Delta Smelt – 2020 Status

In a March 2020 post, I described the status of the Delta smelt through 2019.  This post updates the status with the most recent 2020 information.  Delta smelt continue to be absent from the standard long-term surveys and their related indices.  However, some Delta smelt were collected in 2020 in selected locations of the Bay-Delta during focused intensive special surveys designed to find remaining survivors.  Larval and juvenile Delta smelt were collected in low numbers in the Bay and north Delta (Figure 1).  Pre-adult Delta smelt were also collected in summer trawl surveys (Figure 2).

The north Delta habitats where a few Delta smelt persevere continue to be plagued by constant stressful if not lethal water temperatures (Figures 3 and 4).

As I stated in a prior post, Delta smelt would benefit from increased net flows through the north Delta during the spring and summer.

Figure 1. Numbers of larval and juvenile Delta smelt collected in the spring Enhanced Delta Smelt Monitoring (EDSM) 20-mm nets. Source.

Figure 2. Numbers of pre-adult Delta smelt collected in the summer Enhanced Delta Smelt Monitoring (EDSM) Kodiak trawls. Source.

Figure 3. May through September 2020 water temperature and net tidally-filtered flow in the lower ship channel near Rio Vista. Note water temperatures fall 1-2ºC when net flows increase.

Figure 4. May through September 2020 water temperature and net tidally-filtered flow in Cache Slough near Rio Vista. Note water temperatures generally fall 1-2ºC when net flows increase.

May-September Delta Water Temperature Standard Needed

In a 9/22/20 post, I suggested summer Delta outflow standards. In this post I suggest a spring-summer water temperature standard for the Delta as further protection for salmon and smelt. Water temperatures above 23oC (73oF) are harmful to salmon and smelt, which live and migrate through the north and west Delta throughout the summer. Much of the Delta smelt population that remains is located in these regions especially in dry years.1 Spring-run and winter-run salmon migrate upstream through the area in late spring. Fall-run salmon migrate upriver through the summer.

Harm occurs as stress, higher predation, avoidance reactions, poor growth, and reduced long-term survival and reproduction. At higher temperatures (>23oC) migration blockage and mortality occurs. Such temperatures are commonly reached or exceeded in the north Delta even in wetter, water-abundant years.

High water temperatures occur in the Delta when there are high air temperatures and/or low freshwater inflow and outflow. Such conditions are becoming more frequent with climate change. A good example occurred in water year 2020, which featured low precipitation, low snowpack, and high air temperatures.2 Because water managers cannot control air temperatures or watershed precipitation, they must manage Delta inflows from reservoir releases and outflows through the Delta to improve water temperature control in May-September, especially in drier years.

To protect smelt and salmon, there need to be reasonable water temperature standards in the Delta. The existing water temperature standard in the lower Sacramento River above the Delta is 68oF, but managers of the state and federal water projects pay it almost no heed. There is no existing standard for the Delta. The north Delta water quality standard for the Sacramento channel in wet years should be 70oF (21oC) at Freeport and at Rio Vista. In normal and dry water years, the standard should be 72oF (22oC) at Freeport and at Rio Vista. In critical drought years, the State Water Board needs to require additional Delta inflow and curtail exports as needed to respond to extreme events (e.g., water temperatures greater than 75oF during heat waves). At critical times, a change of only a degree or two will help limit fish stress and mortality.

Higher Delta outflow and lower exports are appropriate prescriptions for maintaining reasonable water temperatures in the Delta (see Figures 1-3 and caption notes). For example, in July and August 2020 (Figures 1-3), increased inflow into the 14,000-16,000 cfs range from 12,000 cfs at Freeport could have held water temperature below 22oC. Note in Figure 3 that increased inflow can be captured by south Delta exports (Figure 3). However, during heat waves under extreme drought conditions, the State Board should also limit exports to retain outflows from the Delta to keep the low salinity zone out of the warmer Delta. Otherwise, exports will reduce the portion of Delta inflows (Freeport flows) that reach Rio Vista.

Such standards are achievable, albeit at significant water supply cost. They are worth the effort. High summer water temperatures, such as those that occurred in wet year 2019 and dry year 2020, must be mitigated. The 23-25oC conditions in summer 2020 (portrayed in Figures 1-3) should not occur, and would not under the suggested Delta water temperature standard. For wet years such as 2019 (Figure 4) and 2017 (Figure 5), water temperatures should be kept at or below 70oF (21oC) by maintaining Freeport near 20,000 cfs as needed.

