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.