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Office of Columbia River

Columbia River Basin
Washington's Columbia River Mainstem: Tier III Results

  • Tier III Results
  • Supply
  • Demand Near Mainstem
  • Mainstem Demand Table
  • Curtailment

Tier III Results

Flows on the Columbia River mainstem are a reflection of flows in upstream areas of the Basin, including areas outside of Washington and tributary areas within Washington. Mainstem water supplies provide instream flows for migrating salmonids, hydroelectricity as part of the federal Columbia River Power System, and water to those in proximity to the river.

Supplies and demands are defined as described in the text box "Definitions of Water Supply and Water Demand Used in the 2011 Forecast." Because all demands exist within a watershed, the bulk of demand results are presented in the section "Washington Watersheds: Tier II Results." However, within the mainstem level, WSU did analyze the proportion of WRIA-level irrigation demand that is within one mile of the Columbia River mainstem.

Columbia River at the Dalles Bridge

Bridge at The Dalles over the Columbia River

Surface Water Supplies Compared to Regulatory and Management Schemes
at Key Points along the Columbia River Mainstem

The Forecast compared modeled historical (1977-2006) and 2030 forecasted surface water supplies at Priest Rapids, McNary, and Bonneville Dams with Washington State instream flows (WA ISF), and the Federal Columbia River Power System Biological Opinion (FCRPS BiOp)* (see figures below). These two regulatory schemes were chosen because of their role in regulating interruptible water rights holders (in the case of the WA ISF) and managing federal dams and the Quad Cities** water permit (in the case of the FCRPS BiOp).

Regulation of mainstem water users is not triggered unless the total forecasted on March 1st at The Dalles is less than 60 million acre-feet. However, on a month-to-month basis, under all flow conditions, forecasted (regulated) surface water supplies prior to meeting demands under average flow conditions were sufficient to meet Washington State instream flow targets in most months at most points along the mainstem. Under average flow conditions, the exception was November water supplies at Priest Rapids Dam, which did not meet State ISF targets.

Under dry flow conditions, in both the historical and 2030 forecast, August surface water supplies failed to meet State ISF targets at Priest Rapids and McNary. November water supplies at Priest Rapids were also below State ISF targets, under both normal and dry flow conditions.

In contrast, water supplies prior to meeting demands were insufficient to meet BiOp flows in more months, in both the historical and 2030 forecast. Under normal flow conditions, at McNary Dam, historical and 2030 forecasted water supplies were below BiOp flow targets for July and August. Historical water supplies were also below BiOp flow targets for April. At Bonneville, both historical and 2030 forecasted water supplies under average flow conditions were below BiOp flow targets from November through January. Imbalances were generally smaller in the 2030 forecast than the historical case for the late winter/spring months, and larger for the late summer. Under dry flow conditions, there were even more months when surface water supplies failed to meet BiOp flow targets. Water supplies during dry flow conditions were below BiOp flow targets at McNary Dam from April through August. Under dry flow conditions at Bonneville, water supplies were insufficient to meet BiOp flow targets from November through February in the historical period, and in the 2030 forecast from November through January.

Fig. 15-16

*The FCRPS Biological Opinion governs operations of dams that are part of the Federal Columbia River Power System, specifying flow targets and an adaptive management framework. The FCRPS BiOp aims to ensure that dam operations do not impede the recovery of endangered salmon and steelhead, is required by the Endangered Species Act, and has been the subject of continued litigation.

**Kennewick, Pasco, Richland, West Richland


Proportion of WRIA-Level Demand along the Columbia River Mainstem

The Columbia River provides an important source of water supply for many WRIA water users within close proximity to the river. With additional infrastructure investments, mainstem water supplies could potentially meet even more of these WRIA-level demands. To give a sense of what portion of WRIA-level irrigation demand was in proximity to the Columbia River mainstem, a one-mile corridor on each side of the Columbia River was defined identifying all lands bordering the Columbia River. The corridor width was selected by OCR as a surrogate for detailed, project-specific analysis. It is possible that demands outside this corridor could be met by Columbia River supplies under some circumstances; however, evaluating all possible supply options was beyond the scope of the Forecast. Unfortunately, existing water rights data do not provide sufficient accuracy to confidently estimate what proportion of this amount is already being met by Columbia River mainstem supplies versus those that could be supplied via new projects. Lastly, the feasibility of serving specific areas with water diverted from the Columbia River was also outside the scope of this Forecast.