In summary, Delta water quality standards should be adopted for inflow, outflow, and water temperature to protect salmon and smelt in the warmer months of the year, May-September. Such standards are needed because of recent changes in water project operations and the effects of climate change.

Figure 1. Water temperature and salinity in the west Delta near Rio Vista in spring-summer 2020. Note Delta draining in neap-tide periods generally brings warmer water downstream into the west Delta, except in mid-August event when a heat wave drove water temperatures up into 23-25oC range. This event was accentuated by higher exports and associated high Delta inflows.3

Figure 2. Water temperature and net river flow (tidally filtered) in the lower Sacramento River at Freeport in the north Delta in spring-summer of dry year 2020. Note that it took flows at or greater than 16,000 cfs to keep temperatures near 70oF (21oC).

Figure 3. Sacramento River flow at Freeport (FPT), water temperature at Rio Vista (RVB), and south Delta exports at Tracy (TRP) and Banks (HRO) pumping plants in south Delta from May-Oct 2020.

Figure 4. Water temperature and net river flow (tidally filtered) in the lower Sacramento River at Freeport in the north Delta in spring-summer of wet year 2019. Note that it took flows at or greater than 16,000 cfs to keep temperatures near 70oF (21oC).

Figure 5. Sacramento River flow at Freeport (FPT-Y1) and water temperature at Freeport (FPT-Y2) and Rio Vista (RVB-Y2) from May-Oct 2017.

Franks Tract Futures Project

The Franks Tract Futures Project is asking for additional comments on the State’s revised concept design.1 The project is an outgrowth of the State’s 2016 Delta Smelt Resilience Strategy, which recognized that Franks Tract is a death trap for state and federally listed Delta smelt.

The original design for the project included tide gates to keep salt and smelt from moving upstream from the western Delta into Franks Tract via the False River channel. Once in Franks Tract, the smelt would most assuredly not survive. A new design “transforms the project from an early focus on establishing habitat for the endangered Delta smelt to a project that has sought input from a broad range of stakeholders.” According to the project leader, Brett Milligan from University of California:

Balancing the project’s goals has been a challenge. The first round of this project, the feasibility study, met the water quality and ecology requirements but did not meet the recreational and local economy (requirements). We heard you loud and clear. More or less, this entire last year has been to try to bring in that third tier and to balance these and see if there’s a way that the project can meet all of these criteria and be beneficial to all. The original project design failed to earn public support after it was presented in January 2018. At a crossroads, the project managers made a critical decision. They scrapped the proposal and formed an advisory committee of stakeholders with varied interests in Franks Tract rather than try to force the initiative through the process, while fighting the public every step of the way.

The new design drops the barrier/gate option as “a non-starter,” Brett explained to me. But that was the essential element of the project – stopping salt (and smelt) intrusion into the interior Delta due to the pull of the south Delta export pumps. A temporary barrier has been installed in False River in drought years to protect Delta water supplies.

The conflict is over recreational access to Franks Tract from the west via False River. A similar barrier on Montezuma Slough further west in Suisun Marsh resolved a similar conflict with a boat passage lock that maintains boating access when the barrier is in use.

At this phase of design and permitting, it would seem wise to evaluate an alternative with the barrier that includes a similar boat passage facility, so that the affected public can understand the tradeoffs. That is the purpose of the environmental review process.

Delta Smelt Sanctuary – Deepwater Ship Channel

In a March 2020 post, I described where the remnants of the endangered Delta smelt population spawn and rear in the Sacramento Deepwater Ship Channel (Ship Channel) in the north Delta (Figure 1). In this post, I describe how the rearing conditions in the Ship Channel are poor. This can be seen by comparing habitat conditions in the Ship Channel with those in the lower Sacramento River channel at Freeport several miles to the east in late spring 2020.

Net Flow

Net flow (cfs) in the Ship Channel remains near zero, since the gate at the north end of the channel near Sacramento remains stuck in the closed position as it has been for several decades (Figure 2).

Water Temperature

Water temperature (oC) is significantly higher in the stagnant flows of the Ship Channel than at Freeport, often reaching into the lethal range 23-25°C for Delta smelt (Figure 3).

Salinity

Salinity (conductivity) is much higher in the Ship Channel because of discharges from urban sewage treatment plants and agricultural operations (Figure 4).

