Inflow and infiltration assessment of a prototype sanitary sewer network in a coastal city in China

Abstract

A 16-month monitoring program was conducted on a prototype sanitary system in a coastal city in China. The groundwater infiltration (GWI) on dry weather days and the rain-derived inflow and infiltration (RDII) on wet weather days were quantified and analyzed. The proportion of monthly averaged GWI to total flow can be as high as 70% during the observation period mainly due to the high groundwater level. The results also show that the ratio of RDII volume to total rainfall volume (defined as R-value) reaches a limited value of approximately 10% for the studied system when the total rainfall depth increases. A reference indicator Rlim for the limited R-value was proposed for assessing the conditions of sewer systems in terms of RDII. The Rlim value depends on local sewer conditions and in general, a lower Rlim value represents a better performance on RDII and vice versa. This study enriches the case studies on the performance of a specific sanitary sewer system on inflow and infiltration in a typical coastal city with exceptionally high groundwater levels, excess rainfall events in the monitoring season and possible typhoon events, which addresses the unique locational and hydrological properties of a representative coastal city. HIGHLIGHTS The time-period for the ‘minimum night flow method’ should be adjusted accordingly.; High infiltration due to high groundwater levels was observed specifically for the study site.; The ratio of RDII volume to total rainfall volume (R-value) tends to be limited as rainfall increases for all RDII events.; The limited R-value for high rainfall events was proposed for assessing the performance of sewer systems.;

Keywords

• asset management
• coastal city
• inflow and infiltration
• sanitary sewer system