< Previous30 for delineating the submodel boundaries, the red polygon of the parent model domain is removed from the MDWA. Once the new (sub) model is submitted for simulation, the results of the parent model are removed from the model domain. Figure 3-9: Example of the hierarchical modeling approach for developing appropriate boundary conditions in the study area. 3.7 Transient Model Settings & Initial Conditions 31 By default, flow simulations in MAGNET are run at steady state. To perform unsteady (transient) modeling in MAGNET, check the box next to ‘Transient’ in the upper-right part of the Default Parameters and Options Menu (see Figure 3-10). Required inputs are the start date and time (hour of the day), the time step, and the simulation length. Use the texts boxes next to ‘State Date’ (year, month, day), ‘Hr’ (hours), ‘Time Step:’ (days), and ‘Simulation Length’ (days) to define user inputs. Check the box next to ‘Run Steady State at t=0’ to use the head distribution solved for steady state conditions as the initial head distribution of the transient simulation (see Figure 3-10). Other options for the initial head distribution are shown in Figure 3-11. The ‘Top’ option will use the Top Elevation surface assigned by the user (see Section 3.3.1). The ‘Parent’ option uses the head distribution of a larger Parent model spanning the new (Child) model domain (see Section 3.6). Head values are interpolated from the (coarse-grid) Parent model to the (finer-grid) Child model. The ‘Constant’ option will assign the value in the text box as a constant head value across the entire domain. Figure 3-10: Options for unsteady (transient) modeling in MAGNET. Default values/parameters are shown. Figure 3-11: Options for assigning an initial head distribution across the model domain. Default value/parameters are shown. 32 Chapter 4 CONCEPTUAL FEATURES: LINES, ZONES & WELLS After creating the model domain and finalizing the model inputs/parameters/options (or simply applying the default settings), additional conceptual features may be added within the model domain. This includes: polylines (e.g., streams, injection trenches, etc.), zones (e.g., lakes, contaminant sources, polygons for water balance analysis, etc.), and extraction/injection wells. Each of the features is discussed in detail in the following subsections. 4.1 Line Features & Attributes To add a polyline feature to the model domain, LM click on the ‘DrawPline’ button along the left-side of the MAGNET Modeling Environment (see Section 2.1). The cursor will become a cross-hair, allowing for placement of polyline vertices with single-clicks of the LM button4. The polyline will appear as a series of green line segments with circles at the vertex locations (see Figure 4-1). The location can of any vertex can be changed by hovering the mouse over it and click-dragging to the new desired location5. Once the last vertex has been placed, LM click the ‘SaveShape’ button to finalize the polyline. This will launch the Polyline Attributes menu (see Figure 4-1). Several options are available for the polyline conceptual feature: prescribed head boundary condition (constant, variable, transient, or equal to the water table elevation); head-dependent flux boundary condition (one-way or two-way) or as a prescribed flux (constant or transient). If the polyline needs to be discarded, LM click the ‘Delete’ button to close the Polyline Attributes menu and remove the polyline feature from the MDWA. 4 Allow for a brief period of time (i.e., at least 2-3 seconds) between LM clicks. Otherwise, the locations of the vertices may not be consistent with what is desired. 5 Any vertex location can also be updated after finalizing the polyline. 33 Figure 4-1: Polyline feature added to the model domain and the Polyline Attributes menu. 4.1.1 Prescribed Head Options Different prescribed head options can be applied using the Prescribed Head option box. The simplest treatment is a constant values at all vertex locations (and at all time-steps, if running a transient simulation). Spatially-constant prescribed head. Select the radio button next to ‘Constant’, and enter the desired head value (in meters) in the text box. To assign spatially-constant but time-dependent head values, leave the ‘Constant’ radio button selected, but also check the radio box next to ‘Transient’. Then LM click the ‘Transient’ button to open the sub-menu for editing transient head data (see Figure 4-2). Indicate the starting data and time with the text boxes next to ‘State Date’ (year, month, day), ‘Hr’ (hours). Then, provide the following inputs for each timestep: TimeN – or the number of days since the starting date and time; and ValueN – the head value corresponding to TimeN. The head values may be entered in any units; however, if meters are not used, make sure to enter the appropriate multiplier in the text box next to ‘Multiplier to meter:’. For example, to convert from ft. to m, enter 0.3048, as 1 ft.