Uncertainty Analysis and Parameter Estimation for a Class of River Dissolved Oxygen Models

Water quality models are essential to the development of least-cost water quality control strategies based on ambient criteria. Such policies are particularly important if financial resources are limited which is currently the case in Central and Eastern European countries. In turn, the derivation of realistic model parameters is a pre-requisite of successful model application. Often, longitudinal water quality profile measurements are performed for the above purpose, but the traditional evaluation of this data encounters significant difficulties due to measurement and other uncertainties. Thus, probabilistic methods are preferred. This paper discusses two of them: the Hornberger-Spear-Young procedure using Monte Carlo simulation and a Bayesian approach. Both methods are rather generic, but they are applied here solely for the traditional Streeter-Phelps model and its extensions, describing oxygen household of rivers. For the purpose of illustration, water quality measurements from the highly polluted Nitra River in Slovakia are employed as a part of a policy oriented study. The BOD decay rate obtained was rather high due to partial biological wastewater treatment and small water depth, but overall, derived parameter values were in harmony with literature findings. Alternative dissolved oxygen models (2-3 state variables and 2-5 parameters) could be evenly calibrated to the data set. Ranges of probability density functions (PDFs) for model parameters were rather broad calling for a well-suited formulation of a water quality management model

Water Quality Management of the Nitra River Basin (Slovakia): Evaluation of Various Control Strategies

The Nitra is one of the most polluted rivers in Slovakia due to numerous municipal and industrial discharges, and the low level of waste water treatment. The ongoing economic transition and lack of financial resources for environmental management calls for the development of short-run least-cost policies on the basis of ambient standards (or a combination of ambient and effluent ones). A water quality control policy model was developed which incorporates dissolved oxygen simulation models, municipal wastewater treatment alternatives, an optimization model based on dynamic programming, a data base, and a graphical user interface. Least-cost policies to achieve various water quality goals were developed and compared to effluent standard based strategies (including that deriving from the application of the "best available technology"). The role of industrial emissions was demonstrated in a sensitivity fashion, while the influence of parameter uncertainty on the developed policies was analyzed in a multiobjective framework. The study shows that significant cost savings are possible in comparison to uniform, effluent standard policies. They also suggest that a long-term strategy should be realized on the basis of a sequence of properly phased least-cost policies corresponding to ambient standards to be tightened gradually

Impact of Climate Change on Global Sensitivity of Lake Stratification

Global climate change could significantly influence hydrophysical processes in lakes and reservoirs and affect aquatic ecosystems. The present work addresses possible impacts on thermal household of standing waters. Sensitivity studies were performed to identify the influence of air temperature changes on lake stratification patterns for different geographic zones of the globe. Ice cover and convective overturn events were selected as indicators. Hypothetical waterbodies used in this series of simulations were assumed typical for shallow, deep, and intermediate lakes. A vertical one-dimensional hydrothermal model developed at the Institute for Water and Ecological Problems (Russia) was used to simulate water temperature and components of the thermal energy budget. The model was cross-checked with a similar model WQRRS (University of California-Davis). Simulation results appear to be consistent with existing stratification-based classification of lakes. Sensitivity analysis showed that effect of changing climate is roughly equivalent to a corresponding change in geographic location, approximately one latitude degree per one degree Celsius of air temperature. Zones of higher sensitivity to air temperature change were revealed where changes were especially profound, namely subtropical zone 30-40 degrees (with respect to cooler climate) and subpolar zone 70-8O degrees (with respect to warming). Subsequently, nine real lakes were selected from the sensitive regions. Future climate conditions were obtained from the GFDL global circulation model, under an assumption of doubling CO2 concentration in the atmosphere. For five selected lakes little or no change in monitored indicators was detected, while for four lakes, changes from an existing stratification pattern were found to be significant

