 4 Y

Experience: Activities around dams and dam reservoirs (camping, water sports, fishing, events, etc.)

Y ? / ,••* ; Space Utilization: Recreation at dams and

/,••** ; on suitable land around dams Y I (tennis courts, athletic parks, walking trails)

Sightseeing: Take advantage of the completion of the dam

Fig.

and dam lake to develop new sightseeing sites (field trips, strolling, industrial tours)

5.11 Schematic change of recreational needs for dam reservoirs.

(2) Projects defined as reservoir redevelopment. The following three categories are included in these projects:

(i) Recovering. This category embraces the recovery of reservoir functions, i.e. storage volume and reservoir level from functional degradations caused, for example, by sedimentation in the reservoir.

(ii) Improving the current functions of already developed (existing) reservoirs in an area wide river basin system. This category includes the increase of storage volume and level of an existing reservoir, with a view to meet the increasing demand.

(iii)Addition/reduction of new objectives (functions) to the current reservoirs and/or readjustment to new situations. "Adding/reducing" and "readjusting" reservoir functions means the addition of new objectives (functions), such as recreation and amenities, to the current functions of the reservoir, or the replacement of some objectives by others (e.g. replacement of some part of the municipal water supply by flood control).

Redevelopment activities may not necessarily be confined to single reservoirs but can be extended to an entire river basin system. To distinguish the former from the latter, they are defined as a "single" reservoir redevelopment and "networking" reservoir redevelopment, respectively.

There are a number of reservoir redevelopment activities which have been implemented, or are still under way or in the planning process, throughout the Japanese Archipelago (Sakamoto et al., 1995). The following box gives an overview of some examples:

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Tsugaru Dam (Aomori Prefecture) Category (i) (ii) Single Miwa Dam (Nagano Prefecture) Category (i) (ii) Single Shin-Maruyama Dam (Figu Prefecture) Category (ii) (iii) Single Amagase Dam: Category (Kyoto Prefecture) (ii) Single Matsubara/Shimouke Dams (Ohita and Kumamoto Prefecture) Category (ii) (iii) Networking Fukuchi Dam (Okinawa Prefecture) Category (ii) Networking Sasabugawa Dam (Fukui Prefecture) Category (iii) Single Asahikawa Dam (Okayama Prefecture) Category (ii) Single Kiyagawa Dam (Yamaguchi Prefecture) Category (ii) Single Kawakami Dam (Yamaguchi Prefecture) Category (ii) (iii) Single Minamihata Dam (Fukuoka Prefecture) Category (ii) Single Kayase Dam (Nagasaki Prefecture) Category (ii) Single Tsuruta Dam (Kagoshima Prefecture) Category (ii) (iii) Single Shin-Nakano Dam (Hokkaido Prefecture) Category (iii) Single Nagasaki Honkouchikoubu/Nishiyama/Urakami/Nakao/Yukiuradaini Dams (Nagasaki Prefecture) Category (iii) Networking

These projects can also be classified corresponding to redevelopment as shown in Fig. 5.12. In what follows the classification of projects is introduced according to this figure.

5.5.3 Legal arrangement for social impacts of dam construction projects

Dam construction projects are different from other ordinary public projects because they greatly affect the residents whose houses and surrounding areas may be submerged after a dam is constructed. Therefore, to promote dam construction projects, it becomes indispensable to take measures for relieving the impacts (denoted measures for reservoir areas) in conjunction with dam construction projects.

For this purpose, it is necessary to maintain the livelihood of the residents concerned and enhance their welfare by reconstructing the living environment and basic production of the reservoir areas in accordance with the Act on Special Measures for the Reservoir Areas Development in addition to the compensation offered by the dam owner. The regional reconstruction plans for the designated dams are planned by the prefectural governors concerned and approved by the Prime Minister after coordination between the involved ministries and the National Land Agency. Projects designated in the plans will be adopted as governmental subsidized projects, and a higher percentage of subsidies is permitted for a large dam by which extensive areas will be submerged. The same measures are also applied to large-scale lake development projects.

