公表調査データの統計解析による市街地ノンポイント汚濁負荷流出量の予測とその信頼性評価

摘要

雨天時における市街地流出を調査している報告書，論文等の文献を収集し(1968〜2011年)，一降雨を単位とした市街地の汚濁負荷(BOD,COD, SS， TN， TP)の負荷流出データベース(DB)をまとめ，一降雨の流量加重平均濃度(EMC)の分布を明らかにした。続いて降雨条件，地理的状況がEMCに及ぼす影響を回帰式で予測し，日本全国の4地点での降雨条件を与えた際の年間流出負荷の予測値とその変動係数を導出した。その予測に基づき，信頼性のある流出負荷量を算出するためにどの程度の降雨の採水頻度が必要になるのかをシミュレーションにより検討した。95%信頼区間を2倍以内程度の誤差とする場合，水質項目によつては年間の全降雨ィべントのうち半分程度を採水する必要があることを明らかにした。%Papers and reports on investigations of the urban drainage in Japan were collected (1968-2011) and a database of urban runoff loading for each measured precipitation event was prepared. The targeted pollutants were BOD, COD, SS, TN， and TP, and their event mean concentrations (EMC) were included in each data set along with their precipitation event conditions. The distribution of loading and the geographic conditions of the basins were clarified, and the dependence of the EMC values on the precipitation and geographic conditions was modeled using the regression equation of a power law. Using this relation, the predicted yearly loading and coefficients of variation were derived for four representative precipitation conditions in Japan. The required sampling frequency to attain a certain accuracy of the annual loading was estimated by a simulation using the above model. From the results, at least half of the precipitation events must be sampled for the 95% confidence interval of annual loading to be within the range of half to double the true value.