Attachment 3: RRCA groundwater model analysis

Reduction in Nebraska impacts under a scenario for 2005-2006

April 18, 2008

As part of an analysis of economic damages due to Nebraska’s failure to comply with the Final

Settlement Stipulation’s water-short year test for 2006, we were asked to develop a groundwater

model scenario for years 2005-2006 that removes groundwater pumping for irrigation within the

model stream cells in the Republican River basin in Nebraska for these two years. All other

conditions were the same as in the RRCA historical model runs for these years. In particular, the

groundwater irrigation area outside the stream cells remains the same as reported for years 2005

and 2006.

As Table 1 shows, this scenario reduced groundwater irrigation pumping by an average of

116,505 acre-feet and groundwater irrigated area by 131,095 acres for years 2005 and 2006.

Nebraska’s impact—i.e., the net sum of Nebraska pumping impacts and Platte River import

credits— is reduced by a total of 41,175 acre-feet from the actual reported impacts for those two

years. Note that both groundwater irrigation pumping and the irrigated area differ between 2005

and 2006, because the amount of irrigation reported by Nebraska and included in the RRCA

historic model runs for those two years was different, and all of it in the model stream cells was

removed for this model simulation.

Table 2 shows impact reductions at each accounting point for years 2005 and 2006, and shows

both averages and sums of impact reductions over years 2005 and 2006.

Table 1. Reduction in groundwater irrigation and pumping, and corresponding reduction of

Nebraska impact on Republican River streamflow, under the scenario simulated.

Year Groundwater

irrigation pumping

reduction

(acre-feet)

Groundwater

irrigation area

reduction

(acres)

Nebraska impact

reduction,

pumping + mound

(acre-feet)

2005 134,105 140,858 14,885

2006 98,905 121,332 26,290

2005-2006 Average: 116,505 131,095 Sum: 41,175

2

Table 2. Impact reductions by accounting point for 2005 and 2006

Year

Account point

2005 2006 Average

2005-

2006

Sum

2005-

2006

Arikaree 73 73 73 146

Beaver 0 0 0 0

Buffalo 74 173 124 247

Driftwood 99 234 166 333

Frenchman 5686 5674 5679 11360

North Fork 131 44 87 175

Above Swanson 2533 3088 2811 5621

Swanson - Harlan -3771 7819 2024 4048

Harlan - Guide

Rock

6845 5445 6144 12290

Guide Rock -

Hardy

1045 995 1021 2040

Medicine 1597 2012 1805 3609

Prairie Dog 0 0 0 0

Red Willow 41 103 72 144

Rock 1 6 3 7

Sappa 0 0 0 0

South Fork 109 379 244 488

Hugh Butler 82 3 43 85

Bonny 0 0 0 0

Keith Sebelius 0 0 0 0

Enders 101 82 92 183

Harlan 96 52 73 148

Harry Strunk 27 11 19 38

Swanson 109 99 104 208

Mainstem Total 6656 17346 12000 24002

Total 14885 26290 20587 41175