INVERSION OF BOREHOLE-RESPONSE TEST DATA FOR ESTIMATION OF SUBGLACIALHYDRAULIC-PROPERTIES

Response tests are widely used in ground-water studies to assess the h ydraulic properties of sub-surface water-flow systems. The simplicity of such tests also makes them attractive for investigation of subglaci al hydraulic conditions. This paper describes a systematic, quantitati ve approach to the analysis of borehole-response test data. The approa ch uses the theoretical model of Stone and Clarke (1993), which descri bes water motion in a coupled borehole-subglacial flow system; this fr amework provides the basis for an inversion scheme that is focused on quantifying physical properties of the basal-flow system, as it is cha racterized in the theoretical model. The inversion procedure was appli ed to response-test data from Trapridge Glacier, Yukon Territory Canad a. Results of the inversions suggest that the subglacial drainage netw ork can be described as a confined layer comprising coarse-sand- to fi ne-gravel-sized sediments, having a thickness of 0.1-0.3 m, and a hydr aulic conductivity of about 5 x 10(-4) m s(-1). Based on the water-dra inage rates from boreholes, as they connect with the subglacial water- flow system specific storage of the sediment layer was estimated to be approximately 1 x 10(-4) m(-1). Further consideration of subglacial w ater-flow conditions suggests that connection-drainage test results ma y tend to underestimate specific storage of the overall glacier substr ate.