Abstract. Le comblement et l'eutrophisation des retenues d'eau constituent des contraintes majeures pour les usages qu'en font les populations riveraines. L'étude bathymétrique a révélé une diminution moyenne de 0,116 m/an de la profondeur sur sept (07) ans. Ce niveau élevé de comblement s'explique par l'érosion des terres due à la dégradation du couvert végétal et le surpâturage. Les mesures directes de la qualité physique : le pH, la température et l'oxygène dissous avec le multi paramètre PC HORIBA WATER QUALITY CHECKER U-10; les paramètres chimiques par la méthode chromatographique ICS 1000 et de dosage de la chlorophylle a avec le spectrophotomètre DR 5000 par la Norme AFNOR T90-117 ont permis d'évaluer le risque d'eutrophisation par la grille de diagnostic d'Ifremer (2000). Les eaux sont dans un état eutrophe. Le comblement et l'eutrophisation de la retenue constituent des menaces potentielles à court terme pour la pisciculture, l'irrigation et la consommation tandis que la disponibilité quantitative de la ressource est menacée à moyen terme. Des relevés bathymétriques périodiques et des actions d'aménagement du bassin versant de la retenue sont nécessaires à la gestion intégrée de la retenue d'eau.
<p><strong>Low flows and irrigation in Mono River basin at Athi&#233;me outlet (West -Africa)</strong></p><p><sup>1</sup>Coffi Justin Noumon, <sup>2</sup>Domiho Japhet Kodja, <sup>2</sup>Ernest Amoussou,<sup> 1</sup>Luc O. Sintondji,<sup>1 </sup>Euloge K. Agbossou.</p><p><sup>1</sup>Laboratoire d&#8217;Hydraulique et de Ma&#238;trise de l&#8217;Eau (LHME), Institut National de l&#8217;Eau, Universit&#233; d&#8217;Abomey Calavi 01 BP 526 Cotonou (B&#233;nin).</p><p><sup>2</sup>Laboratoire Pierre Pagney Climat Eau Ecosyst&#232;mes et D&#233;veloppement (LACEEDE), Institut de G&#233;ographie et Am&#233;nagement du Territoire et de l&#8217;Environnement, Universit&#233; d&#8217;Abomey Calavi 01 BP 526 Cotonou (B&#233;nin).</p><p>Auteur correspondant: <sup>1</sup>Coffi Justin NOUMON (justinoum2001@yahoo.fr)</p><p><strong><em>Abstract</em></strong></p><p>The basic goal of this survey is the assessment of water resources of Mono River at Athi&#233;m&#233; outlet in low flow period where it availability for agriculture uses is problematic. Therefore, daily data (precipitations, ETP, flows) from 1971 to 2016 are collected. It allows to simulate low discharge with GR4J model. Field survey permits the characterization of agriculture uses and the assessment of water requirement for irrigation. Low flows of Mono River at Athi&#233;m&#233; outlet simulation with GR4J showed a good performance of the model to simulate low discharges before the construction of Nangb&#233;to dam in 1988. Criteria values of Nash-Sutcliffe before dam establishment are 69% (calibration) and 71% (validation). The performance of the model is less for the period after the dam establishment: The change in the hydrological regime of the river due to water jets from Nangb&#233;to dam can explain this low performance. Water requirement for irrigated areas estimation has given 42 587 596 m3 in 2020 and 73 007 308 m3 in 2030 mainly for the constraint period production which came from february to may. The comparison of water availability/water requirement shows that the water needs are closely covered monthly but a fine decade period analysis revealed some deficit decades. These results involve a great attention and consequent investments for deep knowledge of the resource in order to plan it sustainable management.</p><p><strong><em>Key words: </em></strong><em>Mono basin, Low flow, GR4J, Irrigation.</em></p>
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