Shasta Experiment #3 – Saving the Cold-Water Pool or Increasing Irrigation Deliveries?

In early April 2021, the Bureau of Reclamation began a series of tests to determine if releases of water that bypass the powerhouses at Shasta Dam could help save Shasta’s cold-water pool through the summer and fall and thus help sustain salmon spawning in the Sacramento River below Shasta.  This post describes the third experiment in the series.

Experiments or tests of the powerhouse bypass continued at Shasta Dam from 4/19-4/24, 2021.  But the apparent goal of conserving cold-water pool volume for later in summer seems to have morphed into an acute operational phase of releasing a lot of water for contractor deliveries early in a critical drought year.  This higher release volume shows little regard for this year’s production of endangered winter-run salmon.  This unprecedented federal operational regime has not been approved by the California State Water Resources Control Board, nor has it been endorsed by the federal National Marine Fisheries Service, which is charged with protecting endangered salmon.

What was billed as a power turbine bypass at the federal Shasta Dam to save cold water storage has turned out to be a unique way to release a lot of Shasta’s remaining critical dry year storage (as well as cold-water pool supply) to Sacramento Valley water contractors.  The approach is both ingenious and insidious, and is likely a leftover planned action by the previous federal administration, whose goal was to maximize water deliveries to Central Valley farmers without regard for an already fragile and weakened ecosystem.

The approach entails releasing warm water from the surface of the reservoir into the upper river outlets (as in the above photo) instead of through the deeper cold water through the power penstocks and powerhouse (five penstocks and powerhouse are to left of spillway in above photo). 1

The problem is that too much warm water is being released, so cold water must also be released to overcome the release of relatively warm surface water (Figure 1), via mixing in downstream Keswick Reservoir before ultimately being discharged into the Sacramento River downstream of Keswick.  Total releases reached 12,000 to 16,000 cfs in the afternoon peak-power-demand periods from 4/19-4/24 (Figure 2).  Water temperatures topped out at 56-58ºF in the non-peak hours (Figure 3), when releases were dominated by spillway releases (Figure 4).  Shasta Reservoir storage dropped approximately 30 TAF (from 2,360 TAF) during the four-day period.  Downstream water temperatures increased up to several degrees during the four-day period (Figures 5-7).  Downstream water deliveries to contractors increased as well, based on differences in gaged flow between the upper and middle river (Figure 8).

In summary, power bypass releases from Shasta reservoir occurred in this critical drought year, resulting in higher downstream river water temperature, no cold-water pool saving, lower reservoir storage, and higher contractor deliveries.  The higher water temperatures (>56ºF) exceed state water quality standards and existing water temperature targets for the upper Sacramento River.

Figure 1. Shasta Dam and reservoir schematic depicting late April 2021 release regime. Warm surface water is released through six upper outlets. Colder layered water is released through five middle gates of the Temperature Control Device (TCD) outlet tower on the face of the dam to the powerhouse via the five penstocks.

Figure 2. Shasta reservoir storage hourly release pattern 4/19 – 4/24, 2021. The graph shows total combined powerhouse and spillway releases. Note powerhouse peaking-power releases generally occurred only in late afternoon or early evenings or mornings. Spillway releases appear to have been continuous: 4,000 cfs on 4/21-22, and 6,000 cfs on 4/23-24

Figure 3. Shasta Reservoir hourly release water temperature pattern 4/19 – 4/24, 2021. The water temperature is that of water below the dam made up of blended spillway and powerhouse releases. Comparison with Figure 2 shows that minimum water temperatures occur during power peaking events that draw from cold-water pool in Shasta Reservoir.

Figure 4. Daily average releases (cfs) from Shasta Dam river outlets to spillway bypassing power house, showing releases from 4/18-4/23.

Figure 5. Water temperature below Keswick Dam 4/19-4/24, 2021. Note gradual increase in water temperature from increasing spillway releases during period.

