Abstract
The heavy pollutant loading is drained out from the urban area of Ishioka City in the watershed of River Sanno. The loading of particulate matter decreases in going down with sedimentation. The amount of decrease was estimated by our two means. The first is the means with loading budget of the lower reaches from the urban area and the second is by observation of sedimentation rate on artificial substrata in river bed. The river sediments are flushed out by storm event without much decrease by decomposition and therefore become major part of storm runoff loading. The transient storage of sediments in river bed does not mean true self-purification. Consequently, for estimation of exact river loading or evaluation of self-purification abilities in river it is necessary to reevaluate sediments as a part of river pollutant loading.