Water Quality Management in the Nitra River Basin

The Nitra River is a tributary of the Vih which enters the Danube downstream of Bratislava. The watershed area is slightly larger than 5000 km2, and more than 650000 inhabitants live there. The quality of the river is one of the poorest in Slovakia due to numerous municipal and industrial discharges and the low level of wastewater treatment. The ongoing economic transition and shortage of financial resources for environmental management call for the development of regional short-run, least-cost policies. The development of such policies was the main objective of this joint study with the participation of IIASA, the Water Research Institute (VUVH, Bratislava) and the Vih River Basin Authority. The present state of emissions and water quality was evaluated on the basis of available, routine types of information (including observations from the basin-wide water quality monitoring network) and additional data collection. It was found that industrial discharges form problems which can be handled mostly locally with a straight-forward strategy. In contrast, the management of municipal discharges -- representing about 70% of the total BOD5 emission in the catchment -- is a more complex issue requiring the development of a regional policy. The definition of ambient water quality criteria (or the usage of a combination of ambient and effluent criteria) reflecting water use is a pre-requisite of the establishment of a least-cost policy. Thus, the application of water quality models is necessary to relate emissions to receiving water quality (as well as their changes). Due to the nature of the problem, a number of oxygen and nutrient balance models were used, ranging from the traditional Streeter-Phelps model to the latest version of U.S. EPA's QUAL model family. The models were calibrated and validated on the basis of two comprehensive longitudinal water quality profile observations. These observations were gathered under low-flow conditions to correspond with the design requirements of the strategy development. Due to the presence of uncertainties of different origins, the methodology of Hornberger, Spear, and Young (based on the so-called "behavior definition") was applied for parameter estimation of simpler models which then were directly incorporated into an optimization model. This optimization model was based on dynamic programming, utilizing structural features of river basin water pollution problems. Elements of the water quality control policy model or decision support system (including the linked hydraulic and water quality model(s), the parameter estimation and uncertainty analysis routines, the dynamic programming, the database, the graphical user-interface, etc.) were developed in a rather generic fashion to allow a transfer from one watershed to another. This philosophy corresponds to the broader goals of IIASA's Water Resources Project dealing with issues of the management of degraded river basins in Central and Eastern Europe and the development of associated methodologies for which the Nitra River served as a case study. Starting from the existing municipal wastewater treatment facilities, a number of alternatives were developed for each site on the basis of various combinations of well-proven physical, biological, and chemical processes to which different effluent quality (BOD-5, TP, NH4-N, NO3-N, etc.) as well as investment, operation, maintenance, and repair costs belong. The technological alternatives (and their major parameters) serve as input to the management optimization model. A special focus was devoted to phased plant development and innovative, cost-effective upgrading of highly overloaded plants by adding chemicals in low dosage. The issue of upgrading was also experimentally analyzed by jar tests at different treatment plants. The objectives of the policy model were formulated in terms of minimizing the total annual cost or the investment cost. Constraints might incorporate ambient water quality (characterized by DO, BOD-5 and NH4-N), effluent criteria, and/or minimum level of treatment. The derived least-cost policies were compared to policies based strictly on effluent criteria and to those based on the application of "best available technology." The effluent criteria based policy stems from the new Slovakian legislation if its ambient criteria element was excluded (the legislation defines the simultaneous usage of effluent and ambient criteria and an eleven-year long transition period after which more stringent standards should be met). The role of industrial emissions was demonstrated in a sensitivity fashion, while the influence of parameter uncertainty on the developed policies was analyzed by an a posteriori Monte Carlo simulation and a multi-objective assessment. The study shows that significant cost savings are possible in comparison to uniform, effluent standard policies. They also suggest that a long-term strategy should be realized on the basis of a sequence of properly phased least-cost policies corresponding to ambient (or regionally variable) standards to be tightened gradually as financial resources become available

System Approaches for the Analysis of Water Quality Management of the Sio, Kapos, Veszpremi-Sed, Malom, Nador, and Gaja River System (Hungary)

