Integrated assessment of urban drainage system under the framework of uncertainty analysis.

Due to a rapid urbanization as well as the presence of large number of aging urban infrastructures in China, the urban drainage system is facing a dual pressure of construction and renovation nationwide. This leads to the need for an integrated assessment when an urban drainage system is under planning or re-design. In this paper, an integrated assessment methodology is proposed based upon the approaches of analytic hierarchy process (AHP), uncertainty analysis, mathematical simulation of urban drainage system and fuzzy assessment. To illustrate this methodology, a case study in Shenzhen City of south China has been implemented to evaluate and compare two different urban drainage system renovation plans, i.e., the distributed plan and the centralized plan. By comparing their water quality impacts, ecological impacts, technological feasibility and economic costs, the integrated performance of the distributed plan is found to be both better and robust. The proposed methodology is also found to be both effective and practical.     

Stormwater quality modelling in combined sewers: calibration and uncertainty analysis.

Estimating the level of uncertainty in urban stormwater quality models is vital for their utilization. This paper presents the results of application of a Monte Carlo Markov Chain method based on the Bayesian theory for the calibration and uncertainty analysis of a storm water quality model commonly used in available software. The tested model uses a hydrologic/hydrodynamic scheme to estimate the accumulation, the erosion and the transport of pollutants on surfaces and in sewers. It was calibrated for four different initial conditions of in-sewer deposits. Calibration results showed large variability in the model's responses in function of the initial conditions. They demonstrated that the model's predictive capacity is very low.     

Integrated flood management.

While there have been a number of international initiatives centred around hydrological sciences and technical approaches, the social, economic, environmental, and legal and institutional aspects of flood management have been dealt with sporadically and in a limited manner. WMO and the Global Water Partnership have established the Associated Programme on Flood Management (APFM) to address these issues and developed a concept of Integrated Flood Management (IFM) in 2002. This article is the result of the integrated flood management approaches through pilot projects and multi-disciplinary approaches launched by the initiative since the establishment of the IFM concept. This approach seeks to integrate land- and water-resources development in a river basin, within the context of Integrated Water Resources Management (IWRM) and aims at maximizing the benefits from floodplains and at the same time reducing loss of life from flooding. This approach identified the key elements of IFM and recommended that these can be put in place by: adopting a basin approach to flood management; adopting a multi-disciplinary approach in flood management; reducing vulnerability to and risks from flooding; enabling community participation; and preserving ecosystems; and addressing climate change and variability, supported by enabling mechanism through appropriate legislation and regulations.     

Integrated modelling of nitrate loads to coastal waters and land rent applied to catchment-scale water management.

The EU Water Framework Directive (WFD) requires an integrated approach to river basin management in order to meet environmental and ecological objectives. This paper presents concepts and full-scale application of an integrated modelling framework. The Ringkoebing Fjord basin is characterized by intensive agricultural production and leakage of nitrate constitute a major pollution problem with respect groundwater aquifers (drinking water), fresh surface water systems (water quality of lakes) and coastal receiving waters (eutrophication). The case study presented illustrates an advanced modelling approach applied in river basin management. Point sources (e.g. sewage treatment plant discharges) and distributed diffuse sources (nitrate leakage) are included to provide a modelling tool capable of simulating pollution transport from source to recipient to analyse the effects of specific, localized basin water management plans. The paper also includes a land rent modelling approach which can be used to choose the most cost-effective measures and the location of these measures. As a forerunner to the use of basin-scale models in WFD basin water management plans this project demonstrates the potential and limitations of comprehensive, integrated modelling tools.     

Integrated odour modelling for sewage treatment works.

