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Office of Columbia River

WRIA 33 (Lower Snake)

  • Overview
  • Supply
  • Demand
  • Supply & Demand
  • Management Context
  • Water Allocation

Overview of WRIA 33 (Lower Snake) Results

The tributary surface water supply forecast for Lower Snake is characterized mostly by small increases in some years from late fall through mid-spring.

As in many other WRIAs in eastern Washington, irrigation demands dominate, and municipal demands are much smaller.

Assuming no change in irrigated acreage, irrigation demands are projected to increase somewhat in most months of future irrigation seasons, with some variation in the magnitude of the increase depending on the economic scenario being considered. Municipal demands are expected to grow 16% by 2030.

If provided, additional water capacity as specified by the proposed projects in the Office of Columbia River "medium" scenario is not anticipated to increase agricultural irrigation water demand in this WRIA compared to 2030 irrigation water demand under the economic base case (a scenario of no additional capacity). Additional capacity will only increase demand in WRIAswhere water is provided for new irrigated land.

In 2030, unregulated tributary supply would be insufficient to meet combined municipal and surface water irrigation demands at the watershed scale on its own during most years for May through October, and in some years in April. Additional water supply is available to some areas from the Columbia Basin Project. Other areas receive Snake River water supplies. Modeling results suggested no unmet demand for this WRIA resulting from curtailment of interruptible water rights holders in the historical or future period. Due to data and resource constraints, the modeling of unmet demand did not consider curtailment of one water user in favor of another more senior water right holder. Water shortages outside the scope of this analysis may also exist in localized areas, and over time periods within months.

Fish listed under the Endangered Species Act that spawn or rear in tributary waters of this watershed include Snake River Basin Steelhead, Snake River Fall Run Chinook, and Snake River Spring and Summer Run Chinook.

Supply

WRIA 33 Supply graph

Modeled historical (1977-2006) and 2030 surface water supply generated within the WRIA for dry (20th percentile, top), average (middle), and wet (80th percentile, bottom) flow conditions. The spread of 2030 flow conditions is due to the range of climate change scenarios considered. Supply includes current major reservoir operations for Yakima (WRIAs 37, 38, and 39); otherwise it is the unregulated supply, without consideration for reservoirs. Supplies are reported prior to accounting for demands, and thus should not be compared to observed flows.

Surface water supplies include only supplies generated on tributaries within the Washington portion of the watershed. They do not include water supplies that enter the WRIA from upstream portions of the watershed, nor do they include water supplies from the Snake River or Columbia River Mainstem. These water supplies are characterized in "Tier II: Supply" and "Washington's Columbia River Mainstem: Tier III results."

Demand

Historical water demand

Modeled historical (1977-2006) and 2030 irrigation water, municipal, and instream flow demands under average flow conditions, and under the middle climate change scenario considered. Forecast 2030 water demands are shown for three economic scenarios: low, medium, and high growth in the domestic economy and international trade. Ground water (GW, brown) and surface water (SW, dark green) irrigation demands are shown at the “top of crop” and include water that will actually be used by plants, as well as on-field losses based on irrigation type. Conveyance losses (light green) are estimated separately. Consumptive municipal demands (yellow) include self-supplied domestic use, but exclude self-supplied industrial use. Instream flows (blue) for both the historical and 2030 forecast are shown using adopted state instream flows or federal flow targets. When more than one instream flow exists at the sub-watershed level for a given month, the largest value (generally also the most downstream) was used to express instream flows at the WRIA level.

Future water demand

2030 forecasted water demands under the 2030 forecast economic base case (medium economic scenario, no additional water capacity, same as "2030 Medium" in the graph above), and under the 2030 medium water capacity scenario (with the addition of 200,000 ac-ft per year of proposed additional capacity). The medium water capacity scenario examined a specific set of water capacity projects across eastern Washington, and assumed that new surface water supplies would be used for two purposes: as replacement water for acreage in Odessa currently irrigated with groundwater, and to grow crops on land that is not currently irrigated. Irrigation water demand is shown under average flow conditions and for the middle climate change scenario considered. It includes groundwater and surface water demands, as well as conveyance losses, as above.

Supply & Demand

Supply & demand

Comparison of surface water supply, surface water irrigation demands, and municipal demand for 2030, using the baseline economic scenario, and the middle value of the range of climate change scenarios considered. Wet (80th percentile), average, and dry (20th percentile) flow conditions are shown for supply. The 80th, 50th, and 20th percentile conditions are also shown for irrigation demand using error bars. Demands and supplies are defined as above. Water curtailment is not considered.

Management Context

Adjudicated Areas NO 
WatershedPlanning NO
Adopted Instream Flow Rules NO
Fish Listed Under the Endangered Species Act*  Snake River Basin Steelhead 
Snake River Fall Run Chinook
Snake River Spring and Summer Run Chinook
[Snake mainstem migratory corridor for Snake River sockeye]
Ground Water Management Area YES (Franklin Co. portions are part of Columbia Basin GWMA)
Ground Water Studies No WRIA level studies found (but see WSU technical report for references on Columbia Basin Ground Water Management Area and Columbia Plateau Regional Aquifer System)

 

*All species that spawn or rear in WRIA waters are identified. Species that migrate through WRIA waters are not individually identified, but migratory corridors for listed fish species that spawn and rear upstream are noted.

 

Water Allocation

Water Allocation graph

To give an indication of the amount of uncertainty related to water claims, permits, and certificate data, total annual quantities of water identified under state level water claims, permits, and certificates in Ecology's Water Rights Tracking System (WRTS) are provided, as well as information on the percentage of documents without information. Water documents that could be identified as exclusively non-consumptive uses (e.g. power, fish propagation) were removed from analysis. WRTS data does not include tribal or federal quantified or unquantified water rights.

 

Definitions 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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