Claude Marche

Experimental Investigation of the Hydraulic Erosion of Noncohesive Compacted Soils

This paper presents the results of a laboratory investigation whose purpose was to evaluate the effects of compaction on the erodibility of cohesionless soils. By means of a recently developed flume experiment, sediment erosion rates and incipient motion, as a function of shear stress, average velocity, and dry density, have been determined for three compacted sand and gravel mixtures. A preliminary comparison of the incipient motion values shows that granular soils compacted at the Proctor optimum have a higher resistance to free surface flow erosion than those compacted at lower and higher densities. This leads one to infer that the Proctor optimum, generally used as a standard for construction, might also be an optimum for hydraulic resistance and stability. Additional comparison of the experimental data with two commonly used incipient motion criteria also suggests that Yang’s criterion is a better predictor of soil detachment than the Shields-Yalin criterion.

An expert system to assist designers of hydraulic systems

Abstract An engineer in charge of the design of a major hydraulic project feels insecure because of the complexity and diversity of the fields involved. As a result, he has to depend on experts in each field and loses some control of the progress of his project. In addition, due to recent developments in Computer Aided Design (CAD), more and more specialized and easy to use mathematical models are available to him and the risk of his misusing them is increased. This paper describes the problem which arises within the specific field of open channel dynamics, and presents an expert system built to assist the engineer in his design. The system has three levels of assistance which provide help in problem definition, resolution strategy and selection of the appropriate analysis scheme searching through uncertain and sometimes conflicting data. An example will help illustrate the type of assistance in solving problems in the field of applied hydraulics, and show the various specialized topics used to build the present version of the knowledge base.

Dam Failure Risk: Its Definition and Impact on Safety Assessment of Dam Structures

The dam structure is typical of facilities which are built to withstand unfavorable natural conditions. Of the 30 000 recorded dams worldwide, only a few are reported in any given year to fail. Structures must now meet design standards intended to make dams withstand extreme phenomena and disasters as damaging as maximum probable flood (MPF). New facilities are therefore safer. The existing facilities also have to conform to the new standards. Risk analysis is a new approach that has become more frequently used the last few years to assess the safety of dam facilities and to establish a priority classification which would make these facilities conform to the recently established standards. The failure of the dyke Cut-away in Saguenay (Canada), the study case referred to in this paper, shows the limits of conventional risk analysis methods. The latter would not clearly detect the dyke’s critical state; other methods of risk qualification are therefore proposed. These methods disclose supplementary aspects of the safety of the construction but they do not necessarily integrate hazards and consequences. The application of these methods to the identified objectives in our paper gives a synthesis of the risks posed by an unsafe construction. When viewed jointly, the methods and synthesis suggest the most effective ways to minimize those risks.

Formulation de fonctions de transfert de débit entre les aménagements hydroélectriques de la rivière Péribonka

Une methode pour representer les comportements dynamiques d’une riviere par des fonctions de transfert fiables est proposee. Elle est appliquee a la riviere Peribonka (Quebec). L’article detaille la creation de ces fonctions entre les centrales Chutes-des-Passes et Chute-du-Diable, incluant la centrale Peribonka en construction (lors de la redaction de cet article). Le logiciel FLDWAV modelise les ecoulements sous des conditions de production variees. Le modele a ete etalonne sur plusieurs saisons estivales grâce aux stations hydrometriques de la riviere Peribonka. Les multiples fonctions de transfert de debit (FTD) obtenues pour diverses conditions de debit et de niveau d’eau ont ete simplifiees en vue de leur usage en optimisation de la production. Elles ont ete validees sur chaque troncon de la riviere. Les tests montrent qu’elles respectent bien la dynamique des ecoulements en eau libre. Toutefois, l’utilisation des memes FTD n’est pas recommandable pour simuler l’ecoulement de l’eau en periode hivernale.

Method for consequence curves as applied to flood risks

This article summarises research intended to expand current study methodologies targeting flood risks with regard to specific issues and emergency preparedness requirements of municipalities. Various methods are currently available to predict the consequences of flooding risks. DOMINO is one such tool used to study flooding risks from natural events or from potential dam breaks. A complementary tool, CONSEQ, was developed to compute the impacts and present them in the form of consequence curves. This tool uses a specific method to assess all tangible and direct damages from exceptional flooding. However, intangible damages and the needs of municipalities downstream of the facility will also be taken into account. This article presents the DOMINO and CONSEQ tools as well as the methodology used to study consequences in relation to these analytical tools. It also describes the requirements of municipal emergency managers in order to draw consequence curves.