Odours from sewage treatment works are a significant source of environmental annoyance. There is a need for tools to assess the degree of annoyance caused, and to assess strategies for mitigation of the problem. This is the role of odour modelling. Four main stages are important in the development of an odour problem. Firstly, the odorous molecules must be formed in the liquid phase. They must then transfer from the liquid to the gaseous phase. They are then transported through the atmosphere to the population surrounding the odour source, and are then perceived and assessed by that population. Odour modelling as currently practised tends to concentrate on the transportation of odorants through the atmosphere, with the other areas receiving less attention. Instead, odour modelling should consider each stage in an integrated manner. This paper describes the development of integrated odour models for annoyance prediction. The models describe the liquid-phase transformations and emission of hydrogen sulphide from sewage treatment processes. Model output is in a form suitable for integration with dispersion models, the predictions of which can in turn be used to indicate the probability of annoyance. The models have been applied to both hypothetical and real sewage treatment works cases. Simulation results have highlighted the potential variability of emission rates from sewage treatment works, resulting from flow, quality and meteorological variations. Emission rate variations can have significant effects on annoyance predictions, which is an important finding, as they are usually considered to be fixed and only meteorological variations are considered in predicting the odour footprint. Areas for further development of integrated odour modelling are discussed, in particular the search for improved links between analytical and sensory measurements, and a better understanding of dose/response relationships for odour annoyance.     

Integrated modelling of two xenobiotic organic compounds.

This paper presents a dynamic mathematical model that describes the fate and transport of two selected xenobiotic organic compounds (XOCs) in a simplified representation of an integrated urban wastewater system. A simulation study, where the xenobiotics bisphenol A and pyrene are used as reference compounds, is carried out. Sorption and specific biological degradation processes are integrated with standardised water process models to model the fate of both compounds. Simulated mass flows of the two compounds during one dry weather day and one wet weather day are compared for realistic influent flow rate and concentration profiles. The wet weather day induces resuspension of stored sediments, which increases the pollutant load on the downstream system. The potential of the model to elucidate important phenomena related to origin and fate of the model compounds is demonstrated.     

Integrated modelling for the evaluation of infiltration effects.

The objective of the present study is the estimation of the potential benefits of sewer pipe rehabilitation for the performance of the drainage system and the wastewater treatment plant (WWTP) as well as for the receiving water quality. The relation of sewer system status and the infiltration rate is assessed based on statistical analysis of 470 km of CCTV (Closed Circuit Television) inspected sewers of the city of Dresden. The potential reduction of infiltration rates and the consequent performance improvements of the urban wastewater system are simulated as a function of rehabilitation activities in the network. The integrated model is applied to an artificial system with input from a real sewer network. In this paper, the general design of the integrated model and its data requirements are presented. For an exemplary study, the consequences of the simulations are discussed with respect to the prioritisation of rehabilitation activities in the network.     

Application of uncertainty and sensitivity analysis in river basin management.

Considering uncertainty in the decision-making process in river basin management is important because uncertainty is regarded as one of the main obstacles to sound decision-making. In case of high uncertainty, the risks of making a wrong decision could be quite high, which may have severe consequences. This paper applies a screening sensitivity analysis method, the Morris method, to investigate the propagation of uncertainty from factors in a flood damage model into the model outputs and explores the importance of factors based on the sensitivity analysis. Uncertainty reduction in the most influential factors identified by the Morris method is proposed as a means to reduce the uncertainty in model outputs. In this way the risks of making a wrong decision could be reduced. The results in this paper show that the Morris method is an efficient approach to help reduce the uncertainty in model outputs.     

Integrated modelling for river basin management: the influence of temporal and spatial scale in economic models of water allocation.

The increasing use of integrated optimization or simulation models to guide river basin management has placed greater attention on the roles that the temporal and spatial scale of each model play in determining a model's suitability and effectiveness. This is especially the case in "economic" models that incorporate monetary incentives and the optimizing behaviour of economic agents to address decisions about the sources and levels of consumptive and non-consumptive water usage within the basin. With respect to spatial scale, models that aggregate behaviour over entire river basins may prove useful for examining inter-sectoral allocations of water, but are unlikely to provide useful information about how these water allocations influence-and are influenced by-choices of crops or of technologies in irrigation, for example. With respect to temporal scale, very short-run models can illustrate options for water management within an irrigation season should unforeseen water surpluses or deficits arise. Conversely, long-run models can allow adjustment time for investments in machinery, infrastructure and changes in land uses and cropping patterns. The basin management alternatives and choices generated by models on each scale are likely to vary considerably. The paper provides specific illustrative examples from recent models of Alberta's Bow River Basin.     

A complementary modelling approach to manage uncertainty of computationally expensive models.

