Tomoharu Hori

Assessment of the caesium-137 flux adsorbed to suspended sediment in a reservoir in the contaminated Fukushima region in Japan.

We estimated the flux of caesium-137 adsorbed to suspended sediment in the Kusaki Dam reservoir in the Fukushima region of eastern Japan, which was contaminated by the Fukushima Nuclear Power Plant accident. The amount and rate of reservoir sedimentation and the caesium-137 concentration were validated based on the mixed-particle distribution and a sediment transport equation. The caesium-137 and sediment flux data suggested that wash load, suspended load sediment, and caesium-137 were deposited and the discharge and transport processes generated acute pollution, especially during extreme rainfall-runoff events. Additionally, we qualitatively assessed future changes in caesium-137 and sediment fluxes in the reservoir. The higher deposition and discharge at the start of the projection compared to the 2090s are most likely explained by the radioactive decay of caesium-137 and the effects of reservoir sedimentation. Predictions of the impacts of future climate on sediment and caesium-137 fluxes are crucial for environmental planning and management.

Estimating the collapse of aggregated fine soil structure in a mountainous forested catchment.

This paper describes the relationship of forest soil dryness and antecedent rainfall with suspended sediment (SS) yield due to extreme rainfall events and how this relationship affects the survival of forest plants. Several phenomena contribute to this relationship: increasing evaporation (amount of water vapour discharged from soil) due to increasing air temperature, decreasing moisture content in the soil, the collapse of aggregates of fine soil particles, and the resulting effects on forest plants. To clarify the relationships among climate variation, the collapse of soil particle aggregates, and rainfall-runoff processes, a numerical model was developed to reproduce such aggregate collapse in detail. The validity of the numerical model was confirmed by its application to the granitic mountainous catchment of the Nagara River basin in Japan and by comparison with observational data. The simulation suggests that important problems, such as the collapse of forest plants in response to decreases in soil moisture content and antecedent rainfall, will arise if air temperature continues to increase.

Real-Time Reservoir Operation for Drought Management Considering Operational Ensemble Predictions of Precipitation in Japan

A method for real-time reservoir operation for drought management considering operational ensemble predictions of precipitation is developed in this study. Two operational ensemble predictions provided by Japan Meteorological Agency, namely One-month Ensemble Prediction (denoted by EPS1 hereafter) and One-week Ensemble Prediction (denoted by EPSW hereafter), are considered here. Ensemble prediction of basin precipitation for the coming 1 month is estimated from the grid point values of precipitation predictions of both EPS1 and EPSW, integrating them by employing the precipitation prediction from EPSW for the coming 8 days and that from EPS1 for the period from 9 days ahead to 1 month ahead. Ensemble streamflow prediction for the coming 1 month is then estimated from the ensemble prediction of basin precipitation by use of Hydro-BEAM (Hydrological River Basin Environment Assessment Model), a cell-grid type rainfall–runoff model. Daily water release from the target reservoir system for water supply is then optimized by use of dynamic programming (DP) approaches so as to minimize drought damage caused by the gap between water supply from the reservoir system and demand in the downstream in the optimization horizon considering ensemble inflow prediction. The proposed method was applied to the reservoir system in the Yoshino River in Japan, showing the effectiveness of the proposed method to introduce operation ensemble predictions of precipitation into reservoir operation for drought management.

Real-Time Reservoir Operation for Flood Management Considering Ensemble Streamflow Prediction and Its Uncertainty

A real-time operation method of a multi-purpose reservoir for flood management considering an ensemble streamflow prediction (ESP) is investigated in this study. The ESP is derived by a distributed rainfall-runoff model from an operational ensemble prediction of precipitation. Japan Meteorological Agency’s One-week Ensemble Forecast of precipitation, which is provided every day and has 51 ensemble members of six-hour precipitations for the coming eight days, is employed here. ESPs with 51 members for the coming eight days are calculated from the ensemble predictions of basin precipitation by use of Hydrological River Basin Environment Assessment Model (Hydro-BEAM), a distributed rainfall-runoff model. Reservoir states such as release or storage are then estimated for each ensemble member of the streamflow predictions to support preliminary release operation. Chance and the expected amount of recovery in storage water at the end of the flood event are also estimated for each scenario of reservoir operation to estimate impacts of the preliminary release operation on water supply operation in the following period, in order to help reservoir manager with making a decision on preliminary release considering the prediction and its uncertainty. The presented method was applied to Nagayasuguchi Reservoir in the Naka River basin in Japan, demonstrating the effectiveness and potential to provide useful information for real-time preliminary release operation of reservoirs.

Integrated Reservoir Operation Considering Real-Time Hydrological Prediction for Adaptive Water Resources Management

Changes in hydrological systems associated with climate change may threaten to reliability of water resources management systems. Sophistication of reservoir operation is considered to be important to enhance existing water resources management systems. In this chapter, an adaptive operation method of a multipurpose reservoir considering real-time hydrological prediction is presented for more robust water resources management under climate change. A method to design and assess integrated reservoir operation for both the flood control and water utilization is developed with consideration of imperfect real-time hydrological predictions in order to enhance the capability of an existing multipurpose reservoir.

A FUNDAMENTAL IMPACT ANALYSIS OF PRIOR RELEASE OPERATION AT A RESERVOIR CONSIDERING INFLOW PREDICTION

A method for impact analysis of a reservoir’s prior release operations precedential to floods is developed as a fundamental study in this paper. A Monte Carlo simulation model of a reservoir’s prior release operation coupled with artificial generation model of inflow predictions is proposed here. The inflow predictions can be generated with random errors based on given accuracies of the prediction so as to take impacts of inflow prediction’s accuracy on the effectiveness of prior release operations into consideration. Impacts of prior release operations on flood mitigation and water storage for water utilization are then analyzed and discussed by use of proposed simulation model for assumed reservoir operations which are derived from an existing multi-purpose reservoir.

Design of an Inference Engine for Dam Operational Rules for Synthesized Reservoir Control Support System

A generalized inference engine which takes charge of application of dam operational regulations is designed for a synthesized reservoir control support system. First, the common expression and logical mechanics of operational regulations established for dam reservoirs in Japan are extracted. Second, an inference engine which can treat these logics such as the mutual reference among the provisions of regulations is explored. The system designed here enables us to accommodate each provision of dam operational regulations into a rule as it is, which will be a useful tool not only for inference itself but for providing support information.

A New Framework for Building Runoff Simulation Models

A basin is composed of a number of basin elements. Corresponding to this, we thought up a new system of building a runnoff model by combining element models. To realize the system, we separate following two problems. One is to build element models and the other is to build runnoff models combining element models. To solve these problems, we extract and pack common functions among element models. This new system will make it easy to correct existing runoff models and to build new one.

Optimal Planning of Flood Control Systems Based on Risk Analyses of Flood Inundation

The aim of this study is to establish the optimal flood control system accounted for the comprehensive criteria on the whole river basin. Especially, for the system consisted of multi-sub basins and multi-defense or reference points, we will examine the effects of the flood control projects on the flood inundation probability in time and space. Project planning is divided into two parts, such as the site and scale problems and the scheduling problem. They are formulated through the screening model, the simulation model and the sequential model in order to be optimized by using Experimental Planning Method, and Dynamic Programming, Branch-bound Method.