SWR Reach Geometry Dialog Box |
SWR Reach Geometry Dialog Box |
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The SWR Reach Geometry dialog box is used for specifying how the volume, wetted perimeter, surface area, and cross sectional area of the reach vary with stage. The same reach geometry can be used with multiple reaches. Each reach can have a different vertical offset of the reach geometry.
The SWR Reach Geometry dialog box is displayed by selecting Model|SWR Dialog Boxes|Reach Geometry...
The top half of the dialog box displays data for which only a single value must be assigned for any particular reach geometry. If a particular reach geometry requires a table of values, the table is displayed in the lower half of the dialog box.
The geometry number (IGEONUM) is assigned automatically by ModelMuse. It based on the order with which the different geometries appear in the table. You can change the order by dragging a row of the table to a new position.
Each different geometry must be given a unique Name. This Name is used to identify a reach geometry in the reach definition. See Reaches in SWR: Surface-Water Routing Process.
There are five different ways to specify the reach geometry. Which one is being used is specified by the Geometry Type (IGEOTYPE). The five types are listed below.
•Rectangular cross section (1): For a rectangular cross section, you specify a bottom elevation and a channel width.
•Trapezoidal cross section (2): For a trapezoidal cross section, you specify a bottom elevation, a channel width, and a side slope.
•Irregular cross section (3): For an irregular cross section you specify a X and bottom elevation (ELEVB) coordinates of the cross section in a table in the bottom half of the dialog box. A plot of the irregular cross section is shown next to the table.
•Table of values (4): For a table of values, you fill a table of values of elevation (ELEV), volume (VOL), wetted perimeter (WETPER), surface area (SAREA), and cross sectional area (XAREA). The table will be in the bottom half of the dialog box. A plot of data in the table is shown next to the table. The data that is plotted depends on which column of the table is selected. If the plot area is too small to plot the data, the data are not plotted.
•Entire cell (5): If a reach occupies an entire cell, MODFLOW can infer the required information from the size of the cell.
Conductance Method (IGCNDOP): IGCNDOP defines the approach used to calculate conductance for the geometry entry. There are four options.
•Fixed conductance (0): Fixed conductance is specified for the geometry entry.
•Specified leakance (1): Conductance is calculated using specified leakance coefficient, reach length, and simulated wetted perimeter. (Leakance is hydraulic conductivity divided by thickness.)
•K from flow package (2): Conductance is calculated using the horizontal hydraulic conductivity, reach length, and simulated wetted perimeter.
•Leakance and K (3): Conductance is calculated using an assumed serial connection (harmonic mean) of the specified leakance coefficient and horizontal hydraulic conductivity.
Manning’s Roughness (GMANNING): GMANNING—a real number that is Manning’s roughness coefficient for the geometry entry (in units of seconds per m1/3 and equivalent to published dimensionless Manning’s roughness coefficients). This value is only used for reaches associated with this IGEONUM and using the diffusive-wave approximation (IROUTETYPE = 3) to solve for surface-water flow between reach groups or reaches connected using an uncontrolled discharge connection structure (ISTRTYPE = 2).
Which of the remaining data must be defined for a reach depends on your choice of Geometry Type and Conductance Method.
Width (GWIDTH): GWIDTH defines the bottom width of the rectangular or trapezoidal cross-section (in units of length).
Bottom Elevation (GBELEV): GBELEV defines the bottom elevation of the rectangular or trapezoidal cross-section (in units of length).
Side Slope (GSSLOPE): GSSLOPE defines the side slope of the trapezoidal cross-section (in units of length per length).
Conductance (GCND): GCND defines the conductance (in units of length squared per time) of the geometry entry. If a reach associated with this geometry type spans more than one layer, GCND is internally distributed based on the length of the wetted perimeter in the layer relative to the total wetted perimeter of the reach.
Leakance (GLK): GLK defines the leakance coefficient (in units of time-1) of the geometry entry. Leakance is hydraulic conductivity divided by the thickness of the material separating the reach from the center of the cell containing the reach.
Average Horizontal Distance to Cell Center (GCNDLN): GCNDLN defines the average horizontal distance from the reach to the center of the finite-difference grid (in units of length).
Extinction Depth (GETEXTD): GETEXTD defines the extinction depth (in units of length) for evapotranspiration from groundwater for cases where simulated evaporation for the reach is less than EVAP.
For irregular cross sections, a table of values defining the geometry of the cross section appears in the bottom half of the dialog box.
X (XB): XB defines the distance relative to the left bank (in units of length) of the geometry type (when looking downstream). By definition, the first value represents the left edge of the cross-section; values for remaining points should be equal to or less than the previous distance.
Bottom Elevation (ELEVB): ELEVB(i) is the elevation (in units of length) of the cross-section point at XB(i).
For reach geometries defined by a table of values, the table appears in the bottom half of the dialog box.
Elevation (ELEV): ELEV is the elevation (in units of length) of the geometry type. By definition, the first value represents the lowest elevation; values for remaining points should be greater than the previous elevation.
Volume (VOL): VOL(i) is the volume (in units of length cubed) of the geometry type at ELEV(i). By definition, the first value represents the smallest volume (and will likely be zero); values for remaining points should be greater than or equal to the previous volume.
Wetted Perimeter (WETPER): WETPER(i) is the wetted perimeter (in units of length) of the geometry type at ELEV(i). By definition, the first value represents the smallest wetted perimeter (and will likely be zero); values for remaining points should be greater than or equal to the previous wetted perimeter.
Surface Area (SAREA): SAREA(i) is the surface area (in units of length squared) of the geometry type at ELEV(i). By definition, the first value represents the smallest surface area (and will likely be zero); values for remaining points should be greater than or equal to the previous surface area.
Cross-Sectional Area (XAREA): XAREA(i) is the cross-sectional area (in units of length squared) of the geometry type at ELEV(i). By definition, the first value represents the smallest cross-sectional area (and will likely be zero); values for remaining points should be greater than or equal to the previous cross-sectional area. The cross-sectional area is used for conveyance calculations for reaches using the diffusive-wave approximation (IROUTETYPE = 3) to solve for surface-water flow.