Flow Volume Summary

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Water Volume Summary for Trinity River Releases and Diversions Since 2001.
Water Year (Oct. 1 through Sept. 30)Forecasted Full Natural Flow Volumes
Forecasted Type
Actual Type
Actual Full Natural Flow Volumes
Allocated Restoration Flow Volumes
Released Restoration Flow Volumes
Ceremonial Release Volumes
Augmentation Flows for the Klamath River
Reservoir Management Releases
Other Releases
Total Volume of Release to the Trinity River
Peak Discharge to River
Volume of Diversion to Central Valley
20062,105,000Ext WetExt Wet2,496,685815,000810,31500408,02201,218,33710,4001,232,967
2014395,000Crit DryCrit Dry381,100369,000370,415064,88300435,2983,460618,595
20172,265,000Ext WetExt Wet2,304,177815,000821,2668,832035,8550865,95312,000628,427
2018530,000Crit DryCrit Dry570,812369,000377,155016,413017,554411,1222,040389,893
2020515,000Crit DryCrit Dry472,416369,000369,14606,89100376,0373,970811,333
2021530,000Crit Dry[TBD][TBD]369,000[TBD][TBD][TBD][TBD][TBD][TBD][TBD][TBD]

Notes: The water year spans Oct. 1 to Sept. 30.

A. The forecasted full natural flow volume is published in the April 1st B-120 Forecast of annual Unimpaired Runoff (50% exceedance) at Lewiston by the California Department of Water Resources at https://cdec.water.ca.gov/snow/bulletin120/. An acre-foot (ac-ft) of water is the volume that covers an acre in one foot of water. This forecast volume determines the volume of water allotted to the Trinity River for restoration as prescribed in the Trinity River Mainstem Fishery Restoration 2000 Record of Decision. B-120 forecasts were not issued for 2001-03.

B. Full Natural Flow is the inflow to Trinity Reservoir multiplied by 1.04 to account for the watershed area between the reservoir and Lewiston. Inflows to the Reservoir are computed by the U.S. Bureau of Reclamation (USBR) from changes in reservoir storage, evaporation, and dam releases. Uncertainty in water storage and evaporation can result in negative inflows that are included in the calculations as reported.

C. Restoration water volume prescribed in the Trinity River Mainstem Fishery Restoration 2000 Record of Decision. Court-ordered restrictions in flow for 2001-2004 resulted in a cumulative reduction of 540,600 ac-ft in this period compared to Record of Decision flows released thereafter.

D. Restoration release volumes are computed from the final daily average flow record published by USGS for the Trinity River at Lewiston after subtracting flows that are released for non-restoration purposes (see E, F, and G).

E. Ceremonial releases occur in odd-numbered years for the Hoopa Boat Dance Festival except a ceremonial release was not made in 2003 because Klamath River augmentation flows satisfied water requirements for the Festival in this year.

F. Flows are released by the U.S. Bureau of Reclamation from Lewiston Dam to augment discharges in the lower Klamath River when needed to aide juvenile salmon rearing and adult migration to spawning grounds.

G. Reservoir management releases occur when necessary to protect against over-filling Trinity Reservoir.

H. “Other releases” include flow events that occur for other than river restoration and can include emergency flows related to dam and flow diversion infrastructures and water temperature management in the Trinity River.

I. The total release to the Trinity River is the sum of columns with notes D through H.

J. The peak flow release is the highest discharge recorded from measurements at 15-minute intervals throughout the water year at the USGS gage at Lewiston. The acronym “cfs” refers to the flow discharge in cubic feet per second.

K. Reported in USBR monthly reports for Lewiston Reservoir.

TBD = To Be Determined

Prior to the 2000 Record of Decision (ROD), diversion to the Central Valley averaged 74%. Under the ROD exports were expected to drop to 52%. This pie-chart shows the actual proportions according to flow measurements beginning from water year 2001. [Reference: USDI 2000, page 20.]

This graph provides information on water releases per water year (colored bands) relative to the reservoir inflow (dark blue line, Full Natural Flow). Total releases need not match the inflows within each year because the reservoir allows storage or usage of water. Periods where the dark blue line rises above the colored bands indicate net increases in reservoir storage while periods where the dark blue line falls below the top of the colored bands indicate net reduction of water storage.


Current Restoration Flow Release Schedule

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Typical Releases

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