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Glen Canyon Dam Long-Term Experimental and Management Plan EIS
Frequently Asked Questions

Glen Canyon Dam Long-Term Experimental and Management Plan EIS

Frequently Asked Questions (FAQs)

A list of frequently asked questions about the LTEMP EIS.

Below is a list of frequently asked questions about the LTEMP EIS. Click a question to see the answer.

Scope-Oriented FAQs

Resource-Oriented FAQs

Preferred Alternative FAQs

Process-Oriented FAQs

Scope-Oriented FAQs

What is the geographic scope of the analysis for the LTEMP FEIS?

In general, the region examined in the FEIS includes the area potentially affected by implementation of the LTEMP (normal and experimental operations of Glen Canyon Dam and non-flow actions). This area includes Lake Powell, Glen Canyon Dam, and the river downstream to Lake Mead. More specifically, the scope primarily includes the Colorado River Ecosystem, which includes the Colorado River mainstream corridor and interacting resources in associated riparian and terrace zones, located primarily from the forebay of Glen Canyon Dam to the western boundary of Grand Canyon National Park (GCNP). It includes the area where dam operations impact physical, biological, recreational, cultural, and other resources. Portions of Glen Canyon National Recreation Area, GCNP, and Lake Mead National Recreation Area are included within this area. For certain resources, such as socioeconomics, air quality, and hydropower, the affected region is larger and includes areas potentially affected by indirect impacts of the LTEMP. The potentially affected regions for these resources are specifically identified in Chapters 3 and 4 of the FEIS.

Did the LTEMP EIS consider effects on water availability for communities or agriculture or on water levels in Lake Powell or Lake Mead?

The LTEMP alternatives considered changes to the monthly, daily and hourly releases from Glen Canyon Dam. Under all alternatives, annual water release volumes from Glen Canyon Dam will continue to be consistent with applicable determinations 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.

The LTEMP will not affect the amount of water that would be available annually for communities and agriculture. However, potential changes to the timing of the water flow between Lake Powell and Lake Mead were considered and evaluated. Nothing in this process will affect water allocation among the Basin States or the Secretary of Interior's responsibility for water deliveries.

Why are additional experiments needed?

Previous experiments have helped us better understand the effects of dam operations. The knowledge we have gained will allow us to make management decisions, but there is more to learn. We have learned from past experiments about beneficial and adverse effects on visitors and resources from different operations. These lessons learned can be applied to experiments in the future that would allow us to better protect resources, continue meeting water requirements for communities and agriculture, and adjust operations in an adaptive management framework

How will the need for specific experiments be determined?

Past, ongoing, and future scientific studies and experimentation were considered in the development of the EIS. The EIS is grounded in the scientific analysis of past experiments and the goals for resource protection. A number of new experiments are being proposed under the LTEMP alternatives including various high-flow experiments, flow and non-flow actions to manage the trout fishery, flow experiments to increase aquatic food base production, and vegetation treatments.

What alternatives were evaluated in the LTEMP EIS?

The EIS assesses the potential environmental effects of seven alternatives being considered: the No-Action Alternative (Alternative A) and six action alternatives (Alternatives B, C, D, E, F, and G), which are described in the Notice of Availability (NOA) available on this website (http://ltempeis.anl.gov).

Was the removal of Glen Canyon Dam considered as an LTEMP alternative?

No, dam removal was not considered because it does not meet the purpose and need of the LTEMP and was considered beyond the scope of the EIS.

Were potential impacts from LTEMP alternatives on Lake Mead water quality evaluated?

Detailed modeling for Lake Mead was conducted by the Southern Nevada Water Authority because of concerns related to the potential effects of LTEMP alternatives on the quality of municipal water supplies. The temperature modeling was performed using the model described in Flow Science (2011). The Lake Mead Model (LMM) model uses the ELCOM (Estuary, Lake and Coastal Ocean Model) code to simulate hydrology and conservative constituents, and CAEDYM (Computational Aquatic Ecosystem Dynamics Model) code for simulating biogeochemical processes. Analysis results are presented in the FEIS in Section

Were potential infrastructure changes such as temperature control devices or sediment augmentation considered for the LTEMP EIS?

