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Seaside Model Report October 26, 2007 Model Development of the model domain also is a no-flow boundary. Likewise, the boundary conditions on the landward and seaward vertical surfaces of the model domain, except for the segment of the Reliz Fault described above, are no-flow boundaries. The leakances for the specified-head boundaries were assigned so as to produce a computed head almost identical to the specified head. Accordingly, the leakances were set to a somewhat arbitrary large value. The leakances were set sufficiently large to produce nearly identical specified and computed heads, but they were set also such that the difference between the specified and computed heads was with the precision of the computer. Solute Transport Where water crosses boundary surfaces as inward flows, due either to the assignment of specified-head or non-zero specified-flux groundwater-flow boundaries, the salinity of the inward flow is assigned. However, except for the boundary surface representing the bottom of Monterey Bay, the specified salinity equals zero. For the Monterey Bay surface, the specified salinity equals unity, which is the dimensionless concentration equivalent to seawater. 3.1.6 Initial Conditions The groundwater-flow and solute-transport initial conditions is an assumed steady-state condition at the end of 1955. The groundwater development at the time was minimal at that time relative to precipitation recharge, and initial conditions were simulated based on the assumed steady state. Groundwater Flow The initial heads for groundwater flow are the calculated steady-state heads representing the long-term average annual recharge, the 1956 groundwater pumping, and the boundary conditions described above. FEMFLOW3D can calculate steady-state initial heads within a transient-state simulation, and that facility was used to specify the initial heads for the Seaside groundwater basin. The resulting steady-state groundwater levels are shown on Figures 3.10a-b. Because the steady-state heads depend on the hydraulic parameters assigned to the hydrogeologic units represented in the model, Figures 3.10a-b are derived from the model calibration, which is described later. Solute Transport The initial salinity for solute transport are the calculated nearly steady-state salinity again representing the long-term average annual recharge, the 1956 groundwater pumping, and the boundary conditions described above. By this construction of initial conditions, the seawater intrusion in the seaward part of the Seaside basin is assumed to be in equilibrium with the 1956 steady-state groundwater flow. Calculating steady-state solute-transport with FEMFLOW3D is not as convenient as for calculating steady-state 21
Seaside Model Report October 26, 2007 Model Development heads. The approach was to make a long-term simulation of solute transport based on the steady-state heads. A simulation period was selected such that near steady-state transport conditions occurred at the end of the simulation. This was achieved with a simulation period of 10,000 years. The resulting steady-state salinities are shown on Figures 3.11a-b. Because the steady-state salinities depend on the hydraulic and transport parameters assigned to the hydrogeologic units represented in the model, Figures 3.11a-b are derived from the model calibration, which is described next. 3.2 Aquifer-Parameter Identification Aquifer-parameters for groundwater flow and solute transport were assigned to the model. The hydraulic parameters for groundwater flow include the hydraulic conductivity, specific storage, and specific yield for each hydrogeologic unit represented in the model. Likewise, the transport parameters include the effective porosity and dispersivity. 3.2.1 Identification Approach Different approaches were used for the identification of the hydraulic and transport parameters. Groundwater-level data are available for the Seaside basin, and hydraulic parameters were identified by calibrating the model to groundwater-level measurements. The basin has been impacted little by seawater intrusion, and no basis exists for identifying the transport parameters by calibration. Correspondingly, transport parameters were assigned based on the textural characteristics of the individual hydrogeologic units. Groundwater Flow Two data sources were used in the identification of hydraulic parameters. With respect to the first data source, parameters were identified by formally calibrating the model to the groundwater levels listed in Table 2.3, which represent measurement is made within the wells listed in Table 2.2. The simulated head for a well follows from the assignment of mesh nodes to each monitoring well, and the simulated head is a weighted sum of the simulated heads for the assigned nodes. The weights are derived exactly as described in Section 3.1.4 for the assignment of well pumping to nodes. With respect to the second data source, parameters were identified by subjectively calibrating the model to qualitative characteristics of the groundwater-level contour maps produced by Yates and others (2005, Figures 12 through 15). Those maps show groundwater levels for Spring and Fall 2002 and respectively for the Paso Robles and Santa Margarita formations. Immediately landward from Monterey Bay and north of the Ord Terrace Fault, the maps show roughly circular areas where groundwater levels are below sea level. Within the Paso Robles Formation, the area is about 5,000 ft in diameter, and the area is contained entirely within the landward part of the groundwater basin, as shown on Figure 1.18a. Within the Santa Margarita Formation, the area is about 12,000 ft in diameter, and the area extends partly into the seaward part of the groundwater system, as 22
Page 1 and 2: GROUNDWATER FLOW AND TRANSPORT MODE
Page 3 and 4: Seaside Model Report October 26, 20
Page 25: Seaside Model Report October 26, 20
Page 39 and 40: Tables
Page 41 and 42: Table 2.2 Monitoring Wells Location
Page 43 and 44: Table 2.3 Merasured Groundwater Alt
Page 45 and 46: Table 2.4a California American Wate
Page 47 and 48: Table 2.4c Annual Pumping from Priv
Page 49 and 50: Table 2.6 ET Corresponding to 1993
Page 51 and 52: Table 3.2 Groundwater Budget for 20
Page 53 and 54: Table 4.2 Groundwater Budget for 20
Page 55 and 56: ® Monterey Bay Marina Seaside Mode
Page 57 and 58: ® Monterey Bay Reliz Fault Ord Ter
Page 59 and 60: NW Monterey Bay Coastline SE El Tor
Page 61 and 62: -700 ® Monterey Bay -600 -500 -120
Page 63 and 64: ® -300 Monterey Bay -75 -200 -100
Page 65 and 66: ® Monterey Bay Model Boundary DWR
Page 67 and 68: ® -20 -10 Marina Monterey Bay 10 0
Page 69 and 70: ® Marina Monterey Bay Seaside Seaw
Page 71 and 72: ® Monterey Bay Marina X X X X X Se
Page 73 and 74: ® Monterey Bay Model Boundary NDVI
Page 75 and 76: ® Monterey Bay Model Boundary NDVI
Page 77 and 78:
® Monterey Bay Model Boundary NDVI
Page 79 and 80:
® Castroville Salinas North Monter
Page 81 and 82:
® Figure 3.2 Finite-element Mesh
Page 83 and 84:
NE SW Seaside Fault Relize Fault Or
Page 85 and 86:
Δh Δh z t-1 Case of Small h z >z
Page 87 and 88:
Well C A C B B A L Δz e Le be Elem
Page 89 and 90:
0 -5 Specified Head (ft) et) -10 -1
Page 91 and 92:
® Monterey Bay Figure 3.10b Initia
Page 93 and 94:
® Monterey Bay Figure 3.11b Initia
Page 95 and 96:
2.0 1.5 Weighted Computed Head (ft)
Page 97 and 98:
® Monterey Bay Figure 3.13b Comput
Page 99 and 100:
® Monterey Bay Figure 3.14b Comput
Page 101 and 102:
® Monterey Bay Figure 4.1b Compute
Page 103 and 104:
® Monterey Monterey Bay Bay Monter
Page 105 and 106:
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