Lower Yakima River

The Lower Yakima River is approximately 51 river miles long beginning near the Yakima County/Benton County border and ending at the Columbia River.

There have been numerous studies and reports detailing the Lower Yakima River with one of the more comprehensive being the Assessment of the Lower Yakima River in Benton County, Washington by the Benton County Conservation District in 2011.

The Lower Yakima River is a critical corridor for many species of fish including numerous salmonid species.

Geography

Mainstem Reaches in this Geographic Unit

The Lower Yakima River below Prosser Diversion Dam is generally considered a high-gradient, bedrock controlled segment with a narrow alluvial floodplain with approximately 2 miles of backwater influence on the Lower Yakima River from the McNary Dam Reservoir (Lake Wallula).

1. Prosser Reach - Yakima River Mainstem
2. Lower Yakima Reach - Yakima River Mainstem

Tributaries to the Lower Yakima River in this Geographic Unit

The tributaries to the Lower Yakima River all drain arid watersheds and are thought to have been intermittent prior to widespread irrigation; today they have perennial flows supported by both surface and subsurface irrigation return flows. Water quality issues are significant, with some of the highest levels of toxic contaminants found in the basin DOUBLE CHECK; significant work has been done by the irrigation districts and partners to reduce delivery of fine sediment and associated legacy toxins (DDT etc) to the Yakima from these creeks. These tributaries do support resident fish and limited numbers of anadromous fish but have generally not been considered priorities for anadromous fish restoration.

1. Spring and Snipes Creeks a left bank tributary that enters the Yakima River river mile 41.8; drains a mix of ag and rural residential
2. Corral Creek a left bank tributary that enters the Yakima River at river mile 33.5.
3. Cold Creek an intermittent left bank tributary that enters the Yakima River at river mile 18.8; drains a large arid area
4. Amon Creek Wasteway a right bank tributary at river mile 2.7 of the Yakima River; drains a rapidly urbanizing watershed in the Tri Cities; lots of work to conserve Amon Creek and adjacent lands as open space

Lower River Flow/Hydrology

Lower Yakima River flow has a long history and is influenced by storage dams in the Yakima headwaters, irrigation dams, diversions, agriculture, tributary streams, groundwater, return flows, power production, fish, recreation, and a number of other factors; making flow complicated.

There are four large diversions in the Lower Yakima River including Kennewick Irrigation District (KID), Columbia Irrigation District (CID), Kiona Irrigation District, and Richland Irrigation District.

Two diversion dams, Prosser Diversion Dam and Wanawish Dam.

One power plant, Chandler Power Plant.

Kennewick Irrigation District and pumping

The Kennewick Irrigation District (KID) currently diverts water from the Yakima River at Prosser, Washington. The water flows down Chandler Canal to the Chandler Pump Station where it is pumped into the KID's Main Canal. Up to 333 cubic feet per second (cfs) of irrigation water is pumped into the Main Canal. The pumps in Chandler Pump Station are hydraulically driven turbine pumps which require approximately 1.25 gallons of water to lift (pump) one gallon of water into KID's Main Canal. Therefore, furnishing KID's irrigation and pumping water requires a peak diversion from the Yakima River of 749 cfs. At Chandler Pump Station, the 416 cfs used to drive the hydraulic pumps is returned to the Yakima River at river mile 35.8.

Yakima River Basin Water Enhancement Program (YRBWEP) and Title XII Flows

Phase II of the YRBWEP was authorized by Title XII of the Act of October 31, 1994 (108 Stat. 4550, Public Law 103-434).

One of the purposes of the YRBWEP is to implement water conservation measures to reduce out-of-stream irrigation water diversions from the Yakima River and its tributaries. Savings achieved through improvements to water delivery systems and changes in operation and management would result in more water remaining in the stream to improve flows for fish and wildlife and the reliability of the irrigation water supply.

YRBWEP established target flows for instream purposes to be maintained past the Sunnyside and Prosser Diversion Dams using criteria based on TWSA. The streamflow targets range from 300 cfs to 600 cfs, depending on the estimate of TWSA. In addition, Phase II of the YRBWEP also provides that, as conservation measures are implemented under the conservation program and irrigation water demands are thereby reduced, the target flows will be increased by 50 cfs for each 27,000 acre-feet of diversion reduction during non-prorated water years. During those years, the target flows obtained through water conservation would be increased above 300 cfs only where irrigation return flows previously entered the Yakima River downstream of Parker gage.

