MEASUREMENT OF HYDRAULIC-PROPERTIES IN DEEP LAKE-SEDIMENTS USING A TETHERED PORE PRESSURE PROBE - APPLICATIONS IN THE HAMILTON HARBOR, WESTERN LAKE ONTARIO

Estimates of groundwater seepage flux in lake bottom sediments require knowledge of the hydraulic gradient at the sediment-surface water int erface and the hydraulic conductivity of the lake-bottom materials. In deep waters, in situ measurement of these parameters can be accomplis hed through the use of piezometer probes lowered and monitored remotel y from a surface vessel. In this research work a new tethered piezomet er probe was developed and tested for use in collecting hydraulic prop erty data in deep-lake bottom sediments. The probe uses avariable-relu ctance transducer to measure the differential sediment pore pressure b etween two ports spaced 100 cm apart. The dissipation of pore pressure transients that develop during rapid emplacement of the probe were ex trapolated in time to estimate equilibrium hydraulic gradients. In add ition, various data analysis techniques were evaluated for determining sediment hydraulic conductivity and specific storage through interpre tation of the pore-pressure dissipation data. The probe was used to es timate groundwater seepage in the bottom sediments of the Hamilton Har bour, at the western end of Lake Ontario. Upward gradients were measur ed at nine locations within the harbor ranging from 0.010 to 0.425 and a downward gradient of -0.015 was recorded at one site along the harb or's eastern boundary. Hydraulic conductivities determined from pore-p ressure dissipation over time ranged from 6.9 x 10(-9) to 4.8 x 10(-7) m/s. Specific storage values ranged from 0.08 to 0.19 m(-1). Calculat ed average linear seepage velocities ranged from 4.3 x 10(-8) to -8.5 x 10(-9) m/s. The groundwater contribution to the harbor through the d eeper, fine-grained sediments was estimated to be 9.1 x 10(-2) m(3)/s, or 2.9 x 10(6) m(3)/yr. This represents approximately 1.0% of the har bor basin's total volume, 15% of precipitation's contribution, 1.2% of the contribution of surface inflows (excluding the Burlington ship ca nal) and 0.22% of the total surface outflow passing through the Burlin gton shipping canal, which connects the harbor to Lake Ontario.