Elodie Zavattero

Decision Support System Architecture for Real-Time Water Management

Management of water uses requests to harmonize demands and needs which are getting more and more complex and sophisticated. During the past three decades, modeling systems for hydrology, hydraulics, and water quality have been used as stand-alone products and were used in order to produce an analysis of a current situation and to generate forecast according to different horizons. The current situation, characterized by the fast increase of monitoring devices mainly in urban environments, requests an integration of the modeling tools into the information systems that are now dedicated to the global management of urban environments and related services. Energy distribution, water distribution, solid wastes collection, and traffic optimization are today major issues for cities that are looking for functional Decisions Supports Systems (DSSs) that may integrate the various components and operate in a sustainable perspective. In addition, the basic requirement of real-time assessment of the situation, the modeling systems identified as main elements of analytics and used for hydrology, hydraulic, and water quality forecasts have to integrate a common framework allowing modular approach and interoperability. This chapter presents the interest for a generic operational approach that could be implemented in order to address the management of water uses in a complex urban environment and to provide real-time assessment and forecasts. The proposed approach is illustrated with the AquaVar project, an application developed on the Var catchment located in the French Riviera and for an area of 3000 km2.

Assessment of Deterministic Model over Long Time Period Hydrological Simulation at Ungauged Mediterranean Catchment

In the Mediterranean area, because of the typical climate with hot dry summer and wet mild winter, the drought and flood hazards occur frequently. The Var catchment, located at the France Mediterranean area has nearly 3000 km2 control areas with elevation variation from sea level up to 3000 m. NICE as the second biggest city in this region, locates at the outlet of this basin which directly affected by the Var catchments. Clearly representing the long time period hydrological process in this catchment will produce an integrated view for the local managers to optimize the regional water resources. However, due to the complexity of the topography and geology in this area, it is difficult to manage series measurements over whole catchment. Hence to catch the hydrological process in this ungauged area, a distributed deterministic model MIKE SHE was applied to achieve our purposes. By collecting the daily rainfall data recorded by Meteo-France from 2008 to 2014, the hydrological model was built to represent the whole hydrological process including rainfall–runoff process and groundwater movement, etc. The model results showed that the rainfall–runoff response time of the catchment is less than one day which is close to the reality effected by the high slope distribution in this catchment. The model results showed that there is an obvious exchange process between the surface and groundwater in the catchment. At summer time when there is less rainfall for saturating the top soil, the channel discharge is relatively low. However, in the winter time after a short period rainfall saturated the soil; the following rainfall events always generate flood peaks. For the local managers, the extreme rainfall events after even a small rainfall in the winter time can produce significant flood damage and require fast social reactions. In conclusion, with the increase of the computer facilities, the distributed deterministic model gains more interest in the hydrological simulation. With the model characteristic which is based on the physical law, the parameters can be estimated by the model calibration. This case study in the Var catchment showed a succeed way to apply distributed deterministic model in an ungauged catchment to well represent the long time period hydrological process. The model strategy could be one of the useful references applying in other ungauged cases.

2D Surface Water Quality Model: A Forecasting Tool for Accidental Pollution in Urban River—Application to the Var River, France

In many countries, urban river is a key subsystem of urban environment and offers services for the surrounding inhabitants: drinking water, agricultural, and industrial water. Actually, the river and the urban development depend on each other. This is why the growth of population and the economic development can cause stress not only on quantity of water but also on its quality. In this context, surface water quality models can be useful tools to simulate and forecast concentrations and risks of chemical pollutants in a given water body. The Var river, located in the French Riviera in the south of France, is an urban river encompassed by various land uses: industries, agricultural fields, and urban areas. Furthermore, the alluvial aquifer, which is connected with this river provides drinking water for nearby cities by using six pumping stations. Hence, this water resource is vulnerable to accidental pollution. Indeed, the wastewater from industries could be a source of contamination and a tanker accident on one of the 6 bridges across the Var river could be occurring. This configuration appears to become a big issue for the municipality. In order to predict the transfer of chemical pollutants, the 2D hydraulic model is an appropriate tool. Actually, numerical models are able to represent hydrodynamics of the river and the pollutant effects on the surface water. This paper compares different ways to model the transfer of pollutant in the Var river. Three hydraulic modeling tools were used to simulate accidental pollutions: Mike 21, Mike 21 FM, and Telemac2D. They are presented in a first section by introducing the equations used, the required parameters and the limitations. After that, the 2D free surface flow model was built (with the three software tools) and calibrated. Then, two scenarios of accidental pollutions were simulated. For the different models the propagation time, the concentration of pollution, and the polluted surface were compared. Therefore, the objective of this study is to point out the differences among the three water quality models built by Mike 21, Mike 21 FM and Telemac2D. The calibrated parameters seem to be different from one modeling tool to another. According to the results, the peak concentration computed by Telemac2D is much lower than the one calculated from Mike 21 or Mike 21 FM. In addition, the decaying aspect appears different in the Telemac2D model. These facts can be explained by the different equations used to model the pollutant transport.

