Analyzing Research Trends in Deep-Tunnel Systems and Evaluation of Stormwater Pollutant Removal for Urban Runoff Management

Deep-tunnel systems are increasingly being recognized as an infrastructure solution for mitigating combined sewer overflows (CSOs) and managing urban stormwater, as evidenced by growing research interest. This study employed a bibliometric analysis method using Scopus to evaluate global research trends in deep-tunnel systems. This method revealed that while early studies primarily focused on flood mitigation, recent research has shifted toward exploring water quality improvements. An initial comprehensive review using keywords from the bibliometric analysis was conducted, highlighting the limited data relating deep-tunnel systems to water quality and underscoring a gap in the literature. A subsequent comprehensive review focusing on urban stormwater runoff was conducted to bridge the knowledge gap between flood mitigation and water quality enhancement in urban stormwater management. The analysis indicated that mixed urban areas showed the highest range of TSS concentrations, with a mean of 238.3 mg/L, while urban roads exhibited the highest mean TN and TP concentrations at 93.6 mg/L and 0.49 mg/L, respectively. For deep-tunnel systems, a design approach that considers the characteristics of pollutants in incoming stormwater and their reduction mechanisms is essential. This study’s findings provide foundational data for the development of deep-tunnel systems with integrated water treatment functions. Such systems could enhance urban resilience by addressing both flood risk and water quality challenges in rapidly urbanizing areas.