Sewer Model Research Articles

Geoanalytical method for linking base wastewater flows with a sanitary sewer model

ABSTRACT This paper presents a methodology for linking base wastewater flow to a sewer model with an arbitrary simplification level. The flow from clients is the main effluent that generates revenue for water utilities, while also being associated with an environmental and health risk. Compiling a sewer model with a suitable fidelity level to analyse these aspects is typically labour intensive. Often, skeletonisation is applied, necessitating the aggregation of clients into groups. In this case, base wastewater flows need to be aggregated into a junction and retaining a record of the linkage becomes relevant. While several approaches exist, they lack the scalability and flexibility to handle different model simplification levels. The approach presented herein aims to fill that gap, by applying a geoanalytical approach to build linkages between a sanitary sewer model and clients in the service area. The method has been tested on an operational water network in Tallinn, Estonia.

Tunable linear feedback control of urban drainage systems using models defined purely from data.

Real-time and model-predictive control promises to make urban drainage systems (UDS) adaptive, coordinated, and dynamically optimal. Though early implementations are promising, existing control algorithms have drawbacks in computational expense, trust, system-level coordination, and labor cost. Linear feedback control has distinct advantages in computational expense, interpretation, and coordination. However, current methods for building linear feedback controllers require calibrated software models. Here we present an automated method for generating tunable linear feedback controllers that require only system response data. The controller design consists of three main steps: (1) estimating the network connectivity using tools for causal inference, (2) identifying a linear, time-invariant (LTI) dynamical system which approximates the network, and (3) designing and tuning a feedback controller based on the LTI urban drainage system approximation. The flooding safety, erosion prevention, and water treatment performance of the method are evaluated across 190 design storms on a separated sewer model. Strong results suggest that the system knowledge required for generating effective, safe, and tunable controllers for UDS is surprisingly basic. This method allows near-turnkey synthesis of controllers solely from sensor data or reduction of process-based models.

Exploring optimal deep tunnel sewer systems to enhance urban pluvial flood resilience in the gangnam region, South Korea

Urban pluvial flooding is becoming a global concern, exacerbated by urbanization and climate change, especially in rapidly developing areas where existing sewer systems lag behind growth. In order to minimize a system's functional failures during extreme rainfalls, localized engineering solutions are required for urban areas chronically suffering from pluvial floods. This study critically evaluates the Deep Tunnel Sewer System (DTSS) as a robust grey infrastructure solution for enhancing urban flood resilience, with a case study in the Gangnam region of Seoul, South Korea. To do so, we integrated a one-dimensional sewer model with a rapid flood spreading model to identify optimal routes and conduit diameters for the DTSS, focusing on four flood-related metrics: the total flood volume, the flood duration, the peak flooding rate, and the number of flooded nodes. Results indicate that, had the DTSS been in place, it could have reduced historical flood volumes over the last decade by 50.1–99.3%, depending on the DTSS route. Regarding the conduit diameter, an 8 m diameter was found to be optimal for minimizing all flood-related metrics. Our research also developed the Intensity-Duration-Frequency (IDF) surfaces in three dimensions, providing a correlation between simulated flood-related metrics and design rainfall characteristics to distinguish the effect of DTSS on flood risk reduction. Our findings demonstrate how highly engineered solutions can enhance urban flood resilience, but they may still face challenges during extreme heavy rainfalls with a 80-year frequency or above. This study contributes to rational decision-making and emergency management in the face of increasing urban pluvial flood risks.

Impact of model structure on radionuclide transport in urban stormwater

This paper compared simulation results from different SWMM model constructions after radiological contamination from a hypothetical dirty bomb. The model constructions included a utility-provided combined sewer model, a high-resolution mesh surface flow model, and a hybrid of the two. The models were run under three different rainfall configurations including a 3-h event, a 24-h event, and a 24-h event with 48 h of drainage to investigate the influence that model structure had on transport of 137Cs. Model structure was found to impact the contaminant loading of the stormwater model from the air modeling. It was also found to impact the amount of contaminant washoff (high resolution modeling produced more washoff), flow of contamination through outfalls (more contamination through outfalls connected to underground pipes), and 137Cs levels per pipe. The implications of these findings are that few stormwater models are considered ready to aid in response and recovery as originally designed.