The fact that the models applied in the 'water domain' are far from reality can be attributed to many reasons. In this context, a systematic analysis of uncertainties reflected by the model error can provide insight into the level of confidence in the model results and how to approach estimation of optimal model parameters. This paper discusses the four commonly used approaches for estimation of model parameters and suggests that an alternative complementary modelling approach should be considered in cases where the traditional model calibration gives limited results and particularly in cases where the computationally expensive models are concerned. It treats uncertainty as modelling the total discrepancy between the model and physical process. The proposed approach combines the results from a physically-based model and Support Vector Machine model into the final solution.     

Operationalising uncertainty in data and models for integrated water resources management.

Key sources of uncertainty of importance for water resources management are (1) uncertainty in data; (2) uncertainty related to hydrological models (parameter values, model technique, model structure); and (3) uncertainty related to the context and the framing of the decision-making process. The European funded project 'Harmonised techniques and representative river basin data for assessment and use of uncertainty information in integrated water management (HarmoniRiB)' has resulted in a range of tools and methods to assess such uncertainties, focusing on items (1) and (2). The project also engaged in a number of discussions surrounding uncertainty and risk assessment in support of decision-making in water management. Based on the project's results and experiences, and on the subsequent discussions a number of conclusions can be drawn on the future needs for successful adoption of uncertainty analysis in decision support. These conclusions range from additional scientific research on specific uncertainties, dedicated guidelines for operational use to capacity building at all levels. The purpose of this paper is to elaborate on these conclusions and anchoring them in the broad objective of making uncertainty and risk assessment an essential and natural part in future decision-making processes.     

Experiences with the NUSAP system for multidimensional uncertainty assessment.

This paper discusses recent experiences with the NUSAP system for multidimensional uncertainty assessment, based on case studies that vary in complexity. We show that the NUSAP method, and especially the pedigree analysis part of it, is useful to assess not only parameter uncertainty but also to systematically reflect upon (model) assumptions and problem frames. A diagnostic diagram can be used to synthesize results of quantitative and qualitative analysis. It provides an analytic tool to prioritize uncertainties according to quantitative and qualitative insights in the limitations of available knowledge. We further show that extension of the pedigree scheme to include societal dimensions of uncertainty, such as problem framing and value-laden assumptions, further promotes reflexivity and collective learning. When used in a deliberative setting, NUSAP pedigree assessment has the potential to foster a deeper social debate and a negotiated management of complex environmental problems.     

超标洪水下堤防失事风险评价及工程应用

基于堤防工程可能的失效模式,修正了水文失事风险率和边坡滑动失稳风险率计算模型.分析了漫顶失事、渗透破坏失事以及边坡滑动失稳的条件概率计算方法,建立了堤防综合失事风险率计算模型;同时,提出了超标洪水下堤防失事风险率的计算方法,结合南京市外秦淮河堤防工程实例,得到超标洪水下外秦淮河堤防综合失事风险率为0.57%.     

Impact of dimension uncertainty and model calibration on sewer system assessment.

Assessments of sewer performance are usually based on a single computation of CSO (combined sewer overflow) volumes using a time series of rainfall as system loads. A shortcoming of this method is that uncertainties in knowledge of sewer system dimensions are not taken into account. Moreover, sewer models are rarely calibrated. This paper presents the impacts of database errors and model calibration on return periods of calculated CSO volumes. The impact of uncertainties is illustrated with two examples. Variability of calculated CSO volumes is estimated using Monte Carlo simulations. The results show that calculated CSO volumes vary considerably due to database errors, especially uncertain dimensions of the catchment area. Furthermore, event-based calibration of a sewer model does not result in more reliable predictions because the calibrated parameters have low portability. However, it enables removal of database errors harmonising model predictions and 'reality'.     

Failure of sewage pumps: statistical modelling and impact assessment.

Sewage pumping stations are directly responsible for affecting performance, i.e. failing pumps may result in combined sewer overflows or flooding. However, failures of sewage pumps are not yet incorporated in sewer assessments due to lack of knowledge and data. This paper presents the analysis of pump failure data provided by two sewer management authorities in The Netherlands. Pump failures have been studied accounting for the nature of the failures, the operation and maintenance procedures of the management authority, the ageing of the pumps and the changes in the environment of pumps. The analysis shows that sewage pumps fail relatively often due to the composition of sewage and the discontinuous operation of the pumps. The interarrival time and the duration of failures are highly variable and independent of the pump type and the specific function of the pump. The results also indicate that the serviceability of sewer systems is significantly affected by failing pumps. As a consequence, part of the environmental damage due to CSOs (combined sewer overflows) can be avoided by improving maintenance of pumping stations.     

