The characteristics of rivers are composed of the interrelationship among flow, sediment transport, morphology and vegetation, and such an interrelating system contributes to multiple functions for rivers to serve such as the safety against flood, the water resources utilization, recreation and amenity for human life and ecosystem preservation. The system is a river landscape, and the river management is a management of this system. The recent development of fluvial hydraulics and hydraulics of flow with vegetation to describe the system and habitat hydraulics to evaluate the ecosystem is helpful for the management of river landscape.
Recent change of river landscape is obvious after some large scale impacts on rivers. To recognize the difference of the present river landscape from that estimated without those impacts clarifies the target landscape for river restoration.
The change of river landscape is brought about not necessarily by steady flood but more dominantly by repetition of floods and low-water stages. The morphology changes and some vegetation may be destroyed during flood, while the vegetation increases its territory to newly formed dried area during low-water stage. The abstracted elementary processes are described by river hydraulics, and integration of such analyses makes it possible to describe the landscape change of a stream corridor.
In order to restore the river system and its functions, large scale experiments such as artificial flood and flushing sediment from reservoirs have been done or are planned. Such challenges are in a framework of " adaptive management " which is a hypothesis driven periodic fine-tuning by monitoring and consensus.

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The author analyzes the various conditions concerning on the environmental planning of Japanese rivers and proposes the future research directions, based on these analyses. At first, from a morphological viewpoint, river planning should be based on longer time scales, especially on the engineering facilities, as being illustrated by several examples of dams. Secondary, any environmental river planning should be taken consideration as a part of the regional planning. And finally, the author claimed a river should be treated as a field of flowing regime, before consideration on biological preservation, by reviewing flow conditions, which are used to be decided by the traditional water usage right for irrigation purposes.

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Recently, nature-oriented river works have been much improved through many case studies. There are positive results by using native species of vegetation, and by preserving the habitat of all species in the surrounding environment before urbanization is begun. However, there are some cases of negative results where too many large stones are used or low water channels are filled to arrange artificial meanderings. Therefore, we have to consider the unique characteristics and the ecosystem of the river basins. If we focus only on the technology and forget, the importance of the river-basin environment and its biodiversity, only massive construc-tion will remain. We should clarify the reason why the restoration is needed, the places where the renaturalization is necessary, the significance of such areas for restoration, and the points of view on these issues.
In this report, I introduced some references with the knowledge obtained from the studies on the disturbances in ecosystems and on their causes. In particular, I demonstrated the causes of natural and artificial disturbances, and the significance of their classifications. I explained the use of the application of the methods in consideration of the entire river basin instead of using only one particular method of natureoriented river works. I introduced the examples of the Kissimmee River in America and the Yahagi River in Japan to support the understanding of my view point.
Furthermore, the hydraulic-model tests using compound open channels of small-size and middle-size rivers where the grouth of reed was allowed resulted in that the maximum transport capacity was only about 70% of the design flood discharge because of an increase in roughness-coefficient due to the vegetation. Therefore, the methods of application and the subjects concerning nature-oriented river works in the future is that the purpose of eco-design is clarified. I pointed out importance of the investigation on the river planning being adjusted to such increase in the roughness-coefficient due to the nature-oriented river works.

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Concept of potential nature in riverine environment is introduced extending the concept of today's potential natural vegetation in ecology. Degradation of the quality of nature in riverine environment in modern age of Japan is analyzed considering major human impacts on riverine environment in view of the concept of potential nature and historical development of modern technology in Japan. Essential advancement of industrialization of modern Japan is summarized into three major steps from historical point of view in human impacts on riverine environment.
Multiple disciplinary approach is desirable for both comprehensive understanding of riverine environment and implementation of river works. Unification of terminology is necessary for meaningful discussion among different disciplines. Several examples are listed and a guideline for unification of terminology is presented.
Natural characteristics of riverine environment are summarized as in the following three items, namely, 1) natural disturbance regime, 2) continuity in a watershed, and 3) diversity of morphology. It is shown that if river works are executed to restore these functions, they satisfy essential requirements of environmental ethics. Quantitative techniques are required in river planning for evaluation of habitat suitability and for providing alternatives for consensus building among administration, experts, residents, and so on. An open system is recommended to be able to revise a sub-model when advancement in technology is established retaining the main frame unaltered. A proposed habitat suitability evaluation system consists of sub-models in hydrology, hydraulics, micro-habitat and macro-habitat suitability, life cycle suitability, environmental economy, uncertainty of natural disturbances, consensus building, and so on. Recent developments in the sub-models are explained through examples.

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Unidirectional transport of material is a prominent and unique feature of river ecosystems. The transportation and accompanying ecological processes are well documented by the river continuum concept. River restoration works should pay enough attentions to the ecological processes attributed by longitudinal continuity and riparian/ channel interactions shown in the concept. Other important ecological processes in river ecosystems are transient storage and subsequent release of organic matters and nutrients from up- to down-streams : ecological spiraling. Benthic animal communities, bio-films (algae, microbes and fine particulate sediment) and leaf-litter packs work as effective biological storage apparatuses. Side channels, bank-side pools and hyporheic zones also work as effective geomorphological storage apparatuses. Upstream migration of fishes and aquatic insects populations works as an important recycling or transport of material from marine or downstream to upstream.

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In this paper, 7 factors of river ecosystem are categorized from the view point of human impacts referring to Karr et al. (1986). The factors are 1) energy sauce ; 2) water quality ; 3) habitat quality ; 4) flow regime ; 5) sediment transport ; 6) biotic interaction ; and 7) human use.
Based on the review of targets of conservation and restoration of river environment, I proposed that the target of river restoration is to restore the equilibrium dynamic system to keep the function of habitat quality.

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Environmental structures and fish fauna were compared between reaches of a spring-fed small stream, Yagawa Stream which has been used for agricultural irregation, a branch of the Kinu River in Tochigi Prefecture. Seven factors were selected for the analysis of emvironmental structures : i.e., 1) riparian plant, 2) driftwood, 3) undercut bank, 4) overhanging vegetation, 5) connected ditch, 6) submerged plant, and 7) gravel riverbed. Measurement of the factors and fish sampling were carried out at 11 sampling sections in each season of 1996 and 1997, and stream types were classified by cluster analysis on the environmental factors. Then the species composition of fishes was compared in relation to each emvironmental factor and the stream types.
As a result of the cluster analysis of the environmental factors, Yagawa Stream was devided into three parts, the slope-side section, the paddy field section and the transitional section. The nektonic fishes inhabited mainly in the slope side section and preferred to driftwood, while the benthonic fishes inhabited mainly in the paddy field section and were closely related with riparian plants, submerged plants and connected ditches. These results agreed well with facts that spawning redds of Oncorhynchus masou masou were found in the slope side section and the transitional section, and that those of Lampetra reissneri were in the paddy field section.

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Backwaters in rivers are important habitats for plants and animals. The flooding frequency on backwaters is an important parameter to define the character of the waters. However, methods for estimation of the flooding frequency have not been developed. In this paper we proposed a practical method to estimate flooding frequency of backwaters with an example studied in the Chikuma River.
Flooding frequency of the backwaters in the Chikuma River was estimated based on the map with contour lines at every 0.25 m. Assuming the water elevation rise to 0.25 m, 0.5 m, the water was estimated to run into the backwaters through the lower part of river terrace. When the water elevation rise to 0.75 m, flooding situation changed drastically. The flooding stream was estimated to occur on the river terrace and many backwaters was inundated. The important point was that flooding frequency at the backwater was not dependent on the backwater elevation.

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