Groundwater Modeling for a Decision Support System: The Lower Var Valley, Southeastern France

Groundwater modeling is an efficient tool for the groundwater management. The accuracy of the groundwater model output depends on both quantity and quality of the input data. In many areas, the data scarcity is often mentioned as a common problem of the model setup. Hence, one of the most important issues in groundwater modeling is to find an approach to build valid and operational models with limited data sets, so that the model is able to provide reliable simulation results that can be applied in the decision-making process. In the current project, a groundwater model is developed on the lower Var river valley. Some simplifications and assumptions are made in order to adapt to data scarcity. The model has been validated with a simulation of 3 years, which contains an extreme flood event and several dry periods. The average Nash coefficient for the 6 points is 0.74 and the average value of the mean absolute error is 0.21 m. The model evaluation indicated that the simplifications and assumptions are able to provide relevant results. This numerical model is therefore implemented into a decision support system for the groundwater management in the lower Var river valley, and the simulated results may help the decision-makers to have a better understanding of the behavior of the aquifer during extreme hydrological events.

Analysis of Flood and Dry Threshold Definition in Two-Dimensional Hydrodynamic Flood Modeling Tools

Extreme hydrological events are more and more frequent due to the ongoing climatic variations. Indeed, flash flood events are more intense and drought periods are increasing significantly. In the meantime, cities are expanding worldwide, concentrating in vulnerable areas, population, and economical assets. With the concern to protect their growing urbanized areas, municipalities tend to use new decision support tools in order to forecast extreme events. These tools include numerical modeling tools which represent the reality by simulating hydrodynamic processes. When flooding on dry land is the issue, modeling objectives clearly focus on the fluid dynamics, thus on the determination of the flooding front. This means that the characterization of the flood extent and its dynamics are directly related to the model definition of wetting and drying areas. With the goal of improving the accuracy of the modeled results, numerical flood and dry transitions should be closer to the reality. The French Riviera is typically an area of strong economic expansion. Furthermore, with its Mediterranean climate, this location faces flash floods and drought periods. In order to prevent the consequences of these extreme events, the local authorities are managing two projects within the French Riviera related to (1) fluvial modeling on the lower Var river catchment and (2) urban stormwater management in subcatchments of Nice city. For partnership purposes, the two-dimensional (2D) hydraulic modeling tools Mike 21 and Mike 21FM (DHI) are used for both research works. These hydraulic software tools have been developed to model 2D free surface flow using the 2D Shallow Water Equations (SWEs) and require the definition of flood and dry thresholds to compute the simulated results. In both cases, issues regarding the choice of the thresholds’ values have been encountered leading to model instabilities or impacting significantly the results. Only few publications are dealing with this topic in the literature and there is a clear need for more investigation. This chapter presents the method followed to answer the question: how to choose the correct value for flooding and drying depth parameters in Mike 21 and in Mike 21FM software tools in case of urban flood, fluvial flood, and drought event? Several scenarios will be tested on theoretical cases and the results will be analyzed in order to conclude on the impact of the flood and dry thresholds definition on the model results.

Water planning in a mixed land use Mediterranean area: point-source abstraction and pollution scenarios by a numerical model of varying stream-aquifer regime

Integrated hydrodynamic modelling is an efficient approach for making semi-quantitative scenarios reliable enough for groundwater management, provided that the numerical simulations are from a validated model. The model set-up, however, involves many inputs due to the complexity of both the hydrological system and the land use. The case study of a Mediterranean alluvial unconfined aquifer in the lower Var valley (Southern France) is useful to test a method to estimate lacking data on water abstraction by small farms in urban context. With this estimation of the undocumented pumping volumes, and after calibration of the exchange parameters of the stream-aquifer system with the help of a river model, the groundwater flow model shows a high goodness of fit with the measured potentiometric levels. The consistency between simulated results and real behaviour of the system, with regard to the observed effects of lowering weirs and previously published hydrochemistry data, confirms reliability of the groundwater flow model. On the other hand, accuracy of the transport model output may be influenced by many parameters, many of which are not derived from field measurements. In this case study, for which river-aquifer feeding is the main control, the partition coefficient between direct recharge and runoff does not show a significant effect on the transport model output, and therefore, uncertainty of the hydrological terms such as evapotranspiration and runoff is not a first-rank issue to the pollution propagation. The simulation of pollution scenarios with the model returns expected pessimistic outputs, with regard to hazard management. The model is now ready to be used in a decision support system by the local water supply managers.