Fabián Rivera-Trejo

The 2007 flood in Tabasco, Mexico: an integral analysis of a devastating phenomenon

A markedly intense rain fell on southeastern Mexico during the period of 29 October–1 November 2007. As a result, the state of Tabasco recorded the gravest flood in the last 50 years. A reconstruction of the event is presented, including the identification of the factors that aggravated the sequels, and a discussion of the actions that were carried out to evaluate the flooding. The phenomenon consisted of a succession of rains in the region, including 3 days of continuous rain with over 403 mm d−1. The operation of a system of dams, the saturation of the soil, and runoff times below 16 h were the factors that generated the catastrophe, in synergy with the meteorological phenomenon. The analysis presented here will aid in understanding the development of the phenomenon in an integral way, and in establishing the minimum procedures to be followed to evaluate similar events in other regions where, as in Mexico, one does not have timely access to information. In the case of this disaster, for example, different versions of the causes of the flood continued to circulate 6 months after it took place, some lacking technical bases and some access-restricted. However, the information generated provided the academic community and state officials with a reference on which to evaluate the event. This analysis also makes a contribution by placing emphasis on the need to establish non-structural mitigation measures such as future urban growth and regulation plans and future early warning systems against flooding, monitoring the variables that were analysed and generating products useful to the decision-makers involved in civil protection systems and in carrying out preventive measures to mitigate the effects of extreme events.

Secondary currents: Measurement and analysis

Fluid 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 the so-called secondary velocities, which are flows formed by the presence of unequal forces between a hydrostatic pressure gradient and centrifugal forces, or by shear stresses at the joining of two flows. In 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 currents is important for the reason that flow behavior is a function of the magnitude of these currents; 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 acoustic recorders. A second objective was to draw the secondary velocities and to show the rotation flow