Potential of supervised machine learning algorithms for estimating the impact of water efficient scenarios on solids accumulation in sewers

Understanding the negative effects of widespread implementation of optimal water efficient solutions may have on existing centralised sewer systems is still limited – one of these effects is the accumulation of solids in sewer pipes. Predicting these effects requires setting up and simulating complex detailed hydraulic sewer network models. Often, precise details of the sewer network layout and diurnal patterns of the wastewater flows are not available, limiting the applicability of using model predictions for such phenomena. In this study, the applicability of supervised machine learning (ML) algorithms for the development of a simplified surrogate model to predict solid accumulation in sewer pipes was investigated. A large number of highly variable sewer networks were synthetically generated and used to produce results that can be generalizable within the limitations of the current study. A hydrodynamic sewer model was set up and simulated for each synthetic sewer network and various scenarios in which different water-efficient solutions were considered. Simulation results indicated that the most impacts are expected to occur in the upstream part of the sewer networks, and that with 50% reduction in (waste-)water flows, 3–20% more pipes are expected to accumulate solids. It was further found that ML algorithms can be used to successfully predict locations of solids accumulation in sewer pipes without using hydrodynamic models. A simple tool based on the findings of this study, sparing the need to conduct complex hydraulic simulations, was developed. It allows the user to enter a set of pipe characteristics and the proportion of flow that is reduced due to the implementation of water efficient solutions, and it predicts whether the pipe will accumulate solids or not. The study results and the proposed ML algorithms can support the implementation of optimal water-efficient solutions that will promote designing and managing the water sensitive cities of the future.

Multi-dimensional dynamic simulation of rainstorm waterlogging in urban communities

One major threat to cities at present is the increasing rainstorm waterlogging hazards due to climate change and accelerated urbanization. This paper explores the mechanism of rainstorm waterlogging and enables the fine simulation of surface water propagation over complex urban terrain. A novel community-scale waterlogging modeling scheme is presented by loosely coupling a one-dimensional sewer model with a two-dimensional overland model under an open-source framework. The coupled model was applied to Waigaoqiao Free Trade Zone located in Pudong New Area of Shanghai. To quantify the influence of rainfall intensity and drainage conditions on the waterlogging, 12 scenarios were constructed by combining four rainfall return periods (3, 5, 10, and 20 a) and three startup water depths (1.5, 2.0, and 2.5 m) of pump stations. The multi-scenario simulation results show that the waterlogging risk increases from north to south in the study area, and that risk zones with water depth above 0.3 m are mostly concentrated in the southwest and southeast corners of the site. The longer the rainfall return period, the larger the submerged area, and the spatial distribution of surface water accumulation is affected by local topography and drainage system. In addition, reducing the startup water depth of pump stations has an obvious effect on inhibiting the severity of water accumulation. The results provide insights into overland flow across an urban area with densely populated buildings and help to reduce the risk of rainstorm-induced waterlogging disasters.

Chance‐constrained model predictive control a reformulated approach suitable for sewer networks

AbstractIn this work, a revised formulation of chance‐constrained (CC) model predictive control (MPC) is presented. The focus of this work is on the mathematical formulation of the revised CC‐MPC, and the reason behind the need for its revision. The revised formulation is given in the context of sewer systems, and their weir overflow structures. A linear sewer model of the Astlingen benchmark sewer model is utilized to illustrate the application of the formulation, both mathematically and performance‐wise through simulations. Based on the simulations, a comparison of performance is done between the revised CC‐MPC and a comparable deterministic MPC, with a focus on overflow avoidance, computation time, and operational behavior. The simulations show similar performance for overflow avoidance for both types of MPC, while the computation time increases slightly for the CC‐MPC, together with operational behaviors getting limited.

Assessment of Human Stability in Sewer Systems during Dry Weather Conditions

Inspection and maintenance tasks are essential to guarantee the correct operation of sewer drainage networks. In combined sewers, these tasks are generally carried out during dry periods when only wastewater flow circulates in the system. When the sewer is big enough to allow the access of people, this inspection is done in person with consequent potential exposure to several hazards such as the presence of toxic gases, the possibility to fall or the loss of stability due to the presence of a continuous wastewater flow. In this context, this paper presents a methodology to assess hazard conditions related to human stability in sewer systems during dry weather periods. Hazard assessment has been performed by applying several hazard criteria to the results of a 1D sewer model simulations regarding a real network in Spain. Results show that the influence of the selection of hazard criteria is relevant, although only a small part of the whole system can be classified as high hazard. Regardless, the proposed method is highly effective to detect these kinds of pipes and we consider them as critical point to improve health and safety procedures during maintenance and inspection tasks.

