Modeling Hydrologic Phenomena [Free opinion]

Afin de suggérer quelques règles pratiques sur l'utilisation des modèles hydrologiques, G. De MARSILY dans sa tribune libre (Rev. Sci. Eau 1994, 7 (3): 219-234) propose une classification des modèles hydrologiques en deux catégories : - modèles construits sur des données (phénomènes observables) - et modèles sans observations disponibles (phénomènes non-observables). Il préconise que pour la première catégorie des phénomènes observables, les modèles développés selon une procédure d'apprentissage ainsi que ceux basés sur les lois physiques sont du type boîte noire. Pour le deuxième groupe de modèles, il propose l'utilisation de ceux à base physique.Les modèles hydrologiques à base physique doivent introduire dans les lois phénoménologiques des coefficients empiriques corrects vis-à-vis des échelles correspondantes d'espace et de temps (GANOULIS, 1986). Des exemples bien connus sont le coefficient de la perméabilité de Darcy à l'échelle macroscopique, dérivé à partir des équations Navier-Stokes au niveau microscopique et les coefficients de dispersion macroscopique provenant des coefficients de diffusion locale de Fick.Une utilisation abusive de ces modèles en introduisant des échelles de temps et d'espace inapropriées et en déterminant les coefficients par étalonnage, n'est pas une raison suffisante pour les considérer de type boîte noire. Les modèles hydrologiques du type boîte noire sont très utiles lorsque des données sont disponibles, mais restent essentiellement empiriques. Ils ne donnent pas de réponses correctes lorsque des restrictions sévères d'unité de lieu, de temps et d'action ne sont pas valables.Concernant la deuxième classe des modèles, nous pouvons remarquer que dans la réalité des phénomènes purement non observables et sans aucune donnée, n'existent pas en hydrologie. Dans les cas d'évenements rares et de systèmes hydrologiques complexes tels que les impacts dus à la radioactivité et les prévisions à grande échelle, les modèles à base physique avec des paramètres adéquats peuvent être utilisés afin d'intégrer les informations rares et les opinions des experts, dans un cadre probabiliste Bayesien (APOSTOLAKIS, 1990).La propriété la plus intéressante des modèles hydrologiques est leur capacité éventuelle à tenir compte des imprécisions et des variabilités naturelles. Les incertitudes peuvent être classées en deux catégories : aléatoires (liées à la variabilité naturelle) et épistémiques (liées à l'approche scientifique). Des modèles hydrologiques probabilistes sont plus convenables pour tenir compte des incertitudes aléatoires. Des modèles basés sur la logique floue peuvent quantifier les incertitudes épistémiques (GANOULIS et al., 1996). Les approches stochastiques et flous sont brièvement expliquées dans cette tribune libre en comparaison avec les modèles hydrologiques déterministes à base physique.With the aim of suggesting some practical rules for the use of hydrological models, G. De MARSILY in his "free opinion" (Rev. Sci. Eau 1994, 7(3): 219-234) proposes a classification of hydrologic models into two categories: - models built on data (observable phenomena) and ; - models without any available observations (unobservable phenomena). He claims that for the former group of observable phenomena, models developed through a learning process as well as those based on the underlying physical laws are of the black box type. For the latter group of unobservable phenomena, he suggests that physically-based hydrologic models be developed.Physically-based hydrologic models should introduce to the phenomenological laws the correct empirical coefficients, which correspond to the proper time and space scales (GANOULIS, 1986). Well-known examples are Darcy's permeability coefficient on the macroscopic scale as derived from the Navier-Stokes equations on the local scale and the macroscopic dispersion coefficients in comparison with the local Fickian diffusion coefficients. Misuse of these models by confusing the proper time and space scales and determining the coefficients by calibration is not a sufficient reason to consider them as belonging to the black box type. Black box type hydrologic models, although very useful when data are available, remain formally empirical. They fail to give correct answers when serious constraints of unity in place, time and action are not fulfilled.Concerning the second class of models, we may notice that purely unobservable phenomena without any available data do not really exist in hydrology. In the case of very rare events and complex systems, such as radioactivity impacts and forecasting of changes on a large scale, physically-based models with adequate parameters may be used to integrate scarce information from experiments and expert opinions in a Bayesian probabilistic framework (APOSTOLAKIS, 1990).The most important feature of hydrologic models capable of describing real hydrologic phenomena, is the possibility of handling imprecision and natural variabilities. Uncertainties may be seen in two categories: aleatory or noncognitive, and epistemic or cognitive. Probabilistic hydrologic models are more suitable for dealing with aleatory uncertainties. Fuzzy logic-based models may quantify epistemic uncertainties (GANOULIS et al., 1996). The stochastic and fuzzy modeling approaches are briefly explained in this free opinion as compared to the deterministic physically-based hydrologic modeling

