Influence of the river mouth geometry on the morphological evolution of river mouth bars: importance of water intake angle and basin bottom slope

Alfonso M Jiménez Robles, Miguel Ortega Sánchez, Miguel Ángel Losada Rodríguez

Friday 3 july 2015

13:30 - 13:45h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 16B. Sediment - Transport

Sediment delivery from rivers to open sea is the fundamental transfer mechanism for continental sedimentation with implication for many social, economic and ecological activities. Many estuaries in southern Spain are having problems due to strong sedimentation both at the navigation channel and at the river mouth, forcing to periodic dredging operations to maintain the inlet depth. Hence, it is still necessary to better understand the processes that govern the formation of mouth bars in front of rivers debouching into the sea, since they play a key role for the delta and coastline configuration. Although many works during last decades analyzed the effects of factors such as tides, wind waves or sediment properties, the control that the geometrical configuration of the river mouth exerts on the sedimentary processes remains unclear. In this work, extensive numerical simulations have been performed using Delft3D, a coupled hydrodynamic and morphodynamic numerical model, to simulate the processes of river mouth bar formation within a sheltered bay in the absence of tides and waves. Keeping all other factors constant, we find that varying the water intake angle and the receiving basin bottom slope, the behaviour of the turbulent jet is modified by changing its direction, spreading rate and stability. This change in the hydrodynamic conditions has significant consequences in the configuration of the river mouth bar. From the numerical results we establish a theoretical framework for the specific morphology of the mouth bar as a function of the river outlet geometry. Hence, our results highlight the importance of this outlet geometry in the morphodynamic evolution of river mouths and should be considered for properly designing managing strategies.