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Single reservoir "redevelopment

Structural -(Rehabilitation of an existing reservoir)

Nonstructural (Change of rules) "

Dredging of buttom sediment (Miwa Dam)

Increasing dam height (Shin-Maruyama Dam)

Improving discharge facilities (Asahikawa Dam)

Reallocation of reservoir . capacity among purposes (Tsuruta Dam)

Changing reservoir operation rules (Asahikawa Dam)

Transfer of ownership (e.g. water right)

Networking of reservoirs

Combination of existing reservoirs redevelopment " (Matsubara-Simouke Dams)

Redevelopment of existing reservoirs and . construction of new reservoirs (Nagasaki Honkochikoubu / Nishiyama / Urakami / Nakao / Yukiuradaini Dams)

Fig. 5.12 Classification by redevelopment means.

Also, the costs required for executing reconstruction projects are some­times partially borne by the beneficiaries in the areas downstream. In addition, as a supplement to the compensation by dam owners and reservoir area re­arrangement projects stated above, a "Fund for Reservoir Areas Development" was established for certain areas with contributions from the Government, prefectural governments and cities concerned. In certain areas the livelihoods of residents whose houses were submerged, are re-organized under this fund.

5.5.4 Water quality conservation measures for dam reservoirs

Some environmental problems have been created at certain dams, such as long-term turbid water in reservoirs due to floods, eutrophication as a result of development around reservoirs, discharge of cold water, landslides around reservoirs, and environmental degradation. Due to people's awareness of the environmental impact of development activities, these problems are considered extremely important in dam construction.

The three major water quality problems of cold water, long-term turbid water, and eutrophication in reservoirs have been studied by many organizations, and countermeasures have been examined. As a result it has

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been demonstrated that cold water and turbid water problems can be solved to a certain degree by installing selective intake facilities (including surface intake facilities) as required. With respect to eutrophication, various measures are being taken as shown in Table 5.2 and Fig. 5.13. Conservation measures suitable for dam reservoirs are being taken as well.

Table 5.2 Methods for improving water quality in reservoirs (Ministry of Construction, 1984).

Measures for dam reservoir catchments (control of nutrient loads into reservoir)

Measures for point sources

Measures for non-point sources

Highly treated sewerage (chemical coagulation treatment) Reduction or elimination of phosphate in detergents Excavation or bypass channel Restricting fertilizers Seepage gutters Filtering by a column of aluminium oxide Removal of phosphorus by pre-reservoir Removal of phosphorus from main inflow rivers Restricting land utilization

Measures for reservoirs

Removal of nutrient salts in reservoirs

Emergency measures for eutrophication

Chemical coagulation in reservoir Dilution and flushing Discharge from deep layer Removal of nutrient salts by removing organisms Drying and removing sedimentation at the bottom of reservoir due to lowered water level Treatment of reservoir bottom (covering bottom)

Aeration (circulation) Control of aquatic plants due to change in water level Physical measures (cutting aquatic plants) Chemical control (use of weed and algae killers) Biological control (treatment by predators)

5.5.5 Rehabilitation of an existing reservoir

Dam refreshing projects (sediment removal projects) Dams constructed as sedimentation measures are designed to guarantee a stipulated sediment capacity. But at some dams, factors such as abnormal flooding or weak geological upstream structures result in large amounts of sediments, far beyond the planned quantity, being deposited within the effective reservoir capacity. At dams in this condition, sedimentation countermeasures are implemented in order to restore the effective reservoir capacity needed to adjust flood waters or supply water to local users and to guarantee new capacity. Specific methods employed are: (a) the use of a pump dredger to

Detour channel)

9

Fig. 5.13 Schematic diagram of water quality improvement techniques in reservoirs.

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perform on-land excavation and dredging, and (b) the installation of permanent dredging facilities (dredging pipelines, dredging gates, etc.).

Increasing dam height By increasing the dam height of an existing dam extra effective storage capacity can be obtained for flood control or water utilization. It has the advantage that a large expansion of effective capacity can be achieved with only a slight enlargement of the dam. However, it involves crucial processes, such as the use of fairly advanced techniques to connect the new and old dam bodies and to improve the foundation, and the difficulty of maintaining normal functioning of the existing dam during the construction period must also be taken into account.

