SFR: Stream-Flow Routing Package Pane

The Streamflow-Routing (SFR) package is used to simulate streams in a model. The flow in a stream is routed instantaneously to downstream streams or lakes. Flow can be routed through lakes defined in the Lake package. Unsaturated flow beneath streams can be simulated. The pane for this package is on the MODFLOW Packages and Programs dialog box under Head Dependant Flux. The pane has two tabs: General and Parameters. However, parameters are only supported in the SFR package if unsaturated flow is not simulated in the SFR package and if streambed properties are defined at segment endpoints rather than at each reach. The Parameters tab is only visible for models in which SFR parameters can be used.

The locations of Stream-Flow Routing boundaries are defined with objects.

On the General tab, the user must choose whether or not to simulate Unsaturated Flow (ISFROPT). (Users who chose to simulate unsaturated flow beneath streams may also simulate unsaturated flow over the entire model domain using the UZF package.)

With Print Streams (ISTCB2) the user can choose to have all information on inflows and outflows from each reach; on stream depth, width, and streambed conductance; and on head difference and gradient across the streambed will be written to the either the main listing file or a separate output file.

In GSFLOW, the format for the SFR package is slightly different from the format used by MODFLOW-2005. If you are generating SFR input for GSFLOW, you should check the Use GSFLOW format check box. The new format is used automatically for MODFLOW-NWT. (This option can now be specified on the Options tab of the MODFLOW Options dialog box.)

The user can choose to specify certain stream properties either at segment endpoints or at each reach in the segment (Streambed properties (ISFROPT)). However, if the properties are defined at each reach, the SFR package does not allow these properties to vary with time. One such property is the vertical conductance at a reach. If the vertical conductance is set to zero, it causes the stream segment to be disconnected from the aquifer. Thus the ability to set the vertical conductance to zero is required to change with time in order to activate or deactivate a stream segment.

The Tolerance (DLEAK) is the tolerance level of stream depth used in computing leakage between each stream reach and active model cell. Its value is in units of length. Usually a value of 0.0001 is sufficient when units of feet or meters are used in model.

Number of trailing wave increments (NSTRAIL) is the number of trailing wave increments used to represent a trailing wave. Trailing waves are used to represent a decrease in the surface infiltration rate. The value can be increased to improve mass balance in the unsaturated zone. Values between 10 and 20 work well, although, for large problems fewer trailing waves are recommend (10) due to memory and computational requirements.

Maximum number of trailing waves (NSFRSETS) is the maximum number of different sets of trailing waves used to allocate arrays. Arrays are allocated by multiplying NSTRAIL by NSFRSETS. A value of 30 is sufficient for problems where the stream depth varies often.

Maximum number of cells to define unsaturated zone (ISUZN) is the maximum number of vertical cells used to the define the unsaturated zone beneath a stream reach. If ICALC is 1 for all segments then ISUZN should be set to 1.

Use transient streamflow routing with kinematic-wave equation (IRTFLG) If checked, transient streamflow routing is active. streamflow will be routed using the kinematic-wave equation (see USGS Techniques and Methods 6-D1, p. 68-69);

Number of divisions per time step for kinematic waves (NUMTIM) NUMTIM is the number of sub time steps used to route streamflow. The time step that will be used to route streamflow will be equal to the MODFLOW time step divided by NUMTIM.

Time weighting factor for the kinematic wave solution (WEIGHT) WEIGHT is the time weighting factor used to calculate the change in channel storage. WEIGHT has a value between 0.5 and 1. See equation 83 in USGS Techniques and Methods 6-D1 for further details.

Closure criterion for the kinematic wave solution (FLWTOL) FLWTOL is a real number equal to the streamflow tolerance for convergence of the kinematic wave equation used for transient streamflow routing. A value of 0.00003 cubic meters per second has been used successfully in test simulations (and would need to be converted to whatever units are being used in the particular simulation).

Gage overall stream budget (OUTTYPE = 8). In the Gage package, OUTTYPE = 8 means to provide a listing of time and the following budget components summed over all stream reaches:

•stream loss;

•stream gain;

•infiltration into the unsaturated zone;

•change of storage in the unsaturated zone;

•recharge; and

•storage in the unsaturated zone.

On the Parameters tabs, the user can define parameters for the Stream-Flow Routing boundaries. These parameters will be multiplied by user-specified multipliers to determine the Stream-Flow Routing conductances defined by parameters. The user can also set up Stream-Flow Routing boundaries that do not involve parameters. Objects must be used to define the locations of the Stream-Flow Routing boundaries.

For each SFR parameter, the user must define one or more instances. For each instance, the user must define, a starting time, an ending time, and a name. These instances are used to define how the conductance multipliers for an SFR parameter vary with time. Instance names can only contain ASCII characters.

Parameters can also be edited in the Manage Parameters dialog box.