Surface-Water Routing (SWR1) Process (version 1.01.0)

The SWR1 Process was modified to allow incorporation of SWR1 derivative terms into the
groundwater flow equation solved by MODFLOW-NWT. The SWR1 Process was also modified to
allow downstream discharge from a SFR2 reach to be routed to a SWR1 reach using an
additional SWR1 surface-water control structure. The SWR1 Process was also modified to
allow surface-water control structures discharging from the SWR1 network (ISTRCONN=0)
to discharge to SFR2 reaches.

SWR1 Process source files that were modified include: gwf2swr7_NWT.f

Modified input instructions for the SWR1 input file

Items 0-1a: As in previous versions of the code.

1b.  CSWROPT [IOPTUNIT]

USE_IMPLICIT_NEWTON_CORRECTION keyword for implicitly calculating 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.

USE_EXPLICIT_NEWTON_CORRECTION keyword for explicitly calculating 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.

By default, Newton corrections are not calculated. Only one of the keywords
  specified above should be used if Newton correction terms for the SWR1
  Process are desired. As a result, SWR1 Process runtimes will be approximately 
  a factor of 2 greater.

Items 2-12: As in previous versions of the code.

13a. ISTRRCH ISTRNUM ISTRCONN ISTRTYPE [NSTRPTS] [STRCD] [STRCD2] [STRCD3] 
     [STRINV] [STRINV2] [STRWID] [STRWID2] [STRLEN] [STRMAN] [STRVAL] [ISTRDIR]
     [ISFRSEG] [ISFRRCH]
     
ISTRRCH  - No changes
ISTRNUM  - Must be 0 if: (1) ISTRTYPE=11; or (2) SFR is specified in the MODFLOW-NWT name
           file and ISFRSEG and ISFRRCH > 0. No changes otherwise.
ISTRTYPE - ISTRTYPE=11 for an inflow structure from SFR2 segment ISFRSEG and reach ISFRRCH. 
           ISTRCONN must be 0 if ISTRTYPE=11. All other surface-water control structures
           detailed in the documentation report are available.
NSTRPTS  - No changes
STRCD    - No changes
STRCD2   - No changes
STRCD3   - No changes
STRINV   - No changes
STRINV2  - No changes
STRWID   - No changes
STRWID2  - No changes
STRLEN   - No changes
STRMAN   - No changes
STRVAL   - No changes
ISTRDIR  - No changes
ISFRSEG  - SFR2 segment that (1) supplies downstream segment discharge to SWR1 reach 
           ISTRRCH or (2) SFR2 segment that receives SWR2 surface-water control 
           structure discharge. ISFRSEG is not read if SFR is not specified in the 
           MODFLOW-NWT name file.
ISFRRCH  - SFR2 reach in SFR2 segment ISFRSEG that receives SWR2 surface-water control  
           structure discharge. Any SFR2 reach number can be specified if ISTRTYPE=11.
           ISFRRCH is not read if SFR is not specified in the MODFLOW-NWT name file.

Items 13b-15: As in previous versions of the code.

Hughes, J.D., Langevin, C.D., Chartier, K.L., and White, J.T., 2012, Documentation of the Surface-Water 
Routing (SWR1) Process for modeling surface-water flow with the U.S. Geological Survey Modular Ground-Water 
Model (MODFLOW-2005): U.S. Geological Survey Techniques and Methods, book 6, chap. A40 (Version 1.0), 113 p.