Author(s): Juan Antonio Garcia-Aragon; Pedro Omar Valencia-Aguilar; Humberto Salinas-Tapia; Klever Izquierdo Ayala

Linked Author(s): Juan Antonio Garcia-Aragon

Keywords: Key words: suspended sediments; Fractal dimension; PTV; Holography; Usumacinta river

Abstract: The Usumacinta river has the largest flow rate in México, average 3100 m3/s at its mouth. Previous studies have shown that a large part of the suspended sediments at Chichicastle station located in the Usumacinta river 25 km upstream the confluence with Grijalva river and at los Idolos station in the Grijalva river upstream their confluence, are fines prone to flocculate (Izquierdo et al. 2021). In order to verify the suspended sediments transport a sampling campaign was developed during the years 2016 and 2017. The suspended sediment samples were analyzed by optical methods, Particle tracking Velocimetry(PTV) in a rotating annular flume able to perform large duration experiments in order to obtain a steady flocculation state and in a glass column using Digital Holography. The main parameter needed to validate a settling velocity model for the aggregates is the fractal dimension (F), that depends not only on aggregates sizes and density but also on hydrodynamic conditions. The experiments consisted to feed the rotating annular flume with sediments of each river and visualize the floc formation during experiments of more than two hours duration. The constant shear rate was controlled by the rotation speed of the flume and fixed according to the average shear rate of the rivers measured in the field. Each five minutes images of the flocs were taken with CCD cameras in a flume section of the channel illuminated by a laser sheet and analyzed with a PTV software in order to obtain the sizes of the aggregates (D) . when the sizes obtained a value that didn´t change with time, the experiment stopped. Samples of the aggregates formed were then introduced in a 1.3 m high glass settling column where at a distance enough to attain the terminal velocity the settling velocity of aggregates was measured. High resolution holograms of the flocs were also obtained and by means of the box counting method the fractal dimension of the aggregates was obtained. Results show that depending on the season where the sampling was taken (low flow or high flow) and the river shear rate, the relationship D vs. F varied considerably. It was concluded that higher turbulence in the Usumacinta river than in the Grijalva river affected the size of aggregates and its fractal dimension. Key words: suspended sediments, fractal dimension, PTV, Holography, Usumacinta river.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221194

Year: 2022