Jean-Pierre Lamagat

MESURE DE LA PERMÉABILITÉ DES SOLS EN PLACE: UN NOUVEL APPAREIL POUR LA MÉTHODE MUNTZ UNE EXTENSION DE LA MÉTHODE PORCHET AUX SOLS HÉTÉROGÈNES

ABSTRACT The authors make a general survey of the methods of measuring soil permeability in the field, looking at them from the point of view of the hydrologist. In the first part they describe new equipment built by the ORSTOM Centre in Lome, Togo, to apply the Muntz method of vertical infiltration under constant head, equipment using a double cylinder and semi-automatic regulation of the discharge. In the second part, the authors make a mathematical analysis of the Porchet method of horizontal infiltration in a borehole full of water: they show that results may be interpreted even with heterogeneous (multi-layered) soils and that the calculations are simplified using a computer programme. In conclusion they deal with some results of measurements obtained by the two methods, and examine their accuracy and their correlation with the physical and hydrodynamics characteristics of the soils.

Modélisation de propagation d’écoulement entre lits mineur et majeur sur les fleuves Sénégal et Niger

RÉSUMÉ In the Senegal River valley and Niger Inner Delta, the annual floods inundate a wide floodplain consisting of a complex network of lakes and channels, where topographic information needed by standard hydraulic models is difficult to obtain. To represent the flood propagation between mainstream and floodplain, we use a model designed for flood propagation in river mainstreams with flat bed and large overflow and without topographic data. Depending on the water level in the riverbed, the model calibrated on the levels observed at two stations gives the level in the floodplains and propagation time between stations. Several cases are tested for various types of hydraulic connections between mainstream and floodplain. The model could correctly reproduce the flood rise and fall in the floodplain, even for a lake connected by a single channel to the riverbed or in the case of a strong attenuation of the flood between very distant stations.