Development of a generalized method for nonpoint source load estimation

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K05828
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 41030:Rural environmental engineering and planning-related
• Research Institution: Kobe University
• Principal Investigator: TADA Akio 神戸大学, 農学研究科, 准教授 (00263400)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: Horvitz-Thompson推定量 / BCRE / 10年平均年河川負荷量 / 低頻度 / 長期モニタリング / 年単位LQ式

Outline of Final Research Achievements

Annual river loads are contributed by point and nonpoint sources and the latter is correlated with land use. A statistically appropriate and more precise method for estimating the relationship between land use and river loads was developed based on the Horvitz-Thompson estimator and the rating curve method, using long-term monthly low-frequency water quality monitoring data and daily flow data. Monthly sampling are commonly employed in monitoring in many countries.
Using the method developed named as the bias-corrected regression estimator (BCRE), we further developed a method for estimating parameters of the inter-annual rating curve or average concentrations of river water quality from land use ratios for several watersheds with different land use ratios. The estimated values gave generally unbiased results, but there is still a problem that the uncertainty of the estimated values is still large.

Free Research Field

地域環境工学

Academic Significance and Societal Importance of the Research Achievements

これまで，多くの国で採用されている月１度程度の低頻度の水質モニタリングデータから，年単位の河川を流下する物質量や水質濃度を偏りなく精度良く推定する手法が開発されていなかった。本研究はこの手法を開発し，多くの水質モニタリング地点での長期データを利用することで精度の高い推定を実現した。この推定法に基づき，日本と米国の複数流域のデータから土地利用と年単位の流量と河川流下物質量の関係式や，河川水質濃度を偏りなく推定する方法も開発した。推定精度に改善の余地があるが，これらの方法は人間活動が水環境に与える影響の定量評価と水質管理に利用することができる。