Satoru Sugio

Numerical Simulation of Nitrate Transport with Unsaturated Flow Condition in Volcanic Soils

The groundwater contamination caused by NO3-N is one of the environmental problems in the agricultural field. In the southern part of Kyushu Island in Japan, the unconfined aquifer is contaminated by NO3-N. In this paper, NO3-N transport in two types of volcanic soil was investigated. In order to understand NO3-N transport process in unsaturated flow condition, two experimental works were carried out under precipitation condition using vertical columns filled up with soils. Simulated rainfall of NO3-N solution was generated on the top of columns. From the experiments, percolation processes of NO3-N in the soils were observed. In addition, the experimental results were simulated by means of one-dimensional numerical model. In the model, advection-dispersion and biochemical reaction term taking heterotrophic processes into consideration was described. According to the simulated results, it was clarified that the characteristics of NO3-N transport in each soil deeply depend on the biochemical reaction and the activity of bacteria in Shirasu was not as robust as it was in Ando soil.

AN OUTLINE OF THE FLOOD DISASTERS IN THE SEADAI RIVER IN JULY 2006 AND THE REVIEW OF FLOOD CONTRORL BY DAM OPERATION

Recently, a heavy rainfall in a short period of time occurs often and causes severe damage from a flood in various regions. The heavy rainfall due to the Baiu front gave severe damage to the southern region of Kyushu Island from July 19 to 23 in 2006. In this paper, an outline of flood disasters for the Sendai river basin in Kagoshima Prefecture from this heavy rainfall was reported. Furthermore, an improvement of the flood control operation of Tsuruda Dam in Kagoshima Prefecture was considered. By introducing the improved operation technique, it is expected that the flood control of Tsuruda Dam works well not only under usual flood conditions but also under unexpected heavy flood conditions.

CASE STUDY ON DISASTER MANAGEMENT SYSTEM OF SELF-GOVERNING COMMUNITIES AND THEIR REINFORCEMENT IN MIYAZAKI PREFECTURE THROUGH T0514

This paper deals with an investigation of a disaster management system of self-governing communities against a natural disaster through a questionnaire survey after T0514 that brought the most serious damages in Miyazaki prefecture widely. Many self-governing communities delay their official announcement of evacuation instruction and directive. One of the reasons is that the most of those selfgoverning communities have no objective criteria for their official announcement. The disaster information that covers a narrow area is desired to announce the evacuation instruction and directive at the best opportunity. The risk communications for natural disaster such as landslide and flood are not sufficient between self-governing community and residents, and improvement of this communication is desired to derive an appropriate evacuation against the natural disaster that exceed a maximum credible level.

RESEARCH ON THE CHANGE OF TOPOGRAPHICAL FEATURES AND VEGETATED REGION ON FLOODPLAIN IN KITA RIVER

This paper describes the relation among the flood, topographical features and the vegetated region on the floodplain at Honmura in the Kita River. The past changes in topographical features and the vegetated region were measured from the aerial photographs. The grain sizes of the gravels were investigated at the several points on the floodplain. As a result, the followings have been understood. 1) Gravels piled up due to the flood in 1997, fine sand mixing clay piled up during 1983-1997 and gravels piled up due to the flood in 1982 are accumulated in the vicinity of the 11.7km section. 2) Gravels on the bare ground of floodplain moved for the flood of 2,000m3/s in discharge. However, the large scale movement of bed materials did not occur for the flood of 3,500m3/s in discharge if the floodplain was covered by the thick vegetation. 3) The forest zone in the river bend had the effect that the topographical feature of floodplain was stabilized. 4) The state that the herbaceous vegetation covered the whole area of the floodplain, recovered from the state of the bare ground when the condition of 1,600m3/s or less in discharge continued for two and half years. 5) The state with thick vegetation recovered when the condition of 1,800m3/s or less in discharge continued for five years.

Inhabitant Senses for River Environment in Urban Area and its Changes

The questionaires are collected from the Komatu river basin in 1985 and 1989 to investigate the inhabitant senses for the river environment in an urban area. These data are anayzed by the Quantitative and Mathematical Methods. From the analysis, the followings are clarified: i) The inhabitants prefer the familiarity with water to the flood control. ii) The preference is essentially unchanged with time and depends on their inhabited district. ii) They are sensitive in the sense to the improvement of their life circumstances.