Frank Blumensaat

Sewer model development under minimum data requirements

Planning, design and operation of urban drainage systems is often based on hydraulic sewer modelling. Sewer models are also increasingly used to quantify pollution loads discharged to aquatic ecosystems (e.g. via combined sewer overflows), which ultimately allows an estimation of the ecological impact emanating from urban drainage systems. The establishment of such network models, however, requires detailed and accurate information about the sewer network structure and the connected surface area. This infrastructure data is often unavailable, confidential or available in ‘paper’ format only. The present paper outlines a novel approach to develop a hydraulic sewer model constrained by a minimum amount of data. The approach combines the application of a surface flow accumulation algorithm to a selectively manipulated Digital Elevation Model (DEM) with a routine for hydraulic network dimensioning to generate a close-to-reality sewer network ready to be implemented in a hydraulic modelling platform. The method is tested for three real-life catchments of which characteristics vary in scale, topography, state of development and network complexity. For all cases the generated network is implemented on the EPA-SWMM platform to allow hydrodynamic simulations. Model performance is assessed by (1) evaluating the spatial match of existing and generated network layout, (2) comparing the estimated hydraulic dimension with real-life infrastructure data and (3) benchmarking simulated runoff with measured data for a defined validation period. The analysis shows that the presented method is capable of reproducing the original network layout, network length and corresponding discharge rates based on little, freely available information. Further research potential is identified to improve the hydraulic dimensioning and the application to complex systems that include control structures. The presented approach is useful to estimate the scope of drainage networks including layout and design (e.g. for preliminary planning in emerging areas) to screen existing networks and to identify critical spots where more precise information is required.

Coupling hydrogeological with surface runoff model in a Poltva case study in Western Ukraine

This paper presents the hydrological coupling of the software framework OpenGeoSys (OGS) with the EPA Storm Water Management Model (SWMM). Conceptual models include the Saint Venant equation for river flow, the 2D Darcy equations for confined and unconfined groundwater flow, a two-way hydrological coupling flux in a compartment coupling approach (conductance concept), and Lagrangian particles for solute transport in the river course. A SWMM river–OGS aquifer inter-compartment coupling flux is examined for discharging groundwater in a systematic parameter sensitivity analysis. The parameter study involves a small perturbation (first-order) sensitivity analysis and is performed for a synthetic test example base-by-base through a comprehensive range of aquifer parametrizations. Through parametrization, the test cases enables to determine the leakance parameter for simulating streambed clogging and non-ocillatory river-aquifer water exchange rates with the sequential (partitioned) coupling scheme. The implementation is further tested with a hypothetical but realistic 1D river–2D aquifer model of the Poltva catchment, where discharging groundwater in the upland area affects the river–aquifer coupling fluxes downstream in the river course (propagating feedbacks). Groundwater contribution in the moving river water is numerically determined with Lagrangian particles. A numerical experiment demonstrates that the integrated river–aquifer model is a serviceable and realistic constituent in a complete compartment model of the Poltva catchment.

The HSG procedure for modelling integrated urban wastewater systems

Whilst the importance of integrated modelling of urban wastewater systems is ever increasing, there is still no concise procedure regarding how to carry out such modelling studies. After briefly discussing some earlier approaches, the guideline for integrated modelling developed by the Central European Simulation Research Group (HSG - Hochschulgruppe) is presented. This contribution suggests a six-step standardised procedure to integrated modelling. This commences with an analysis of the system and definition of objectives and criteria, covers selection of modelling approaches, analysis of data availability, calibration and validation and also includes the steps of scenario analysis and reporting. Recent research findings as well as experience gained from several application projects from Central Europe have been integrated in this guideline.

Water quality-based assessment of urban drainage impacts in Europe - where do we stand today?

