Objectives
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Increase mainstem river temperature to increase humpback chub growth and recruitment.
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Trigger
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Initial experiment:
- Three months: July, August, and September
- 8,000 cfs and relatively little fluctuation (±1,000 cfs per day)
- In the second 10 years of the LTEMP period (2026-2036)
- The projected annual release volume is less than 10 maf
- A target temperature of ≥14°C at the LCR can be achieved only with a low summer flow
Required release temperatures:
- July = 10.8°C
- August = 11.0°C
- September = 11.7°C
Subsequent experimental use if:
- Initial test was successful or if there were major confounding factors with the initial test
- Humpback chub population concerns warrant their use
- Water temperature has been colder for a period of years
- The desired warming could be achieved only with low summer flows
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Metrics of Success
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- Determined by an independent scientific panel review
- If it can be determined that they produced sufficient growth of YOY humpback chub and that growth resulted in an increase in recruitment
- Avoided unacceptable increases in warmwater nonnative fishes, trout, or aquatic parasites, or resulted in unacceptable adverse impacts on other aquatic resources
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Offramps
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- Low summer flows do not increase growth and recruitment of humpback chub
- Increase in warmwater nonnative species or trout at the Little Colorado River
- Longterm unacceptable adverse impacts on the resources listed in Section 1.3 are observed, or
- Sufficient warming does not occur as predicted
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Costs and Risks
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- desiccating the nearshore environment with the reduction in flow between June and July, and
- reducing drift with the reduction in daily fluctuation.
- Increased bioenergetic demands of humpback chub via warmer water while decreasing food supply and availability.
- Increased sediment transport during the high releases in the months prior to the LFS test in order to get the annual volume commitment to the Lower Basin.
- Increased potential for nonnative fish and parasites to proliferate throughout the Grand Canyon and impact humpback chub and other native fish populations.
- The cost to hydropower users from the 2000 Low Summer Steady Flow Experiment was estimated to be $26.4 M, which probably made it the single most expensive environmental science experiment in US history.
| Annual volume
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Sediment transport during normal operations
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Sediment transport during an LSF
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| 8.23 |
320,664 |
390,053 |
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| 9.0 |
482,967 |
740,732 |
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| 9.5 |
624,609 |
1,112,489 |
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 LSF monthly volumes with various annual release volumes
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Implementation Issues
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- It may be difficult to model release temperatures far enough in advance to start making releases in order to meet annual release requirements.
- It may be difficult to schedule mid-year monthly releases in order to meet annual release requirements. Monthly volumes of October-December are typically pre-determined to release 2.0 MAF. Annual release volumes are typically only set after the April 1 inflow forecasts leaving April, May, and June as the only months water could be moved into from July, August, and September for the LSF.
- Short notice for science planning to monitor affects. One of the primary flaws with the 2000 Low Summer Steady Flow Experiment was that due to the short amount of time available for planning and implementation and the lack of long-term monitoring, scientists were unable to determine whether or not the experiment achieved its objectives.
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- Habitat maintenance flow (a 4-day spike at a powerplant capacity of 877 m³/s) and sustained high releases in April and May (averaging 509 m³/s) resulted in [increased] sediment export
- The habitat maintenance flow resulted in some mid-elevation sandbar building
- Backwaters warmed more than other shoreline environments during the day, but most backwaters returned to mainstem water temperatures overnight
- Humpback chub and other native fishes, did not respond in a strongly positive or strongly negative
- The mean total length of YOY native fishes was similar to the mean length from previous years, but the abundance of YOY native fish was greater in 2000
- The close proximity of the Little Colorado River to Glen Canyon Dam precluded sufficient warming of the mainstem down to the confluence with the Little Colorado River (RM 61) to reach optimal growth and spawning conditions for humpback chub
- Supported tamarisk seedling establishment
- Increased travel time for whitewater rafting, reduced time spent at attraction sites, increased the availability of low-water camps, and initially increased the number of boating accidents at rapids
- Commercial fishing guides in Lees Ferry lost business during the habitat maintenance flows
- Increased costs of approximately $26.4 million to power users
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Confounding factors of the 2000 LSSF
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- The short amount of time available for planning and implementation and the lack of long-term monitoring.
- The 4-day habitat maintenance flow in September interrupted persistent habitats for YOY fishes and may have confounded the results.
- The high abundance of salmonids in the mainstem before the experiment and predation by them may have affected the number and size of native fish that were caught.
- Native larval fish survival in the tributaries that is unrelated to mainstem environments and flow manipulations also can affect relative abundance observed in the mainstem.