Several infrastructure additions and modifications were initially discussed by the DOI during alternative development, including (1) sediment augmentation, (2) a temperature control device, (3) retrofitting of the bypass tubes to install power generation, and (4) re-engineering of the spillways if needed to allow for more frequent use.

The DOI considers any infrastructure modifications or additions to be outside the scope of the LTEMP EIS because they are currently economically infeasible and would require additional congressional authorizations. However, the DOI does not rule out future new infrastructure if resource conditions warrant.

Resource-Oriented FAQs

What resources, impacts, and issues were addressed in the LTEMP EIS?

Direct, indirect, and cumulative impacts of the effects of the proposed action, in combination with the effects of past, present, and reasonably foreseeable future projects, were analyzed in the LTEMP EIS for the following impact topics:

  • Water resources, including annual, monthly, and hourly patterns of releases, water temperature, and water quality;
  • Sediment resources, including sand and sandbars within the active river channel, and sand that accumulates in the Colorado River delta of Lake Mead;
  • Natural processes that support ecological systems within the Colorado River Ecosystem;
  • Aquatic ecology, including aquatic food base for fishes, nonnative fishes (warmwater, coolwater, and trout), native fishes (including the endangered humpback chub and razorback sucker), and aquatic parasites;
  • Vegetation, including Old High Water Zone vegetation, New High Water Zone vegetation, wetlands, and special status plant species;
  • Wildlife, including terrestrial invertebrates, amphibians and reptiles, birds, mammals, and special status wildlife species;
  • Cultural resources, including archeological resources, historic and prehistoric structures, cultural landscapes, traditional cultural properties, and ethnographic resources important to American Indian Tribes;
  • Tribal resources, including vegetation, wildlife, fish, and wetlands, water rights, traditional cultural places, traditional knowledge, and continued access to important resources within Glen and Grand Canyons;
  • Visual Resources in Glen Canyon National Recreation Area, Grand Canyon National Park, and Lake Mead National Recreation Area;
  • Recreation, visitor use, and experience as related to fishing, boating, and camping activities in the Colorado River and on Lakes Powell and Mead;
  • Wilderness and visitor wilderness experience;
  • Hydropower, including the amount and value of hydropower generation at Glen Canyon Dam, marketable electrical capacity, capital and operating costs, and rate impacts;
  • Socioeconomics, including recreational use values, nonuse economic value, employment and income, and environmental justice;
  • Air quality effects related to changes in Glen Canyon Dam operations, including air emissions; and
  • Climate change, including the effects of Glen Canyon operations on greenhouse gas emissions and the effects of climate change on future impacts of Glen Canyon Dam operations.

Did the LTEMP EIS consider effects on recreational users and the recreation industry downstream of Glen Canyon Dam, or on visitor experience?

Effects on recreation were considered in the LTEMP EIS. Scientific information, mathematical modeling, and public input were considered. Recreational considerations focused on fishing, rafting, and camping/beach use along the Colorado River; hiking and wilderness experience; and both use and non-use recreation values. The EIS also considered other recreation such as boating use on Lake Powell and Lake Mead, to evaluate if any alternatives had impacts on these resources. See Section 4.10 of the FEIS.

What are the current dam release patterns?

Dam releases currently follow the Modified Low Fluctuating Flow (MLFF) regime established in the 1996 Record of Decision for operation of Glen Canyon Dam. The table below presents the established release constraints for flow parameters under MLFF.

