Tsuyoshi Kinouchi

Numerical simulation of infiltration and solute transport in an S-shaped model basin by a boundary-fitted grid system

Abstract The boundary-fitted grid method, which transforms a complicated computational domain into a rectangular domain, is applied for the moisture and solute transport problems in the unsaturated soil layer of an S-shaped model hillslope. In the transformed domain, the fundamental equations of moisture and solute transport (i.e. the Richards equation and the Fickian equation) can be easily discretized into the finite-difference form. For three types of rainfall pattern (a unit rainfall, two-unit successive rainfalls and two unit ranfalls with a lag between them), hydrographs of total (pre-event and event water) and event water discharges, contour lines of soil moisture, pressure and total hydraulic head distributions, and flow velocity vectors are compared. For a relatively thick soil layer or for a relatively light rainfall, the capillary fringe effect plays an important role, whereas for a relatively thin soil layer or for a relatively heavy rainfall, overland flow from a variable source area is superimposed on the capillary-fringe-type runoff.

Modeling watershed-scale 137Cs transport in a forested catchment affected by the Fukushima Dai-ichi Nuclear Power Plant accident

The Fukushima nuclear accident in 2011 resulted in 137Cs contamination of large areas in northeast Japan. A watershed-scale 137Cs transport model was developed and applied to a forested catchment in Fukushima area. This model considers 137Cs wash-off from vegetation, movement through soils, and transport of dissolved and particulate 137Cs adsorbed to clay, silt and sand. Comparisons between measurements and simulations demonstrated that the model well reproduced 137Cs concentrations in the stream fed from the catchment. Simulations estimated that 0.57 TBq of 137Cs was exported from the catchment between June, 2011 and December, 2014. Transport largely occurred with eroded sediment particles at a ratio of 17:70:13 of clay, silt, and sand. The overall 137Cs reduction ratio by rainfall-runoff wash-off was about 1.6%. Appreciable 137Cs remained in the catchment at the end of 2014. The largest rate of 137Cs reduction by wash-off was simulated to occur in subwatersheds of the upper catchment. However, despite relatively low initial deposition, middle portions of the watershed exported proportionately more 137Cs by rainfall-runoff processes. Simulations indicated that much of the transported 137Cs originates from erosion over hillsides and river banks. These results suggested that areas where 137Cs accumulates with redeposited sediments can be targeted for decontamination and also provided insight into 137Cs transport at the watershed scale to assess risk management and decontamination planning efforts.

Investigation and modeling of water and heat transport in an urbanized catchment

The water and energy transport dynamics in urban catchments are investigated to facilitate better understanding of thermo-hydrological impact of urbanization on the receiving water. For this purpose, meteorological and hydrological variables have been monitored in a catchment with an area of 12.2ha located in the central Tokyo District. The amounts and dynamic patterns of urban wastewater showed quite reasonable results compared with existing survey reports. The time variation of sewage temperature showed a distinct diurnal pattern, which reflects water and energy consumption characteristicsin residential houses and is insensitive to a day of the week and season. In a thunderstorm event, the impact of summertime urban heating on the runoff was revealed by an abrupt increase of storm temperature. Finally, a dynamical model was proposed to estimate sewage temperature in response to hydrological and meteorological conditions as well as human behavior of water and energy consumption.

THE INFLUENCE OF WATER HEAT ENERGY USE ON STREAM TEMPERATURE IN URBAN RIVERS UNDER TIDAL VARIATION

To predict the water temperature in lower reaches of urban rivers, field measurements and model development were performed for simultaneous transport of water and heat in a stream. Detailed information on river flow and heat transport under tidal motion was obtained through an intensive measurement in the lower reach of the Ara River. Based on the knowledge of time variations and cross-sectional profiles of the flow and the stream temperature, a onedimensional dynamic model is developed to predict flow and water temperature in tidally affected urban streams. The model takes into account of tidal motion, longitudinal dispersion, water exchange with tributaries, wastewater effluent and the heat exchange between the atmosphere and the stream water. Using the calibrated model, effects of heated water discharge on the stream temperatures due to the district heating and cooling system were estimated for a possible scenario in which the river thermal energy is used through the water heat pump technology.

STUDY ON THE METHOD OF EVALUATING HUMAN COMFORT FOR THE COMBINED OUTDOOR ENVIRONMENT IN URBAN AREAS

都市の屋外空間は人間の聴覚, 視覚, 嗅覚, 触覚に対して様々な剌激を与える複合的な環境条件にある. 本論文では, 水辺, 公園, 街路, 住宅地などの都市の屋外空間における快適性の支配構造を明らかにして複合的環境条件における快適性の評価手法を提案した. まず, 屋外空間の音環境, 視環境, 熱環境に, 大気環境を表す環境条件と心理反応の閲系について検討を行い, 各環境を代表する指標を明らかにした. 次に, これらの指標を入力層に持つニューラルネットワークを用いて快適感を推定する手法を構築し, 本手法により未学習データに対して精度の良い快適感推定ができることを確認した. また, ニューラルネットワークを用いて各環境条件と快適感の間の非線形的な関係を明らかにするとともに, 快適感への影響度合いの大きい順番は景色の美感, 体感温度, 天空率, 自然音指数, 芳香指数であることがわかった.

Development of a simplified Water Balance Model in an Urban watershed

Urban surfaces covered with asphalt and concrete have been changing hydrological cycle in urban river basin. To assess the effects of various measures for conserving natural water balance, its appropriate quantification must be carried out.As a detailed model for estimating hydrological cycle requires a lot of hydrologic data and computational resource. We tried to buildup a simple model which utilize existent data source to grasp monthly water balance. The model was applied to the Tsurumi river basin to verify the accuracy in estimating flow rate and other hydrological variables. It is found that the model is likely to be useful in assessing monthly water balance both in rainfall and non-rainfall periods.