Review on diagnostic technologies of illicit discharge and groundwater infiltration in the storm drainage network

Stormwater network is an important municipal infrastructure to mitigate urban waterlogging and improve water environmental quality. Owing to the aging and corrosion, and improper construction of pipes, and so on, the urban stormwater network after construction in China often confronts the challenges of illicit discharge and groundwater infiltration, which restricts the efficient functioning of stormwater network. Technologies of diagnosing inflow and infiltration into drainage system can provide important support to identify and locate the illicit discharge and groundwater infiltration of stormwater network. The basic principles, research processes and applicable characteristics of the diagnostic technologies for inflow and infiltration into drainage networks (including geophysical detection, flow analysis, tracer parameter analysis, and hydrodynamic inversion model technologies) were reviewed, and then the practicalities, the key points of application, diagnostic levels, and development stages of these technologies were analyzed and compared. According to this, the future development trend of diagnostic technologies was proposed. The results showed that: 1) The tracer parameter analysis technology could identify and quantify the illicit discharge and groundwater infiltration without interfering with the normal operation of stormwater network, and provide retrofit priorities, resulting in significant economic and environmental benefits. 2) The fiber-optic distributed temperature sensing (FDTS) technology and hydrodynamic inversion model technology had outstanding advantages in non-interference locating of the illicit discharge and groundwater infiltration into stormwater network. The former was easy to implement and had high locating accuracy, while the latter had the characteristics of low cost and could be used to evaluate the levels of illicit discharge and groundwater infiltration. These two technologies could be selected according to local conditions. 3) The future development trend of diagnostic technology would be towards low-cost, non-interference, quantifiable, and locatable direction. By evaluating the comprehensive application effects of different technologies in the current and future, it was found that single diagnostic technology was difficult to possess the desired characteristics, while a hierarchical diagnostic system based on tracer parameter analysis technology coupled with FDTS technology or hydrodynamic inversion model technology had the advantage potential of achieving the future development goal. This study could provide references to carry out scientific application and optimization innovation of diagnostic technologies.