| The 3D hydrostratigraphic model (3DHSM) represents the conceptual model of the aquifer system architecture consisting of 7 granular units overlying 2 bedrock units. The 9 hydrostratigraphic layers built in LeapFrog Hydro were then reassigned to 14 layers. The top 7 layers of the 3DHSM represent the unconsolidated sediments, whereas the lower 7 layers represent the 2 bedrock units. All the 14 geologic layers were integrated in the 3D groundwater flow model (3DGFM) built with FEFLOW.
The model includes Dirichlet and Neumann types of boundary conditions. Northwest and southeast lateral boundaries of the 3DGFM were set as no flow boundary condition to approximately represent the groundwater divides. Along the coast, all nodes with elevation greater or equal to sea level (0 m) were simulated with the seepage face boundary condition. For nodes along the coast with an elevation below sea level (0 m), a constant head equal to the sea level (0 m) was imposed, thus assuming horizontal flow at the coast. The basal layer is a no flow boundary in the model.
No information was available to assess the groundwater contribution from the mountain areas. The recharge rate of the intrusive crystalline bedrock was estimated to adjust the position of the water table. This recharge rate was adjusted during the calibration process. Seepage conditions were used to represent groundwater discharge observed along the flanks of the main rivers. Thus, when simulated hydraulic heads are larger than the elevation of the ground elevation, excess water is evacuated from the model. This excess water becomes part of the baseflow in the water budget analysis.
The recharge rate over the lowland area was assessed based on the separation of the baseflow from the river hydrographs and adjusted during the calibration. Recharge rate values were obtained for each watershed.
In addition to the hydraulic head, a baseflow calibration was conducted for the lowland part of Nile Creek, Big Qualicum, Little Qualicum and Englishmen Rivers. Important components of a streamflow are direct precipitation, surface runoff, baseflow and hypodermic flow. Baseflow can be estimated from the analysis of streamflow records and, for assumed steady state flow condition, baseflow can be used as an estimation of the recharge rate to the aquifer. The relative proportion of baseflow in the lowland and in the mountain region was estimated for the streamflow records from two stream gaging stations located along the Big Qualicum River at the edge of the mountains and in the lowland, respectively. The same proportion was then applied in the other watersheds assuming comparable surface water and groundwater dynamics. The baseflow for each watershed was then estimated as a sum of the flux extracted from the model at nodes corresponding to seepage faces.
Hydraulic conductivity (K) was used as a calibration parameter. Most initial K values for each hydrostratigraphic unit were obtained from the analyses of available pumping tests. Other K values were drawn from the literature, in particular for the low-K units.
The 3DGFM was calibrated for a saturated steady state condition assuming that the model represents average annual flow conditions. The parameters adjusted during the calibration process were: K, groundwater recharge and the influx from the mountain regions. The calibration parameters were modified until a satisfactory match between the simulated and observed hydraulic heads and baseflow values. Refinement and fine adjustment was carried out applying the numerical inversion within the Pest algorithm.