Figure 6. Water temperature above mouth of Clear Creek ten miles below Keswick Dam 4/15-4/24, 2021. Note increase from increasing spillway releases beginning on 4/19. Note existing target temperature for this gage is daily average 56ºF.

Figure 7. Daily average water temperatures in the lower Sacramento River 4/1-4/24, 2021. Note RDB (Red Bluff) is lowermost gage. Note sharply higher water temperatures during the 4/19-4/24 test period. See Figure 9 for location map.

Figure 8. Daily average river flows in the lower Sacramento River 4/19-4/24, 2021. Note the difference between WLK and KWK gages represent approximate water deliveries to contractors. Note VON (Verona) is lowermost gage and is influenced heavily by Feather River inflows. See Figure 9 for location map.

Figure 9. Gage locations


Shasta Experiment #2 – Saving the Cold-Water Pool

In the afternoons of 4/15 and 4/16, the Bureau of Reclamation conducted a second set of experiments or tests of the powerhouse bypass at Shasta Dam with the apparent goal of conserving the volume of Shasta Reservoir’s cold-water pool for later in the summer.    Reclamation released warm surface water from Shasta Reservoir into upper Keswick Reservoir through the upper river outlets to the dam spillway (see inset at right), bypassing the TCD and powerhouse.  Water temperature immediately below Shasta Dam reached values greater than 70ºF in the early afternoon on the 14th and 15th (Figure 1).  The river outlet releases occurred between the normal daily peak-power releases through the powerhouse (Figure 2).  In the prior test (Exp #1) in the early morning hours of 4/11, water temperature below the dam reached only 55ºF, as some cold water was also being released through the powerhouse.

After mixing occurred in Keswick Reservoir, water temperature of the Keswick release water to the Sacramento River increased approximately 2ºF to 52ºF (Figure 3).  The total reservoir release also increased about 1,300 cfs to 6400 cfs from the Exp #1 release level (Figure 4).

Overall, the test showed that bypassing the powerhouse can potentially save cold-water pool volume in Shasta Reservoir, although this bypass increases water temperatures in the upper Sacramento River.  As long as Keswick release temperature remains below its upper limit (in this case 53ºF), the option of bypassing power appears to have promise in conserving cold-water pool volume in Shasta Reservoir.

In this particular case, with the increase in total release to 6500 cfs, it is difficult to determine the amount of cold-water pool saved.  With the dam’s river-outlet water temperatures higher than 70ºF, it takes a lot of cold-water powerhouse release to cool it down to meet target levels in the upper Sacramento River.  It appears that operators were able to maintain normal peaking power levels while also releasing some warm reservoir surface water, with only a small increase in downstream river water temperature.  However, the additional loss of Shasta storage, in this case approaching 3000 ac-ft per day, will negatively affect the summer cold-water pool supply.

Figure 1. Water temperature immediately below Shasta Dam on 4/15-4/16, 2021. Note afternoon peaks corresponding to upper outlet releases

Figure 2. Dam release 4/14-4/16, 2021. Note afternoon upper outlet releases were 3000 cfs on 4/14-15. High 13,000 cfs releases between spillway releases late on 4/15 were for peaking power and were necessary to cool Keswick Reservoir to 50ºF below dam (see Fig 1).

Figure 3. Below Keswick, water warmed to 52ºF in the afternoon of 4/15.

Figure 4. Keswick release increased to 6500 cfs on 14th.


Summer Shasta Releases Are Too High and Lower Sacramento River Summer Flows Are Too Low: Lessons Learned – #5

Following an introductory post, this is the seventh post in a series on the lessons learned by the National Marine Fisheries Service (NMFS) from the 2013-2015 drought that devastated Sacramento River salmon populations.  This post addresses Lesson #5.

The reason for high summer releases to the Sacramento River from Shasta and Keswick reservoirs is to meet the demands of Sacramento Valley water contractors for stored water.  For example, in 2012, summer releases to the Sacramento were 15,000 cfs, with roughly 7000-8000 cfs diverted in the Sacramento Valley for water supply use (Figure 1).