A distributed hydrodynamic model for urban storm flood risk assessment

Hydrodynamic models have been increasingly applied to urban flood simulations, but still encounter challenges because of complicated urban landscapes, buildings and structures, as well as insufficient sewer data. In order to improve the applicability in real-life urban environments, a distributed hydrodynamic model for urban storm flood risk assessment (DHMUrban) is developed in this study. It is based on the two-dimensional shallow water flow equations simplified by neglecting the convection terms in the momentum equations. The sharp variation of ground surface often happening in urban areas is specially treated with the broad-crested weir flow equation. The rainfall, infiltration and sewer drainage are considered at each overland cell. Two connection approaches between the overland model and the sewer model are proposed depending on the availability of sewer data. The overland cells and the sewer nodes are connected physically in areas with complete sewer data, and connected conceptually through a drainage relationship in areas where sewer data are insufficient or unavailable. The present model has been evaluated in five cases, showing comparable reliability and stability. It has been applied to a real-life urban catchment in Shenzhen City, and demonstrated to be capable of presenting well the ground surface flooding, adapting adequately to the real-life urban areas with different data availability and providing practical and reliable solutions for urban storm flood risk assessments.

Uncertainty analysis of rising sewer models with respect to input parameters and model structure using Monte Carlo simulations and computational fluid dynamics.

Modelling conversion processes in sewers can help minimize odour and pipe corrosion issues, but model uncertainties and errors must be understood. In this study, the Wastewater Aerobic/Anaerobic Transformation in Sewers (WATS) model is implemented in two different frameworks; 1-D (CSTR-in-series) and computational fluid dynamics (CFD) to study the uncertainties due to model parameters and its mathematical form. The 1-D model is used to conduct uncertainty/sensitivity analysis using Monte Carlo simulations. Time-averaged outputs were represented using a general linearized model to quantify the importance of specific parameters. The sulfide formation rate per unit area of the biofilm is the most influential parameter. Parameters controlling anaerobic hydrolysis and fermentation are also significant. Uncertainty due to model structure is studied using CFD to explore the influences of non-homogeneous surface reactions and solids settling. These showed that the 1-D model provides a reasonable characterisation of the process for simple flows in pressure mains.

WITHDRAWN: An evaluation and analysis of a sewerage system for Tondiarpet, Chennai - A case study

Abstract The network of sewerages forms a crucial part in the infrastructure of any society and also supports the environment. It should take away domestic wastes from the municipal areas such that it does not produce any health-related issues. Also, nowadays, awareness for the treatment of wastewater is increasing due to the rise in damage and pollution of the environment. This study focuses on the devising of a sewage network for Tondiarpet, Chennai. It includes the applications of SewerGEMS V8i software. It is a multiplatform, dynamic, and combined sewer modeling solution. The layout of the sewerage system of the study area is depicted by this software based on gravity flow condition. Analysis has also been made based on the slope condition of the area. Properties such as self-cleansing velocity, non-scouring velocity, and silting are also considered in the analysis. SewerGEMS V8i seems to be an effective tool in the investigation of stability analysis of sewerage networks.

Sanitary Gravity Sewer Design using Sewer GEMS Software Connect Edition for Utsav Vihar, Karala

The paper presents modeling, design and analysis of sewage network of Utsav Vihar by means of Sewer GEMS software which helps in the achievement of project results in a shorter period of time in an effective way and at reasonable prices. In the present study the sewerage was designed for Utsav Vihar area in North – West Delhi District. Sewer GEMS software eases the designing for engineers because of unique features to offer a fully dynamic and multi-platform sanitary and combined sewer modeling solution which otherwise tends to consume a lot of time and energy. The software uses derived equations and theorems for calculating the hydraulic model. It enables engineers to analyze all sanitary and combined sewer networks in a single package. The hydraulic design section includes the calculation and determination of the transit, total flow and hydraulic modeling for network pipes diameters or slopes. The application generates reports, layouts, longitudinal or transverse cross section.

