CATEGORIZATION OF RAINFALL EVENTS USING RAINFALL CHARACTERISTICS REFLECTING CSO VOLUMES IN TOKYO WARDS AREA

Abstract

 Minato City has developed a forecasting system to determine the safety period of bathing at Odaiba Seaside Park using the database of model-calculated E. coli concentration change for each categorized rainfall. However, there are challenges to improve E. coli concentration prediction. Therefore, we revised the characteristics for categorizing rainfall in Tokyo wards area so that they could directly reflect CSO volumes which are related to fecal pollution. First, we estimated the rainfall intensity threshold for CSO occurrence, and defined new rainfall intensity and cumulative rainfall to reflect the CSO volumes. In addition, we proposed the use of net rainfall time which does not contain the no-rainfall period. Then, rainfall categorization results were compared between the revised method and the conventional method considering the maximum hourly rainfall intensity, the whole rainfall duration, and the accumulated rainfall. The revised method significantly reduced the variations of CSO volumes within each rainfall group compared to the conventional one. It indicated that the revised method categorizes rainfall events with similar CSO volumes and spatial distribution.