ANDRIAZAFIMAHAZO

The sustainable management of the Lake Alaotra-Mangoro system, a vital ecological and socio-economic resource in eastern Madagascar, is severely threatenedby rapid anthropogenic pressures and climate change. This study aimed to characterize the complex lacustrine and fluvial dynamics and predict the system'sbehavior to support informed conservation and planning efforts. We employed a rigorous two-dimensional (2D) hydrodynamic modeling approach usingtheInternational River Interface Cooperative (IRIC) software. The model integrated comprehensive topographical, hydrological, and meteorological data to simulateflow behavior over a transient event. The analysis revealed critical insights into the system's vulnerability. Simulation outputs accurately defined areas susceptibleto localized flooding and quantified seasonal water level variations. Hydrodynamic analysis confirmed complex flow interactions, including the concentrationof maximum velocity and depth within the channel's thalweg and the presence of a downstream backwater effect indicated by an inverse water surface elevationgradient. Furthermore, cross-sectional profiles validated the model's ability to capture asymmetrical channel geometry, which is crucial for bank erosionriskassessment. Supporting land-use analysis highlighted significant land degradation and marshland loss, exacerbating the hydrological response. In conclusion, theIRIC model provides robust predictive capability for evaluating the cumulative impacts of environmental change. A primary recommendation is the urgent needto strengthen the local hydrometeorological monitoring network to enhance data quality and model reliability. The findings facilitate the proactive planningof adaptive strategies, including the construction of protective dikes, targeted reforestation, and essential agricultural adjustments, ensuring the long-termresilienceof the Lake Alaotra watershed. Keywords: Lake Alaotra, Hydrodynamic Modeling, IRIC, Flood Risk, Land Use Change.

The knowledge of the local solar radiation characteristics is indispensable in the survey of any system exploiting solar energy in any location. The author is particularly interested by the global solar radiance upon tilted surface per time unit to help operators using solar energy in their work. The target is, among others, helping solar drying operators that need while tuning drying system the knowledge of the global solar radiation that could be received on inclined solar captors in implantation site. The aim of this paper is to use neural network method to search for solar radiation upon a tilted surface. Multilayered neural networks (MNN) trained by gradient back-propagation are used to determine numeric values of monthly means and hourly variations of the global solar radiation upon a titled surface per time unit. The numerical calculations are made with the geographical and meteorological parameters (latitude, longitude and clearness index) of the location of Fianarantsoa, Madagascar.

This survey consists in determining the drying speed in thin layer of non shelled shrimp with the help of a climatic chamber. The experiences made permitted to elaborate a universal model. The considered parameters are the drying air temperature, the product absolute humidity as well as the drying air relative humidity and its speed. The adsorption curve of the product is also established. The model is validated through confrontation between experimental and theoretical results.

Cet article consiste à présenter un autre modèle appliqué à la détermination de la vitesse de séchage du produit hygroscopique. Ce modèle est obtenu par la ressemblance entre la cinétique chimique et la cinétique de séchage. L’intérêt de ce présent travail c’est de trouver un modèle simple, facile et fiable pour caractériser la vitesse de séchage du produit. En adoptant ce modèle, nous avons obtenu un autre modèle mathématique de la cinétique de séchage du maïs. Nous validons le modèle adopté par rapport à l’autre modèle, nous observons que les résultats sont en accords. Mots-clés : Modèle, vitesse séchage, cinétique de séchage, produits hygroscopiques, maïs.