Dispersion et disparition des bactéries conformes dans la baie de Thessaloniki

Dans les baies presque fermées de la Méditerranée, le taux de renouvellement et le pouvoir dispersif du milieu marin sont faibles. Ceci amène à des concentrations souvent élevées de bactéries califormes à la sortie des stations d'épuration, même munies de filières biologiques. L'élevage de coquillages dans ces baies constitue une contrainte supplémentaire aux concentrations maximales de bactéries permises selon les normes de la CEE.Le problème a été posé pour le fonctionnement de la station d'épuration de la ville de Thessaloniki. Le but de cette étude a été l'analyse quantitative de la dispersion et de la mortalité des bactéries coliformes. Pendant le premier semestre 1990, plusieurs campagnes de mesures ont permis l'échantillonnage et la détermination des concentrations de bactéries coliformes à quatre stations, situées au voisinage d'une source de contamination bactérienne. Parallèlement un modèle mathématique basé sur la simulation de la marche au hasard a été mis au point.Après étalonnage, ce modèle a servi comme outil pour simuler les impacts, sur les sites de conchyliculture, des eaux usées de la ville.In this paper, the contamination of coastal waters by coliform bacteria is considered. The problem is studied in the bay of Thessaloniki (N. Greece) using sampling, laboratory analysis and computerized mathematical modelling. The case study is typical for semi-enclosed bays in the Mediterranean sea. The water renewal and dispersion capacity of the sea are very low and high concentrations of coliform bacteria can be expected. This is the case when modern technology (biological treatment) is used in the sewage treatment stations and chlorination or other types of disinfection are kept low in order to avoid the formation of THM (Tri-Halo-Methanes). The problem of meeting the water quality standards is more difficult, when shellfish growing waters are to be protected.Impacts to marine environment from sewage and industrial effluents depend on 1) the degree of wastewater treatment, 2) the location of the disposal site and 3) the receiving capacity of coastal waters. The later means the maximum quantity of pollutants that a given area can receive without adversing effects (e. g. eutrophication, change of colour, odours). In the marine environment the receiving capacity is very difficult to assess, as it varies with very irregular way both in space and time. For coliform bacteria, the receiving capacity of a coastal area depends on the dispersive characteristics of the bay and the morality conditions of the bacteries. These are studied here for the case of the bay of Thessaloniki.The bay of Thessaloniki is located in the NW Aegean sea (Eastern Mediterranean). It is a shallow, semi-enclosed basin communicating with the open sea from the south boundary only. The northern part of the bay has a total area of 300 Km2 and a maximum depth of 30 m. it is actually heavily polluted by untreated sewage coming from the city of Thessaloniki. Pollutant loads are estimated as 150 000 m3/d of sewage and 60 000 m3/d of industrial effluents.The sewage treatment station of the city has started now operating. The provisional disposal site is located in the west toast, three Km from Paliomana, where marine farms for mainly mussels and other shelffishes have been developed. In view of the economic importance of these activities and the need to protect the public health, it is important to assess the impacts from wastewaters to the coastal area.The main objective of the study is the quantitative evaluation of the dispersion and mortality conditions of coliform bacteria in the bay of Thessaloniki. The ain of the project is the choice of the disposal site of the sewage after treatment, by predicting the water impacts from sewage discharges. During the tire semester of 1990 (February-July 90) sampling and laboratory analyses of E. coli concentrations have been made every 15 days in 4 stations. Some of the samples have been taken during the night. Statistical analyses of the results gave the distribution in space of the max, min, median and C80 values of E. coli (C80 is the concentration which is not exceeded for 80 % cases).The tale of bacteries in the marine environment is described by the convective-dispersive equation, including the decay term. A linear dependance between bacterial morality and bacterial concentration is assumed. Over the years the advective dispersive equation has been extensively investigated and numerically approximated by numerous methods. Finite differences and finite elements have been used and produced stable numerical results. However, significant errors are introduced in ail these numerical simulations. These are due to the fact that only a limited number of terms in the Taylor series expansions are taken into account. Explicit algorithms suffer from the so-called numerical diffusion. This is an artificial diffusion related to the truncation errors. It is superimposed on the physical diffusion and leads to an excessive attenuation of the input signals. Implicit finite difference algorithms introduce trading effects because the initial signals are propagated at velocities that differ from the physical ones. It seems that particle methods based on random walks are more flexible and easy to use and lead to relatively accurate results.A random walk computerized mathematical algorithm is developed to simulate the dispersion and mortality of coliform bacteria in the bay. By use of a large number of particles (103 - 104) which move with the current velocities and by random dispacements following a Gaussian distribution, the contour lines of equal concentrations are obtained. The couple of values for the dispersion coefficient D and the mortality time T90, which simulate better the space distribution of C80 values is : D = 4 m2/s, T90 = 5 h.The same value of the dispersion coefficient has been independently found by tracking flotting drogues in similar wind conditions (moderate wind). It is concluded that the above values of dispersion and bacterial mortality reflect the characteristic conditions of the bay and can be used to predict the impacts from sewage discharges

