Republican River Compact Administration
Groundwater Model Update 2001-2003

Changes to the RRCA groundwater model from V12p7 to the 2001, 2002 and 2003 model update consists of three types:
  1. Changes to the model;
  2. Changes to the state inputs;
  3. Changes to pre- and post-processing programs.
For model years 2004 and beyond, further changes may be required as a result of changes in the available data, but these changes should generally be incrementally small compared to the changes described here.

In addition to model runs for 2001, 2002 and 2003, the model was also run for 1993 through 2000 to ensure that the new model results agree with the V12p7 model.

Changes to the model.

Experts for Nebraska pointed out a problem with the stream routing on Medicine Creek above Harry Strunk. In essence, the problem was that nine model river cells between the Medicine Creek above Harry Strunk Lake gage and Harry Strunk Lake were omitted in the V12p7 stream package starting with the construction of Harry Strunk reservoir.

A correction to this problem called V12s was implemented by restoring the omitted stream cells above Harry Strunk reservoir by extending the stream segment 170 from the Medicine Creek above Harry Strunk Lake gage to Harry Strunk Lake, and shortening stream segment 183 to consist only of Harry Strunk Lake.

As a result of the change to the stream package, the accounting point on Medicine Creek above Harry Strunk Lake was updated to reflect the change.

The V12s correction was reviewed by the RRCA on January 7, 2004 and the RRCA decided that this correction would be applied to the model starting in model year 2001. The V12s stream package therefore applies to the 2001, 2002 and 2003 model years, and in future model years.

Changes to State Inputs

The pumping and return flow recharge calculations for Kansas were substantially modified from V12p7 to the 2001 to 2003 updates. Starting in 2001, Kansas applied water user reports to calculate these quantities on an individual field basis, whereas in V12p7 calculations were made on a county basis and distributed to individual wells.

The pumping and return flow calculations for Colorado remain identical to what was used in V12p7. However, instead of using the appropriated acreage defined on individual well permits for the precipitation recharge calculation, the actual irrigated acreage as defined by the appropriate County Assessors Office is used in the pumping calculations that are relevant to the precipitation recharge calculations starting in 2001.

In V12p7, all Nebraska pumping was calculated using electrical power records. Starting in 2001, because of the quality of the district's well meter program, Nebraska decided to use metered values of pumping for the Upper Republican Natural Resource District (Perkins, Chase and Dundy Counties). Nebraska continues to use the power-record methodology for all other counties. In V12p7, private canals and river pumpers were treated separately, while starting in 2001, these categories are subsumed in the surface water category.

Changes to pre- and post-processing programs.

In order to facilitate running the model on a yearly basis, the pre- and post-processing programs and directory structure were reorganized. Cosmetic changes were made to the pre- and post-processing programs to use the new directory structure.

Binary files are used to transfer heads from one run to the next. Therefore, the results produced by running the model on an annual basis are absolutely identical to running the model for multiple years.

In V12p7, sub-basin factors were used to change the ET area over time. From 1993, this area does not change. The ET pre-processing program mket was modified to use an ET area distribution that does not change with time.

The procedure by which the maximum monthly ET is calculated was streamlined. The new streamlined procedure was not used in 2001 through 2003, but will be used starting in 2004. The ET Changes section describes the changes in more detail.

The stream package pre-processor mkstr was modified to allow both the V12p7 and the V12s stream routing to be used. The V12p7 routing is used until model year 2000 for model verification purposes. The V12s routing is used starting in 2001.

The accounting program acct was modified to summarize impacts on an annual basis. The county-by-county summary program mkcty was enhanced to calculate additional water budget terms for each county.

A number of utility programs were developed to streamline running the model. For example, the mkinp program creates the input files needed by MODFLOW and other pre-processing programs. These programs as well as other pre- and post-processing programs are described in detail in the User Manual.

Model V12s
ET Changes
User Manual (Draft)
Data Files
Well Pumping
County Summaries
Head Change
Predicted Impact