Yasuharu Watanabe

Characteristics of Watershed in Central Kalimantan

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.

LATERAL DIFFUSION OF SUSPENDED SOLIDS AND SCOURING AND DEPOSITION OF FINE SAND ON THE FLOODPLAIN DURING FLOODS

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 Observation on Growth Characteristic of Pruned Riparian Woodland

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.

Velocity Distributions around a Spur-Dike

In river planning, it is necessary to study the influence of river construction to the river flow and the river bed. A flow affected by the river construction is a three-dimensional complicated flow.Sand deposition and scour around the construction is caused by this complicated flow which make it difficult to grasp the river change with the construction.To investigate the mechanism of flows induced by spur-dike, we need the field survey around a spur-dike.we are reporting new results obtained from the occurrence of secondary flow behind the spur-dike.

Lateral bedload transport for bank materials with wide distribution of size considering the slope effect

Lateral bedload function for fractional particle sizes on the tilting side slope was developed by following Parkers method. On the slope with near angle of repose, tangential component of the gravity force acts on the surface particles in equivalent intensity comparing with the tractive force. Thus the full non-linear equation for a particle motion was solved numerically. Thickness of the bedload layer was given from extending Ashida Michiue equation to consider the gravity effect and to use Egiazaroff equation for critical tractive force of fractional particles. Summation of the lateral sediment discharge for each fractional particle size calculated from the product of the moving particle velocity and bedload layer fairly well agree with the observed data obtained from large scale bank erosion experiments using volcanic ashes for the bank material.