Flood estimation is often required in hydrologic design and has important economic significance. For example, in Australia, the annual spending on infrastructure requiring flood estimation is of the order of $650 million ARR (I.E. Aust., 1998). Rainfall-based flood estimation techniques are most commonly adopted in practice. These require several inputs to convert design rainfalls to design floods. Of all the inputs, loss is an important one and defined as the amount of precipitation that does not appear as direct runoff. The concept of loss includes moisture intercepted by vegetation, infiltration into the soil, retention on the surface, evaporation and loss through the streambed and banks. As these loss components are dependent on topography, soils, vegetation and climate, the loss exhibits a high degree of temporal and spatial variability during the rainfall event. In design flood estimation, the simplified lumped conceptual loss models were used because of their simplicity and ability to approximate catchment runoff behaviour. In Australia, the most commonly adopted conceptual loss model is the initial losscontinuing loss model. For a specific part of the catchment, the initial loss occurs prior to the commencement of surface runoff, and can be considered to be composed of the interception loss, depression storage and infiltration that occur before the soil surface saturates. ARR (I. E. Aust., 1998) mentioned that the continuing loss is the average rate of loss throughout the remainder of the storm. At present, there is inadequate information on design losses in most parts of Australia and this is one of the greatest weaknesses in Australian flood hydrology. Currently recommended design losses are not compatible with design rainfall information in Australian Rainfall and Runoff. Also design losses for observed storms show a wide variability and it is always difficult to select an appropriate value of loss from this wide range for a particular application. Despite the wide variability of loss values, in the widely used Design Event Approach, a single value of initial and continuing losses is adopted. Because of the non-linearity in the rainfall-runoff process, this is likely to introduce a high degree of uncertainty and possible bias in the resulting flood estimates. In contrast, the Joint Probability Approach can consider probability-distributed losses in flood estimation. In ARR (I. E. Aust., 1998) it is recommended to use a constant continuing loss value in rainfall events. In this research it was observed that the continuing loss values in the rainfall events were not constant, rather than it decays with the duration of the rainfall event. The derived loss values from the 969 rainfall and streamflow events of Queensland catchments would provide better flood estimation than the recommended design loss values in ARR (I. E. Aust., 1998). In this research, both the initial and continuing losses were computed using IL-CL loss model and a single median loss value was used to estimate flood using Design Event Approach. Again both the initial and continuing losses were considered to be random variables and their probability distribution functions were determined. Hence, the research showed that the probability distributed loss values can be used for Queensland catchments in near future for better flood estimate. The research hypothesis tested was whether the new loss value for Queensland catchments provides significant improvement in design flood estimation. A total of 48 catchments, 82 pluviograph stations and 24 daily rainfall stations were selected from all over Queensland to test the research hypothesis. The research improved the recommended design loss values that will result in more precise design flood estimates. This will ultimately save millions of dollars in the construction of hydraulic infrastructures.

L’objectif de notre thèse est de comprendre et d’expliquer les modes d’intégration des systèmes comptables des entreprises à partir de quatre cas (deux grandes entreprises et deux entreprises moyennes). Nous nous sommes appuyés sur la théorie de la différenciation-intégration de Lawrence et Lorsch (1967) pour interpréter les situations d’intégration étudiées. Cette théorie montre que les entreprises ayant des structures très différenciées disposent des mécanismes d’intégration sophistiqués tandis que celles dont les structures sont peu différenciées ont des mécanismes de coordination rudimentaires. Nous avons également mobilisé l’approche événementielle et multidimensionnelle de Sorter (1969) qui propose un cadre théorique de l’intégration informatico-comptable. Les progiciels ERP constituent une application très concrète de cette approche. Notre analyse qualitative de quatre cas en termes de similitudes et de différences, appuyée sur la théorie de la différenciation-intégration, a permis d’expliquer les situations d’intégration des sous-systèmes comptables observées mais aussi de montrer la pertinence de l’approche événementielle, comme cadre de conception du système d’information de structures diversifiées et différenciées. Nos résultats montrent, à l’instar de Lawrence et Lorsch, qu’il existe des modes différents d’intégration des systèmes comptables adaptés à des contextes différents. Nous avons ébauché une typologie de quatre configurations types des systèmes comptables (quatre situations d’intégration-différenciation) : (1) Système classique bidimensionnel, (2) Système quasi-intégré centralisé, (3) Système intégré, (4) Système multidimensionnel. La stratégie et la taille paraissent être, au-delà de toutes autres considérations, les principaux déterminants de l’intégration comptable ; viennent ensuite, l’environnement et certains autres éléments du contexte tels que la structure de gestion et le système de contrôle. Cependant, l’impact de la taille diffère d’une entreprise à l’autre. Lorsque la taille est combinée à une stratégie de diversification (et par extension à des environnements variés et dynamiques) son effet différenciateur sur l’organisation (et le système comptable) est très important, ce qui nécessite des mécanismes compensateurs d’intégration développés. Les deux entreprises diversifiées (POULINA et MEDDEB) ont mis en place un système comptable intégré voire multidimensionnel pour maitriser leurs sous-systèmes différenciés. Lorsque la taille est la conséquence d’un simple développement d’une activité unique (monoactivité) son effet différenciateur-intégrateur sur l’organisation et le système comptable est moins important. Les deux entreprises ayant des activités et des structures homogènes (SONEDE et SME) se sont contentées d’un système comptable peu intégré voire bidimensionnel. / The objective of this thesis is to understand and explain the modes of integration of accounting systems of companies from four cases (two big and two medium-sized enterprises). We relied on the theory of differentiation-integration of Lawrence and Lorsch (1967) to interpret the studied integration situations. This theory shows that companies with very different structures have sophisticated mechanisms for integration while those whose structures are poorly differentiated have rudimentary coordination mechanisms. We have also mobilized the event and multidimensional approach of Sorter (1969) who proposes a theoretical framework for the accountant integration. The ERP is a highly practical application of this approach.Our qualitative analysis of four cases study in terms of similarities and differences, supported on the theory of the differentiation-integration, helped to explain the observed situations of integration of accounting subsystems but also to show the relevance of the event-based approach, as part of system design information structures diversified and differentiated. Our results show, like Lawrence and Lorsch, that there are different modes of integration of accounting systems tailored to different contexts. We have developed a typology consisting of four configurations of accounting systems (four situations integration-differentiation): (1) Conventional two-dimensional system, (2) Quasi-integrated centralized system, (3) Integrated system,(4),Multidimensional,system.Strategy and size appear to be, beyond all other considerations, the main determinants of the accounting, followed, environment and other elements of the context of the accounting system such as the management structure and system management control. However, the impact of the size differs from one company to another. When the size is combined with a strategy of diversification (and by extension to various and dynamic environments) its differentiating effect on the organization (and the accounting system) is very important, requiring developed integration compensatory mechanisms. Both diversified firms (POULINA and MEDDEB) have implemented an integrated accounting system to unify their subsystems differentiated. When the size is the result of a simple development of a single activity (monoactivity) its integrator-differentiator effect on the organization and the accounting system is less important. Companies with activities and homogeneous structures (SONEDE and SME) have been content to a poorly integrated accounting system or two-dimensional.