Solution Options

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The Solution Options pane is on the SWR: Surface-Water Routing Process Pane of the MODFLOW Packages and Programs dialog box.

This pane contains options related to solving the surface-water flow problem.

Only surface water routing (no groundwater) (ISWRONLY): If this option is selected, all the cells in the groundwater model will be treated as inactive cells in MODFLOW and only surface-water flow will be calculated.

Continue even if model does not converge (USE_NONCONVERGENCE_CONTINUE): Selecting this option will allow the simulation to continue running even if a solution was not achieved in one or more time steps. This is similar to the STOPERROR option in MODFLOW but it applies to both the surface-water and groundwater flow processes.

Use upstream weighting for diffusive wave (USE_UPSTREAM_WEIGHTING): An upstream-weighting approach will be used to simulate lateral flow between reach groups that use the diffusive-wave approximation (IROUTETYPE = 3). The area and wetted perimeter of the reach-group with the highest stage are used in equation 6 of Hughes and others (2012).

Use inexact Newton (USE_INEXACT_NEWTON): An inexact Newton method will be used. See appendix 3 of Hughes and others (2012) for more information.

Use steady-state storage (USE_STEADYSTATE_STORAGE): The pseudo-transient continuation approach is used for steady-state stress periods.

Use lagged stages and flows (USE_LAGGED_OPR_DATA): The current estimates of reach stages and flows are used to surface water control structure operations.

Use linear depth scaling (USE_LINEAR_DEPTH_SCALING): Linear-depth scaling is used.

Scaling: There are three options for scaling.

•None

•Diagonal scaling (USE_DIAGONAL_SCALING): The Jacobian is scaled using symmetric diagonal scaling.

•L2Norm scaling (USE_L2NORM_SCALING): The Jacobian is scaled using symmetric ℓ2-norm scaling.

Reordering: Reordering can reduce the memory requirements of the Surface-Water Routing process by reducing the bandwidth. There are three reordering options.

•None: Do not reorder the reaches.

•USE_RCMREORDERING: Active reach groups are reordered using reverse Cuthill-Mckee reordering.

•USE_RCMREORDERING_IF_IMPROVEMENT: Active reach groups are only reordered if reverse Cuthill-Mckee reordering reduces the Jacobian bandwidth.

Newton-Correction: This determines how the Newton correction term will be calculated.

•None:

•Implicit (USE_IMPLICIT_NEWTON_CORRECTION): activates implicit calculation of the Newton correction term for the groundwater flow equation. This option requires solving SWR1 equations using the current and perturbed heads. As a result, SWR1 Process runtimes will be approximately a factor of 2 greater.

•Explicit (USE_EXPLICIT_NEWTON_CORRECTION): activates explicit calculation of the Newton correction term for the groundwater flow equation. This option calculates the Newton correction terms using the current SWR1 stage solution and current and perturbed heads within the aquifer-reach exchange calculation routine (SSWR_CALC_QAQ). This option does not have a significant effect on SWR1 Process runtimes and is sufficient for the test problems evaluated.