The Bureau of Reclamation learned during the 2012-2015 drought that, if the previous year was wet, it must still limit water releases in summer of dry years to 12,000-13,000 cfs (Figures 2 and 3) to preserve Shasta Reservoir’s cold-water pool supply.  One consequence of this limitation as implemented has been less flow in the lower river 150-200 miles downstream.  This reduced flow has exacerbated water temperature problems in the lower river.  Reclamation has likely also reduced water deliveries in the Sacramento Valley to some degree, but the extent of any such reductions is difficult to tease out.

Because of the lessons learned, Reclamation in 2018 targeted a 53oF water temperature limit in the main spawning reach of winter-run salmon from Keswick Dam (RM 300) down to the mouth of Clear Creek (RM290) (Figure 4).  In the past, the water temperature limit had been higher (56-58oF).  In 2020, the target was once again set higher to sustain a depleted cold-water pool supply through the summer and fall. The target in the spawning reach in drought years 2014 and 2015 was 56oF, which proved ineffective at providing egg/embryo survival.

One of the actions to sustain the cold-water pool has been to limit June-July Keswick releases (Figure 5) to near 11,000 cfs in wet years (2017 and 2019).  Such action cuts into water supply deliveries and leads to reduced flows (Figure 6) and excessive water temperatures (>70 oF, Figure 7) in the lower 200 miles of river.  Without simultaneous reductions in Sacramento Valley water deliveries, reductions in Keswick releases lead to excessive water temperatures downstream of the upper 10-mile salmon spawning reach.   This violates the Central Valley Basin Plan’s temperature standard for the lower reaches of the Sacramento River (68oF).  It causes stress on rearing and migrating salmon and sturgeon, and if high enough severely retards upstream migration of adult salmon.

The obvious lesson learned is that Reclamation must limit summer Shasta cold-water storage releases and maintain sufficient lower river flows.  This will necessarily require Reclamation to more greatly restrict water supply deliveries in the Sacramento Valley than it has historically and recently.

Figure 1.

Figure 2.

Figures 1-3. Sacramento River flow (cfs) at Keswick Dam (rm 300) and Wilkins Slough (rm 120) in summer of dry years 2012, 2018, and 2020. Note: the difference between

Figure 4. September-October water temperatures in the upper Sacramento River at Clear Creek (river mile 290) from 2012-2020. Note loss of temperature control in 2014 and 2015. Note limited control in 2013, 2018, and 2020. Note meeting target 53oF 2012, 2016, 2017, and 2019

Figure 5. Flow rates below Keswick Dam in June-July 2012-2020.

Figure 6. July-September Sacramento River flow rates at Wilkins Slough (rm 120) 2015-2020. Note flows were compromised in summer 2016 and 2017 to help preserve Shasta’s cold-water pool supply and upper river water supply deliveries.

Figure 7. Water temperatures in Sacramento River at Wilkins Slough (river mile 120) May-Oct, 2015-2020

Shasta Water Temperature Experiment #1 4/10-4/11, 2021

In the evening of 4/10 and early morning hours of 4/11, the Bureau of Reclamation began releasing warm surface water from Shasta Reservoir through the upper river outlets to the dam spillway (see inset at right), bypassing the Shasta Temperature Control Device (TCD) and the Shasta powerhouse,  forgoing power production.

Figure 1 shows the warm water beginning at 20:00 4/10 and continuing to 8:00 4/11.  Reclamation changed the recent pattern of midnight releases, raising releases from about 3000 cfs releases to about 6000 cfs (Figure 2).  This was possible due to the available capacity of the upper-level river outlets on the dam spillway.  Reclamation also curtailed peaking power releases through the TCD and penstocks on the evening of 4/10.  The 55ºF temperature in Figure 1 immediately downstream of Shasta Dam reflects the temperature of the lake’s surface water at the upper level outlets (Figure 3).

During and after the experiment, water temperatures in the Sacramento River downstream increased less than 1ºF, both immediately below Keswick Dam (Figure 4) and 10 miles further downstream at the Clear Creek gage (Figure 5).