Traditionally, design and optimisation of urban drainage systems was mainly driven by cost efficiency, surface flood prevention, and later by emission reduction. More recent procedures explicitly include ecological conditions of the receiving water in the definition of acceptable pollutant discharges via sewer system and treatment plant outlets. An ambient Water Quality based impact Assessment (WQA) principle therefore requires an integrative system optimisation. However, a broad range of mostly national WQA protocols exist across Europe varying in structure and complexity, assessment concept, spatial and temporal scope and handling of uncertainty. This variety inherently implies a considerable risk of subjectivity in the impact assessment with highly variable outcomes. The present review identifies differences and similarities of WQA protocols in use and discusses their strengths and weaknesses through: (i) a systematic comparison of WQA protocols by selected attributes, (ii) a review of real-life cases reported in the literature and expert interviews, and (iii) an illustration of our main findings by applying selected WQA in an instructive example. The review discusses differences in structure and concept, which are mainly identified for simplistic WQA protocols. The application of selected protocols to an example case shows a wide variety of numerical results and conclusive decisions. It is found that existing protocols target different questions within the decision making process, which users should be more aware of. Generally, to make assessments more reliable, further fundamental research is required to fully understand the relationship between stressors and stream ecosystem responses which will make assessments more reliable. Technically, tools suggested in WQA protocols show severe deficiencies and an uncertainty assessment should be mandatory.

Parameter estimation of hydrologic models using a likelihood function for censored and binary observations

Observations of a hydrologic system response are needed to accurately model system behaviour. Nevertheless, often very few monitoring stations are operated because collecting such reference data adequately and accurately is laborious and costly. It has been recently suggested to use observations not only from dedicated flow meters but also from simpler sensors, such as level or event detectors, which are available more frequently but only provide censored information. Binary observations can be considered as extreme censoring. It is still unclear, however, how to use censored observations most effectively to learn about model parameters. To this end, we suggest a formal likelihood function that incorporates censored observations, while accounting for model structure deficits and uncertainty in input data. Using this likelihood function, the parameter inference is performed within the Bayesian framework. We demonstrate the implementation of our methodology on a case study of an urban catchment, where we estimate the parameters of a hydrodynamic rainfall-runoff model from binary observations of combined sewer overflows. Our results show, first, that censored observations make it possible to learn about model parameters, with an average decrease of 45% in parameter standard deviation from prior to posterior. Second, the inference substantially improves model predictions, providing higher Nash-Sutcliffe efficiency. Third, the gain in information largely depends on the experimental design, i.e. sensor placement. Given the advent of Internet of Things, we foresee that the plethora of censored data promised to be available can be used for parameter estimation within a formal Bayesian framework.

Assessing antibiotic resistance of microorganisms in sanitary sewage

The release of antimicrobial substances into surface waters is of growing concern due to direct toxic effects on all trophic levels and the promotion of antibiotic resistance through sub-inhibitory concentration levels. This study showcases (1) the variation of antibiotics in sanitary sewage depending on different timescales and (2) a method to assess the antibiotic resistance based on an inhibition test. The test is based on the measurement of the oxygen uptake rate (OUR) in wastewater samples with increasing concentrations of the selected antibiotic agents. The following antibiotics were analysed in the present study: clarithromycin (CLA) was selected due to its high toxicity to many microorganisms (low EC50), ciprofloxacin (CIP) which is used to generally fight all bacteria concerning interstitial infections and doxycyclin (DOX) having a broad spectrum efficacy. Results show that CLA inhibited the OUR by approximately 50% at a concentration of about 10 mg L⁻¹, because Gram-negative bacteria such as Escherichia coli are resistant, whereas CIP inhibited about 90% of the OUR at a concentration equal to or greater than 10 mg L⁻¹. In the case of DOX, a moderate inhibition of about 38% at a concentration of 10 mg L⁻¹ was identified, indicating a significant antibiotic resistance. The results are consistent with the corresponding findings from the Clinical and Laboratory Standards Institute. Thus, the presented inhibition test provides a simple but robust alternative method to assess antibiotic resistance in biofilms instead of more complex clinical tests.

