Conceptos y aplicaciones sobre flujos densos en la hidráulica de ríos

BREA, J.D.; SPALLETTI, L.A.; HOPWOOD, H.J.; SPALLETTI, P.D.

INGENIERIA DEL AGUA

Año: 2005 vol. 12 p. 189 - 200

1134-2196

Hyperconcentrated flows have been studied from different disciplines, like geology and hydraulics. Generally, the approaches for the treatment of the processes of transport by dense flows and its products in the two mentioned specialties, have followed parallel ways, being very little points of convergence. Perhaps the reasons for it can be due to that geologists insist on the products (sediments, deposits) to which lead these processes, whereas engineers have paid attention to the hydrologic and reologic questions, that is to the functioning of these mechanisms of transport in mass. In spite of the differences, the conceptual ordering between geology and the hydraulics is from interest, because it allows a better comprehension and understanding, making easier the interdisciplinary tasks in this type of problems. This comparative work between geological and hydraulic engineering concepts referred to dense flows, shows that many points in common arise, perhaps more than what could have supposed. Thus for example, the use by the hydraulic engineers of hyperconcentrated flows to denominate mud floods, mud flows and detritus flows is perfectly compatible with which it occurs in the field of geology, although the use of gravitational sediment flow or dense flow is still much more frequent as words of general reach. The differentiation between cohesive and non-cohesive dense flows that is made at the moment in geology is adaptable without difficulty to the field of engineering. The concept of mud flood used in hydraulics is similar to the one of swellings in the geologic slang. An absolute agreement exists in addition in which it talks about the use of mud flow. The point of greater divergence is related to the use of detritus flow, since while in hydraulics it is referred to a non-cohesive dense flow, in the geologic field it is oriented to characterize a cohesive dense flow. However, being so ample the universe of the presented definitions, is possible that in a certain frame, we get to agree. In fluvial hydraulics the quantification of the processes is necessary because the objective are practical engineering applications. For that reason, and always within the universe of definitions and existing classifications, the developments  based on the physics of the problem, which try to explain the behavior of dense flows from the participants forces, and that define equations to solve dynamics, are the most suitable. In that context, complex expressions which try to include the variables that affect the phenomenon based on the reologic behavior of dense flows, like which they arise from the studies of Julien, Lan, O´Brien, among others, and which allow their study with numerical modeling, have been developed. In the bibliography, from similar approaches, relations to define the different classes of hyperconcentrated flows have been developed, too. The absence of the necessary initial data and the difficulty to determine or to define them in the application of these developments, it makes difficult to use these tools, and in the engineering practice, empirical expressions are usually used. As an example, an application to the Bermejo river in the north of Argentina, appears, in which the characteristics of the phenomenon and the information available are analyzed, describing also the expressions that give the basic parameters to use in the structure design. The empiric expressions of calculation offered in the bibliography are valid applications for the conditions in that they were developed. A suitable knowledge and interpretation of the physics of the phenomenon, complemented with field data, will allow to correctly face the work project, those that anyway will be of experimental type, in natural scale.