La gestion de l'eau à l'aube du 3ème millénaire: Vers un paradigme scientifique nouveau [Tribune libre / Article bilingue] Water resources management at the turn of the millennium: towards a new scientific paradigm [Tribune libre]

L'objectif de cette tribune est d'analyser la nouvelle approche concernant la gestion des ressources en eau qui a été adoptée par la communauté scientifique au seuil de ce nouveau millénaire. Après une révision de cette nouvelle approche, une méthodologie scientifique est proposée permettant d'exprimer le nouveau concept, qui est plutôt général et descriptif, en termes analytiques et quantitatifs, de façon qu'il soit appliqué dans des cas pratiques.Depuis quelques dizaines d'années déjà, il a été bien établi que la nouvelle approche va dans le sens de la gestion durable. Ceci veut dire qu'elle intègre des préoccupations sociales et environnementales aux critères traditionnels de performance technique et d'efficacité économique. La question qui se pose maintenant est comment le concept complexe de la durabilité, qui jusqu'à présent a été exprimé seulement de façon générale et qualitative, pourrait être formulé en termes analytiques et quantitatifs d'une méthodologie scientifique.Sur le plan méthodologique, la modification des critères dont on doit tenir compte dans un cadre cohérent d'hypothèses et de raisonnements, suggèrent une évolution vers un paradigme scientifique nouveau. Le cadre général de ce paradigme que nous proposons est celui de l'analyse quantitative du risque à plusieurs dimensions.Traditionnellement, l'objectif général de la gestion de l'eau, était la satisfaction de la demande dans diverses utilisations, comme l'agriculture, l'eau potable et l'industrie, en utilisant les ressources en eau disponibles de manière techniquement fiable et économiquement efficace. Dans cette approche, des solutions structuralistes et le plus souvent technocratiques, ont été proposées et réalisées dans plusieurs pays du monde. La construction de barrages et de réservoirs d'eau, la modification des lits des rivières et la dérivation des cours d'eau ont eu cependant, dans de nombreux cas, de sérieux impacts négatifs sur l'environnement et les conditions sociales. De plus, le gaspillage dans l'utilisation de cette ressource précieuse et la pollution galopante provenant de tous les secteurs d'utilisation de l'eau ont mis en question ce mode de gestion. Le concept de la gestion durable des ressources en eau a été évoqué, tout d'abord en 1972 à Stockholm, pendant la Conférence Mondiale des Nations Unies, puis à Rio, en 1992, avec l'Agenda 21.La nouvelle philosophie est basée sur la gestion intégrée de l'eau à l'échelle du bassin versant. Elle met l'accent sur la protection de l'environnement, la participation active des collectivités locales, la gestion de la demande, les aspects institutionnels, et le rôle de l'éducation continue tout le long de la vie de tous les utilisateurs d'eau.Sur le plan méthodologique, la gestion intégrée de l'eau reste encore un problème ouvert où plusieurs approches cherchent à définir un paradigme cohérent. Dans cette tribune, nous en proposons un que nous appelons " le paradigme 4E " : Epistémique, Economique, Environnemental, Equitable. Il est basé sur l'analyse quantitative du risque à plusieurs dimensions : scientifique, économique, environnementale