Integrated chemical--physical processes kinetic modelling of multiple mineral precipitation problems.

A three-phase (aqueous/gas/solid) mixed weak acid/base chemistry kinetic model is applied to evaluate the processes operative in the aeration treatment of swine wastewater (SWW) and sewage sludge anaerobic digester liquor (ADL). In both applications, with a single set of constants (except for the aeration rates which are situation specific), close correlation could be obtained between predicted and measured data, except for the Ca concentration-time profile in the SWW. For this wastewater, the model application highlighted an inconsistency in the measured Ca data which could not be resolved; this illustrates the value of a mass balance-based model in evaluating experimental data. From the model applications, in both wastewaters the dominant minerals precipitating are struvite and amorphous calcium phosphate (ACP), which precipitate simultaneously competing for the same species, P. The absolute and relative masses of the two precipitants are governed by the initial solution state (e.g. total inorganic C (C(T)), Mg, Ca and P concentrations), their relative precipitation rates (struvite > ACP) and the system conditions imposed (aeration rates and time applied). It is concluded that the kinetic model is able to predict correctly the time-dependent weak acid/base chemistry reactions and final equilibrium state for situations where multiple minerals competing for the same species precipitate simultaneously or sequentially, a deficiency in traditional equilibrium chemistry-based algebraic models.     

Reflections on uncertainty in risk assessment and risk management by the Society of Environmental Toxicology and Chemistry (SETAC) precautionary principle workgroup.

Quantitative uncertainty assessments and the distribution of risk are under scrutiny and significant criticism has been made of null hypothesis testing when careful consideration of Type I (false positive) and II (false negative) error rates have not been taken into account. An alternative method, equivalence testing, is discussed yielding more transparency and potentially more precaution in the quantifiable uncertainty assessments. With thousands of chemicals needing regulation in the near future and low public trust in the regulatory process, decision models are required with transparency and learning processes to manage this task. Adaptive, iterative, and learning decision making tools and processes can help decision makers evaluate the significance of Type I or Type II errors on decision alternatives and can reduce the risk of committing Type III errors (accurate answers to the wrong questions). Simplistic cost-benefit based decision-making tools do not incorporate the complex interconnectedness characterizing environmental risks, nor do they enhance learning, participation, or include social values and ambiguity. Hence, better decision-making tools are required, and MIRA is an attempt to include some of the critical aspects.     

An integrated system for nonpoint source pollution modelling and management.

Modelling the impact of nonpoint source pollution (NSP) is a complex problem that has troubled water resource managers for many years when trying to set up proper management practices in catchment areas. In this paper, an integrated decision support system, NPSDSS (nonpoint source decision support system), was introduced to resolve this problem in a relatively easy way. The system was developed in a unique platform and integrated with the IMPULSE (integrated model of nonpoint source pollution processes) model, a stand alone geographic information system (GIS) toolbox, a well-structured database, a measure screening model, and an expert system, as well. The system has been applied in the Dianchi Lake catchment area and shown to give a good perspective on providing useful recommendations for appropriate NSP management.     

A framework for implementing spatial and temporal uncertainty in integrated water resources modelling

This study discusses research that develops a general framework and presents a specific implementation of a stochastic modelling system, using linked overland flow and routing simulation models. The specific implementation uses the Gridded Surface Sub‐surface Hydrological Analysis (GSSHA) overland flow model, and the reservoir routing and quality model CE‐QUAL‐W2, to develop the stochastic modelling system. For stochastic simulations, modellers can define up to six GSSHA parameters for stochastic treatment, select the appropriate probability density functions and range, and determine the number of runs in the simulation. The tools described herein then create the correct input and output files, run the linked simulation models using the defined stochastic parameters, and aggregate the voluminous results. Interactive tools were developed to compute credible intervals from the results, and create reports that present the variability in a manner that is easily understood and communicated. Model set‐up and development, stochastic and statistical parameter input, stochastic simulation execution and results analysis were implemented using the Watershed Modeling System, model pre‐ and postprocessing system. This study presents the tools, algorithms and user interfaces developed to implement the linked stochastic modelling system, as well as a simple example demonstrating the tools and the type of analysis supported by this system.