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A braided gravel-bed river provides essential habitats for various plants and animals. However, human regulation of rivers, such as dams, channelization, and other engineering works, alter flow and sediment regimes, which generally cause the degradation of river and riparian ecosystems. One of the prominent changes prevailing in Japanese rivers is forest expansion over gravel bars, and many native plants and animals that depend on gravel-bar habitat are now endangered. The Satsunai River is typical of rivers experiencing forest expansion, so the Japanese government launched a restoration project in 2012 to partially restore its riparian ecosystems. This is a large-scale experiment developed jointly by an interdisciplinary science team and river managers, who conduct monitoring and evaluation under an adaptive management scheme. The main measure to restore gravel bed habitat was an artificial flood regime, releasing a maximum water volume of 120 m3/s, which was a 2-year return period flood before dam construction. A unique feature of the project is that we considered the role of high-magnitude floods with recurrence intervals greater than 20 years after dam construction. We hypothesize that the artificial floods can be timed seasonally to create sites for regeneration and nesting of riparian species, and the high-magnitude floods contribute to maintaining a shifting mosaic structure of floodplain forest and unvegetated gravel-bar patches. We also used critical non-dimensional shear stress analysis to define “flood-disturbance areas” that can be disturbed under the artificial flow regime created by a dam. Artificial floods have been initiated once a year since 2012 at the end of June, synchronized with the seed dispersal period of Salix arbutifolia, which is endangered and a high conservation priority in the project. Thus far, the idea of setting floodplain-disturbance areas and the strategy of using both artificial and high-magnitude floods to restore a shifting mosaic of floodplain habitat patches is appropriate, as we found successful regeneration of S. arbutifolia and an exponential decay curve of the age distribution of floodplain forest patches. However, the sediment regime regulated by the dam was not addressed in this research, so future monitoring should track changes in river morphology associated with reduced sediment supply caused by the dam.

The variation of the water level at Palangka Raya is well described by the Nearest Neighbor Method (NNM) and the prediction can be made with 1-month lead time. A rainfall runoff model, traditional Tank Model, is applied to analyze the rainfall runoff to predict the water level at Palangka Raya using the data of several rainfall gauging station. The water balance is evaluated at Palangka Raya from the rainfall, the discharge and the evaporation.

Relationships between variations in river topography, such as riffles and pools, and fish, benthos, etc., have long been studied. The topographical classification of riffles and pools, however, is still conducted qualitatively. To take measures for the restoration or improvement of habitats, it is necessary to quantify these relationships and explain them in hydraulic terms. Meanwhile, studies on river -bed morphology have been conducted from the sediment hydraulics viewpoint, allowing for expression with physical indices. This paper examines the quantitative classification of riffles and pools of mountain streams, based on the findings of sediment hydraulics, to clarify their characteristics.

Conditions of watershed and rivers are closely connected with coastal environments. Suspended sediment is important to water quality on the coast. In particular, at times of flooding a large quantity of suspended sediment is transported to the coast, and the majority of phosphorus is transported in particle form rather than dissolved form. But not all sediment phosphorus circulates to the coast, for example apatite phosphorus. For this reason, a quantitative analysis on the chemical form of phosphorus was conducted. Suspended sediment was sampled during flooding of the Ishikari, Shiribetsu and Mukawa rivers, and the phosphorus chemical combined forms of the samples were analyzed. The results show that more than 60% of the phosphorous in the suspended sediment is circulating phosphorous, and that the total phosphorous content is related to the suspended sediment diameter and is different for each river according to land use.

To control suspended material transport in rivers, we must study the effect of the suspended material on the coastal sea area near river mouth in the end. In April and May, 2000, we investigated the transport of suspended material at the snowmelt flood at Mukawa river and the coastal sea at the same time. Snowmelt flood is dominant in the suspended material transport in a year in Hokkaido. Once suspended material of the river flows into the sea, it is transported by the coastal current directly, or goes to the bottom and rises again due to the ocean waves and is transported by the current near the bottom. On this investigation we used the acoustic Doppler current profiler (ADCP), which is designed for measuring current velocity and scattered intensity at the same time. Scattering intensity is related to turbidity, and if turbidity is related to concentration of suspended material, we can calculate the mass of suspended material. In this way, we estimate the direction and the mass of suspended material transport.