et sociale. Ce paradigme utilise soit la théorie des probabilités soit la logique du flou (ou les deux à la fois) afin d'évaluer et d'intégrer les risques technico - économiques et socio-environnementaux dans une perspective de gestion durable des ressources en eau.The aim of this article is to analyze the new approach to water resources management adopted by the scientific community at the turn of the millennium. After reviewing the basic concept of this approach, a scientific methodology is proposed, in order to express the general and mostly descriptive new concept in analytical and quantitative terms, so that it may be applied in practical cases.For several decades now the general concept of this new approach has been developing along the lines of sustainable development. This means that social and environmental considerations have been added to the traditional objectives of technical performance and economic effectiveness. The question now being raised is how the complex concept of sustainability, which until now has been expressed in general and descriptive terms only, may be formulated in the analytical and quantitative terms of a scientific methodology.On the methodological level, the fact that several criteria and objectives within a coherent framework of hypotheses and reasoning are taken into account may suggest a move towards a new scientific paradigm. The general framework of the paradigm proposed in this paper is that of multidimensional quantitative risk analysis.Traditionally, the general objective of water management has been the satisfaction of demand for various uses, such as agriculture, drinking water or industry, using available water resources in technically reliable and economically efficient ways. This approach has led to structural and mostly technocratic solutions being suggested and implemented in several countries. However in many cases, building dams, modifying riverbeds and diverting rivers has had serious negative repercussions on the environment and on social conditions. Moreover, waste in the use of this precious resource and rampant pollution in all areas of water use have raised doubts about this form of management. The concept of a sustainable management of water resources was first mentioned in Stockholm in 1972, during the United Nations World Conference and then at the Rio summit in 1992 with Agenda 21.The new philosophy is based on the integrated management of water at the watershed basin level. Emphasis is placed on environmental protection, the active participation of local communities, the management of demand, institutional aspects and the role of continuous and lifelong education of all water users.On the methodological level, integrated water management remains an open question and several different approaches are seeking to define a coherent paradigm. One possible paradigm is proposed in this article and may be called the " 4E paradigm " : Epistemic, Economic, Environmental, Equitable. It is based on risk analysis, with a multidimensional character: Scientific, Economic, Environmental and Social. This paradigm uses either the theory of probability, or fuzzy logic, or both, in order to assess and integrate technico-economic and socio-environmental risks in a perspective of sustainable management of water resources

