To clarify water quality and pollutant loads in the Edo, Ara and Tama Rivers, we examine the temporal changes of water pollution using monitoring data obtained by local governments and continuous monitoring data for COD. We also evaluate yearly-averaged SS, COD, T-N and T-P fluxes in these rivers by conducting the field measurements under several hydrologic events. The trend analysis for COD continuously monitored in the Edo River indicates that the changes of COD under low flow conditions are not similar to those under flood conditions. The estimated COD, T-N and T-P fluxes in these rivers reveal that non-point sources are comparable to point sources. These facts demonstrate that previous data and analysis methods for pollutant loads into Tokyo Bay should be examined carefully.

To clarify influences of large-scale floods on water quality of Tokyo Bay, we performed field measurements on pollutant loads under flood conditions, evaluated the long-term trends of SS, organic materials, and nutrient fluxes, and investigated its relation with DO and nutrients in Tokyo Bay. The large flood event caused by the attack of typhoon no. 0709 was observed to have significantly huge environmental impacts on Tokyo Bay. The comparison between the pollutant loads and DO in Tokyo Bay indicates that subsurface hypoxia at the head of the bay was developed after large flood conditions mainly due to decomposition of organic materials appreciably transported through influent rivers. It is also found that the large flood events influenced the nutrients in the benthic layer.

Kyosuke SHIGETA, Yasuo NIHEI, Ayako SAKAI and Satoshi OOTSUKATo examine the suspended-sediment transport from inland to costal areas in Tokyo Bay, we have monitored the suspended-sediment transport in main rivers flowing into Tokyo Bay, which are the Edo, Ara, Tama, Naka and Sumida Rivers. In the field surveys, we have installed an optical sensor for measuring turbidity and water samplers to measure the sediment concentration and particle size under flood flow conditions. The observed results reveal that the fine sediments of particles less than 71 μm are mainly transported in the main rivers under several flood flow conditions. The transports of finer and coarser sediments are relatively dominant in the Ara River and the Edo and Tama Rivers, respectively.

To clarify sediment transport and qualities of sediment in rivers flowing into Tokyo Bay, we performed field measurements and numerical simulation for suspended-and bed-load transports and sediment qualities in the influent rivers. Particle size and ignition loss (IL) of sediment in several influent rivers were found to be similar to those in coastal area. Bed-load transport of coarse and fine sands, which are found in sediments of tidal flat, were larger than the corresponding suspended-load transport, indicating the importance of the bed-load transport for the sediment supply to tidal flat. It is also found that one third of the total sediment yield in the whole basin of Tokyo Bay was trapped in dams located in the basin.

and Satoshi OOTSUKA 1 学生員 学(工) 東京理科大学大学院 理工学研究科土木工学専攻修士課程 (〒278-8510 千葉県野田市山崎2641) 2 正会員 博(工) 東京理科大学准教授 理工学部土木工学科(同上) 3 非会員 学(工) 埼玉県(元東京理科大学学部生) 4 非会員 学(工) 東京都文京区(元東京理科大学学部生) 5 非会員 東京理科大学 理工学部土木工学科 Previous evaluation of pollutant loads for the basin of Tokyo Bay are not accurately treated with the influence of flood-flow conditions. In the present study, we attempt to clarify the nutrients and COD loads in the main influent rivers under hydrologic events. For this purpose, we mounted automatic water samplers at the Edo, Ara, Tama and Naka Rivers. The observed results indicate that specific relations between river discharge Q and water quality are found in each river. The pollutant loads in the Ara and Naka Rivers are dominant in flood and low flow conditions, respectively. The large amount of the nutrients and COD loads were transported under flood flow conditions in all rivers.