Maximuma25,000 cfs
Minimum5,000 cfs
8,000 cfs
7:00 p.m. to 7:00 a.m
7:00 a.m. to 7:00 p.m.
Ramp Rates
Ascending4,000 cfs/hour
Descending1,500 cfs/hour
Daily Flow Range b5,000 to 8,000 cfs
  1. May be exceeded for emergencies and during extreme hydrological conditions.
  2. Daily flow range limit is 5,000 cfs for months with release volumes less than 0.6 maf; 6,000 cfs for monthly release volumes of 0.6 maf to 0.8 maf; and 8,000 cfs for monthly volumes over 0.8 maf.

Will the LTEMP affect dam release patterns?

The LTEMP alternatives consider changes to the monthly, daily, and hourly releases from Glen Canyon Dam. Annual water release volumes from Glen Canyon Dam will continue to be consistent with applicable determinations 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.

Currently, Glen Canyon Dam releases follow the preferred alternative from the 1996 Record of Decision for operation of Glen Canyon Dam. This release regime, which has been in place since 1996, referred to as "Modified Low Fluctuating Flows" is the "No Action" alternative which all other alternatives are compared to in the LTEMP EIS. The preferred alternative (Alternative D) would have the same maximum and minimum flows as MLFF, a more even monthly pattern of releases than has occurred under MLFF, and relatively comparable fluctuation levels to those under MLFF. These differences in release patterns are expected to have relatively minor effects on lake elevations. See Section 4.2 of the FEIS.

Will the LTEMP affect hydroelectric power production?

Effects of alternative releases patterns on hydroelectric power production were analyzed in the LTEMP EIS. Impacts were determined using scientific information and modeling of the Salt Lake City Area/Integrated Projects power system of which Glen Canyon Powerplant is the largest facility. This analysis determined that there would be some difference among alternatives in the value of hydropower generation and capacity because of differences among alternatives in the seasonal timing of powerplant releases, within-day fluctuation levels, and experimental releases that bypass the power turbines. There are a number of factors that could affect hydropower production at Glen Canyon Dam that are not connected to the LTEMP process including maintenance schedules, lake level elevation changes from drought or climate change, and power demand. See Section 4.13 of the FEIS.

What have been the effects of previous high-flow experiments on beaches and other resources?

The Glen Canyon Dam Adaptive Management Program has conducted six HFEs (the first was called a Beach Habitat Building Flow), which occurred in 1996, 2004, 2008, 2012, 2013, and 2014, to study the controlling factors that act together to build and maintain sandbars. The primary goal of an HFE is to rework sediments contributed by the Paria River, the Little Colorado River, and ungaged tributaries from the riverbed up to sandbar features that are at elevations above operational flow stages. The first three HFEs conducted have been extensively studied and reported on. Overall, these types of sediment-enriched flows were found to be effective at building sandbars, although post-HFE erosion of sandbars did occur at varying rates depending on flow conditions. See Sections in Chapter 3 of the FEIS, particularly Sections 3.3 and 3.5.

What have previous experiments told us about the humpback chub?

Since 1982, scientists have been conducting and evaluating experiments related to determining the effects of dam operations on a variety of resources, including humpback chub and other aquatic species. These results have identified several potential flow and non-flow strategies for protecting and enhancing populations of humpback chub. One of the objectives of the LTEMP EIS process is to evaluate the scientific results of past experiments and apply these results to formulating a long-term experimental plan that addresses scientific uncertainties and identifies operations that would protect humpback chub populations. See Section 3.5 of the FEIS.

Preferred Alternative FAQs

Is there a preferred alternative for the LTEMP?