Financial factors in the investment decisions of firms : theory and evidence

This thesis examines the effects of informational imperfections in the financial system on the investment decisions of firms. Its main theme is that such imperfections are relevant for the dynamic aspects of investment decision making, for they affect the cost of flow of new financing. Since their source is ultimately the decentralized nature of the system, where some of the creditors of the firm have not access to the firm' s internal operations, the costs involved are likely to arise in every type of financial market and in the use of every kind of financial instrument. The only source of funds not affected by the informational problems is the flow of internal financing, but this is either constrained or involves rising costs for the insiders. Therefore, there are costs of adjustment in capital accumulation that are related to the financial arrangements of the system. A dynamic optimization model is built to examine the combined financial and investment decisions of a firm operating in an asymmetric information environment. The resulting policies are compared with those of a firm facing conventional adjustment costs and a strongly efficient financial system. The importance of internal financing is confirmed. The role and problems of the equity market as a source of finance is also illuminated. Equity finance is found to differ from debt in so far as equity claims give the right of access to the internal operations of the firm. A model with both types of adjustment costs is also examined. When conventional adjustment costs are dismantling costs (when investment is negative), asymmetries arise between under- and over-leveraged firms with possible implications for policy. Also, Tobin's Q investment approach is re-examined in a model with both type of costs. The Q variable is found to contain interesting information even when capital markets are not strongly efficient. An empirical model is built after examining the behaviour of firms in output markets when facing a stochastic demand. The model is tested with panel industry level data from Greece for the manufacturing sector in 1973-1983. An error correction specification is used. The results confirm the importance of the impact effect of net profitability. Demand and the associated capacity utilization are also found to have a significant effect in the short and in the long run. The evidence is less clear for the user cost of capital and the gross profit margin

Impacts of Climate Change and Land Use on River Catchment Hydrology Using Model Downscaling

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Financial liberalization and house price dynamics in Europe

This paper investigates the determinants of house prices in a sample of European countries over the period 1970-2004. Focusing on the role of financial liberalization, we find that it has mainly affected the short term dynamics of residential prices. In particular, the impulse effects on house prices of income and mortgage debt have become smaller. On the other hand the effects of interest rates, past house prices and, to a lesser degree, stock market have strengthened. In other words, there seems to have been a certain “de-linking” of short term house price dynamics from income, whereas the housing market may have become more similar to a financial asset market, with interest rates and expectations of capital gains playing a more prominent role

DO HEAVY METALS AFFECT ON DEHYDRATION RATE OF BRASSICA NAPUS, TRITICUM SPP., ZEA MAYS AND HORDEUM VULGARE?

Dependence of dehydration rate of Brassica napus, Triticum spp., Zea mays and Hordeum vulgare from heavy metal concentrations in plants after its growth in contaminated media has been studied in the laboratory and results are summarized in this paper. We found water loss reduction in all plant species germinated in sewage sludge (somewhere soil) after 18 day in comparison with control samples, presented by garden compost. Moreover, water loss was reduced significantly in root part of the plants. At the same time water loss was increased in Brassica napus, Triticum spp. and Hordeum vulgare germinated in sewage sludge after 30 day in comparison with control samples that could have been caused by metals interactions with plants’ metabolic processes within the cells

Involving stakeholders in transboundary water resource management: The Mesta/Nestos ‘HELP’ basin

Alternative options for new private and public investment projects in the transboundary Mesta/Nestos River catchment between Bulgaria and Greece involve new dams and water storage reservoirs, agricultural irrigation systems, new touristresorts and various water-related facilities for urban and industrial water supply. These developments are designed to be implemented in both parts of the basin (in Greece and Bulgaria), where different socio-economic conditions prevail, resulting in each country having different preferences and objectives. Alternative options should consider environmental consequences, to the impact on ecosystems and human health, and also financial and social risks. Any negative impacts on the environment, and whether these negative impacts can be prevented, should be weighted against the economic and social benefits foreseen.Sustainable implementation of private or public utility projects cannot be achieved without public participation and a clear consensus between stakeholders. The UNESCO HELP (Hydrology for the Environment, Life and Policy) initiative provides a rationale for breaking the ‘paradigm lock’ existing between the most recent scientific findings on the one side and the public, stakeholders and decision makers on the other. In this paper stakeholder involvement in the decision making process is promoted firstly by communicating the results of integrated modelling of water resource management at the basin scale, and secondly by suggesting alternative models and software in order to facilitate negotiations and final decision making processes in transboundary water resource management These models help to rank alternative projects according to the attributes of stakeholders in each country; the aggregated attributes of the stakeholders in both countries; and the aggregated goals of each country.Keywords: integrated water management, modelling, public participation, decision support, conflict resolutio