Author(s): David Lopez Gomez; Miguel De Blas Moncalvillo; Angel Gasso Sanchez

Linked Author(s): David López Gómez, Miguel de Blas Moncalvillo

Keywords: Reservoir sedimentation; Floods; Numerical simulation

Abstract: Andújar sits on the right bank of Guadalquivir River. Its origin predates the arrival of Romans. During the 20th century, small hydroelectric waterfalls were built in its surroundings. The closest is the Marmolejo reservoir, 16 km downstream. It is a concrete dam regulated with gates, which raises about 20 m the water level surface. It had a capacity of 11.4 hm3. The level of exploitation places the reservoir tail in the Roman bridge of Andújar. In the 90s there were major overflows in the Guadalquivir valley, which came to affect Andújar with flows that traditionally did not generate problems. The Guadalquivir Hydrographic Confederation, as the competent hydraulic Administration, carried out a series of actions, such as longitudinal weirs and dredging, with little success. CEDEX began to collaborate in this study, after the April 2013 flooding episode. A new hydrodynamic two-dimensional modeling was carried out with Iber, taking into account the riverbed sedimentary evolution thanks to the available bathymetries of 1962, 1997, 2001, and 2014. In 1997 the reservoir had lost 81% of its capacity, and that the accumulated sediment considerably raised the flood levels. Therefore, Andújar's first defense measure against flooding is to control the reservoir sedimentation level. It was found that the avenues of 2010 and 2013 had dragged a large amount of sediment, leaving the capacity at 65% of the initial one. This shows that the sedimentation process is reversible. To analyze the sedimentation process of the reservoir, six other bathymetries have been obtained since 2018. They have been carried out strategically, before and after flood events, or dry periods, in which the reservoir level is maintained elevated. Suspended sediment gauging field campaigns are also being carried out. It has been found that the rates are very high mainly due to high soil erosion. The reservoir basin has an area of 313,200 ha, of which 58% are olive groves. ENDESA, the reservoir owner, has collaborated in these works. Currently are being numerically simulated the sedimentation processes with the Ariathurai&Arulanandam model (1978) for cohesive material. The evolution of the reservoir has been simulated in the periods between the different bathymetries, which has let to calibrate shear stresses of erosion and sedimentation. The reservoir sedimentation is highly conditioned by its exploitation, during dry periods, which can sometimes last for years, the reservoir level remains at the exploitation level, favoring sedimentation. During flood events, a large amount of sediment is dragged. With the numerical model, the best management strategies are being studied that allow maintaining the profitability of the hydroelectric plant compatible with maintaining low sedimentation levels that guarantee the safety of Andújar against floods.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221692

Year: 2022