Turbidity

Turbidity is much higher in the Ship Channel due to higher plankton production and port-bound ship traffic in the relatively shallow and narrow Ship Channel (Figure 5).

Dissolved Oxygen

Dissolved oxygen levels are much lower in the Ship Channel because of warmer water, high concentrations of suspended organic sediments, and higher plankton production (Figure 6).

Interpretations and Conclusions

Delta smelt are attracted to the Sacramento Deepwater Ship Channel in winter and early spring to spawn in the relatively warm, low salinity, turbid, and more productive water. The adult smelt can also easily tidal-surf up the ship channel without having to content with strong downstream currents of the Sacramento River channel. Their eggs hatch early to an awaiting abundant plankton food supply. However, in spring the Ship Channel lacks net downstream flows to carry the young smelt to the Bay. By late spring, water temperatures in the Ship Channel reach lethal levels for the young smelt.

Opening the gate at the north end of the Ship Channel would help to alleviate the problems by providing net flow with cooler water temperatures, and by flushing and diluting the stagnant waste waters in the Ship Channel. An operable gate at the head of the Ship Channel would allow adaptive management of the habitat conditions for smelt.

Figure 1. Locations where Delta smelt young were captured in EDSM surveys in July 2019. Circles represent regions. Numbers are total July catch in region. The 94 represents the young smelt captured in the Deepwater Ship Channel.

Figure 2. Net daily flow (cfs) in the Ship Channel and in the Sacramento River at Freeport in June 2020. The green line shows flow in the Ship Channel.

Figure 3. Water temperature in the Ship Channel and Sacramento River at Freeport in June 2020. The blue/purple line shows the water temperature in the Ship Channel.

Figure 4. Conductivity (salinity) in the Ship Channel and Sacramento River at Freeport in June 2020. The green line shows salinity in the Ship Channel.

Figure 5. Turbidity in the Ship Channel and Sacramento River at Freeport in June 2020. The blue/purple line shows turbidity in the Ship Channel.

Figure 6. Dissolved oxygen in the Ship Channel and Sacramento River at Freeport in June 2020. The green line shows dissolved oxygen in the Ship Channel.

 

 

Franks Tract – Smelt Trap

In a May 2019 post, I described the central Delta as a salmon trap for juvenile salmon. This post describes the “smelt trap.”  Franks Tract in the central Delta (Figure 1) is a longfin and Delta smelt trap.  Longfin smelt were vulnerable to the trap in March 2020 (Figures 2 and 3).  Flow was reversed in False River (Figure 4) because of south Delta exports.

It’s not just the net flow that makes Franks Tract a smelt trap.   It is also tidal pumping of 50,000 cfs in-and-out.  What goes into Franks Tract on the flood tide does not come back out the same (Figures 5-9).  It is different water, warmer, clearer, with less plankton, and probably less smelt larvae and juveniles.  Smelt are simply tidally-pumped into the central Delta where they are susceptible to warmer, less turbid, predator-laden waters of Franks Tract and the central and south Delta.  Most young smelt probably succumb before reaching the south Delta export pumps.

This is another reason why winter Delta exports need restrictions and why the Franks Tract restoration project with its tide gate on False River needs to proceed as part of the state’s program to recover longfin and Delta smelt.  For more detail on the proposed project see: https://mavensnotebook.com/2019/02/07/bay-delta-science-conference-franks-tract-feasibility-study-applying-the-guidance-of-a-delta-renewed/ .

Figure 1. Franks Tract and False River gage location in west Delta.

Figure 1. Franks Tract and False River gage location in west Delta.

Figure 2. Longfin smelt distribution in March 2020 20-mm Survey #1.

Figure 2. Longfin smelt distribution in March 2020 20-mm Survey #1.

Figure 3. Longfin smelt distribution in March 2020 Larval Smelt Survey #6. Station 901 is in Franks Tract.

Figure 4. False River net daily tidally filtered flow (cfs) in March 2020.

Figure 5. Hourly flow at False River gage March 29 to April 5, 2020.

Figure 6. Hourly water temperature at False River gage March 29 to April 5, 2020.

Figure 7. Hourly turbidity at False River gage March 29 to April 5, 2020.

Figure 8. Hourly chloropyll at False River gage March 29 to April 5, 2020.

Figure 9. Hourly EC at False River gage March 29 to April 5, 2020. Note slightly brackish water (300-500 EC) moves upstream in False River on flood tides (Figure 5), but returns fresher on ebb tide from mixing in Franks Tract.