The current challenge for water quality management in Central Europe and Eastern Europe is to identify feasible and cost-effective strategies for achieving sustainable progress towards improved water quality. This goal is set against a background of existing water quality standards which are strong but difficult to enforce, the changing role of the public sector after the fall of central planning, limited financial resources and the uncertainty and weak economic conditions of the transition. Within this context, successful water quality management requires strategies that are: (a) administratively enforceable; (b) strengthen and stabilize water quality management institutions; (c) financially feasible; (d) promote economic efficiency; and (e) fairly distribute costs over responsible parties. The Sio, Kapos, Veszpremi-Sed, Malom, Nador and Gaja River System epitomizes this need and confronts nearly all of the serious water management problems now facing Hungary. It is the home to the majority of Hungary's chemical industries receiving high wastewater loads from both industrial and municipal sources. The government seeks to clean up the river system, especially the Veszpremi-Sed River and Malom and Nador Channels, but is concerned about the costs of the chemical industry and the economically stressed municipalities and their customers. Local water and environmental authorities face the controversial challenge of satisfying the various demands on the system while taking into account constraints on both quality and supply. In this microcosm of Hungary and Central and Eastern Europe a water quality modeling and management tool developed by IIASA's Water Resources Project will be applied to help identify effective water quality management alternatives. This introductory Working Paper describes the nature of the water quality management problem, the policy setting and the management strategies which will be assessed

Longitudinal Water Quality Profile Measurements and their Evaluation in the Nitra River basin (Slovakia)

The Nitra River is one of most polluted rivers in the Slovak Republic, due to numerous industrial and municipal emissions, and low level of wastewater treatment. Policy-oriented water quality management study on the basin was undertaken jointly by IIASA, the Water Research Institute in Bratislava (VUVH), and the Vah River Basin Authority. One of the components of the research were the water quality profiles experiments incorporating both emission and river water sampling, followed by an analysis with mass balance method. Two experiments were performed in the basin, in August 1992 and June 1993, respectively. The first experiment was focused on the "conventional" water quality parameters affecting dissolved oxygen balance, such as BOD, COD and nitrogen. The second, although limited only to certain regions of the basin, was aimed at understanding more detailed water quality processes in the river such as sedimentation and hydrolysis of organic material. Rough estimates of the process rates were obtained with mass balance method. The results of the work were used for calibration of water quality models essential for the formulation of economically feasible wastewater treatment policy in the basin based on water quality criteria

DESERT: Decision Support System for Evaluating River Basin Strategies

An integrated PC-based software package for decision support in water quality management on a river basin scale has been developed. The software incorporates a number of useful tools, including an easy-to-use data handling module with a dBase style database engine, simulation and calibration of hydraulics and water quality, display of computed data with the help of external spreadsheet software, and optimization based on dynamic programming algorithm. The main utility of the package is to provide useful and powerful instrument for water quality assessment and decision making in emission control, including selection of wastewater treatment alternatives, standard setting and enforcement at the river basin level. Two versions of the decision support software are presented, the current version and development of a follow-up program with extended features

On Reconciliation of Traditional Water Quality Models and Activated Sludge Models

Models of the oxidation of organic material developed for river water quality management and for biological wastewater treatment differ widely in state variables and process descriptions due to their development history, environmental conditions and the objectives of the two approaches. The IAWPRC/IAWQ Activated Sludge Model No. 1 (ASM-I) resulted from a coordinated effort of a dedicated specialist group at the mid 1980s and thus free of the inconsistencies inherent in ambient water quality models such as QUAL2E developed in the course of the past three decades. The reconciliation of the ASM-1 and QUAL2E attempted in the present work may help in developing integrated pollution abatement strategies considering treatment and riverine processes in a unified way. It is shown that, after some modifications, a model similar to ASM-1 can be successfully applied to riverine conditions. It is also demonstrated that simple first-order kinetics models (such as the Streeter-Phelps and extended Streeter-Phelps ones) can be derived from the ASM-1 and QUAL2E as their asymptotic forms under the assumption that "fast" variables attain their long-term equilibrium levels. Models of ASM-1 type should, therefore, be applied when there are abrupt temporal or spatial changes in the system, otherwise simpler models adequately reflect the behavior of the oxidation system. Finally, an international effort to develop a standardized and improved river water quality model following the procedure of ASM-I looks more than desirable

