Abstract
The vast majority of reservoirs, although built for irrigation and water supply purposes, are also used as regulation tools during floods in river basins. Thus, the selection of the most suitable model when facing the simulation of a flood wave in a combination of river reach and reservoir is not direct and frequently some analysis of the proper system of equations and the number of solved flow velocity components is needed. In this work, a stretch of the Ebro River (Spain), which is the biggest river in Spain, is simulated solving the Shallow Water Equations (SWE). The simulation model covers the area of river between the city of Zaragoza and the Mequinenza dam. The domain encompasses 721.92 km2 with 221 km of river bed, of which the last 75 km belong to the Mequinenza reservoir. The results obtained from a one-dimensional (1D) model are validated comparing with those provided by a two-dimensional (2D) model based on the same numerical scheme and with measurements. The 1D modelling loses the detail of the floodplain, but nevertheless the computational consumption is much lower compared to the 2D model with a permissible loss of accuracy. Additionally, the particular nature of this reservoir might turn the 1D model into a more suitable option. An alternative technique is applied in order to model the reservoir globally by means of a volume balance (0D) model, coupled to the 1D model of the river (1D-0D model). The results obtained are similar to those provided by the full 1D model with an improvement on computational time. Finally, an automatic regulation is implemented by means of a Proportional-Integral-Derivative (PID) algorithm and tested in both the full 1D model and the 1D-0D model. The results show that the coupled model behaves correctly even when controlled by the automatic algorithm.
Highlights
As extreme phenomena, flood events raise concern among governments, institutions and general society
The discretisation of the full 1D model is the same used in the former subsection, while the 1D-0D model is characterised by a partial discretisation of the domain embedding the reservoir zone within the outlet boundary condition
The performance of several modelling approaches has been compared in order to evaluate their results and computational requirements in a transient river flow event in a reach of the Ebro river (Spain) that includes a reservoir covering a large area
Summary
Flood events raise concern among governments, institutions and general society. To ensure enough water supply for agricultural activities or energy production, and as hydraulic structures for discharge adjustment and control during flood events Basin authorities manage their operation focusing on available space in the reservoir, maximum acceptable downstream discharges, and peak arrival times. In this context, the development of predictive tools that provide information about the temporal and spatial evolution of water level and discharge along a river during flood events can help to quantify the damage caused and has been widely addressed in last decades [3]. Due to the particularity of the simulated section and the Mequinenza reservoir, which transports flood waves almost immediately, an aggregated alternative technique is applied This approach formulates the reservoir flow globally by means of a volume balance model. Our focus is on checking if the results obtained are similar to those provided by the fully
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