Power Subordination

Power subordination for fish resource protection: Power subordination occurs when power generation is reduced or shutdown, allowing the power water diversion flows to remain in the river system to protect the fishery resources or to enhance fish passage. Reclamation subordinates power production of Chandler Power Plant to various flows passing over Prosser Diversion Dam throughout the year. In the spring, the subordination target is 1,000 cfs over Prosser Dam through the end of June. During the remainder of the irrigation season, the subordination target is 450 cfs or the YRBWEP target flow, whichever is higher.

Passage Flows: Flows are supported by project operations for fish movement (usually salmonids). Passage flows are flow volumes that allow fish to move un-impeded through the river system. There are three river reaches in the system with passage flow issues that are annually reviewed. Target flows for the individual river reaches are set by the Field Office Manager following consultation with SOAC and others, considering current and future water management needs. The relevant river reach in the Lower Yakima River is from Prosser Diversion Dam to Yakima River below the Chandler Power Plant return flow.

Flushing/Pulse Flows: Flows are supported by project operations to facilitate the out-migration of anadromous salmonid smolts. The necessity for, magnitude, and timing of out-migration flushing/pulse flows are determined by the Field Office Manager, with input or recommendations provided by SOAC, irrigation district managers, Reclamation environmental staff, and others.

Target Flows: Target flows are set for spawning, incubation, rearing, passage, and power subordination as determined by the Field Office Manager, with input or recommendations provided by SOAC, irrigation managers, and others.

Stream Gages

There are two gages in the mainstem Lower Yakima River

BOR (YRPW) Prosser Stream Gage just below Prosser Dam at river mile 46.3, see BOR Gage

USGS stream flow monitoring at Kiona, located at river mile 30, see USGS Gage.

See Yakima Basin combined stream flow monitoring links page

Facilities

Prosser Diversion Dam: A 9-foot-high concrete weir diversion dam on the Yakima River near Prosser. The Prosser Diversion Dam feeds the Chandler Canal which serves Kennewick Division of the Bureau of Reclamation's Yakima Project.

Chandler Canal:

Prosser Hatchery and Enumeration Facility

Chandler Power Plant: Constructed and operated by the Bureau of Reclamation. the Chandler Power Plant is located 11 miles downstream from Prosser. Water is diverted at the Prosser Diversion Dam into the Chandler Canal (up to 1,500 cfs) and is delivered to the pumping and power plant 10 miles down the canal. A maximum of 334 cfs is pumped to the Kennewick Irrigation District and the rest of the water is discharged to the Yakima River at river mile 35.8. The Chandler Power Plant operates year around and us subject to power subordination agreements for fish resource protection. The power output i s marketed and sold by the Bonneville Power Administration as part of the Federal Columbia River Power System.

Wanawish Dam (Horn Rapids Dam)

• Columbia Irrigation District
• Barker Ranch

Benton Irrigation District

Lewis and Clark Irrigation District

Badger Mountain Irrigation District

Water Stargrass (Heteranthera dubia)

Water stargrass is a perennial plant that has become well established in the lower 43 miles of the Yakima River, below Prosser Dam.

See separate page on Water stargrass

Yakima Delta

The Yakima delta and confluence is a critical link to the entire Yakima River both historically and today. The confluence was an important tribal fishing ground as noted in the Lewis and Clark Journals.

It provides an important link for fish as an adult and juvenile migration corridor.

However, much of the original floodplain/delta has been significantly developed, altered, or submerged as a result of the construction of McNary Dam downstream in the Columbia River. The reservoir now formed by McNary Dam extends nearly 2 miles up the Yakima River, changing flow and sediment deposition patterns in the delta.

The construction of the Bateman Island Causeway around 1940 further constrained the flow patterns of both the Yakima River and Columbia River in the delta.

For more info see the Yakima Delta page.

Water Quality

Water quality concerns in the lower Yakima River include high water temperature, low dissolved oxygen, high pH, high suspended sediments, high turbidity, and high levels of toxic substances.

Stream Temperature

The lower Yakima River is known to reach levels nearing 85°F (30°C) in the summer, creating a migration barrier for salmonids.

The primary causes of high stream temperatures in the Lower Yakima River are: 1) hot air temperatures, 2) a wide, shallow river with little riparian vegetation to provide shade, 3) loss of floodplain and riparian functions due to channelization and development, and 4) low flows due to water diversions.

Habitat Quality

The Lower Yakima River below Prosser Diversion Dam is generally considered a high-gradient, bedrock controlled segment with a narrow alluvial floodplain.

Channel Complexity

Large Wood

Vegetation

Refuge Habitat

Fish Use

Salmon and Steelhead Bull Trout

Non-Natives

Predation (Piscivore and Avian)