Annual SS (Suspended Solids) load from the Hiromi river to the Shimanto river was estimated based on the 33-months continuous daily observation data. The water quality of the Shimanto river, which is often called "the last clear stream of Japan", is observably deteriorated especially during rice transplanting period. Suspended load prediction models were established and the effect,of rice transplanting activities to the rivers' suspended load was also estimated. Results showed that the amount of annual SS load to the Shimanto river from the Hiromi river was 9.8x106 kg and if drainage from paddy fields during rice transplanting is completely stopped, the amount could be reduced by 8.0-12x104 kg SS.
