Jordi Prats

Genetic programming and standardization in water temperature modelling

An application of Genetic Programming (an evolutionary computational tool) without and with standardization data is presented with the aim of modeling the behavior of the water temperature in a river in terms of meteorological variables that are easily measured, to explore their explanatory power and to emphasize the utility of the standardization of variables in order to reduce the effect of those with large variance. Recorded data corresponding to the water temperature behavior at the Ebro River, Spain, are used as analysis case, showing a performance improvement on the developed model when data are standardized. This improvement is reflected in a reduction of the mean square error. Finally, the models obtained in this document were applied to estimate the water temperature in 2004, in order to provide evidence about their applicability to forecasting purposes.

Mixing dynamics at the confluence of two large rivers undergoing weak density variations

Simulations of tracer experiments conducted with a three-dimensional primitive-equation hydrodynamic and transport model are used to understand the processes controlling the rate of mixing between two rivers (Ebro and Segre), with distinct physical and chemical properties, at their confluence, upstream of a meandering reservoir (Ribarroja reservoir). Mixing rates downstream of the confluence are subject to hourly scale oscillations, driven partly by changes in inflow densities and also as a result of turbulent eddies that develop within the shear layer between the confluent rivers and near a dead zone located downstream of the confluence. Even though density contrasts are low—at most O(10−1) kg m−3 difference among sources—and almost negligible from a dynamic point of view—compared with inertial forces—they are important for mixing. Mixing rates between the confluent streams under weakly buoyant conditions can be of up to 40% larger than those occurring under neutrally buoyant conditions. The buoyancy effects on mixing rates are interpreted as the result of changes in the contact area available for mixing (distortion of the mixing layer). For strong density contrasts, though, when the contact area between the streams becomes nearly horizontal, larger density differences between streams will lead to weaker mixing rates, as a result of the stabilizing effect of vertical density gradients.

Aportaciones de la limnología a la gestión de embalses

This article describes some of the contributions of limnology to reservoir management according to a literature review and the authors’ experience. After explaining the main challenges that reservoir managers have to face, some examples of management measures are given and the need to take into account the different management scales are underlined, whether temporal (multiannual, annual, daily) or spatial (catchment, river reach, reservoir or reservoir chain). The available methods for the study of reservoir ecological status are also reviewed.