Author(s): Nilson Garcia Ramos; Samuel Quisca

Linked Author(s): Samuel Quisca

Keywords: DCP; Transient flows; Friction factor; General scour; Central and lateral bars

Abstract: The objective is to develop a numerical modeling of 2D transient flows in thick sediment beds, considering friction coefficients variable in space and time. The specialized literature review reports that Graf and Song (1995) analyze non-uniform bottom shear stress in stationary flow in open channels by three methods. The friction velocity in transient flow reaches its maximum value in the ascending branch of the hydrograph. Haizhou and Graf (1993) present a study on the friction factor in transient flow on gravel beds. It is shown that for a given hydrograph, the friction velocity is generally greater on the upward branch than on the downward branch. Bathurst (1985) presents an empirical approach, which allows the calculation of the friction factor from relative submergence, observing a zone of large, medium and small roughness. The methodology of the investigation included the following aspects: Numerical experimentation is applied to the Huatocay Sector of the Chillón River. The final cross section is a trapezoidal channel type with a slope and uniform bed. Topographical survey at the beginning and end of the transit of the hydrograph. A program of extraction of 17 samples is made for the elaboration of the granulometric curve along the river in 2 km. Measurement of speed, water depth and flow with an ADCP corresponding to a medium and high flow. Implementation of a computational algorithm that integrates the numerical modeling of permanent flow, the elaboration of input information for the numerical modeling, the equations of variable friction factor in space and time and the general scour. The period of the numerical modeling is from 1/12/2018 to 31/5/2019 (182 days) at daily step and cell size of 0.5 m x 0.5 m. The results suggest that numerical modeling allows the study of morphological transient behavior, for values of water depth lower than 0.7 m, for higher values the numerical modeling does not allow the study of morphological transient behavior in mesoforms. The high or low variability of the friction factor with respect to the variability of the water depth in time has an inverse relationship characteristic of alluvial rivers. From the analysis it was found that the scour is intensified for low values of friction factor around 0.03. As a conclusion, the numerical modeling of 2D transient flows in thick sediment beds, considering friction coefficients variable in space and time, allowed capturing morphological changes, such as central and lateral bars for a range of water depth. Acceptable results are obtained in the vertical deformation of the bed with thick sediments for water depths less than 1.13 m.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022601

Year: 2022