Abstract
Clean-up of dikes and dry bed is one of the most important river management in terms of flood control, water use, and environmental conservation. Clean-up activities are basically conducted by river managers, however, many citizen groups take part in these activities and contribute to river management. However, quantitative information of the activities remains uninvestigated. We conducted questionnaires and on-site surveys on 129 organizations in 51 water systems which are engaged in clean-up activities in rivers. We indexed the human and temporal resources investing in the clean-up activities as the active mass, and estimated the contribution to the clean-up activities . As a result of the analysis, the total active mass invested for clean-up by the targeted citizen groups was 13,902,582 [person·hour] per year, and the active mass per group was 14,520 [person·hour] per year. Conversion of the cleaning amount related to the activities of the group to distance enables it to cover about 114% of t the river section under the jurisdiction of the Ministry of Land, Infrastracture, Transport and Tourism. In Onga River, it was suggested that such activity is equivalent to ca. 75% of the annual expenses for estuary weir mantenance.
