Documents found
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427.More information
AbstractSilting and solid transport constitute, by their importance, a major problem in Algeria (agricultural land degradation, silting up of reservoirs). Hydrotechnical design and planning studies very often come up against the problem of the lack or of the reduced availability of data on solid transport. Many researchers try to find a work around to tackle this problem by developing models specific to the watersheds studied. These are used to fill the gaps due to the lack of measurement data and to extend the existing series according to the water flow information that is often measured. The purpose of this study was to quantify solid transport and erosion rates in the Sikkak river basin, to determine periods of active erosion and to establish a model relating the transport of solids to the flow rate (Qs as a function of Ql). The Sikkak basin is located in north-western Algeria, covers an area of 218 km2, and includes the Sikkak dam with a capacity of 30 Hm3. We used instantaneous water discharge and suspended sediment loads measured at the Aïn Youcef station from September 1972 to August 1990. Results of analysis of the instantaneous values of suspended solid flow and their relations with water discharge show the existence of two periods of active erosion. The annual solid and liquid contributions vary greatly from one year to the next. The mean of the soil erosion rate is evaluated at 170 t•km‑2•yr‑1, varying between 4 and 745 t•km‑2•yr‑1. These values are very moderate compared to those reported for other basins of the Algeria and the Maghreb, but are very close to the values for some of the Tafna basins.
Keywords: Sikkak, Tafna, érosion, sédiment, débit liquide, transport solide, modèle, Algérie, Sikkak, Tafna, erosion, suspended sediment, water discharge, transport, model, Algeria
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428.More information
Phosphorus exchange at the sediment-water interface was studied in the Al Massira reservoir. This reservoir, located on the Oum Errbia river, is the most important freshwater resource in Morocco. It provides drinking water to the whole population of Casablanca and contributes to farming and to the functioning of several industrial plants. Our investigations were made in October 1991 and coincided with low oxygen concentrations in the deep layers. The measurements of phosphorus exchange have been made in sitn with a benthic chamber device.The results showed that these exchanges were regulated by a combination ofthe physical chemical variability of the environment and the geological composition of the catchment basin.The pH, which permanently exceeded 7 in Massira, suggests that calcium-bound phosphorus was primarily CaHFO4. Moreover, given the high phosphonrs inputs into the reservoir (570 tonnes. year-1), and despite the fact that, as soon as it reached the reservoir, a large fraction of this element was associated with to calcium, it's likely that the Massira reservoir is subject to eutrophication.In low oxygenated deep layers, we observed an increase in particulate phosphorus concentrations of the overlying water, due to the simultaneous presence of calcium-phosphorus, iron-phosphorus and manganese-phosphorus forms. Under anoxic conditions, the reduction ofthese complexes resulted in an increase of phosphorus concentrations.Bacterial cell numbers and total phosphorus concentratioru showed a comparable temporal behaviour. This would suggest that attached bacteria contributed at least partially to the total particulate phosphoms concentrations.We suggest that a drastic control of phosphorus inputs into the waters must be done through a program of dephosphorylation of tributaries to avoid the dissocation of calcium-, iron-, manganese-bound phosphorus with release upwards of bioavailable phosphorus.
Keywords: Retenue, échanges, sédiment, phosphore, bactéries, eutrophisation, Resevoir, exchanges, sediment, phosphorus, bacterin, eutrophication
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429.More information
In fry ponds at Deroua farm, the phytoplankton was represented by a temporal succession of taxa groups.This study showed a similar variability of physical and chemical parameters in fishponds. The statistical analysis proved a variability of these parameters depending of human interventions.At the end of fry period, the phosphorus concentration in B3 and B4 ponds allowed a development of Cyanobacteria
Keywords: Peuplement, phytoplancton, Cyanobactéries, alevinage, traitement statistique, Fry ponds, phytoplankton, Cyanobacteria, statistical analysis
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430.More information
Using a real case of gender mainstreaming carried out by CIDA in three ministries of Morocco, this article examines the factors that have contributed to, or to the contrary hindered, its implementation. The results show that, despite the adoption of gender mainstreaming plans, it has come up against resistance linked to the social system, the organizational culture and the mode of change implementation. Giving priority to the technical aspect of gender mainstreaming, structured essentially on studies of the inequalities, creation of organizational structures and training activities, the examined projects tend to ignore the cultural aspect of change, at the risk of moving away from the needs and realities of the local organizations and in so doing, limit the purely participative and endogenous strategic possibilities.