Overall, the experiment shows that forgoing some peaking power by bypassing penstocks and releasing warmer upper-level lake water in April can save cold-water-pool volume, although with a small increase (0.5ºF in this case) in downstream water temperatures under these specific conditions.

Figure 1. Water temperature immediately below Shasta Dam at gage SHD 4/7-4/12, 2021. Note substantial increase from 20:00 4/10 to 06:00 4/11 during Exp #1.

Figure 2. Inflow to Keswick Reservoir from Shasta Dam 4/7-4/12, 2021. There was also 400-750 cfs of Trinity water entering Keswick from Spring Creek Powerhouse.

Figure 3. Water temperature profile in lake at Shasta Dam on 4/14/2021. Note water temperature in mid-50s at level of the upper six outlets to the spillway, in contrast to the cooler 50ºF water entering the penstocks via the middle gates of the TCD.

Figure 4. Water temperature of water released from Keswick reservoir 4/7-4/12, 2021. Note temperature increased up to 0.5-0.8ºF during and after the experiment.

Figure 5. Daily average water temperatures at selected gages 4/1-4-12, 2021. Note temperatures at Clear Creek confluence (CCR, in bold), with little increase on 4/10-4/11.

Are Sacramento River Water Temperatures Related to Flow: Lessons Learned – #4

Following an introductory post, this is the sixth post in a series on the lessons learned by the National Marine Fisheries Service (NMFS) from the 2013-2015 drought that devastated Sacramento River salmon populations.  This post addresses Lesson #4.

NMFS’s lesson #4 states that the summer water temperatures in the 10-mile reach of the Sacramento River downstream of Keswick dam, the most heavily used reach for spawning by winter-run salmon, are not “correlated with flow.”  The lesson is important in that if generally true, high summer flow releases are not important in managing summer water temperatures for the salmon spawning and egg-embryo incubation that takes place close to Keswick Dam.  The magnitude of flow releases from the dam appears to have minimal effect on how much summer water temperatures increase in the upper 20 miles of river.  Rather, water temperature in this river reach is more a function of distance from the dam and the temperature of the water when released from Keswick.

Keswick is a small re-regulating reservoir that takes in water as it is released from Shasta Dam’s peaking power plant and from the Spring Creek Powerhouse, which generates power with water imported to the Sacramento from the Trinity River.  The water from the powerhouses is mixed in Keswick Reservoir as it enters the reservoir at times of day when power is most valuable.  “Re-regulation” means that Reclamation holds releases from Keswick to the Sacramento River downstream relatively constant over the course of the day.  The water temperature may be cold enough for salmon in the 20 miles of river immediately downstream of Keswick Dam, but water in the river warms quickly, depending on flow, as it moves further downstream through the remaining 200 miles of the lower Sacramento River.

1) Effect of Flow on the Water Temperature of Shasta/Keswick Releases

Water temperature immediately below Keswick in drier years 2014 and 2020 was most certainly related to flow (Figure 1), but not in the sense one might expect.  In 2014, high flow magnitudes (releases) caused a loss of access to the cold-water pool in Shasta Reservoir.  In 2020, high early summer releases led to reduced late summer releases to conserve the cold-water pool.  In both cases, spring-summer water deliveries to downstream water contractors were excessive, leading to limited access to Shasta’s cold-water pool by fall, resulting in high salmon egg-embryo mortality.

2) Effect of Flow Magnitudes into Keswick Reservoir on Temperature Increases within the Reservoir

There is some evidence that the temperature of water increases as it moves through and mixes within Keswick reservoir.  Keswick releases are often slightly warmer than upstream Shasta Dam releases into Keswick Reservoir (Figure 2), although the relationship is complicated by releases from Spring Creek Powerhouse of warmer water imported from the Trinity River system.  Again, as described above in point 1, the water temperature in Keswick Reservoir and water released from it in the late summer and fall of 2014 was primarily the result of gradual decline in the availability of cold water from the bottom of Shasta Reservoir.

