2011 Water Year Update

Updated: October 2, 2011

The 2011 water year is in the books. As of Octber 1, we are now in water year 2012. 2011 turned out to be a very good year for Trinity Lake. The lake exited September as the 2nd highest level ever for that date. The lake seemed virtually full all summer with the Bureau taking most of its summer water from Shasta Lake. Compared to one year ago, the lake elevation is 44.6' higher, with 613,000 acre-feet more water. The lake is the 2nd highest it has ever been on October 1, with only 1963 a bit higher at 2,153.9'. Even we have a normal amount of precipitation this winter, the lake should be full again next season!

The 11,000 cfs flow experiment did not make a noticeable dent in the lake elevation. In fact, the lake was held within 18" of the spillway for many days, ensuring that all water passing through the dam was used for power generation.

Tourism improved noticeably. While not yet back to the heydays when seemed alwmost crowded, the campgrounds were full for many nights, and the slips were full at the marinas.

Forecast for this winter: The Bureau plans to take the lake down at least to 2,347' by November 1. And then depending on how the rainy season starts, they may take it down as much as 10' more in anticipation of the winter season. If this pans out, we should see the low point this year somewhere between 2,337' and 2,347'. However, at the current rate, they will drop below 2,347' by November 1, so stay tuned.

What does that mean? If the lake stays above 2,338', according to our analysis, this would be the highest the lake has ever been at its annual low point since the lake filled — the highest low water mark ever! And the Trinity Center double-lane ramp would stay in the water all the way to next summer. Keep those fingers crossed: it's working!!

We'll update the relevant graphs when we have time to download all the new data.

Updated: May 13, 2011

The USBR and USFWS who jointly manage the Trinity River Resoration Project for the Dept. of Interior approved the Trinity Management Council (TMC) recommendation to adopt the 11,000 cfs flow experiment as this year's release schedule. Instead of the ROD flow peak of 8,500 cfs for 5 days, the Bureau released 10,000 cfs on May 3, and then averaged 11,000 cfs for the subsequent 3 days. At one point, due to an error in flow gauging, they released about 12,100 cfs for a few hours.

This was an experiment to see what river scouring they can get with 11,000 cfs and to ensure that the river bed and surrounding infrastructure can handle 11,000 cfs from the dam. The TMC voted 7-1 to adopt this schedule with, as is so often the case, the Hoopa Tribe voting against it.

There are TAMWG (Trinity Adaptive Management Working Group) and TMC meetings scheduled for next week, so we should hear some data on the effects of the grand experiment. The TLRA is now a seated member of TAMWG to represent the interests of the people of the North Lake area.

The Department of Water Resources and NOAA declared this year a "Wet" year for the Trinity River watershed for the purposes of the Trinity River Restoration Project. According to the Department of the Interior Record of Decision, a "Wet" year means that 701,000 acre-feet of water will be sent down the river.

Also, since the river only gets 48-50% of the water release from Trinity Lake, that means another 701,000+ acre-feet of water could be sent over the hill to the Central Valley.

What does this mean to us? The difference between a "Normal" year (such as 2010) and a "Wet" year results in something like 10-12 feet in additional draw-down over the course of the summer. However, with more scheduled maintenance on the Carr tunnel and powerplants, and with a full Shasta Lake just over the hill, we may be spared several feet of drawdown (as we were last year) for water going to the Central Valley.

Doing some rough math, we figured that the ramp up to and including the 11,000 cfs will take about 85,330 acre-feet of water. At today's lake elevation that volume equals about 6-8 feet in lake elevation. The lake peaked at 2361.79' Saturday afternoon, April 30. By mid-May, the lake was holding at 2,357', so the big release cost us about 4-5' of lake elevation. The difference was made up by the beginning of the spring snowmelt.

The forecast for lake levels based on the available data shows that Trinity Center ramp should remain in the water for this entire season. Also, if we get any more significant precipitation this spring, that will all be gravy since precipitation after April 1 is not counted toward this water year.

Final Water Year Forecast

The California Department of Water Resources in partnership with NOAA, released their forecast of the total water inflow, or water yield, for Trinity Lake in 2011.

They presented the 4/8/11 Bulletin 120 Summary data, http://cdec.water.ca.gov/snow/bulletin120/index2.html, the forecasted water yield for Trinity Lake is 1,800 TAF (thousands of acre-feet).

Bulletion 120 water yield

Per the Record of Decision (ROD), the river restoration water year is determined by the forecast “50% exceedance probability” inflow into Trinity Lake. So, the 1,800 TAF forecast puts Trinity Lake at the top end of a Wet Water Year.

water year

The inflow forecast is based on 3 gauges on the major lake tributaries, plus snowmelt forecast, plus rainfall on the lake, plus an estimate of minor tributary inflow, plus a guess at precip for the rest of the year -- to come up with the total water year yield (or inflow).