An organism relies on its habitat to survive. For the promotion of rivers rich in organisms, it is therefore essential to establish a policy on how habitats should be maintained. In order to establish such a policy, it is important to clarify the relations among aquatic organisms and matter which forms the river environment. This report describes the results of our survey, which aimed to clarify the relations of the fish population with the discharge, water depth., bed material size, water temperature and material volume (suspended sediment, organic mater, nutrient salt, etc.). And it also describes the classification of riffle and pool by local Froude number.

In light of the fact that river life is affected by sediment, nutrients and other factors on which river ecosystems are based, i t is equally importanto understandth e statuso f these factorsa s well as theirb ehaviorc hangest hat may result from river channel alterations. It has been pointed out that most of the nutrients that stored in river channels are absorbed by fine sands and transported in times of flood, before being deposited at their subsequent locations. However, the behavior during floods of such very fine sands that have absorbed nutrients has yet to be sufficiently clarified, and its earliest possible clarification is required to help further promote future river projects. This report considers the flow down process of suspended solids, based on data obtained from flood observation of the Mukawa Rivera nds ubsequents urveyo n riverbankd eposits. And the behavioro f suspendeds olidsa t the timc of a flood was reproducible using the unsteady-flow and bed variation calculation model.

Riparian woodland on waterfronts is indispensable, for it functions as buffer space and helps in maintaining ecosystem. On the other hand, when trees grow in river channels, there are many disadvantages in the flow capacity of channel. It is very important subjects that the maintenance method of riparian woodland is established. Field observations on the growth characteristic of pruned riparian woodland were conducted at the Toyohira River. Observations were made of the growth rate of trees, thenumber of sprouts and shape of trees. The following become clear as a result of the investigations. The growth capacity of willow is very high and recovered in one season depending on circumstances. The quantity of twig growth becomes less when the trees submerged in current. The quantity of twig growth becomes less when pruning method that remains trunk is conducted.

The concentration of suspended solids was measured at the Mukawa Bridge located 2.6km upstream of the Mukawa River mouth, and at the Hobetsu Bridge located 40.7km upstream of the river mouth. The lateral diffusion of suspended solids was measured by comparing the concentration of suspended solid at the center of river course and shores. Suspended solids are transported toward the center from the shore in the early flood stage and afterward move to the shore from the center. Observations of sediments on the floodplain were conducted before and after flood at the Mukawa River to understand the relationship between suspended solids and sediment on the floodplain. The scouring of the sediment on the floodplain and the deposition of the particles, which have the same size as suspended solids on the floodplain, was verified. From these investigations, it is shown that suspended solids and the sediment are interchanged during floods.

Field observations were performed on the Mukawa Bridge located 2.6km upstream of the Mukawa River mouth during the 1998 snowmelt flood. Observations were made of water level, discharge, bed material and various components of water quality. The following became clear as a result of the investigations.There is strong correlation in the concentration of the Nitrogen and the Phosphorus, which is adsorbed to by the suspended solids, with the average grain size of the suspended solids. Some water-quality components increase with discharge, and other components do not change with discharge. The waterquality components, which increase in concentration at the time of the flood, are primarily the undissolved elements. It seems that the rise in concentration of undisolved solids at the time of the flood was due to the suspension of flood plain and near bank deposits.

When trees in river channels drift during flood, those that are stacked in rivers sometimes cause flooding of river water. In addition, when they lodge against river structures, such as bridge piers, the structures may be destroyed due to an increased pressure of the river flow. Therefore, the plans for felling and planting trees in river channels need to be made so that trees do not lodge or drift during flood. The purpose of this research is to understand how the critical lodging value calculated from the results of the general test on felling trees fluctuates during flood. The results of the examination on relevant factors affecting the critical lodging value are reported in this paper.

Hydraulic condition for alternate-bar formation in open channel flows with suspended sediment are determined by stability, analysis. It is shown that the condition for alternate bar formation in the flow with suspended sediment is much different from in the flow without suspended sediment. The theory demonstrate the effect of suspended sediment on the formation of alternate bars. When bed load and suspended load are present, the value of the neutrally stable stage is stable for the bed load only case and unstable for the suspended load only case. Thus, the two modes of transport produce opposite effects and the region where they balance identifies the neutrally stable case.