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The NSE project found that annual apparent survival of juvenile humpback chub (size at tagging < 100-mm total length, TL) did not differ significantly between the extant fluctuating flows and the experimental steady flow treatments (Finch et al. in-review A). The NSE project also documented that juvenile humpback chub were able to survive and rear in the mainstem Colorado River even at small sizes of 40-100 mm TL (Finch et al. in-review B). A somewhat surprising finding was that growth in juvenile humpback chub declined during these short-term steady flows versus fluctuating flows even though water temperatures were generally similar (Finch et al. in-review B). Reasons for this counter intuitive growth response are not known, but Finch (et al. in-review B) hypothesizes that food availability in the drift (primarily aquatic insects) is higher in fluctuating flows than in steady flows.
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Links
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LTEMP Experimental Action: Aquatic Resource-Related Experimental Treatments (LTEMP, Chapter 2, pages 67-70) [1]
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Low summer flows could be considered a potential tool for improving the growth and
recruitment of young humpback chub if temperature had been limiting these processes for a
period of years. Low summer flows may lead to warmer water temperatures in the Little
Colorado River reach and farther downstream, as well as contribute to enhanced growth rates of
young humpback chub. There are also potential negative effects from low summer flows on
several resources such as hydropower, sediment, water quality, vegetation, and recreation. Low
summer flows may also negatively affect humpback chub due to an increase in warmwater
nonnative fish or a decrease in the aquatic food base. There was one test of low steady summer
flows below Glen Canyon Dam in 2000; however, the results relative to humpback chub were
not conclusive (Ralston et al. 2012).
Because of the uncertainty related to the effects of low summer flows on humpback chub,
other native fish, warmwater nonnative fish, water quality, and potentially other resources, DOI
will ensure that the appropriate baseline data are collected throughout the implementation of the
LTEMP. In addition, DOI will convene a scientific panel that includes independent experts prior
to the first potential use of low summer flows to synthesize the best available scientific
information related to low summer flows. The panel may meet periodically to update the
information, as needed. This information will be shared as part of the AMWG annual reporting
process.
It is thought that the potential benefit of an increase in temperature could be greatest if a
water temperature of at least 14°C could be achieved, because these warmer temperatures could
favor higher humpback chub growth rates (nearly 60% higher). For comparison, the July through
September growth increments of YOY humpback chub are estimated to be 4, 7, 11, 14, and
17 mm at temperatures of 12, 13, 14, 15, and 16°C, respectively, based on a growth-temperature
regression in Robinson and Childs (2001). Note that reduction in summer flows would
necessitate increasing flows in other months relative to base operations (Table 2-10;
Figure 2-22).
If tested, low summer flows would occur for 3 months (July, August, and September),
and only in the second 10 years of the LTEMP period. The duration of low summer flows could
be shortened to less than 3 months in successive experiments if supported by the scientific panel
described above or based on the scientific data and observed effects. The probability of
triggering a low summer flow experiment is considered low (about 7% of years), because the
water temperature conditions that would allow such a test occur infrequently (see Appendix D).
Low summer flows would only be implemented in years when the projected annual
release was less than 10 maf, and if the temperature at the Little Colorado River confluence was
below 14°C without low summer flows, and the release temperature was sufficiently high that
14°C could be achieved at the Little Colorado River with the use of low summer flows.
The ability to achieve target temperatures at the Little Colorado River confluence by
providing lower flows is dependent on release temperatures, which are in turn dependent on
reservoir elevation. For example, using the temperature model of Wright, Anderson et al. (2008)
in an 8.23-maf year, release temperatures of 10.8°C, 11.0°C, and 11.7°C would be needed in
July, August, and September, respectively, to achieve a target temperature of 14°C at the Little
Colorado River confluence at flows of 8,000 cfs.
Release temperatures fall into three categories for any temperature target: (1) too low to
achieve the target temperature at the Little Colorado River even at low flow; (2) high enough to
achieve the target temperature at the Little Colorado River only if low flows (5,000 cfs to
8,000 cfs) are provided; and (3) high enough to achieve target temperature at the Little Colorado
River regardless of the flow level. Low summer flows would only be triggered in years that fell
into the second category.
Implementation of a low summer flow experiment is complicated by two factors: the
earliest date at which it could be determined that a target temperature of at least 14°C could be
achieved in all 3 months, and the ability to release the remaining annual volume once that
determination is made. The earliest time a determination could be made would be in early April
of each year, and it would be based on the April 1 forecast of reservoir elevation. Because low
summer flows could be implemented in the 3 months at the end of the water year, it is possible
that by the time a determination was made to conduct a low summer flow experiment, it may not
be possible to release enough water in the remainder of the spring to compensate for the low
flow period. A low summer flow experiment would only be tested in years when performing the
experiment would not result in a deviation from the annual Glen Canyon Dam release volumes
made pursuant to the Long-Range Operating Criteria for Colorado River Basin Reservoirs,
which are currently implemented through the 2007 Interim Guidelines for Lower Basin
Shortages and Coordinated Operations for Lake Powell and Lake Mead.