5.5.6 Improvement of the management and operation of dam reservoirs

Changing reservoir operation rules In Japan, flood water period or summer period maximum reservoir levels are established, and dam managers take steps to keep the reservoir level at each dam at or below the stipulated level from June to September. A high volume of water flows rapidly into the reservoirs during these months as a result of the extensive rain brought by the late spring and early summer seasonal rain fronts and by typhoons. When it is possible to keep the restricted flood period water level at the dam flexible, and adjust it step by step in conjunction with using the preliminary release method, it helps ease the conflict between the needs for flood control and water utilization during the same period. Thus, by allowing more water to be used, an extra water storage capacity can be guaranteed. Methods of forecasting extensive rainfall and flood water levels must become more accurate, and fully equipped evacuation and warning systems have to be provided.

Another use of dams is electric power production, but hydroelectric plants form dry river beds between the dam and the power plant outlet, and these dead water sections adversely affect both the rivers' recreational functions and the living organisms which inhabit them. Dam managers are encouraged to discharge a stipulated volume of water in order to eliminate these dead water sections. When the interrelationships between various aspects of the physical environment, living organisms, the ecosystem, flow volume, water levels, scouring of the river bed, sedimentation processes etc. are eventually elucidated, fluctuations in the river maintenance flow volume suitable for co­existence with living organisms and the ecosystem should be approved and dams used to rationally control these fluctuations.

Dam integration projects and comprehensive water utilization systems A dam integration project involves the linking of a number of existing adjacent

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dams with channels so that the existing storage capacity can be used more effectively by allowing dams to send their uncontrolled outflow to other dams for storage. A drought protection dam, once designed and built with sufficient capacity to deal with drought conditions as shown in Fig. 5.14, guarantees the minimum amount of water needed during drought conditions. Projects of this kind are undertaken to permit water circulation and provide the minimum required amount of water during drought conditions, but, in order to guarantee a highly reliable stable water supply during both normal and drought conditions to meet the growing water demand of the large cities, it is important to revive the idea of improving dam facilities by implementing the integrated water utilization system shown in Fig. 5.15.

In other words, future plans should be based on so-called integrated water utilization planning and management theory that considers the possibilities for obtaining water from a number of different sources such as river water from reservoirs, groundwater, recycled treated waste water, rain water, and desalinated sea water in urban regions, as well as the construction of urban storage facilities corresponding to the quality of the source water and its intended uses, and provision of double pipes and other improved lifeline facilities to supply water and link the system to water conveyance works outside the watershed through neighbouring dams or regulation ponds.

5.5.7 Regional promotion and regional planning centred around dams

Because the construction of a dam has a large impact on the society of the region and the foundations of the life of the local people by submerging their

Fig. 5.14 Dam against extraordinary drought. Time

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Sea WateADesalinization Plant

Use of

River

Recycled [Treated

-e Sewage Treatment

Y Low-quality Water Network

£ 7 Water storage under ground

Waste Water £ ;

High-quality Water Network

Plant

Use of Recycled Treated Waste Water

Urban Area

Water Conveyance works

Dam as measeure for extraodinary drought Water Conveyance works

River

Fig. 5.15 Comprehensive water utilization scheme.

land, dam planning should include provisions for the improvement of the surrounding environment in order to reduce the impact and to permit the dam to serve as a basic facility contributing to a revitalization of the surrounding region. Furthermore, each dam should be planned so that both the dam and its improved environment will be attractive not only to people living close to the dam, but also to those in the downstream region, allowing a growing number of people to take part in communal events near the dam, or simply to visit the facility.

Public access dam projects In response to the recently growing public need for greater access to the natural environment and recreational facilities the promotion of the use of dams and dam reservoirs and their surroundings as open space filled with water and natural greenery, as well as the efforts to preserve their natural environments, will definitely make an important

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contribution to regional stimulation. For this reason, "Public Access Dam" projects intend to take advantage of the creativity and innovative spirit of the local populace and provide dams accessible to the public. Encouragement is given to the use of these dams in order to increase the local people's familiarity with them and, in this way, to stimulate development of the region.