Yes, Alternative D was identified by the DOI as the preferred alternative in the FEIS. Alternative D was also identified by the DOI as the environmentally preferred alternative. DOI received positive feedback about this alternative from a number of Cooperating Agencies and AMWG stakeholders. It was developed by the DOI based on the results of the analysis of the other six alternatives. Alternative D adopted many of the best-performing characteristics of Alternatives C and E. The effects of operations under these latter two alternatives were first modeled, and the results of that modeling suggested ways in which characteristics of each could be combined and modified to improve performance, reduce impacts, and better meet the purpose, need, and objectives of the LTEMP. Alternative D would result in monthly release patterns that would be relatively even compared to current operations and would have comparable fluctuation levels to MLFF. The alternative adopts a condition-dependent approach to implementation of experiments for sediment retention and sandbar building, trout fishery management, humpback chub conservation, enhancement of the aquatic food base, and improvement of vegetation conditions along the river. Alternative D is expected to result in an improvement in conditions for humpback chub, trout, and the aquatic food base; have the least impact on vegetation, wetlands, and terrestrial wildlife; improve sandbar building potential and conserve sediment; sustain or improve conditions for reservoir and river recreation; improve preservation of cultural resources; respect and enhance Tribal resources and values; and have limited impacts on hydropower resources.

Will release patterns and flows change under the preferred alternative?

The preferred alternative, Alternative D, would provide a more even monthly release pattern than currently occurs. This pattern more closely matches seasonal patterns of electricity demand and is expected to reduce resource impacts downstream from the dam. Fluctuations will be proportional to monthly volume and comparable to current levels of fluctuation, with the maximum daily change retained at 8,000 cfs.

Will river level fluctuations change under the preferred alternative?

Under current operations, the within-day fluctuation level is set at 5,000 cfs, 6,000 cfs or 8,000 cfs depending on the monthly volume. Under the preferred alternative, fluctuations will be tied to a percentage of the monthly volume rather than an absolute value, but will be no greater than 8,000 cfs. The highest fluctuations will be in January, July, and August, much like they are now.

What will be the minimum and maximum releases under the preferred alternative?

For normal operational flows, allowable minimum and maximum daily releases will be the same as under current operations, i.e., a maximum release of 25,000 cfs and minimum releases of 5,000 cfs between 7 p.m. and 7 a.m., and 8,000 cfs between 7 a.m. and 7 p.m. Maximum releases will be increased to up to 45,000 cfs during high-flow experiments.

What kind of experiments will be done under the preferred alternative?

The intent of the preferred alternative is to provide for continued adaptive management through implementation and monitoring of a set of potential experiments. Annually, resource conditions will be considered in the planning of these experiments and coordination will occur with agencies, stakeholders, and Tribes. Experiments under the preferred alternative may include:

  • Sediment-triggered Fall HFEs
  • Sediment-triggered Extended Duration Fall HFEs
  • Sediment-triggered Spring HFEs
  • Proactive Spring HFEs
  • Macroinvertebrate Production Flows
  • Trout Management Flows
  • Low Summer Flows
  • Vegetation Treatments

Process-Oriented FAQs

What is an Environmental Impact Statement (EIS)?

An EIS is a tool for making decisions. It describes the beneficial and adverse direct, indirect, and cumulative environmental effects of major federal actions. An EIS is required whenever a federal agency proposes to take an action that could have significant impacts on the environment.

Purpose of an EIS

An EIS is a document that describes the effects of a proposed federal action on the environment. "Environment," in this case, is defined as the natural and physical environment and the relationship of people with that environment. This means that the "environment" considered in an EIS includes land, water, air, structures, living organisms, environmental values at the site, and social, cultural, and economic factors. An "impact" is a change or consequence that results from taking the proposed action. Impacts can be beneficial, adverse, or both. An EIS describes impacts, as well as ways to "mitigate" impacts. To "mitigate" means to lessen or remove adverse impacts.

EIS Requirements

Federal laws and regulations require the federal government to evaluate the effects of its actions on the environment and to consider alternative courses of action. National Environmental Policy Act (NEPA) regulations require, among other things, that federal agencies include discussion of proposed actions and a range of reasonable alternatives in an EIS. The EIS must include sufficient information for reviewers to evaluate the relative merits of each alternative. The Council on Environmental Quality (CEQ) regulations provide the recommended format and content of EISs.

Why is the Long-Term Experimental and Management Plan (LTEMP) EIS needed?

