Dirk Muschalla

Modelling Real-Time Control Options on Virtual Sewer Systems

The study presents a benchmarking methodology to assess the performance of sewer systems and to evaluate the performance of real-time control (RTC) strategies by model simulation. The methodology i...

Single- and Multievent Optimization in Combined Sewer Flow and Water Quality Model Calibration

Over the last three decades, storm-water quality modeling has been used increasingly commonly to describe the general system behavior and assess the pollution loads transferred in and spilled out of combined sewer systems. The calibration of quality models is, in most cases, based on conventionally obtained calibration data, e.g., by automated sampling. Long-term high-resolution online measurement data are available for the Graz West catchment (Graz, Austria), allowing an assessment of the full dynamics of discharge and pollution concentrations. This paper focuses on the application and comparison of single-event and two different multievent optimization schemes for sewer-water quality model calibration. While both single- and multievent optimization lead to satisfying results for the calibration events in discharge calibration, it is shown that validation events are better reproduced by using multievent calibration. Single- and multievent autocalibration of pollution concentration is based on the best dataset obtained from the discharge calibration. As for discharge, the pollutographs are reproduced satisfactorily, and multievent calibration is more stable. In all cases, the two multievent approaches performed equally well.

Performance evaluation of real time control in urban wastewater systems in practice: Review and perspective

Real time control (RTC) is generally viewed as a viable method for optimising the performance of urban wastewater systems. A literature review on the performance evaluation of RTC demonstrated a lack of consensus on how to do this. Two main deficiencies were identified: omitting uncertainty analysis and applying limited evaluation periods. A general methodology to evaluate the performance of RTC in practice, that takes into account these deficiencies, is proposed. The methodology is either data or model driven and the (dis)advantages of each are discussed. In a case study for a combined sewer system with limited discharge to a WWTP, it is demonstrated that the successful application of RTC and the possibility to determine a significant effect is very much dependent on the goal. It also clearly illustrates the need for taking uncertainties into account and that careful consideration in the chosen evaluation period is required.

Systematic material and crack type specific pipe burst outflow simulations by means of EPANET2

The calculation of outflow from pipe bursts is of interest for water utilities, as the discharged water may cause large amounts of damage to the adjacent infrastructure. Therefore, the crack type specific relationship between leakage outflow and pressure is of interest. Recent findings offer new opportunities for burst outflow calculations with hydraulic models. In this paper, we compare two calculation approaches according to uncertainties caused by input parameters and give recommendations for the applicability of the methods. Simulations in a case study area have shown large leakage outflow differences between the two approaches for longitudinal cracks. For circumferential cracks, the differences are smaller. Further, due to the uncertain leak size and form of probable bursts we involved Monte Carlo simulations in the model approach. These allow the derivation of mean values and standard deviations of leakage outflow per pipe section to make the uncertainty of the results more transparent.

A new dynamic water quality model for stormwater basins as a tool for urban runoff management: Concept and validation

In the context of real-time control of a stormwater basins outlet gate to improve the rivers water quality, while guaranteeing population safety, it is necessary to define and test scenarios over various environmental conditions and perform long term simulations. This paper presents a new dynamic model for stormwater basins, which can reproduce the evolution of the water quality in the basin. The developed model describes the behaviour of pollution associated with particles, accounting for the distribution of particle settling velocities. After detailing the model, simulation results of an experiment representing settling under quiescent hydraulic conditions, are presented to validate the developed models concepts. The dynamic behaviour of a pollution associated with three particle settling velocity classes is presented before concluding on the perspectives that can be offered by such a model.

Using the duration of combined sewer overflow events for the calibration of sewer hydrodynamic models

Abstract This paper compares two calibration approaches to enhance the ability of hydrodynamic models to describe the performance of combined sewer overflow (CSO) structures. One approach is based on the duration of CSO events (monitored by low-cost sensors) and the other focuses on the overflow volume. Both were applied to the West-Graz catchment model to simulate the discharge from the CSO overflow channel under small, medium and large rain episodes. The methodology includes sensitivity analysis of the model parameters and automatic calibration through optimization. The results revealed that the calibration using the CSO duration led to results similar to those of the approach that used overflow volume, with less than 12% error differences between approaches for medium and large rain episodes.

Cause and effect oriented sewer degradation evaluation to support scheduled inspection planning.

Managing the subsurface urban infrastructure, while facing limited budgets, is one of the main challenges wastewater utilities currently face. In this context targeted planning of inspection and maintenance measures plays a crucial role. This paper introduces a cause and effect oriented sewer degradation evaluation approach to support decisions on inspection frequencies and priorities. Therefore, the application of logistic regression models, to predict the probability of failure categories as an alternative to the prediction of sewer condition classes, was introduced. We assume that analysing the negative effects resulting from different failure categories in extension to a condition class-based planning approach offers new possibilities for targeted inspection planning. In addition, a cross validation process was described to allow for a more accurate prediction of sewer degradation. The described approach was applied to an Austrian sewer system. The results show that the failure category-based regression models perform better than the conventional condition class-oriented models. The results of the failure category predictions are presented with respect to negative effects the failure may have on the hydraulic performance of the system. Finally, suggestions are given for how this performance-oriented sewer section evaluation can support scheduled inspection planning.

Selecting a series of storm events for a model-based assessment of combined sewer overflows

ABSTRACT The hydraulic verification of combined sewer systems as well as the assessment of combined sewer overflows (CSOs) can be conducted using a hydrodynamic model. Unfortunately, long-term simulations with hydrodynamic models for the assessment of CSOs can cause unacceptably long computation times. Using only a series of storm events instead of a precipitation continuum can reduce this time and enables parallel simulation of single storm events. We introduce a method to select this series of storm events. The method’s parameters have been optimized to replicate the overflow volume of the continuous simulation and to minimize the overall computation time. This optimization revealed a generally applicable parameter set that results in series of storm events that are shorter than the precipitation continuum by 86.2–95.2% for the investigated cases. Additionally, the deviation of overflow volume between continuous simulation and series simulation ranges between only 0.1% and 4.1%.

Online Monitoring of Combined Sewer Systems: Experiences and Application in Modeling

The full understanding of flow dynamics and pollutant concentrations in combined sewer systems is an important issue in the management and design of these syst…