Optimisation du système d’assainissement des eaux urbaines Réseau-STEP-Milieu récepteur par une approche de gestion intégrée

Water management is a recurring problem that has occupied mankind for years. Nowadays, the multiple stakeholders involved in this management have the willingness to cooperate to make it more integrated and take into consideration all social, economic and environmental components across an ideal functional unit which is the hydrological watershed. The urban wastewater system plays a central role because of its triple dimension Sewer, Wastewater treatment plant, Receiving water and well often determines the quality of the water on which depend many other sectors. Insurance that the system is in a good health allows having a functional and efficient water resources management. This work explores the possibilities of optimization of the urban wastewater system by the establishment of an integrated management which takes into account the three subsystems. For this, an understanding of the process of optimization and the knowledge about the conventionally used algorithms is deepened. Furthermore the importance of modeling and real time control for the improvement of knowledge and decision making is emphasized by a review of the available tools involved in concrete examples. An approach of integrated management of the urban wastewater system is proposed, focusing on two aspects : the identification of the critical points of the system by analyzing performance indicators and the implementation of the optimization process. This approach is applied to a case study and allows highlighting the presence of important overflows at a pumping station due to the infiltration of parasitic clean water. At this problematic station the optimization process is applied with the help of CVX tool on matlab. This optimization reduces spills using existing infrastructure while following sizing, economic and environmental constraints established by the system. This study shows that improvement of the urban wastewater system performance by following an integrated management approach exists and can be considered in Switzerland.

BIOPHYSICAL CONTROLS ON EVAPOTRANSPIRATION: NUMERICAL MODELS AND EXPERIMENTAL OBSERVATIONS

Federico Croci

Water and food are basics of human life, unfortunately climate changes and water pollution have reduced the amount of water available for human uses. In this context the study of the hydrologic cycle is becoming of growing importance in order to optimize the anthropogenic exploitation of water resource. Evapotranspiration is the term used to describe the part of the water cycle which removes liquid water from an area with vegetation into the atmosphere by the processes of both transpiration and evaporation. Evapotranspiration is an important part of the hydrologic cycle because it represents a considerable percentage of water losses in watersheds. This process is also one of the main consumers of solar energy at the Earth's surface. The estimation of evapotranspiration it is of great importance for agriculture and water resources management, for example, by knowing the rate of water loss from a region, farmers will be better placed to efficiently manage the irrigation strategies. The rate of evapotranspiration at any location on the Earth's surface is controlled by several factors such as energy availability, humidity gradient, wind speed immediately above the surface, water availability, type of vegetation, stomatal resistance and soil characteristics. The problem of estimating evapotranspiration has been widely studied. During the past several decades, different approaches have been proposed and many formulas are available in the literature to fulfill this task. The complexity of the phenomena and its great variability all over the world make difficult to find a universal and robust method for the evapotranspiration prediction and estimation. Evapotranspiration can be obtained by many estimation methods. Some of these methods need many weather parameters as inputs while others need fewer. Factors such as data availability, the intended use, and the time scale required by the problem must be considered when choosing the evapotranspiration calculation technique. The Penman-Monteith equation was derived from the classic Penman equation adding to the terms already considered in the Penman formulation (aerodynamic resistance and energy balance) the canopy resistance. This approach requires many meteorological data, such as maximum and minimum air temperatures, relative humidity, solar radiation, and wind speed. If some of these data are not available, alternative techniques have been developed to overcome this drawback. However, this estimations of meteorological data affect the quality of the result, alternatively, in such cases other simpler methods may be used. The Penman-Monteitu equation is assumed to be the most reliable because is based on physical principles and because it considers all the climatic factors, which affect evapotranspiration.

