Naoki Shirakawa

Use of economic measures for establishing environmental flow in upstream river basins

Abstract Environmental flow is a hot and current issue in water resources management in many countries in the world. In upstream river basins, it introduces a new constraint to hydropower sector. In the implementation stage of environmental flow economic aspects play a key role in river basin management. Economic measures are useful tools in management because they give strong incentive to conventional water users to change their behavior. We can take advantage of economic measures such as levy and subsidy to achieve consensus among all stakeholders in river basin management. A subsidy system for setting environmental flow release from hydropower stations is proposed based on a benefit function of environmental flow formulated in terms of flow rate. Under this subsidy, each hydropower station estimates the possible amount of subsidy to compensate the power production loss by flow release. Consequently, environmental flow is determined by optimum decision procedure by each hydropower station. This paper provides decision support system to water resources management in upstream river basins. Economic impact of management policy is large in some regions but not so much in others. We clarify that regional variation of economic impacts is a function of fraction of hydropower in total electric output, hydrological condition, and size of local economy. The subsidy system developed in this study is able to provide an economic measure to mitigate the inequity.

REUSING RECLAIMED WATER FOR ENVIRONMENTAL FLOW AND ITS EVALUATION METHOD

河川の減水区間対策の水源として下水処理水に着目し, 上水取水点まで導水・放流して河川流量を増強した場合の効果と費用を計算した.効果は水理量 (水面幅・水位), 水質 (BOD), それに流況曲線を用いた順序統計学的手法により評価した, 導水量を変化させて各ケースの費用対効果を算出したところ渇水基準と低水基準の間に差が生じた.事業規模を大きくして複数処理場を組み合わせると, 水質影響はほぼ事業費用に比例したが流量影響には組み合わせによる優劣がみられ, 代替案の比較や取捨選択に有効な結果が得られた