ESTIMATION OF SUBGLACIAL HYDRAULIC-PROPERTIES FROM INDUCED CHANGES INBASAL WATER-PRESSURE - A THEORETICAL FRAMEWORK FOR BOREHOLE-RESPONSE TESTS

In this paper we develop a theoretical model describing water motion i n a coupled borehole-subglacial flow system. The theory applies to bas al drainage systems having multiple and extensive interconnected flow paths. Within this domain it encompasses a broad range of flow regimes , from laminar Darcian flow in a thick permeable unit to turbulent she et flow in a very thin layer. Important terms in the model are highlig hted by recasting the problem in dimensionless form. The non-dimension al formulation indicates that there are four free parameters in the co upled system. These parameters characterize skin friction in the boreh ole, and diffusion, transmissivity and turbulent transport in the subg lacial flow layer. Dimensionless results show that, under most circums tances, the effects of skin friction in the borehole are negligible. D iffusion, transmissivity and especially turbulent transport in the bas al layer are found to influence subglacial water flow strongly. We use our model to predict fluctuations of borehole-water levels that resul t from different types of disturbances. We show how this framework can be used to estimate subglacial hydraulic properties by comparing mode l results with data collected during field experiments on Trapridge Gl acier, Yukon Territory, Canada, in 1989 and 1990.