Abstract Several theoretical and semi-empirical studies indicate a near linear relationship between the specific capacity (F) of boreholes in bedrock aquifers and apparent transmissivity (T) of the form T=F/, where =c. 0.9. For several boreholes in Hvaler and Trondheim, Norway, the specific capacity of individual fractures has been determined by plotting QA (the yield of water from the aquifer during pumping or recovery) against s (drawdown). Individual apparent fracture transmissivities can be calculated, as can average apparent hydraulic conductivities for individual borehole sections. The method presented is easily performed, requires modest amounts of data, is not mathematically difficult, and is believed to yield at least an order-of-magnitude estimate of transmissivity. Given that hydraulic conductivity in bedrock aquifers can range over seven or eight orders of magnitude, even such a coarse estimate can be of significant use. This is verified by comparison of hydraulic conductivities derived from testing of boreholes in Hvaler with conductivities deduced from water leakage into a nearby subsea tunnel in the same lithology.
Rsum: Plusieurs tudes thoriques et semi-empiriques font envisager un relation pratiquement linaire entre la capacit demmagasinement spcifique (F) de forages dans des aquifres de socle et la transmissivit apparente (T), de la forme T = F/a, o a = 0,9 c. Pour plusieurs forages de Hvaler et de Trondheim (Norvge), la capacit spcifique de fractures individuelles a t dtermine partir de la relation Q (dbit dalimentation de laquifre au cours du pompage ou de la remonte) en fonction de s (rabattement). On a pu calculer les transmissivits individuelles apparentes des fractures et, quand ctait possible, les conductivits hydrauliques apparentes moyennes de portion de forages. La mthode propose est facile mettre en oeuvre; elle demande peu de donnes, nest pas difficile mathmatiquement et parait donner au moins un ordre de grandeur de la transmissivit. Etant donn que la conductivit hydraulique dans les aquifres de socle peut couvrir 7 ou 8 ordres de grandeur, une estimation, mme grossire comme coll-ci, peut tre significative. Ceci est vrifi en effectuant la comparasion entre les conductivits hydrauliques, obtenues en testant les forages de Hvaler, et celles dduites de ltude de fuites dans un tunnel sous-marin voisin, dans les mmes formations gologiques.