Evaluation of the overflow failure scenario and hydrograph of an embankment dam with a concrete upstream slope protection

The standard procedure in Quebec, Canada, for evaluating the failure of an embankment dam, per the Loi sur la sécurité des barrages, specifies a 30-min-long failure scenario with a breach width equal to four times the maximal height of the dam. We demonstrate a new method for evaluating the flood overtopping failure scenario for embankment dams with concrete upstream slope protection, using Toulnustouc dam for example computations. Our new methodology computes safety factors for a range of potential failure mechanisms taking into account geotechnical, hydraulic, and structural factors. We compile the results of our investigations of the various dam failure mechanisms and compare the corresponding dam failure hydrographs to the current hydrograph specified in the standard analysis procedures. Our investigations tend to invalidate the current standard procedures for evaluating the failure of rock-fill dams with concrete upstream faces, by indicating that the current standard procedures underestimate the peak failure discharge and overestimate the time to the peak discharge.

Un simulateur d'écoulement en temps réel comme aide à la prévision et à la gestion des rivières

The development of watersheds complicates the management of hydraulic facilities. Managers are facing economic and social imperatives that are potentially conflicting. Generally, their decisions are based on operational rules established by experience. However, these rules do not ensure that certain minimal conditions be respected and they do not determine future conditions for the river as a whole. Therefore, the communication of these conditions between managers of a same river is difficult. The present paper provides an approach to improve this situation. The real time simulator XSIM, with a graphical interface, has been developed in order to assist managers in control, design, analysis, and information transmission. It is designed based on an intumescence model functioning in an unsteady flow regime. It allows the managers to input the considered operations and provides them with the design conditions in a format adapted to their needs. It ensures the distribution and the availability of the results b...

Les digues fusibles, un élément de sécurité additionnelle dans un aménagement hydro-électrique

A lot of existing hydroelectric developments do not meet current spillway capacity design standards. Statistics compiled indicate this is one of the main causes of dam failure. It is not, however, necessary to continually increase discharge capacity to maintain an acceptable risk level at a given development. In hydroelectric systems with large reservoirs, the very design of the many structures controlling the reservoirs and the introduction of the concept of fuse-plug spillways offer attractive alternative solutions. The digital tools required for a real impact and risk analysis were developed. This paper describes their use in a preliminary study of the La Grande 3 reservoir in Quebec. Key words: dams, safety, failure flow.[Journal translation]

Développement et usage d'un système expert pour le choix des évacuateurs de crues

Expert systems are computer tools allowing the management of nonnumerical, qualitative knowledge. In that way, they depart from the numerical tools used for solving complex equation systems in computer assisted design. The integration of both types of tools is therefore desirable. Typically, the design of spillways involves long and tedious calculations, dependant on the type and nature of the structure. An expert system was developed to assist the design engineer in the initial and crucial task of choosing the baseline conditions. This expert system is based solely on technical criterion and integrates the knowledge of several experts in the field. A management tool for this multiple-source knowledge was therefore developed and integrated to the many design criterions. The system, currently being developed and implemented in an industry, was tested against approximately 40 worldwide existing structures. The responses, very promising, are presented with the system structure and its technical content. Key ...

An efficient finite element incompressible Navier-Stokes solver that approximates nonlinear terms with finite differences

Abstract A new method for solving the steady-state incompressible Navier-Stokes equations in primitive variable form is presented. The approach uses finite difference operators for the convective terms within the framework of a penalty finite element method. The technique is shown to be computationally very efficient. Indeed, not only does the penalty function method remove one degree of liberty per node, but also the special treatment given to the nonlinear terms yields a global coefficient matrix that is both symmetric and banded. Both storage needs and calculation time are reduced tremendously. Furthermore, for all flow cases tested, the authors have been able to reach a convergent and stable solution up to Reynolds number of the order of those normally attained by “conventional” finite element models using an identical space discretisation. Results are given for the popular benchmark problem of the driven cavity, as well as for a practical application in the Port of Montreal.