José Pedro Matos

Battle of the Water Networks II

The Battle of the Water Networks II (BWN-II) is the latest of a series of competitions related to the design and operation of water distribution systems (WDSs) undertaken within the Water Distribution Systems Analysis (WDSA) Symposium series. The BWN-II problem specification involved a broadly defined design and operation problem for an existing network that has to be upgraded for increased future demands, and the addition of a new development area. The design decisions involved addition of new and parallel pipes, storage, operational controls for pumps and valves, and sizing of backup power supply. Design criteria involved hydraulic, water quality, reliability, and environmental performance measures. Fourteen teams participated in the Battle and presented their results at the 14th Water Distribution Systems Analysis conference in Adelaide, Australia, September 2012. This paper summarizes the approaches used by the participants and the results they obtained. Given the complexity of the BWN-II problem and the innovative methods required to deal with the multiobjective, high dimensional and computationally demanding nature of the problem, this paper represents a snap-shot of state of the art methods for the design and operation of water distribution systems. A general finding of this paper is that there is benefit in using a combination of heuristic engineering experience and sophisticated optimization algorithms when tackling complex real-world water distribution system design problems

Hydrological modelling of the Zambezi River Basin taking into account floodplain behaviour by a modified reservoir approach

ABSTRACT Floodplains are regions of great interest for environmental assessment as they constitute important ecological reserves and contribute efficiently to natural flood attenuation. However, the implementation of a model describing the basic hydrological behaviour of floodplains is not an easy task due to the complexity of the processes included. Although several attempts have been made to simulate floodplain effects in global rainfall-runoff models, no satisfactory routines have been developed yet. In this study, an adapted version of the Soil and Water Assessment Tool (2009) reservoir model is proposed and applied to the Zambezi Basin at daily time step with the intention of adequately modelling floodplain behaviour. The model separates the outflow of the reservoir simulating the floodplain into main channel flow and flow over the floodplain area. The improved solution was compared with the original model regarding its potential to simulate observed discharges in terms of volume ratio, the Nash–Sutcliffe coefficient and hydrograph plots. These evaluation criteria attest, for both calibration and validation periods, that the modified model is superior to the original one for simulating the discharge downstream of large floodplains. A sensitivity analysis is carried out at two geographical levels: at the outlet of a floodplain and at the outlet of the entire basin. The results show that upper flow parameters are more sensitive than base flow parameters.

Hydraulic–hydrologic model for water resources management of the Zambezi basin

The paper focuses on the development of the hydraulic–hydrological model used to simulate water resources management scenarios in the Zambezi River basin. The main challenges of the implementation of the model are the scarcity of continuous reliable discharge data and the significant influence of large floodplains. The Soil and Water Assessment Tool, a semi-distributed physically based continuous time model, was chosen as simulation tool. Given the complexity and the size of the basin under study, an automated calibration procedure was applied to optimize the relative error and the volume ratio at multiple stations. Using data derived from satellite observations, the model is first stabilized during two years, then calibrated over six years and finally validated over three years. The study evidences the importance of evaluating the model at different points of the basin and the complementarities between performance indicators.

Towards Safer Data-Driven Forecasting of Extreme Streamflows

Predicting extreme events is one of the major goals of streamflow forecasting, but models that are reliable under such conditions are hard to come by. This stems in part from the fact that, in many cases, calibration is based on recorded time series that do not comprise extreme events. The problem is particularly relevant in the case of data-driven models, which are focused in this work. Based on synthetic and real world streamflow forecasting examples, two main research questions are addressed: 1) would/should the models chosen by established practice be maintained were extreme events being considered and 2) how can established practice be improved in order to reduce the risks associated with the poor forecasting of extreme events? Among the data-driven models employed in streamflow forecasting, Support Vector Regression (SVR) has earned the researchers’ interest due to its good comparative performance. The present contribution builds upon the theory underlying this model in order to illustrate and discuss its tendency to predictably underestimate extreme flood peaks, raising awareness to the obvious risks that entails. While focusing on SVR, the work highlights dangers potentially present in other non-linear regularized models. The results clearly show that, under certain conditions, established practices for validation and choice may fail to identify the best models for predicting extreme streamflow events. Also, the paper puts forward practical recommendations that may help avoiding potential problems, namely: establishing up to what return period does the model maintain good performances; privileging small λ hyperparameters in Radial Basis Function (RBF) SVR models; preferring linear models when their validation performances are similar to those of non-linear models; and making use of predictions made by more than one type of data-driven model.