Both historically and in the 2030 forecast, more than half of the surface water irrigation demand was within one mile of the Columbia River mainstem for the following WRIAs (see table):

Alkali-Squilchuck (WRIA 40)
Moses Coulee (44)
Foster (50)
Lower Lake Roosevelt (53)
Middle Lake Roosevelt (58)

In addition, Esquatzel Coulee (36) and Lower Crab (41) each have more than 50,000 acre-feet per year of surface water irrigation demand within one mile of the Columbia River mainstem, although this does not represent a large proportion of WRIA-level irrigation demand, as there are large numbers of irrigated acres in both these WRIAs.

Estimation of the average historical (1977-2006) and forecasted 2030 WRIA-level surface water top of crop irrigation demand (excluding conveyance losses) within one mile of the Columbia River mainstem.

WRIA WRIA Name Total modeled WRIA-level irrigation demand  Modeled WRIA-level irrigation demand within one mile of the Columbia River mainstem
acre-feet/year acre-feet/year As a percentage of WRIA-level demand
    Hist 2030 Hist 2030 Hist 2030
29 Wind-White Salmon 6,237 6,600 290 298 5% 5%
30  Klickitat 17,616 18,284 0 0 0% 0%
31  Rock-Glade 401,521 395,150 87,118 87,900 22% 22%
32  Walla Walla 209,049 208,996 7,504 7,445 4% 4%
33  Lower Snake 159,315 163,629 0 0 0% 0%
34  Palouse 28,687 29,548 0 0 0% 0%
35  Middle Snake 1,523 1,579 0 0 0% 0%
36  Esquatzel Coulee 1,166,218 1,185,731 194,190 200,891 17% 17%
37  Lower Yakima 1,435,031 1,476,659 2,840 2,909 0% 0%
38  Naches 94,821 105,019 0 0 0% 0%
39  Upper Yakima 429,379 466,141 0 0 0% 0%
40  Alkali-Squilchuck 41,535 41,916 38,818 39,060 93% 93%
41  Lower Crab 1,824,122 1,829,532 83,342 84,668 5% 5%
42  Grand Coulee 96,813 95,847 0 0 0% 0%
43  Upper Crab-Wilson 84,196 83,931 0 0 0% 0%
44  Moses Coulee 55,869 61,384 36,049 40,707 65% 66%
45  Wenatchee 34,281 36,472 2,289 2,863 7% 8%
46  Entiat 1,726 1,793 0 0 0% 0%
47  Chelan 26,783 28,944 9,737 10,070 36% 35%
48  Methow 13,165 14,600 4,785 5,385 36% 37%
49  Okanogan 102,845 110,050 17,719 18,535 17% 17%
50  Foster 26,314 31,674 26,314 31,674 100% 100%
51  Nespelem 0 0 0 0 0% 0%
52  Sanpoil 230 245 0 0 0% 0%
53  Lower Lake Roosevelt 7,065 7,443 3,947 4,130 56% 55%
54  Lower Spokane 16,522 16,360 0 0 0% 0%
55  Little Spokane 4,449 4,629 0 0 0% 0%
56  Hangman 1,295 1,416 0 0 0% 0%
57  Middle Spokane 371 404 0 0 0% 0%
58  Middle Lake Roosevelt 1,942 2,089 1,674 1,782 86% 85%
59  Colville 26,719 29,970 0 0 0% 0%
60  Kettle 3,737 4,223 0 0 0% 0%
61  Upper Lake Roosevelt 1,220 1,386 549 616 45% 44%
62  Pend Oreille 0 0 0 0 0% 0%
   TOTAL 6,320,598 6,461,645 517,167 538,932 8% 8%



Curtailment Along the Columbia River Mainstem

Water rights holders whose water use can be "interrupted" when flows fall below the levels specified by regulation are vulnerable to potential impacts of water shortages. Along the mainstem, there are 379 interruptible water rights (see figure below), the majority of which are agricultural surface water rights. When The Dalles flow forecasted is below 60 million acre-feet for April through September, these users may be required to stop using water in weeks when flows do not meet requirements. The highest total annual quantity of interruptible water is located in Lower Snake (WRIA 33), while Rock Glade (31), Alkali/Squilchuck (40), Moses Coulee (44), Okanogan (49) and Foster (50) include high numbers of impacted water rights holders.

Fig. 17

Amount of water associated with interruptible water rights along the 1-mile corridor within the Columbia River Program.


Definitions of terms used in this Forecast

Basin-Wide Results Tier 1 WRIA Results Overview Tier 2 Mainstem Results Tier 3 WDFW Instream Results


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