賀茂川水系の汚濁負荷流出過程の解析

Abstract

下水道整備により特定汚染源(Point Source)である生活排水・工場排水の浄化処理が進み，河川水系に放流される汚濁負荷は減少しているが，不浸透化が進んだ都市域では非特定汚染源(Non-point source)から雨天時に流出する汚濁負荷と合流式下水道越流負荷が増加している。本研究では鴨川水系の下水道排水区域を対象として，雨天時に河川に流入する雨水量および汚濁負荷量を算定したところ全流出量は比較的よく再現されたが，最大流出量生起時刻は早く計算されたのでこれについて考察を行った。また表流水と地下水間の水・物質移動の収支が算定評価できるモデルを用いて合流式下水道越流水が及ぼす河川水質への影響および河川水質と河床との相互関係を考慮した晴天時・雨天時を連続させた水質解析の準備を行った。今後このモデルの再現性を観測に基づいて評価した上で，盆地水系全体の水・物質流動およびその収支の解析を進める。

Recently, construction of sewerage system has reduced pollutant load flowing into urban rivers and river water quality has been gradually improved. But combined sewerage system has inadequate drainage capacity for designed rainfall intensity and is bringing very often overflow including much pollution. On the other hand, the increasing of impermeable urban surface and urban activities have caused another pollutant runoff during rainfall events which so-called diffuse pollution mainly derived from sedimentation on the urban surface and the drainage channel. It becomes the principal pollutant source in urban river water. The pollutant settled on the river bed is considered to become additional factor for river water quality analysis during dry-weather condition. In this study, the water quality mechanism was analyzed including the inter-transportation between river water and river bed. It could estimate the potential of river bed sedimentation as the pollutant source in river basin.