=0.3048m. After all desired changes have been made, LM click the ‘OK’ button. Or click ‘Cancel’ to discard all changes and close the sub-menu. 34 Figure 4-2: Sub-menu for editing Transient prescribed head data. Spatially-variable prescribed head. Multiple options are available if a spatially-variable prescribed head is desired. First, one may select the radio button next to ‘Equal to Y (e.g., Water Table) to assign a head value equal to the water table elevation at each point along the polyline. Another option is to select the radio button next to ‘Variable’ option from the Prescribed-Head option box, then LM click the ‘>>more’ link to open the Edit Polyline Attributes sub-menu (see Figure 4-3). This sub-menu provides information on the Vertex ID (VertexID) and the longitude and latitude coordinates (Long(degree) and Lat(degree), respectively). By default, the head value at each location is: the top aquifer elevation, as indicated by the checked box next to ’Head = TopE minus’ and the value of 0 in the corresponding text-box shown in Figure 4-3. An offset may be applied by entering a non-zero number in the text box. If the head is known at each vertex location, the user can edit the head value (in meters) by LM clicking anywhere within a cell in the Head(m) column (note that each row corresponds to a different VertexID). After all cells have been updated, uncheck the box next to ’Head = TopE minus’. After all desired changes have been made, LM click the ‘Save and Exit’ button. Or click ‘Cancel and Exit’ to discard all changes. 35 Figure 4-3: Edit Polyline Attributes sub-menu for assigning unique head values at different vertex locations. Default values/options are shown. Transient head from a T File. This feature is not available in the current version of MAGNET. 4.1.2 Head-Dependent Flux Options Two-way or one-way head-dependent flux boundary conditions may be applied for polyline features. One-way head dependent flux allows water to leave the aquifer system in the case that the hydraulic head exceeds the top aquifer elevation, but water may not enter the aquifer system (e.g., surface seepage to a drain or ditch). “Two-way” allows for water to enter or leave the aquifer system depending on the direction of the head gradient between the surface water stage and the aquifer head. Two-way head-dependent flux. Select the radio button next to ‘Two way’ in the Head Dependent option box to apply two-way head-dependent flux boundary conditions. LM click the ‘>>more’ link to open the Edit Polyline Attributes sub-menu (see Figure 4-4). By default, the stage along the polyline is equal to the aquifer top elevation, as indicated by the checked box next to ’Stage = TopE minus’ and the value of 0 in the corresponding text-box shown in Figure 4-4. An offset may be applied by entering a non-zero number in the text box. If the stage is known at each vertex location, the user can edit the stage value (in meters) by LM clicking anywhere within a cell in the Stage(m) column (note that each row corresponds to a different VertexID). 36 Similarily, the leakancy (Leak(m/day)), bottom elevation (BotE(m)), and stream order (Order) can be customized for any cell in the table. After all cells have been updated, uncheck the box next to ’Stage = TopE minus’. After all desired changes have been made, LM click the ‘Save and Exit’ button. Or click ‘Cancel and Exit’ to discard all changes. Figure 4-4: Edit Polyline Attributes sub-menu for assigning polyline attributes needed for computing two-way head dependent flux. Default values/options are shown. One-way head dependent flux. The steps to apply One-way head dependent flux are similar to that of two-way. Select the radio button next to ‘One way’ in the Head Dependent option box, then select LM click the ‘>>more’ link to open the Edit Polyline Attributes sub-menu (see Figure 4-5). By default, the “drain elevation” (i.e., the elevation used to compute the head gradient) is equal to the aquifer top elevation, as indicated by the checked box next to ’Stage = TopE minus’ and the value of 0 in the corresponding text-box shown in Figure 4-5. An offset may be applied by entering a non-zero number in the text box. If the drain elevation is known at each vertex location, the user can edit the drain elevation values (in meters) by LM clicking anywhere within a cell in the BotE(m) column (note that each row corresponds to a different VertexID). Similarly, the leakancy (Leak(m/day)) and stream order (Order) can be customized for any cell in the table. After all cells have been updated, uncheck the box next to ’Drain = TopE minus’. After all desired changes have been made, LM click the ‘Save and Exit’ button. Or click ‘Cancel and Exit’ to discard all changes. 