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RESUMENque describen la distribución de velocidades. Algunos fenómenos naturales que presentan estas funciones son los huracanes, los cuales son generados por las diferencias de presión; los ciclones, cuya fuente primaria de energía es el gradiente horizontal de temperatura, y los remolinos, que están ligados al gradiente de presión hidrostático. En el caso particular de los remolinos, éstos generan velocidades secundarias, las cuales son fenómeno también se observa en tornados, donde la fuerza centrífuga es mayor en la parte superior y luego va disminuyendo hacia el fondo, mientras que en los ríos se detecta particularmente en curvas y uniones -terización es fundamental. El objetivo de este estudio fue estimar las velocidades secundarias en la unión de dos ríos, a partir de mediciones de campo realizadas con medidores acústicos Doppler. Un segundo objetivo lo que su entendimiento ayudará a pronosticar cambios morfológicos en los ríos. ABSTRACTFluid dynamics has the purpose of understanding the movement of liquids and gases by functions that describe the distribution of velocities. Some natural phenomena that present these functions are hurricanes, generated by pressure differences; cyclones, developed by the horizontal temperature gradient; and eddies, associated with a hydrostatic pressure gradient. In the particular case of eddies, they generate addition, this phenomenon is observed in tornados, where the centrifugal force is greater in the upper layer and decreases towards the bottom, whereas the pressure gradient moves from a high to a low pressure; while in rivers it is detected particularly in bends or joins. Understanding the development of secondary hence their characterization is fundamental. The objective of this study was to obtain the secondary velocities developed as an effect of the union of two water currents, based on data acquired from Doppler Atmósfera 29 (1), 23-34 (2016(1), 23-34 ( ) doi: 10.20937/ATM.2016 © 2016 Universidad Nacional Autónoma de México, Centro de Ciencias de la Atmósfera. This is an open access article under the CC BY-NC-ND License (http://creativecommons.org/licenses/by-nc-nd/4.0/). 24 G. A. Priego-Hernández and F. Rivera-Trejo effect, a kind of results that are difficult to obtain in any other way. The flow mechanisms are related with erosion and sedimentation processes; therefore, understanding them might help to evaluate and predict morphological changes in rivers.

Flow discharge and hydrodynamic field measurements are essential data for understanding aquatic ecosystems. The objective of this study was to compare the use of three Acoustic Doppler Current Profilers (ADCPs) in measuring flow discharge and hydrodynamics in the Carrizal River located in southeastern Mexico. The evaluated ADCPs operate on frequencies of 2 000 kHz, 1 500 kHz and 600 kHz. The measurements were carried out in a 100-m-wide cross section, five times each for each ADCP, within an estimated time of 5 min. The obtained data were: 1) flow velocity components; 2) depth; 3) transversal distance between each vector; 4) total distance of the cross section and; 5) geographic position of each vector. Tecplot® graphics were made with the collected information.The results showed that velocity magnitudes were low in bank areas, while high in the center. For a 5-m depth range, the 2 000-kHz ADCP keeps a more homogenous velocity distribution in comparison with the other equipment. The results showed that discharge measurements varied by no more than 5% among ADCPs. It is concluded that the most important variable in choosing an ADCP for a hydrodynamic study is its operating frequency

Aim of the studyRecently, the use of acoustic Doppler current profilers (ADCP) gains in popularity. Considering the use of various equipment, a question arises whether there are any differences in measuring with ADCP that works at different frequencies. The aim of this study was to compare and evaluate three ADCPs operating at different frequencies: 2,000 kHz, 1,500 kHz, and 600 kHz under field conditions. Material and methodsFollowing parameters were applied for a transverse section of 100 m in width and 7 m in depth: (1) components of velocity flow, (2) depth, (3) transverse distance among vectors, (4) total distance and (5) geographic position of each vector. Results and conclusionsThe results showed that velocity magnitudes were low in margin areas, while high in the center. In comparison with other devices the 2,000 kHz ADCP keeps a homogeneous velocity distribution up to 5.0 m in depth. Also, the statistical and graphic analysis demonstrated that flow measurements did not differ by more than 5%. Nevertheless, the review of velocities showed significant differences between ADCPs. High frequency means more detailed data, but less deep range, particularity in zones with upper sediments concentration. Low frequency means less detailed data, but deeper range. Furthermore, our findings suggest that measurements performed in rivers provide results, which sometimes are entirely different from results obtained in laboratory.