Hydrostratigraphic Unit [Kxy (m/s); Kz/Kxy]
Lake bottom [8.3 x 10-8; 1]
Capilano-Salish [3.8 x 10-4; 1]
Capilano (glaciomarine) [8.1 x 10-7; 1]
Vashon-Capilano (coarse) [7.7 x 10-6; 1]
Vashon (till) [4.6 x 10-8; 1]
Quadra [2.1 x 10-5; 1]
Cowichan-Dashwood [8.1 x 10-9; 1]
Dashwood-Mapleguard [1.1 x 10-7; 1]
Bedrock <10 m [9.0 x 10-6; 1]
Bedrock 10-20 m [7.0 x 10-6; 0.1]
Bedrock 20-70 m [3.8 x 10-6; 0.94]
Bedrock 70-120 m [1.3 x 10-8; 0.01]
Bedrock 120-170 m [9.8 x 10-9; 0.01]
Bedrock 170-220 m [1.2 x 10-9; 0.01]
Bedrock 220-280 m [1.2 x 10-10; 0.01]
Bedrock > 280 m [1.2 x 10-11; 0.01] |
| The 3D hydrostratigraphic model (3DHSM) represents the conceptual model of the aquifer system architecture consisting of 7 granular units overlying 2 bedrock units. The 9 hydrostratigraphic layers built in LeapFrog Hydro were then reassigned to 14 layers. The top 7 layers of the 3DHSM represent the unconsolidated sediments, whereas the lower 7 layers represent the 2 bedrock units. All the 14 geologic layers were integrated in the 3D groundwater flow model (3DGFM) built with FEFLOW. The model includes Dirichlet and Neumann types of boundary conditions. Northwest and southeast lateral boundaries of the 3DGFM were set as no flow boundary condition to approximately represent the groundwater divides. Along the coast, all nodes with elevation greater or equal to sea level (0 m) were simulated with the seepage face boundary condition. For nodes along the coast with an elevation below sea level (0 m), a constant head equal to the sea level (0 m) was imposed, thus assuming horizontal flow at the coast. The basal layer is a no flow boundary in the model. No information was available to assess the groundwater contribution from the mountain areas. The recharge rate of the intrusive crystalline bedrock was estimated to adjust the position of the water table. This recharge rate was adjusted during the calibration process. Seepage conditions were used to represent groundwater discharge observed along the flanks of the main rivers. Thus, when simulated hydraulic heads are larger than the elevation of the ground elevation, excess water is evacuated from the model. This excess water becomes part of the baseflow in the water budget analysis. The recharge rate over the lowland area was assessed based on the separation of the baseflow from the river hydrographs and adjusted during the calibration. Recharge rate values were obtained for each watershed. In addition to the hydraulic head, a baseflow calibration was conducted for the lowland part of Nile Creek, Big Qualicum, Little Qualicum and Englishmen Rivers. Important components of a streamflow are direct precipitation, surface runoff, baseflow and hypodermic flow. Baseflow can be estimated from the analysis of streamflow records and, for assumed steady state flow condition, baseflow can be used as an estimation of the recharge rate to the aquifer. The relative proportion of baseflow in the lowland and in the mountain region was estimated for the streamflow records from two stream gaging stations located along the Big Qualicum River at the edge of the mountains and in the lowland, respectively. The same proportion was then applied in the other watersheds assuming comparable surface water and groundwater dynamics. The baseflow for each watershed was then estimated as a sum of the flux extracted from the model at nodes corresponding to seepage faces. Hydraulic conductivity (K) was used as a calibration parameter. Most initial K values for each hydrostratigraphic unit were obtained from the analyses of available pumping tests. Other K values were drawn from the literature, in particular for the low-K units. The 3DGFM was calibrated for a saturated steady state condition assuming that the model represents average annual flow conditions. The parameters adjusted during the calibration process were: K, groundwater recharge and the influx from the mountain regions. The calibration parameters were modified until a satisfactory match between the simulated and observed hydraulic heads and baseflow values. Refinement and fine adjustment was carried out applying the numerical inversion within the Pest algorithm. Hydrostratigraphic Unit [Kxy (m/s); Kz/Kxy] Lake bottom [8.3 x 10-8; 1] Capilano-Salish [3.8 x 10-4; 1] Capilano (glaciomarine) [8.1 x 10-7; 1] Vashon-Capilano (coarse) [7.7 x 10-6; 1] Vashon (till) [4.6 x 10-8; 1] Quadra [2.1 x 10-5; 1] Cowichan-Dashwood [8.1 x 10-9; 1] Dashwood-Mapleguard [1.1 x 10-7; 1] Bedrock <10 m [9.0 x 10-6; 1] Bedrock 10-20 m [7.0 x 10-6; 0.1] Bedrock 20-70 m [3.8 x 10-6; 0.94] Bedrock 70-120 m [1.3 x 10-8; 0.01] Bedrock 120-170 m [9.8 x 10-9; 0.01] Bedrock 170-220 m [1.2 x 10-9; 0.01] Bedrock 220-280 m [1.2 x 10-10; 0.01] Bedrock > 280 m [1.2 x 10-11; 0.01] |
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