Benzha, F., Taoufik, M., Dafir, J.E., Kemmou, S. and Loukili, L. (2005). Impact of drainage operation on water quality of Daourat Reservoir

The Oum Rbia River is the longest river in Morocco with a total length of about 550 km. Studies conducted on this river have shown that agricultural activity is the main factor affecting the water quality. The current study focused on Daourat Reservoir, a part of the Oum Rbia River. The aim of this study was to investigate the water quality of the Daourat reservoir (physico-chemical parameters, nutrients and chlorophyll a) in order to estimate its eutrophication status. The influence of draining reservoir on water quality was also analysed. This survey also included a regression analysis that permitted the determination of the relationship between phosphorus and chlorophyll a, as well as an assessment of the level of eutrophication of the Daourat reservoir. Significant nutrient loading to the reservoir came from sediment resuspension on December 23, 2001 and by internal loading from sediments during the summer. The upstream reservoirs (Al Massira and Imfout) had minimal influence and were in fact responsible for the reduced fluvial contributions to the Daourat Reservoir. The increase in nutrient loads in the reservoir was responsible for high phytoplankton biomass, indicated by the high chlorophyll a values. The trophic state of the Daourat Reservoir was classified as hypereutrophic. Due to the large intra-annual variability of water quality, a properly designed monitoring program of reservoir water is recommended.Original Abstract: Ce travail concerne l'etude de la qualite physico-chimique de la masse d'eau du reservoir Daourat au Maroc ; situe sur le cours inferieur du bassin Oum Rbia. Une vidange du reservoir a lieu le 23 decembre 2001, l'impact de cette vidange sur la qualite physico-chimique de l'eau a ete deduit a travers l'augmentation du debit a l'entree et a la sortie du reservoir en decembre ; l'elevation du taux de la matiere en suspension ; des concentrations en elements nutritifs et de la chlorophylle " a ". Cette etude inclue egalement une analyse de regression qui a permis de determiner une relation entre le phosphore et la chlorophylle " a " ; ainsi qu'une evaluation du niveau d'eutrophisation du reservoir Daourat. Les resultats fournis par les parametres physico-chimiques ont revele que la masse d'eau ne presente aucune stratification thermique ni anoxie et que le pH est alcalin. L'evolution des concentrations en elements nutritifs dans la masse d'eau du reservoir depend des apports exogenes et endogenes. Les apports exogenes sont domines