A first test of low summer flows would feature low flows of 8,000 cfs and relatively little
fluctuation (±1,000 cfs per day). Depending on the results of the first test with regard to warming
and humpback chub response, the magnitude of the low flow could be adjusted up or down
(as low as 5,000 cfs), and the level of fluctuation also modified up to the range allowed under
Alternative D (i.e., 10× monthly volume [in kaf] in July and August, and 9 × monthly volume
[in kaf] in September).
The first test of low summer flows will be determined to be successful or unsuccessful
for humpback chub based on input from an independent scientific panel review. If the first test
was determined to be unsuccessful (and it was determined to have been implemented without
major confounding factors), then additional tests would not be performed. Low summer flows
would be considered successful if it can be determined that they produced sufficient growth of
YOY humpback chub and that growth resulted in an increase in recruitment, but avoided
unacceptable increases in warmwater nonnative fishes, trout, or aquatic parasites, or resulted in
unacceptable adverse impacts on other aquatic resources. If it was determined to be successful,
then additional low summer flows would occur only when humpback chub population concerns
warranted them and water temperature has been colder for a period of years, and the desired
warming could be achieved only with low summer flows. The temperature target could be
adjusted 1°C higher based on the results of the first test or the limitations between predicted and
measured temperatures.
Implementation of low summer flows would consider resource condition assessments and
resource concerns using the processes described in Sections 2.2.4.3 and 2.2.4.4. Low summer
flows may not be conducted in years when there appears to be the potential for unacceptable
impacts on the resources listed in Section 2.2.4.3.
The effects of low summer flows on Lake Mead water quality are an identified concern.
DOI will coordinate with relevant water quality monitoring programs or affected agencies prior
to implementing any test of low summer flows. There are additional concerns related to the risk
of warmwater nonnative fish expansion or invasion (e.g., the elevation of Lake Mead was high or
the number of warmwater nonnative fish was high). These issues are potential off-ramps as
described in Section 2.2.4.3 using the process described in Section 2.2.4.4.
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LTEMP Experimental Action: Aquatic Resource-Related Experimental Treatments (BA, pages 30-41) [2]
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Low summer flows (LSF) may be tested in the second 10 years of the LTEMP period (2026-2036), for the purpose of achieving warmer river temperatures (≥14°C) to benefit
humpback chub and other native species. Under low summer flows, daily fluctuations would be less than under base operations (e.g., approximately 2,000 cfs). Investigating the anticipated effects of and options for providing warmer water temperatures in the mainstem Colorado River through Grand Canyon is an identified management action in the 2002 Humpback Chub Recovery Goals (USFWS 2002a).
It should be noted that the 2002 Humpback Chub Recovery Goals were dismissed as a result of a federal lawsuit by Grand Canyon Trust and have not yet been re-filed or supplemented. [3]
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Papers and Publications
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Other Stuff
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How steady were the pre-dam flows on the Colorado River through Grand Canyon?
Page 42: These analyses indicate that, prior to the
closure of Glen Canyon Dam, the duration of flows varied
substantially over multi-year and decadal time scales.
These analyses also indicate that the discharge of the predam
river was fairly steady over sub-daily time scales, and
that the daily range in discharge was the most extreme
during the summer thunderstorm season.
Page 45: The two wettest decades, the 1920s and 1940s, had the largest
median daily ranges in discharge, 808 and 566 ft3/s,
respectively. The 1930s were the driest decade with the
lowest discharges, but had the second smallest median
daily range in discharge, 516 ft3/s. The 12-year period
from January 1, 1951, through March 12, 1963, was
slightly wetter than the 1930s, but had the smallest
median daily range in discharge, 416 ft3/s. The month
with the greatest median daily range in discharge was
June during the snowmelt flood (fig. 26 and Appendix G),
although the daily ranges in discharge were most extreme
during the summer thunderstorm season of July through
October (fig. 26). The pre-dam daily range in discharge
was largest on September 13, 1927, when discharge
increased by 68,100 ft3/s at Lees Ferry to a peak discharge
of 125,000 ft3/s as the result of a flood that mostly
originated within the San Juan River drainage basin
(fig. 21B). Although such extreme examples exist, large
daily ranges in discharge were rare during the pre-dam
era, with only 1 percent of all days having a daily
discharge range in excess of 10,000 ft3/s (fig. 27).
In addition to radically changing the
hydrology, operation of the dam for power generation has
introduced daily fluctuations in discharge that are much
larger and more common than those that generally
occurred prior to closure of the dam (figs. 21B and 25A).
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