Прочность гибкой оболочки пневматической рессоры

The strength for a flexible shell of a vehicle pneumatic spring during movement relative to a rail track has been studied in the paper. The calculation has been carried out using the finite element method implemented in the SolidWorks software environment. For this purpose, 3D drawings of a balloon-type pneumatic spring have been reproduced. A specific  feature of the design is that the distance between the upper and lower bottoms in static conditions is unchanged – thanks to the body position regulator, which maintains its constancy relative to the trolley frame. The results obtained have made it possible to conclude that there are certain reserves for the level of stresses, i.e.,  in addition to the vertical, it is possible to take into account also transverse mutual displacements of the air spring bottoms which will occur when the trolley moves relative to the body.  At the next stage, the stresses in the material of the flexible shell are investigated for mutual transverse displacements of the bottoms, which are observed with transverse displacements of the trolleys relative to the body of the vehicle when  traveling along curved sections of the track. At the same time, the maximum stresses in the material of the flexible shell of  the pneumatic spring are about 11 MPa, even with twice the nominal air pressure and transverse mutual displacements of the bottoms of 40 mm, that is, they are much less than the breaking strength (30 MPa). The carried out researches allow to draw  a conclusion that the design and parameters of a flexible shell of a balloon-type air springs ensure its strength under operational loading schemes. Therefore, in order to improve the dynamic qualities of vehicles, it is proposed to use a flexible shell  of a pneumatic spring as a component of the spring suspension.Исследована прочность гибкой оболочки пневматической рессоры транспортного средства при движении относительно рельсовой колеи. Расчет проведен с использованием метода конечных элементов, реализованного  в среде программного обеспечения SolidWorks. Для этого воспроизведены чертежи пневморессоры баллонного типа  в формате 3D. Особенностью конструкции является то, что расстояние между верхним и нижним днищами в статике неизменно – благодаря регулятору положения кузова, который поддерживает его постоянство относительно рамы тележки. Полученные результаты позволили сделать вывод, что имеются определенные резервы по уровню напряжений, т. е. дополнительно к вертикальным возможно учесть еще и поперечные взаимные смещения днищ пневморессоры, которые будут возникать при смещениях тележки относительно кузова. На последующем этапе исследованы напряжения в материале гибкой оболочки в случае взаимных поперечных смещений днищ, наблюдающиеся при поперечных смещениях тележек относительно кузова транспортного средства во время движения по кривым участкам пути. При этом наибольшие напряжения в материале гибкой оболочки пневморессоры составляют около 11 МПа даже при вдвое большем номинальном давлении воздуха и поперечных взаимных смещениях днищ 40 мм, т. е. они значительно меньше разрывной прочности (30 МПа). Проведенные исследования позволяют сделать вывод о том, что конструкция и параметры гибкой оболочки пневморессоры баллонного типа обеспечивают ее прочность при эксплуатационных схемах нагружения. Поэтому с целью улучшения динамических качеств транспортных средств предлагается использовать гибкую оболочку пневморессоры как составляющую рессорной подвески

Use of a Fourier Decomposition Technique in aquatic ecosystems modelling

A quasilinear system of ordinary first-order differential equations of the type frequently used in ecosystems modelling (including mathematical models of aquatic ecosystems) is considered. It is assumed that the system is subject to periodical changes in coefficients and/or right-hand sides (due to diurnal or seasonal character of the described ecological processes). The periodic component of the state variables caused by these disturbances is considered to be small enough to allow usage of first-order Taylor formulae. Under these assumptions a decomposition of the system dynamics into “the slow motion” component and first-order Fourier harmonics is performed. The resulting set of equations can be solved with large time steps, still preserving information on the periodic as well as the smooth average components of dynamical behavoir of the initial system. The performance of the method is evaluated using an algae growth equation, the only growth limiting factor being that of light availability. The results acquired suggest the proposed method is useful both for adjusting the average motion component and for evaluation of the diurnal dynamics of algae. Further uses of the method are discussed and proposed