The MODFLOW-2000 program is run five times, once to simulate historical conditions, three times to simulate the the absence of Colorado, Kansas and Nebraska pumping, and once to simulate the absence if the surface water imports in the Nebraska mound area. In each of the four impact simulations, groundwater pumping and return flows, or surface water return flows in the mound impact scenario, are set equal to zero. In each simulation, the associated groundwater or surface water acreage is also set equal to zero.
For each of the five simulations, the model calculated stream flows at selected locations along the stream network are extracted using the HYDMOD package and saved to a file. The acct program then reads these files and calculates the impacts for Colorado, Kansas and Nebraska pumping and the Nebraska mound as the difference between the historical stream flow and stream flow for the corresponding impact run.
Impacts for the 24 time steps in a calendar year are converted to a volume and accumulated to produce the annual total impact. Impacts less than ten acre-feet per year are considered numerical noise and are set equal to zero.
Impacts are then written out as an HTML table where the columns represent the different impact scenarios, and rows represent the different stream segments.
acct 2002The program uses the V12s stream network by default. It reads the file ../data0/acct.12s to obtain the accounting definitions. Alternately, if the -12p flag is specified, it will read the file ../data0/acct.12p instead. For example, to run the program for the year 1995 using the V12p7 stream network, the program would be run as
acct -12p 1995
The program reads HYDMOD files named for the year. For example, for the year 2002, the program would read a file named 2002.sfi for the historical run, 2002a.sfi for no Colorado pumping, 2002b.sfi for no Kansas pumping, 2002c.sfi for no Nebraska pumping and 2002d.sfi for no Nebraska mound imports. It will then produce a file name 2000.htm that contains the impact output table.
The sign of the impacts shown in the tables differ between the pumping and mound import columns. A positive value in the pumping impact for a state is a liability for that state, while a negative value indicates a credit. For the Nebraska mound, a positive value means a credit to Nebraska, while a negative value would mean a liability.
The first entry on each line is the name of the segment. The name is enclosed in double quotes (") in order to permit embedded spaces. When the name starts with an asterisk (*), the segment is counted as part of the main stem.
Subsequent entries on each line are HYDMOD names for gage locations prefixed by a plus or minus sign, indicating whether the gage location should be added to or subtracted from the segment total.
For example, the Arikaree net gain is simply the flow at the Arikaree accounting point at the confluence of the Arikaree and the North Fork of the Republican River. This point is known as AcctArikaree, and is defined in HYDMOD as the stream inflow to segment 139 reach 3. This is known in HYDMOD parlance as SI139003AcctArikaree. The Arikaree is not counted as part of the main stem. Therefore the Arikaree definition line reads
" Arikaree" +SI139003AcctArikaree
The net gain on the main stem from Harlan County reservoir to Guide Rock is defined as the difference between the flow at Guide Rock and the flow below the Harlan County reservoir. The accounting points at Guide Rock and below Harlan County reservoir in the model are SI253006RRGuideRock and SI234002RRBloHarlan, respectively. The definition for this segment is therefore
"*Harlan - Guide Rock" +SI253006RRGuideRock -SI234002RRBloHarlanNote that the asterisk at the beginning of the file name adds the gain for this segment to the main stem total. The plus before SI253006RRGuideRock and minus before SI234002RRBloHarlan indicates that the difference between these two gages defines the net gain.
On Frenchman creek, the net gain is defined as the flow at the confluence with the main stem SI197004AcctFrenchma plus the inflow into Enders Reservoir as SI1470106831500 as measured by the USGS gage 6831500. Therefore the Frenchman definition is
" Frenchman" +SI197004AcctFrenchma +SI1470106831500
The Above Swanson segment is an example of a segment with multiple inflows. The North Fork of the Republican River at the Colorado-Nebraska state (SI153012AcctNFRepublican) line is the upper end of this segment, while the inflow to Swanson reservoir (SI202005RRAbvSwanson) is the lower end of the segment. The South Fork of the Republican River (SI185007AcctSFRepublican), the Arikaree River (SI139003AcctArikaree), Buffalo Creek (SI133001AcctBuffalo) and Rock Creek (SI131002AcctRock) flows into this stream segment. All of these tributaries are accounted for separately an must therefore be subtracted out. Therefore the Above Swanson segment is defined as
"*Above Swanson" +SI202005RRAbvSwanson -SI153012AcctNFRepublican -SI185007AcctSFRepublican -SI139003AcctArikaree -SI133001AcctBuffalo -SI131002AcctRock
The order in which the definition lines appear or the order of the gages on each definition line is not important. However, the order in which the definition lines appear controls the order in which the lines appear in the output table. Since subsequent programs may depend on the format and layout of this table, the order of these lines should not be changed.