The need for the proposed action stems from the need to use scientific information developed since the 1996 ROD to better inform DOI decisions on dam operations and other management and experimental actions so that the Secretary may continue to meet statutory responsibilities for protecting downstream resources for future generations, conserving Endangered Species Act-listed species, avoiding or mitigating impacts on National Register of Historic Places-eligible properties, and protecting the interests of American Indian Tribes, while meeting obligations for water delivery and the generation of hydroelectric power.

What is the purpose of the LTEMP?

The purpose of the proposed action is to provide a comprehensive framework for adaptively managing Glen Canyon Dam over the next 20 years consistent with the Grand Canyon Protection Act (GCPA) and other provisions of applicable federal law. The proposed action will help determine specific dam operations and actions that could be implemented to improve conditions and continue to meet the GCPA's requirements and to protect, mitigate adverse impacts to, and improve the downstream natural, recreational, and cultural resources in the two park units, including resources of importance to American Indian Tribes.

Why are the Bureau of Reclamation and the National Park Service joint-leads on the LTEMP EIS?

The Bureau of Reclamation has the primary responsibility for operating Glen Canyon Dam, and the National Park Service has the primary responsibility for managing the resources of Glen Canyon National Recreation Area, Grand Canyon National Park, and Lake Mead National Recreation Area. Both agencies are part of the U.S. Department of the Interior.

Was there a public scoping process for the LTEMP EIS?

Public scoping is a phase of the National Environmental Policy Act analysis process, and is intended to give the public the chance to comment on the LTEMP, recommend alternatives, and identify and prioritize the resources and issues to be considered in the EIS analysis. The public scoping phase of the EIS process gives interested parties the opportunity to comment and provide early ideas about the EIS.

Public scoping for the LTEMP EIS began on July 6, 2011, and continued through January 31, 2012. The public was provided the opportunity to submit written comments electronically through a public comment form and via regular mail as part of scoping. A summary of the comments received during public scoping is available on this website (http://ltempeis.anl.gov).

How can I participate in the LTEMP EIS process?

The FEIS was published on October 7, 2016. There are no more public comment opportunities, however, members of the public have an opportunity to read the FEIS and related documents, read the Record of Decision, and learn about the EIS on this website (http://ltempeis.anl.gov).

When was the Draft EIS (DEIS) published?

The DEIS was filed with the U.S. Environmental Protection Agency on January 8, 2016, and made available for downloading from this website (http://ltempeis.anl.gov) at the same time.

When was the Final EIS (FEIS) published?

The FEIS was filed with the U.S. Environmental Protection Agency on October 7, 2016, and made available for downloading from this website (http://ltempeis.anl.gov) at the same time.

How can I get a copy of the FEIS?

A Notice of Availability was published in the Federal Register when the FEIS was released in October 2016. The Notice of Availability provides instructions for obtaining copies of the FEIS. This website, http://ltempeis.anl.gov, also has specific instructions for downloading the FEIS.

When was the Record of Decision (ROD) signed?

The ROD was signed by the Secretary of the Interior on December 15, 2016, and is available for download on this website (http://ltempeis.anl.gov).

Are there any Cooperating Agencies involved with the LTEMP EIS?

Yes, the following agencies participated as cooperating agencies in the development of the LTEMP EIS: Arizona Game and Fish Department, Bureau of Indian Affairs, Colorado River Board of California, Colorado River Commission of Nevada, Havasupai Tribe, Hopi Tribe, Hualapai Tribe, Kaibab Band of Paiute Indians, Navajo Nation, Pueblo of Zuni, Salt River Project, U.S. Fish and Wildlife Service, Upper Colorado River Commission, Utah Associated Municipal Power Systems, and Western Area Power Administration. Cooperators have been involved in all phases of LTEMP EIS development including providing background information; providing input on LTEMP EIS goals, objectives, alternatives, and modeling metrics; reviewing modeling methodologies and results; participating in a formal structured decision analysis process; and in reviewing and commenting on pre-public drafts. Interactions with Cooperating Agencies was accomplished through numerous teleconferences, webinars, and in-person meetings over the last five years.