Quantifying effects of interacting optimisation measures in urban drainage systems

A vast amount of resources is being spent on system development for Water Framework Directive compliance. Owing to the increased numbers of possibilities given for system optimisation the available budget maybe split and a package of single measures are applied in parallel. This paper discusses the application of single optimisation measures compared to the parallel application of several single measures in one scenario with regard to existing synergistic (or antagonistic) effects using a multi-criteria evaluation system that includes emission based, operational and water quality based aspects. The question to be answered is to which extent and why does the global effect differ from the sum of single effects and what are the prerequisites for a sustainable system development. Theoretical analysis is supported by real-life investigations on a case study for which a model-based scenario assessment has been carried out to quantify the effect of different management scenarios. Different effects have been evaluated by means of a summary index and criteria-specific indices. The results show that two measures which solely applied give a positive effect do not necessarily give the same positive effect if they are applied in parallel. In case of one scenario combination the (still positive) effect is even lower than the effect of a single measure. Furthermore, the role of ‘index design’ is discussed by means of a simple example as the selection of evaluation criteria can obviously influence the decision to be made considerably.

Supporting decisions in water management by exploring information and capacity gaps: experiences from an IWRM study in the Western Bug River Basin, Ukraine

Abstract Key problems of Integrated Water Resources Management refer to interactions between various levels, scales and existing coordination gaps, such as inadequate governance structures and insufficient knowledge and capacities. In this study we describe a management framework that aligns model-based systems analysis with capacity assessments suggesting a concept for improving cross-scale interactions and thus for overcoming both, water-related pressures and coordination gaps. In the study we (i) identify the missing link between technical development approaches and capacity development, (ii) outline interrelations between environmental pressures on aquatic systems and capacity and information gaps in a transparent way, and (iii) introduce a practice-relevant method to combine model-based system planning with capacity assessments for deriving management options that support water management actors in reducing pressures and gaps. The results of the integrated analysis are made explicit by introducing a matrix approach that is inspired by an existing framework to systematically differentiate water quality-related pressures (cf. Blumensaat et al. 2013). The approach confronts pressures and gaps and so jointly addresses technical issues, institutional challenges, organizational development, information needs, and human resources development. The concept supports a transparent decision making process by identifying knowledge and capacities required for the implementation of corresponding technical intervention options and vice versa. The application of the method in the International Water Research Alliance Saxony model region ‘Ukraine’ is illustrated to demonstrate the added value as a boundary object between scales that is supporting actors in streamlining model-based planning and capacity development.

Integrated Water Resources Management: Approach to Improve River Water Quality in the Western Bug River Basin

The Western Bug is a transboundary river with relevant environmental impact on the Vistula and the Baltic Sea. On entering the EU it must comply with the European Water Framework Directive, which demands an integrated water resources management (IWRM) on river basin scale. In this paper a systematic approach addressing the IWRM principles is proposed and applied for the upper part of the Western Bug. The existing pollution regime in the W.Bug catchment area to the gauge W.Bug – Kamianka Buska is assessed by application of a five step methodology including system screening, compilation of pressures, comparison with biological status, detailed process analysis of relevant interactions, definition of response measures based on a multi-criteria evaluation. Survey of previous studies, analysis of regional monitoring data, MFA modelling with MONERIS tool and carried measurements campaigns have shown, that in a row with extremely high point source input load on a watershed border (Lviv WWTP), such diffuse sources of nutrients as tile drained areas, rural areas without waste water treatment and erosion compose a nutrients input over an entire basin (approx. 2,500 km2) comparable to the mentioned point source. Moreover, the emission patterns partitioning is different for DIN and TP. During the measurements campaign the results of MFA modelling were supported and other deficits, such as extinction of the natural Poltva river ecosystem and nitrate pollution of the uppermost aquifers were found. Therefore, for detailed process analysis two main subsystems have been identified: (i) River Poltva and River Bug downstream from the confluence with the River Poltva, (ii) the uppermost aquifers. Already at this stage of study it was found that water quality formation in W.Bug is subject to acute deficits in the settlements sanitation systems in the basin while diffuse pollution due to agricultural activities is (under the current socio-economic conditions) of lower relevance.