Charles V. Stern and Ashley J. Lawson wrote this CRS report (4 April 2023): 'Long-Term Drought and Glen Canyon Dam - Potential Effects on Water Deliveries and Hydropower'.
Download CRS_Report_L-T_Drought_ GCDam_Potential Effects_Water_Power_4April2023
Click on graphics to enlarge them. Footnotes are excluded from the text below. See the full document.
Summary
The Bureau of Reclamation (Reclamation) owns and operates the Glen Canyon Unit (near Page, AZ) as part of the federal Colorado River Storage Project. The unit includes Glen Canyon Dam, on the Colorado River, and its impounding reservoir, Lake Powell—one of the largest man-made reservoirs in the United States. The reservoir provides for the storage and regulation of water flows in the Colorado River Basin between the Upper Colorado River Basin (Colorado, New Mexico, Utah, and Wyoming) and the Lower Basin (Arizona, California, and Nevada). The dam also allows the Upper Basin to meet its obligations under a 1944 treaty with Mexico and generates low-cost hydropower for Western Area Power Administration (WAPA) customers in the Southwest.
Lake Powell’s water storage levels have been declining due to a combination of long-term drought in the basin and demand for water resources that outstrips available supplies in most years. As Lake Powell’s storage levels fall, Glen Canyon Dam’s ability to generate hydropower also decreases. If the lake were to fall below a certain level (referred to as minimum power pool), the dam would be unable to generate hydropower. Decreased reservoir storage at Lake Powell also threatens Reclamation’s ability to release flows from the Upper Colorado River Basin to the Lower Basin through the dam and to meet obligations under the 1922 Colorado River Compact and other subsequent agreements. Below a certain level (i.e., dead pool), Glen Canyon Dam could prevent water from flowing to the Lower Basin.
It is unclear what the legal or practical effects would be if low storage levels in Lake Powell rendered the Upper Basin unable to meet its obligations under the various compacts, laws, and other provisions that govern water allocations (i.e., the Law of the River). Reclamation would likely face decisions on whether to ration whatever flows were bypassed to the Lower Basin and Mexico, with delivery priority based on a complex set of factors. Such a scenario also could trigger litigation between the Upper and Lower Basins and/or an international treaty dispute with Mexico.
When federal hydropower is not available (i.e., when generation levels at Glen Canyon Dam are low), WAPA customers experience higher costs. However, these customers have varying levels of dependency on WAPA power, so the relative impact on their costs varies. Low hydropower output at Glen Canyon Dam can affect the wider region, as well. Potential impacts may include higher electricity prices, increased electric reliability risks, and higher greenhouse gas emissions. However, Glen Canyon Dam’s relatively small contribution to the regional electricity grid generally limits the magnitude of these effects.
The federal government and states in the Colorado River Basin have engaged in efforts to increase water storage levels in Lake Powell, and precipitation in the winter of 2022-2023 appears likely to increase Lake Powell volumes in the short term. However, Reclamation’s projections continue to show a chance of Lake Powell falling to minimum power pool levels in the coming years. As a result, Reclamation is considering structural and operational modifications at Glen Canyon Dam. Basin states and Reclamation also are implementing new and ongoing efforts to improve storage in Lake Powell, and new proposals are under consideration. In addition, some stakeholders have proposed efforts to mitigate the potential effects of Lake Powell’s decreasing storage levels (e.g., effects on hydropower customers).
Congress has been involved in approving drought mitigation agreements related to the Colorado River Basin and the Glen Canyon Unit, and additional congressional authorization and/or appropriations would be required for many of the changes under consideration. Issues for Congress may include consideration of which, if any, efforts to support related to drought in the Colorado River Basin in general and Glen Canyon Unit facilities in particular. Congress may consider the costs and benefits of various proposals in the context of long-term drought in the basin, as well as their potential for creating precedents for other drought-prone areas.
