Abstract. Estimates of groundwater seepage flux in lake bottom sediments require knowledge of the hydraulic gradient at the sediment-surface water interface and the hydraulic conductivity of the lake-bottom materials. In deep waters, in situ measurement of these parameters can be accomplished through the use of piezometer probes lowered and monitored remotely from a surface vessel. In this research work a new tethered piezometer probe was developed and tested for use in collecting hydraulic property data in deep-lake bottom sediments. The probe uses a variable-reluctance transducer to measure the differential sediment pore pressure between two ports spaced 100 cm apart. The dissipation of pore pressure transients that develop during rapid emplacement of the probe were extrapolated in time to estimate equilibrium hydraulic gradients. In addition, various data analysis techniques were evaluated for determining sediment hydraulic conductivity and specific storage through interpretation of the pore-pressure dissipation data. The probe was used to estimate groundwater seepage in the bottom sediments of the Hamilton Harbour, at the western end of Lake Ontario. Upward gradients were measured 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 harbor's eastern boundary. Hydraulic conductivities determined from pore-pressure 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 -•. Calculated 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 deeper, fine-grained sediments was estimated to be 9.1 x 10 -2 m3/s, or 2.9 x 106 m3/yr. This represents approximately 1.0% of the harbor basin's total volume, 15% of precipitation's contribution, 1.2% of the contribution of surface inflows (excluding the Burlington ship canal) and 0.22% of the total surface outflow passing through the Burlington shipping canal, which connects the harbor to Lake Ontario.
IntroductionComplete water balance calculations in surface water bodies require estimates of groundwater seepage fluxes through the bottom sediments. To estimate these fluxes, hydraulic gradients must be determined at the water-sediment interface along with values of the sediment hydraulic conductivity. Conventional groundwater-surface water studies commonly rely on piezometers placed in the bottom sediments to measure hydraulic gradients [Welch and Lee, 1989]. Single-well response tests (slug tests) performed within these piezometers are routinely used to estimate hydraulic conductivity [Hvorslev, 1951]. Alternatively, seepage meters [Lee, 1977;Lee and Cherry, 1978] can be used to measure groundwater seepage directly. At water depths greater than about 8 m, however, these methods are impractical owing to the difficulties encountered with installation and monitoring.To collect the required hydraulic data in deeper water bod- To our knowledge, the only document...