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Methodology for inflow and infiltration management utilizing PySWMM: A case study of the BX pumping station in Suzhou's central city area, China

Abstract

Inflow and Infiltration (I/I) are prevalent issues within sewage networks, which can be addressed by pipe network diagnosis and repair, as well as drainage system optimization. However, the majority of approaches require substantial labor and material resources, are time-consuming, and require an urgent solution to manage the I/I prior to project completion. This study presents a short-term control approach for I/I. This study focused on the BX pumping station area in Suzhou and developed a multiple linear regression model to examine the control equations of I/I during the dry and wet seasons, utilizing data on river, pumping station, and groundwater levels. By integrating Python with Storm Water Management Model (SWMM) to incorporate the control equations into the model for the development of the I/I module, and based on the analytical results of the model, recommendations for the regulation and control of the pumping station are presented. This approach can efficiently regulate the I/I in a brief timeframe, requiring less labor than mending the pipe network through engineering interventions.

Introduction

The administration and maintenance of sewer systems has become essential because of swift urbanization in recent decades, with approximately 52% of the global population residing in urban areas [1]. The initial construction and insufficient maintenance of sewage systems in numerous cities has led to system degradation, resulting in external water intrusion (including I/I) or sewage outflow [2]. Typically, detecting I&I within an urban sewer network, especially large I&I events, is crucial for ensuring the protection of the urban water environment [3]. The I/I of the external water occupies the capacity of the sewage system, diminishing the system's effective hydraulic capacity. Concurrently, dilution with external water increases the intake of sewage treatment plants and decreases the concentration of incoming water, thereby affecting the operational efficiency of these plants [4]. Substantial volumes of rainwater entering sewage systems during precipitation events can result in sewage overflow or contamination of stormwater networks, thereby compromising the quality of aquatic environments. Current infiltration results in a 25–50% increase in overall utility expenses. Consequently, the I/I ratio of sewage systems has emerged as a global issue, making its analysis and management a prominent subject of research.

Recent research on I/I in sewage systems has primarily focused on analysis, simulation, and prediction, with the ultimate objective of addressing the I/I issue. Staufer et al. used two analogous catchments in Germany as a control group, one of which had undergone sewage system rehabilitation. They gathered hydrological data, including precipitation and groundwater table volume, from both catchments for regression analysis and concluded that the rehabilitation of the pipe network could diminish groundwater infiltration by 23.9% [5]. Engineering methods are labor-intensive and time-consuming; therefore, a temporary solution is required to mitigate I/I when a pipe network is restored. This study serves as a foundation for further research on this issue.

Over the past 25–35 years, researchers from many countries have devised numerous techniques for monitoring and evaluating I/I, which can be categorized into qualitative and quantitative assessment [6]. Qualitative analyses include the smoke test, CCTV inspection, DTS, and electronic scanning methods [7,8], including the pollutant time series, water balance, triangulation, and stable isotope methods [[9], [10], [11]]. Water-balancing methodologies rely on quantifying the flows inside pipe networks. When the flow data are more comprehensive, it becomes simpler to derive valuable conclusions regarding the response of pipe networks to external flows. The water balancing method encompasses the nightly minimum flow technique [12], triangulation method [13], and moving minimum flow method [14]. However, various methods exhibit distinct differences and limitations; for instance, the nighttime minimum flow method is more economical but yields greater errors in megacities, while the triangulation method is less precise in assessing daily I/I, and the moving minimum flow method effectively captures daily, monthly, and seasonal variations. However, the 21-day duration determination is merely an empirical rule, devoid of a definitive theoretical foundation and physical importance. Consequently, additional investigations into the analytical methodology of I/I and the principles of water balance are essential.

Recent advancements in computer technology and computational fluid dynamics (CFD) have facilitated the application of hydrological and hydraulic models to simulate and quantify the infiltration processes of sewage systems, resulting in enhanced outcomes [15]. Sewage system modeling software with further applications includes SWMM [16], InfoWorks ICM [17], MIKE Urban [18], and the secondary development of SWMM [19]. The SWMM is the most prevalent urban hydrological model for assessing water quantity and quality and is capable of executing intricate hydraulic calculations for sewage systems; its open-source framework enables academics to engage in secondary development. PySWMM can invoke various modules, including node, simulation, and connection modules, within a Python programming environment, facilitating seamless interaction with SWMM files. Compared with other commercial software packages, it has the advantages of being open-source and exceptionally adaptable [19].

The management of I/I presently depends on long-term strategies, such as engineering repairs, and there is a lack of research regarding short-term control measures for I/I. This study employed a unique method to rapidly regulate the I/I, diminishing these volumes at the cost of pipeline network integrity. This approach entailed the secondary creation of the model, utilizing PySWMM as the interface and integrating control equations and drainage system mechanism models to create a drainage system.

Conclusions

This study employed the PySWMM as an interface because of the severity of I/I in urban sewage systems and the lack of emergency management solutions. The control equation was integrated with a mechanistic model of the sewage system to formulate a kinetic model for I/I. Subsequently, we simulated the sewage discharge process at different pumping station water levels and examined the response mechanism between the pumping station water level and I/I. The BX pumping station in Suzhou City was