Difference between revisions of "Low Summer Flow Experiment"

Increase mainstem river temperature to increase humpback chub growth.

Initial experiment: in the second 10 years of the LTEMP period (2026-2036) when target temperature of ≥14°C can be achieved only with low summer flow

Subsequent experimental use if:

1. Initial test was successful,
2. Humpback chub population concerns warrant their use,
3. Water temperature appears to be limiting recruitment, and
4. Target temperature of ≥14°C could be achieved only with low summer flow.

• 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

• Reduced food availability to humpback chub by

1. desiccating the nearshore environment with the reduction in flow between June and July, and
2. 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 science experiment in US history.

LSF monthly volumes with various annual release volumes

• 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.

• The 2000 Low Summer Steady Flow Experiment
• Temperature Page
• Humpback Chub Page

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.

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]

• Summary report of responses of key resources to the 2000 Low Steady Summer Flow experiment, along the Colorado River downstream from Glen Canyon Dam, Arizona, 2011 USGS-GCMRC Open-File Report
• Water temperatures in select nearshore environments of the Colorado River in Grand Canyon, Arizona, during the Low Steady Summer Flow experiment of 2000
• Grand Canyon Monitoring and Research Center Updates

How steady were the pre-dam flows on the Colorado River through Grand Canyon?

• Topping et al. 2003. Computation and analysis of the instantaneous-discharge record for the Colorado River at Lees Ferry, Arizona, May 8, 1921 through September 30, 2000: U.S. Geological Survey Professional Paper 1677, 118 p.

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).