Throughout Japan, improvement projects are in progress at a total of 25 dams designated as "Public Access Dams". Figure 5.16 shows an example: the Hiyoshi Dam on the Yodogawa River system, which is now under construction, and which is combined with a memorial park downstream of the dam. Facilities in concert with the surroundings are being provided around the reservoir, and the land around the reservoir is being landscaped and reforested.

Recreational water improvement projects As a result of the recent increase in the amount of leisure time enjoyed by the people, a growing number are seeking means for spiritual repose. To increase the hydrophilic properties of reservoirs to meet the new needs, dam administrators are drawing on the resources of the private sector to create environmental water surfaces

Fig. 5.16 Hiyoshi Dam memorial park.

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(recreational lakes) and to promote the development of resorts around dam lakes. For example, recreational lakes with constant water levels are developed by installing a secondary dam which simultaneously improves the water quality and stores sand at the upstream end of the dam lake.

Dam site environment improvement projects These projects improve dam reservoir surroundings and contribute to improved dam management at the same time as they provide places for relaxation close to dams. Specific measures include the improvement of river banks, reforestation and the provision of footpaths on the river banks, the installation of protective fences and warning equipment, the provision of environmental conservation facilities etc.

5.5.8 Other issues

Constructing large dams on main river courses or on large tributaries is an effective way to prevent flooding and supply water to water users. However, because of the serious socio-economic and environmental impacts of the construction of such dams, it is more difficult than ever to carefully implement such projects. This is likely to become even more difficult as a consequence of the growing need to preserve the environment and promote co-existence with natural organisms and the ecosystem. This means that it is vital to establish planning and management policies for constructing small capacity dams at a number of sites on small tributaries which would have the same capacity as a single large capacity dam; but which would produce small amounts of sediment. It is also vital to carry out an integrated management of the combined capacity of these small dams. This approach would permit a regulation that provides the water volume needed for both flood control and water utilization at the same time as it would reduce the impact of dams both on the environment and on human society. Its implementation would, of course, increase the importance of linking dams and developing integrated dam management technology including forecasting technology.

Reservoir redevelopments can be interpreted as a developmental activity aimed at sustainability. For example, given that in developed countries like Japan suitable dam sites in a river basin are becoming increasingly difficult to find, it is imperative that the following conditions are met:

• growth of limits (rather than limit to growth);

• co-existence with nature;

« co-existence with future generations;

« ultra-long-range management;

• self-supporting, recycle-oriented maintenance.

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Reservoir redevelopments can be regarded as a typical example of a development activity where "nature is created" by paying special attention to the above conditions. Stated in another way, a new planning process and methodology should be conceived to systematically design an inter-generational, long-range, self-supporting implementation/maintenance system for river basins with manmade reservoirs.

It may be useful to list essential problems which may come about in planning and applying a methodology to the above-stated sustainable reservoir redevelopments. They are:

• water resources reallocation for a single or networking reservoir redevelopment;

• benefit allocation for a single or networking reservoir redevelopment;

• cost allocation for a single or networking reservoir redevelopment;

• inter-generational, long-range, self-supporting implementation/maintenance, multi-phase planning strategy.

In 1982, Nagasaki City experienced a large-scale flood disaster. The rapid urbanization was one of the reasons for this disaster. The plan of the Nagasaki emergency flood control project, set up to deal with just such a problem, was to create a flood control capacity in the existing reservoirs located upstream of Nagasaki. These reservoirs had been used as sources for municipal water supply. A reallocation of the reservoir capacity leads to a reduction of the amount of municipal water supply. This project planned to compensate the reduction by constructing new reservoirs in different river basins. Cost allocation became a difficulty in realizing the project. One reason was that the project involved many reservoirs. Another reason was that the reorganization of reservoirs did not modify the amount of water provided for municipal water supply. Because this project was only for flood control, the waterworks bureau had no incentive to pay. No methodology has been established for this type of cost allocation.

5.5.9 Conclusion on the Japanese study

This study has outlined the laws and regulations, technological measures, and project policies required in Japan to construct future dams, maintain the water storage functions of existing dams, and contribute to regional and watershed development. The environment surrounding dam provision may become increasingly severe, but we are confident that the new developments described above will overcome these difficulties and contribute to sustainable development.