A Hybrid Model for Fast and Probabilistic Urban Pluvial Flood Prediction

AbstractUrban flooding is highly uncertain, so the use of probabilistic approaches in early flood warning is encouraged. While well‐established 1‐D/2‐D hydrodynamic sewer models do exist, their deterministic nature and long computational time undermine their applicability for real‐time urban flood nowcasting. Aiming at meeting the needs of fast and probabilistic flood modeling, a new hybrid modeling method integrating a suite of lumped hydrological models and logistic regression is proposed. The lumped models are configured using graph theory techniques, based on the sewer system's topology and characteristics, to account for the spatial heterogeneity and physical processes and properties. The logistic regression models are calibrated to lumped models' results and Yes/No flooding information. Due to its conceptual and data‐driven nature, the hybrid model makes fast probabilistic flood predictions at manhole locations. In two case studies, the results showed that when incorporating most dominant physical processes and properties in the model setup, the hybrid model can achieve up to 86% accuracy for flood warnings issued at 50% probability, with 96% computation saving, compared with a traditional 1‐D hydrodynamic model. When such a detailed model is in place, the hybrid model is set up easily, but the accuracy could be further increased when historical flooding observations are considered.

Prioritization of stormwater management sites in urban areas

Multiple pressures as urbanization, densification and climate change lead to the need for adaptation of sewer systems within urban environments. To increase the adaptive capacity of stormwater management systems, there is a shift towards decentralized nature-based solutions (NBS). Especially in densely built areas the availability of land can be a limiting factor for the implementation of NBS. To consider the spatial framework conditions in planning we developed an integrated modelling framework for prioritizing sites for NBS implementation for stormwater management within built urban structures. The implementation potential of NBS from a settlement structure model and a street typology model are combined with the discharge reduction potential from a sewer model. In effectiveness matrices priorities for stormwater management sites for individual NBS are identified. This modelling framework offers a transparent and flexible approach to decision making for the implementation of NBS.

Groundwater Contribution to Sewer Network Baseflow in an Urban Catchment-Case Study of Pin Sec Catchment, Nantes, France

Sewer systems affect urban soil characteristics and subsoil water flow. The direct connection observed between baseflow in sewer systems under drainage infiltrations and piezometric levels influences the hydrological behavior of urban catchments, and must consequently be considered in the hydrologic modeling of urban areas. This research studies the groundwater contribution to sewer networks by first characterizing the phenomenon using experimental data recorded on a small urban catchment in Nantes (France). Then, the model MODFLOW was used to simulate the infiltration of groundwater into a sewer network and model dry weather flows at an urban catchment scale. This application of MODFLOW requires representing, in a simplified way, the interactions between the soil and the sewer trench, which acts as a drain. Observed average groundwater levels were satisfactorily simulated by the model while the baseflow dynamics is well reproduced. Nonetheless, soil parameters resulted to be very sensitive, and achieving good results for joint groundwater levels and baseflow was not possible.

Predicting impacts of water conservation with a stochastic sewer model.

Population growth and climate change put a strain on water resources; hence, there are growing initiatives to reduce water use. Reducing household water use will likely reduce sewer input. This work demonstrates the use of a stochastic sewer model to quantify the effect water conservation has on sewer hydraulics and wastewater concentration. Probabilistic discharge patterns have been developed using SIMDEUM WW® and fed into hydraulic modelling software InfoWorks ICM® to produce likely flow and quality profiles for five future water use scenarios. The scenarios tested were developed to outline how commercial and political factors may change water use in future. Scenario testing revealed that 15-60% water reduction reflected a 1-48% drop in the morning peak flow. The water use reduction was predicted to increase wastewater concentrations of chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN) and total phosphorus (TPH) by 55-180%, 19-116% and 30-206% respectively. The sewer flow model was developed, calibrated and validated using a case study in the Wessex Water region of the UK and all future scenarios were compared to the validated baseline case. This wastewater flow and quality model allows scenario testing, which could help redesign future sewer networks to better prepare for water conservation strategies.

