|In riverfront design planning, consensus building for citizens is important. However, these processes are not systematized because they are often performed at the discretion of the river manager. Therefore, in this study, we tried to quantitatively analyze the amount of efforts for consensus building. The index used was the “volume of investment for consensus building”, that is, the number of people and hours spent for consensus building. In this case of the Onga River, the total volume of investment (people and hours) until consensus building was 1100, and the volume was concentrated on the planning phase (400) and the construction-utilization planning phase (400). Regarding the opinions of participants, the percentage of positive opinions (28-100%) consistently exceeded the percentage of negative opinions (0-48%). Through such an analysis, we examined the perspective of evaluation on consensus building.