Introduction
The Bureau of Reclamation (Reclamation) owns and operates the Glen Canyon Unit (near Page, AZ) as part of the federal Colorado River Storage Project (CRSP). The unit includes Glen Canyon Dam, on the Colorado River, and its impounding reservoir, Lake Powell—one of the largest man-made reservoirs in the United States. The reservoir provides for the storage and regulation of water flows in the Colorado River Basin between the Upper Colorado River Basin (Colorado, New Mexico, Utah, and Wyoming) and the Lower Basin (Arizona, California, and Nevada). The dam also allows the Upper Basin to meet its obligations under a 1944 treaty with Mexico and generates low-cost hydropower for Western Area Power Administration (WAPA) customers in the Southwest.
Lake Powell’s water storage levels have been declining due to a combination of long-term drought in the basin and demand for water resources that outstrips available supplies in most years. As Lake Powell’s storage levels drop, Glen Canyon Dam’s ability to produce hydropower also decreases. If water storage were to reach a certain level (referred to as minimum power pool), the dam would be unable to generate any hydropower. Decreased reservoir storage at Lake Powell also threatens the dam’s ability to bypass flows from the Upper Basin to the Lower Basin and to meet Upper Basin obligations under the 1922 Colorado River Compact and other agreements. If Lake Powell storage levels decline past minimum power pool and reach a level referred to as dead pool, Glen Canyon Dam could prevent water from flowing to the Lower Basin.
The federal government and Colorado River Basin states are implementing new and ongoing efforts to try to increase water storage levels in Lake Powell, and precipitation in the winter of 2022-2023 appears likely to increase Lake Powell storage in the short term. However, projections continue to show a chance of water storage falling to minimum power pool in the coming years. As a result, Reclamation is considering new proposals, including structural and operational modifications at Glen Canyon Dam, some of which would need congressional authorization and appropriations. Some stakeholders also have proposed efforts to mitigate the potential effects of Lake Powell’s decreasing storage levels.
This report provides background on management of Colorado River Basin waters, with a focus on Glen Canyon Unit facilities (i.e., Glen Canyon Dam and Power Plant and Lake Powell). It also discusses the potential ramifications of drought and falling water storage levels at these facilities and addresses related issues for Congress. For broader information on federal management of Colorado River and Lower Basin issues, see CRS Report R45546, Management of the Colorado River: Water Allocations, Drought, and the Federal Role.
Background on Federal Development of the Colorado River Basin
The Glen Canyon Unit is a significant component of the federal system managing the waters of the Colorado River. This system is collectively governed by the Law of the River, a phrase that refers to the multiple compacts, federal laws, court decisions and decrees, contracts, and regulatory guidelines governing Colorado River operations. The seminal Law of the River document apportioning the waters of the Colorado River Basin is the Colorado River Compact of 1922. In an effort to resolve basin conflicts and avoid litigation, Congress gave its consent for the states and Reclamation to enter into the Colorado River Compact to apportion Colorado River water supplies. The compact allocated the river’s water supplies between the Upper Basin and to be shared equally between the Lower and Upper Basins. As a result, pursuant to the Colorado River Compact and the 1944 treaty, the Upper Basin must bypass (i.e., pass through the dam) an average of at least 8.25 MAF per year to the Lower Basin.
Over time, Congress has authorized Reclamation to construct numerous federal facilities to improve storage and conveyance of Colorado River waters. Most Lower Basin facilities (the largest being Hoover Dam, near the Nevada/Arizona Border) were authorized and constructed decades prior to Upper Basin facilities, which were constructed following congressional enactment of legislation in the 1950s and 1960s (see below section, “Glen Canyon Unit”). Congress did not allow projects authorized for study in the Upper Basin to proceed with federally funded construction until Upper Basin states determined their individual water allocations, which allocations in terms of percentage.following approval of the Upper Basin Compact (i.e., the baseline for allocations under the Law of the River).
The remainder of this report focuses on current issues related to long-term drought in the Colorado River Basin and its effects on the Glen Canyon Unit.
Figure 1. Colorado River Basin Allocations
"This lake exceeds anything I ever beheld in beauty." - Percy Bysshe Shelley (speaking of Lake Como, Italy)
Comments