3) Effect of Flow Magnitudes on Water Temperature in Sacramento River immediately below Keswick Dam

Higher flow magnitudes immediately downstream of Keswick Dam do not always translate into lower water temperatures, because the temperature of the source water in Shasta is more important (Figure 3).  Temperature increases a short distance from Keswick Dam are small (Figure 4).  Even in summer of wet-year 2019, water temperature increases over the 10-mile spawning reach were similar to those in 2020 (Figur e 5).  In 2019, flow magnitude had relatively little influence on water temperature even as far downstream as Balls Ferry.

It is worth noting that when dam release temperatures are at or above the upper limit of safe survival (53oF) as they were in summer 2020, then any temperature increase in the 10-mile spawning reach becomes a critical issue for the survival of the eggs and embryos of winter-run salmon.  However, the solution is not to increase flow to reduce warming within the 10-mile spawning reach, because that depletes the Shasta cold-water pool and trades a short-term benefit for the long-term impact of reducing the size and accessibility of the Shasta cold-water pool.  Rather, the solution is to keep releases low enough over the course of the spring and summer to allow those releases to maintain temperatures lower than the 53ºF threshold.

4) Effect of Flow Magnitudes on Water Temperature in Lower Reaches of the Sacramento River

Summer water temperature in the lower reaches of the Sacramento River is heavily influenced by magnitude of flow (Figures 6 and 7).  Lower flows promote higher water temperatures.  Downstream of Red Bluff, water temperature depends on air temperature, the magnitude of flow, and how fast the river flows.  Lower flow magnitudes reduce the speed with which water moves downstream.  Smaller thermal mass of water at low flows, combined with the slower rate with which water moves downstream, causes water to pick up more thermal energy and get warmer quicker.  In the lower reaches of the Sacramento River, water no longer depends on the temperature of the water released from Shasta and Keswick reservoirs.

In summary, water temperature in late spring through early fall in the Sacramento River immediately downstream of Keswick Dam is primarily determined by the water temperature of the water released from the dam, not the magnitude of flow.  In contrast, flow is the primary management tool available to reduce water temperature in the lower 200 miles of the Sacramento River from late spring through early fall.

Figure 1. Comparison of water temperature and flow from Keswick Dam in late summer and early fall between critical drought year 2014 and dry 2020.

Figure 2. Water temperature immediately below Shasta and Keswick dams, and flow rate below Keswick Dam in September 2014, a critically dry year when access to Shasta Reservoir’s cold-water-pool became limited. Blue line is flow downstream of Keswick. Orange line is Keswick release water temperature. Green line is Shasta release water temperature.

Figure 3. Comparison of 2019 and 2020 summer water temperature and flow below Keswick Dam in the upper Sacramento River. Note substantial loss of water temperature control in mid-September 2020, a consequence of source water temperature, not lower flows.

Figure 4. Water temperature in the 10 miles of spawning reach below Keswick Dam in late summer and early fall 2020. Water temperature over the 10 miles increased about 1.0 to 1.5oF. Blue line is Keswick release temperature. Orange line is water temperatures in the Sacramento River at Highway 44, 5 miles downstream Keswick Dam. Green line is the Clear Creek gage on the Sacramento River, 10 miles downstream of Keswick Dam.

Figure 5. Summer water temperature in the upper 20 miles of the Sacramento River below Keswick Dam, 2019. Note the increase is about 2-4 degrees over the 20 miles. CCR is the Sacramento River at Clear Creek. BSF is Sacramento River at Balls Ferry, 20 miles downstream of Keswick Dam. SAC is Sacramento River at the Highway 44 bridge. KWR is release temperature from Keswick Dam.

Figure 6.  Summer water temperature in the lower Sacramento River at Wilkins Slough (RM 120) 2015-2020.  Note the water quality standard is 68oF.

Figure 7. Summer river flow magnitude in the lower Sacramento River at Wilkins Slough (RM 120) 2015-2020.