Notes: The water year spans Oct. 1 to Sept. 30. All water volume values are rounded to the nearest 100 ac-ft.
A. Total annual water volume is computed from the final daily average flow record published by the US Geological Survey for the Trinity River at Lewiston Stream gage 11525500. The measurement error applies to the accuracy of the published stream flow record for a given day within the water year. The total error of a sum of values tends to be less than the error associated with an individual value because positive and negative errors may cancel each other when summed. The US Geological Survey has not conducted the statistical analysis to understand how stream flow measurement errors behave when summed. Consequently, the listed accuracy for published daily average stream flow record is used for the cumulative annual water volume. The true error for the annual water volume totals are expected to be less than those listed.
B. Volume calculated for flows above the TRRP recommended release schedule for restoration (including summer and winter baseflows).
C. Computed from daily average record provided by the Bureau of Reclamation. Reported negative daily inflow values included "as is" in calculations.
D. Restoration water volume limited by Court order 2001-2004. Court ordered volumes varied by year. Court-ordered release restrictions between 2001 and 2004 resulted in a cumulative reduction of 540,600 ac-ft during that time period, as compared to full Record of Decision flow releases.
E. Long-term average annual inflow to Trinity Reservoir (ac-ft/year) from 1911-2007 as provided by the Bureau of Reclamation = 1,254,000 ac-ft.
F. Water year type based on the April 1 st B120 Forecast of Unimpaired Runoff (50% exceedance) from the Department of Water Resources California Cooperative Snow Surveys.
G. Restoration water volume as prescribed by the Trinity River Mainstem Fishery Restoration 2000 Record of Decision.
H. The Full Natural Flow is computed by multiplying estimated inflow to Trinity Reservoir by 1.04 to account for the local watershed area between Trinity Dam and the Lewiston Streamgage. The estimated inflow to Trinity Reservoir is computed by the Bureau of Reclamation based on changes in reservoir storage, evaporation, and dam releases. Uncertainty in the reservoir storage and evaporation estimates can lead to negative inflow values being reported. Negative inflow values are erroneous and have been excluded from the calculation of the full natural flow.
I. Beginning in WY2011 the Full Natural Flow at Lewiston is sourced from Unimpaired Runoff calculations in California Dept. Water Resources basin summary reports. Those reports are subject to correction without notice; TRRP strives to capture corrections.
J. The peak rate of release is based on USGS approved 15-minute flow values at Lewiston.
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.