37 Figure 4-5: Edit Polyline Attributes sub-menu for assigning polyline attributes needed for computing one-way head dependent flux. Default values/options are shown. The drop-down menus next to each ‘>>more’ link provide different naming option for the polyline feature that will be used in displaying results, e.g., when performing water balance analyses (see Section 6.2). By checking the radio box next to ‘Allow to apply recharge’, the cell-specific recharge will be applied to cells in which the polyline feature occupies (e.g., when using the one-way head-dependent flux option). By checking the radio box next to ‘Overide Drain’, this allows the polyline (used as a boundary condition) to override surface seepage (only one sink is allowed per cell). If this radio box is left uncheck, surface seepage will apply and the polyline boundary conditions will be ignored. 4.1.3 Prescribed Flux Options Users may assign a prescribed flux boundary condition along the polyline by selecting the ‘Prescribed Flux’ radio button and choosing one of the units of input: 1) ‘Per unit length’ – prescribed flux per unit length (square meters per day) along a polyline (e.g., in the case where stream thickness is negligible), which is the default setting; 2) ‘Total’ – total prescribed flux across the entire polyline-aquifer interface ; and 3) ‘Per unit area’ – the prescribed flux per unit area along the polyline. Note that all three options apply for steady conditions (i.e., no changes in flux with time) and spatially-constant flux along the polyline. To assign time-dependent (total) prescribed flux boundary conditions, leave the ‘Prescribed Flux’ radio button selected, but also check the radio box next to ‘Transient’. Then LM click the ‘Transient’ button to open the sub-menu for editing transient flux data (see Figure 4-6). Indicate the starting data and time with the text boxes next to ‘State Date’ (year, month, day), ‘Hr’ (hours). Then, provide the following inputs for each timestep: TimeN – or the number of days since the starting date and time; and ValueN – the flux value corresponding to TimeN. The flux values may be entered in any units; however, if cubic meters per day is 38 not used, make sure to enter the appropriate multiplier in the text box next to ‘Multiplier to m3/day’. For example, to convert from ft3/day. to m3/day, enter 0.0283, as 1 ft3 = 0.0283 m3. Figure 4-6: Sub-menu for editing Transient prescribed head data. 4.1.4 Display and Analysis Options Polylines need not be used for the purposes of assigning boundary conditions. To use them simply for display purposes (e.g., for highlighting features in the background map or simulation results), select the radio button next to ‘Non-specified’ at the top of Polyline Attributes menu. This is useful for highlighting features in the background map or simulation results. ‘Calculate and display flux across the polyline’: this feature is not available in the current version of MAGNET (coming soon). 4.1.5 Editing Attributes of Existing Polylines When the simulation is complete/paused, any pre-exiting polyline feature can be edited by clicking the ‘AttrPlines’ button from left-side of the MAGENT Modeling Environment. This turns all pre-existing polylines red within the model domain (see Figure 4-7). Click once on the polyline to be edited, and select ‘OK’ from the prompt to confirm editing. This opens the Polyline Attributes menu for updating parameters/options of the polyline feature. Click ‘Save and Exit’ to apply the changes to the polyline feature, and continue editing other polyline features, if desired. Once all changes have been made, click on the ‘AcceptEdits’ button on the left-side of the MAGNET 39 Modeling Environment. This applies all updates and turns the polylines back to green objects in the MDWA. Figure 4-7: Editing attributes of a pre-existing polyline feature. 4.2 Zone Features & Attributes Zones can be added to the model domain to: • Perform zone budget (water balance) analyses; • Assign flow, elevation, and recharge properties/values different from those assigned in the Default Input and Parameters menu (see Figure 2-3) for a subregion of the model domain; • Define diffusion, dispersion, retardation and decay parameters/coefficients for the purposes of solute transport modeling; • Create two-way head dependent sources/sinks (e.g., a lake), one-way head dependent sinks (e.g., a groundwater spring or a groundwater-dominated wetland), and prescribed head sources/sinks; and • Create solute sources defined by a prescribed mass flux or source concentration. MAGNET will assign zone attributes to every cell in which the center node lies inside of the defined zone area. If two zones overlap, the attributes of smaller zones will take precedence over larger zones. Any cells outside of zones added to the model domain will utilize the attributes/parameters assigned in the Default Parameters and Options menu (see Chapter 3). To add a zone feature to the model domain, LM click on the ‘DrawRect’ button to create a rectangular-shaped modeling domain within the MDWA, or use the ‘DrawZone’ button to trace out a polygon of any shape as the zone feature (e.g., to follow along a wetland or lake boundary). Next >