Combining the Wet Year releases to the Trinity River, USBR's diversions into the Sacramento River, and the 2011 water yield forecast being at the high end of a Wet Year, Trinity Center's boat ramp should have 6+ feet of water on Sept 1. This doesn't take into account the Hoopa Boat Dance release for one week, probably before Labor Day (ramping up to 3,000 cfs for one full day and then down again.)

The USBR has a right to take their full 52% inflow allocation this year (about 759,416 af), but they are anticipating a full Shasta Lake and other near-full reservoirs in the Central Valley Project. Also, maintenance work is still going on at the Carr Powerplant so only one of the Clear Creek tunnels can be used at a time again this year. Therefore, the USBR will probably take less.

Lake Elevation Forecast

A new set of number have not been compiled yet using the April 1 data.

The following are forecast lake elevations using March data.


On April 1 -- elevation 2,353
On August 1 -- elevation 2,328
On September 1 -- elevation 2,316

The following is a graph of the lake elevation forecast from last July to June 2011 using March data.

Trinity Lake ramp elevations

Flow Schedule

Below is a chart showing the ROD flow schedule for all water years. The goal with these release schedules is to try and mimic the natural flow into the Trinity River. (Click on images for larger versions)

ROD Flows

Next is last year's release schedule:

2010 flow release schedule

Below is a graph showing the two flow alternatives for 2011 that were presented at the April 12 TAMWG meeting in Weaverville. The graph shows the standard ROD release schedule for a Wet Year, an 11,000 cfs option with an early release, and an 8,500 cfs option that is like the ROD but shifted earlier in the year. The TMC voted to adopt the Wet 11-B schedule. This schedule is a modification of the standard ROD Wet Year schedule, but uses the same volume of water. It merely adjusts the timing and intensity of the releases

The thought behind the high release of 11,000 cfs is to mimic a "flood" in the river. Flooding is important for the creation and maintenance of fish habitat in the river. The Trinity River has not had a flood since the dam was completed. And a release flow this high has only been done before as part of the restoration program. In 2006, a short release at the 10,100 cfs level was done due to the high lake levels.

High, pulse releases are thought to help scour the river banks, move more sand for habitat, and clean out holes used by adult fish during the year.

2011 Normal year alternatives
Click for larger image

Below is a portion of the preliminary daily release schedule from Lewiston Lake. The data show release number for a standard ROD Wet and Normal year and the two proposed 11k and 8.5k releases. On Wednesday, April 13, the TMC voted to adopt the Wet 11-B option. You can download the full schedule as a PDF.


River Temperature

One issue that has been brought up about the high 11,000 cfs is that upon modeling this type of release and its impact on river temperature, it appears that this 11k cfs release in a Normal water year could cause early warming of the river.

The ROD and other rulings set out river temperature objective that the USBR must attempt to comply with.

River Temp Objectives
Click for larger image

We must remember that the reason for keeping the river cool is that, with the construction of Trinity Dam, the Trinity River lost some 109 total miles of salmon spawning area. The adult fish used to migrate to Coffee Creek to spawn in cool water. Now the fish can only get to Lewiston.

Therefore, the TRRP is attempting to recreate the 109 miles of the Trinity River headwaters environment below the dam for 49 miles. The theory is that cold water must be released to keep that 49 miles as cool as Coffee Creek.

As you can begin to see, trying to restore the fishery in the Trinity River is extremely complex.

If you would like to learn more about the factors that impact Trinity Lake, please review the Trinity Lake Revitalization Alliance's Powerpoint presentation "Where is Trinity Water Going?" from April 2010. (PDF file, 2.1MB)

Since early last year, the Trinity Lake Revitalization Alliance has been asking the TRRP how the lake's inflow forecast is determined.

Lake Inflow Forecasting

In March, we learned that the Calif Dept of Water Resources (DWR) and NOAA's California-Nevada River Forecast Center (CNRFC) work together to come up with the inflow number.

On April 12, at the TAMWG meeting, we got "the rest of the story." And our speculation that the snow data and snow pillow sites are flawed is correct.

In the Sierras, the water content of a snow pack is determined using snow pillows that weight the snow, but have low reliability; snow surveys, which the USFS stopped performing in the Trinity watershed due to a helicopter crash; and SNOTEL systems of which there are none in Trinity.

The closest SNOTEL sites are in Modoc county and Sierra counties. The data from these stations are used but given low weighting.

DWR has checked the Shimmey Lake snow pillow the last two years.

A verbal comment from NOAA was that because there is no good snow data for the Trinity Lake watershed, there is a "20% uncertainty" in the yearly inflow forecast.

The TRRP is getting clarification on what "20%" means. Having a solid forecast with good data is extremely important for the lake in years when the water year is teetering between water year types. TRRP is also working with CNRFC to scope basin snow surveys and determine a cost estimate and scope of work statement for 2012 funding.

TLRA will work with TRRP and DWR to determine how to get better snow pack gauges in the watershed.


[an error occurred while processing this directive]