Probabilistic flood prediction for urban sub-catchments using sewer models combined with logistic regression models

ABSTRACTThis paper proposes a hybrid modelling approach for early urban flood warning and forecasting purpose. The hybrid model structure proposed combines a deterministic sewer model with a probabilistic logistic regression model. By varying the sewer model structures from complex hydrodynamic models to simple conceptual models, different hybrid models are constructed in order to accommodate different levels of available knowledge and data about the urban hydrological system. The hybrid models are optimized using crowdsourced flooding records. They can predict the probability of flooding at the urban sub-catchment scale. The proposed methodology is tested for two cases in Antwerp, Belgium. Promising results show its potential in making fast and reliable urban flood predictions. Reasonable predictions are made even by the simplest model form, indicating the method could work also for sub-catchments with limited information. It also shows that the proposed methodology allows identifying the most dominant hydrological processes explaining urban flooding.

Relationship between infiltration, sewer rehabilitation, and groundwater flooding in coastal urban areas.

The aging of sewer networks is a serious issue in urban areas because of the reduced functionality of the system that can have negative impact on the urban environment. Aging pipes are not water-tight anymore and they can leak untreated sewage or allow infiltration of groundwater. In the latter case, more frequent combined sewer overflows (CSOs) may occur. Generally, prompt intervention to repair damaged conduits is envisaged. However, in low-lying coastal regions, sewer systems may provide an unplanned drainage that controls the groundwater table from flooding the urban ground. Here, a study is presented to investigate the influence of the repair of damaged sewer on the water table of an urban shallow aquifer. Sewer and groundwater models were built to describe the effect of sewer replacement. Based on a real dataset, simulations were run for a city located along an estuary. Results show that the presence of infiltration into the sewer system increases the frequency of CSOs, which trigger the discharge of untreated sewage after a minor precipitation or even in dry weather conditions. As the sewer is repaired, CSO spills diminish occurring only upon significant precipitation. However, the water table rises and eventually, during the high tide, the groundwater floods the low-lying part of the city. Overall, this work highlights the susceptibility of shallow aquifers in coastal urban areas and suggests that they should be regarded in flooding predictions.

An Efficient and Structured Procedure to Develop Conceptual Catchment and Sewer Models from Their Detailed Counterparts

Modelling flow rates in catchments and sewers with a conceptual, also known as hydrological, approach is widely applied if fast simulations are important. In cases where a detailed hydrodynamic model exists, it is common to start conceptualizing from this detailed counterpart. Unfortunately, no generalized procedure exists, which is surprising as this can be a complex and time-consuming task. This research work proposes a procedure that is validated with two independent combined sewer case studies. The conceptual models provide the targeted results with respect to representation of the flow rates and reduction in the computational time. As the desired performance could be reached for different levels of model aggregation, it is concluded that the conceptual model can be tailored to the points where accurate flow rates need to be predicted. Furthermore, the comparison of the conceptual model results with flow measurements highlights the importance of analyzing and eventually compensating for the limitations of the detailed model.

Modelling micropollutant fate in sewer systems – A new systematic approach to support conceptual model construction based on in-sewer hydraulic retention time

Conceptual sewer models are useful tools to assess the fate of micropollutants (MPs) in integrated wastewater systems. However, the definition of their model structure is highly subjective, and obtaining a realistic simulation of the in-sewer hydraulic retention time (HRT) is a major challenge without detailed hydrodynamic information or with limited measurements from the sewer network. This study presents an objective approach for defining the structure of conceptual sewer models in view of modelling MP fate in large urban catchments. The proposed approach relies on GIS-based information and a Gaussian mixture model to identify the model optimal structure, providing a multi-catchment conceptual model that accounts for HRT variability across urban catchment. This approach was tested in a catchment located in a highly urbanized Italian city and it was compared against a traditional single-catchment conceptual model (using a single average HRT) for the fate assessment of reactive MPs. Results showed that the multi-catchment model allows for a successful simulation of dry weather flow patterns and for an improved simulation of MP fate compared to the classical single-catchment model. Specifically, results suggested that a multi-catchment model should be preferred for (i) degradable MPs with half-life lower than the average HRT of the catchment and (ii) MPs undergoing formation from other compounds (e.g. human metabolites); or (iii) assessing MP loads entering the wastewater treatment plant from point sources, depending on their location in the catchment. Overall, the proposed approach is expected to ease the building of conceptual sewer models, allowing to properly account for HRT distribution and consequently improving MP fate estimation.