![]() The latter model is more realistic, but more scale modelling will have to be performed to permit development of viable interpretational procedures. Attempts were made to interpret the HLEM results quantitatively using two models: a three-layer medium and a valley discontinuity. Despite the high background level of in-phase and quadrature components, which varied with thickness and conductivity of the weathered layer, aquifers could be detected at a depth greater than 30 m. Therefore, different interpretational procedures had to be developed for granitic and volcano-sedimentary areas. The weathered layer is a source of distinctive HLEM anomalies, which are characteristic of the underlying rocks. Of the 24 holes drilled so far, 23 are productive. During the 1980 field season, 35 target areas were surveyed. The results obtained with a multifrequency, horizontal-loop EM (HLEM) system were satisfactory in all investigated areas. Because of the limited choice of transmitting stations reccivable in Upper Volta, the VLF method is not sufficiently sensitive to detect conductors with a strike between 45° and 105°. Our studies suggest that the task can be performed faster, cheaper and more accurately by VLF and EM methods. Traditionally, resistivity profiling has been used as the means of locating the fractured zones in the field. Because of the small size of the aquifers, a location error of 5 m can make the difference between a productive well and a dry hole. Such zones can be identified on aerial photographs, but their precise location on the ground is virtually impossible by visual means. Economic aquifers in Precambrian terrains are deep (15–50 m) and usually occur in fractured zones accompanying faults. First, a survey of available water supplies is performed. This anthem was replaced in 1984 by a new anthem, the Ditanyè.The “Autorité des amenegements des valées des Voltas (AVV)” is establishing new rural settlements in the Volta valleys. We will make you stronger and more beautiful Nous te ferons et plus forte, et plus belle Thomas Sankara (4 August 1983 to 14 October 1987). ![]()
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