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Office of Columbia River

WRIA 48 (Methow)

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

Overview of WRIA 48 (Methow)

The tributary surface water supply forecast for Methow is characterized mostly by increases in the late winter through late spring and slight decreases in late spring and summer.

WRIA 48 has much larger instream flow requirements than irrigation demands, and even smaller municipal demands. Because the instream flows specified in Chapter 173-548 WAC are sometimes higher for the middle Methow River near Twisp than for the lower Methow River near Pateros, instream requirements are shown as the higher of these two instream flow requirements for each month, for both the historical and future period. Assuming no change in irrigated acreage, irrigation demand is projected to increase in future summers under all economic scenarios that were considered, with small variations in impact when alternate economic scenarios are considered. Municipal demands are forecasted to grow by 20% by 2030.

If provided, additional water capacity as specified by the proposed projects in the Office of Columbia River "medium" scenario is 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 increase demand in all WRIAs where water is provided for new irrigated land.

In 2030, at the watershed scale, combined municipal and surface water irrigation demands and adopted instream flows are projected to outstrip unregulated tributary supply generated within the Washington portion of the watershed during many years from July through November, and in some years from December through February. Upstream portions of the watershed outside of Washington provide additional supplies, but may also have additional demands. Additional water supplies from the Columbia River are available to meet demands in some areas of the WRIA, and a separate analysis indicates that a bit more than a third of agricultural demand is within a mile of the Columbia River (results shown in "Washington's Columbia River Mainstem: Tier III Results"). Modeling of curtailment of interruptible irrigation water rights indicated that it occurred in 80% of years between 1977 and 2006. The resulting unmet demand ranged from 14 to 2,217 ac-ft per year depending on yearly flow conditions, with an average of 622 ac-ft per year. Simulation of future curtailment occurred in 93% of years for the middle climate scenario. The resulting unmet demand per year ranged from 12 to 2,594 with an average of 1,465 ac-ft per year. 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. Although not shown here, unmet demands due to a failure to meet adopted instream flows are shown in the technical report. Water shortages outside the scope of this analysis may also exist in localized areas, and over time periods within months.

Methow spring Chinook are a key component of the ESA-Endangered Upper Columbia Spring Chinook run. Adults spawn from late July through October, and most juveniles outmigrate in April-May. Juvenile salmon rearing occurs year-round. Bull trout in the Methow are part of the ESA-Threatened Upper Columbia Bull Trout listing unit.

Supply

WRIA 48 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.

Fish Status & Utilization by Species

WRIA 48 Fish Table

Fish use of WRIA waters (provided by Washington Department of Fish and Wildlife)

Management Context

Adjudicated Areas Beaver Creek  
Bear Creek & Davis Lake  
Libby Creek  
Gold Creek  
McFarland Creek  
Black Canyon Creek
Wolf Creek
Thompson Creek (incomplete)
Watershed Planning Phase 4 (Implementation)
Adopted Instream Flow Rules YES (Chapter 173-548 WAC)
(interruptible users curtailed annually)
Fish Listed Under the Endangered Species Act* Upper Columbia River Bull Trout
Upper Columbia River Spring Run Chinook
Upper Columbia Steelhead 
[Columbia mainstem migratory corridor]
Ground Water Management Area NO
Ground Water Studies YES (references listed in WSU technical report)

 

*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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