2013

A Systems-Based Generic Decision Support System Application to Urban Water Management

Colin Schenk

In the field of environmental management, inefficient piecemeal sectorial approaches are still widespread, particularly in water resources management, where concerns and decisions are usually split among a set of rather weakly linked stakeholders. Planning and management problems to be addressed are in most cases complex and need to be tackled in a global, integrated and holistic way, including information from the different areas of science and knowledge from the various stakeholders. Therefore, the sharing and integration of data, knowledge and models has become a major issue. A lot of effort has been made in recent years to develop such integrative tools, including information systems (IS), decision support systems (DSS) or integrated modelling frameworks (IMF). Although these tools achieved great progress in terms of linkages, there is currently no environment providing a full integration of the various kinds of data, models, and their visualisation. This is the general issue tackled by the present thesis, with developments based on a semantic, systemic formalism, and applications focusing on water management issues. The first development step taken was the creation of a systemic description of water management. Albeit the various aspects of water management are abundantly documented and well-known, an integrated description including interconnections was lacking. Therefore, a graphic representation of interconnected system elements annotated with definitions was created. This innovative result constitutes an ontology (a formal representation of a knowledge domain) providing a robust reference and a fairly exhaustive reminder of the complexity of the water management field, including transdisciplinary aspects. In the second step, a data model was created, based on the new SYSMOD language. The latter proposes a new graphical language uniting the ontological and systemic approaches, with a strong emphasis on interactions. Whereas existing data models are generally specific to a field or designed for a target application, this new data model is generic and transdisciplinary. It can handle any kind of systemically organised data, which potentially includes any sort of environmental data. To visualise and manage the systems-based, generic data stored within the database (created on the basis of the generic data model) a new kind of visualisation was developed, proposing diagrams of interconnected nodes. Whereas existing information systems are often data warehouses without a user-friendly graphical user interface, or geographic information systems focussing on spatial data, this new diagram visualisation proposes views including spatial and non-spatial system elements (such as lakes, power plants, stakeholders or laws) interconnected by interactions (such as fluxes or influences). Bound to the database, the tool was called an "information system on the system" (ISS). It provides a way of graphically managing and integrating the systemically organised, generic, transdisciplinary data. Furthermore, the systems approach fosters the apprehension and communication of complex situations in a holistic way (involving many different elements, influences and interactions from various fields), through their representation into thematic views. In complement to the diagram visualisation, a reporting tool was developed to display the data linked to system elements (numeric values, comments, files, etc.) in a web-browser fashion. To interoperate with external models, another module was developed on the top of the ISS. Finally, a fully-fledged general user interface was created to integrate all the previous developments into a single environment. To visualise the different facets of system elements, a geographic and a chart view were added, in complement to the reporting view. This final tool was called the generic decision support system (GenDSS), as its application to given situations can give rise to a series of views and linkages to models, thereby providing specific DSS functionalities for these situations. The successive developments were tested in Birmingham (United Kingdom). Test results indicated that the GenDSS is currently limited to managing a few hundred elements; beyond this quantity, the loading times and the user interface reactivity can become long and unresponsive. On the other hand, the application also demonstrated the strengths of the GenDSS which provides an innovative integrated solution to centralise transdisciplinary data in various formats (e.g. numeric values, texts, geometries, files), to holistically describe situations using complementary visualisations, and to test scenarios using externally-linked models. Thus, the GenDSS may prove an adequately versatile solution for large institutions or enterprises dealing with complex situations, heterogeneous and transdisciplinary data, and where requirements are continuously evolving, such as: a car manufacturing corporation (which would involve several different production and research sites in different countries with different regulations), a hospital, or a strategic environmental planning network (where the tool could help to break the transdisciplinary, sectorial barriers). In the case of water, the GenDSS system could prove very useful to achieve a truly integrated water management approach.

EPFL2010

Towards an information system on the water system

André Mermoud, Bastien Roquier, Colin Schenk

Integrated water resources management is generally considered a relevant methodology given the pressing necessity to use water in a sustainable manner. However, its application framework still needs refinements. As a first step towards the creation of such an improved framework, a system model for water management has been proposed, including a broad view upon the elements involved directly or indirectly (such as the energy, the public health or the housing conditions) in water management. The model may be applied to large entities such as regions or cities. This could lead to the creation of “information systems about the system”, systemic views with access to detailed data regarding the water-related infrastructures, ecosystem, natural and human resources, and legislative context, including relationships between these elements.