How have Tribes been involved in the LTEMP process?

Tribes were formally invited to participate as Cooperating Agencies and have been involved as sovereign nations collaborating directly with the Department of Interior, Reclamation, and the National Park Service to determine their desired nature and level of involvement. Several American Indian Tribes have been very involved as Cooperators in this NEPA process, including the Havasupai Tribe, Hopi Tribe, Hualapai Tribe, Kaibab Band of Paiute Indians, Navajo Nation, and Pueblo of Zuni. Tribes provided background information and monitoring data; provided input on LTEMP EIS goals, objectives, alternatives, and modeling metrics; participated in a formal structured decision analysis process; provided text for Tribal perspectives in the EIS; and reviewed and commented on pre-public drafts. Interactions with Tribes were accomplished through numerous informal consultation meetings over the last four years. See Section 5.1.3 of the FEIS for more information.

What is the Glen Canyon Dam Adaptive Management Program?

The Glen Canyon Dam Adaptive Management Program (GCDAMP) was established by, and has been implemented pursuant to the Secretary's 1996 Record of Decision on the Operation of Glen Canyon Dam, in order to comply with monitoring and consultation requirements of the Grand Canyon Protection Act (GCPA). The GCDAMP includes a federal advisory committee known as the Glen Canyon Dam Adaptive Management Work Group (AMWG), a technical work group, a scientific monitoring and research center administered by the U.S. Geological Survey (USGS), and independent scientific review panels. The AMWG makes recommendations to the Secretary concerning Glen Canyon Dam operations and other management actions to protect resources downstream of Glen Canyon Dam consistent with the GCPA and other applicable provisions of federal law.

What is the relationship between the LTEMP and the existing Glen Canyon Dam Adaptive Management Program?

As stated in the July 6, 2011, Notice of Intent, "The LTEMP process will build upon the input and recommendations from the Adaptive Management Working group (AMWG), which is a subcomponent of the Glen Canyon Dam Adaptive Management Program (GCDAMP), as well as on input received from public scoping, internal scoping, and analysis of more than 15 years of scientific information." The LTEMP will be coordinated with the existing GCDAMP.

What is Adaptive Management?

Adaptive management is a decision process that promotes flexible decision making. Under adaptive management, decisions can be adjusted in the face of uncertainties, as outcomes from management actions and other events become better understood. Careful monitoring of these outcomes advances scientific understanding and contributes to adjusting policies or operations as part of an iterative learning process. Adaptive management also recognizes the importance of natural variability in ecological resilience and productivity. It is not a "trial and error" process, but rather, emphasizes learning while doing. Adaptive management does not represent an end in itself, but rather, a means to more effective decisions and enhanced benefits. Its true measure is in how well it (a) helps meet environmental, social, and economic goals; (b) increases scientific knowledge; and (c) reduces conflicts between stakeholders.

What is the relationship of the LTEMP EIS to the two EAs on nonnative fish control and high-flow experiments?

The LTEMP EIS is a separate process, but it incorporates the information from the 2011 EAs for non-native fish control and high-flow experiments. If an action alternative is selected as a result of the NEPA process, that alternative will replace and supersede these EAs.

What is a Structured Decision Analysis (SDA) process and how was that process used in developing the EIS?

The joint leads used a structured decision process to support the evaluation of alternatives in response to requests from some of the Glen Canyon Dam AMWG stakeholders to have additional substantive input into the DEIS. The joint leads view structured decision analysis as a structured, scientific method to help evaluate complex alternatives, integrate information and critical uncertainties regarding the effects of independent environmental processes and resource response on outcomes, and bring additional transparency to the DEIS process. Input from some Cooperating Agencies, some Tribes, and other stakeholders was used to prepare a final set of performance metrics used in the LTEMP EIS analysis. The resulting performance metrics are presented in Appendix B of the FEIS.

While structured decision analysis informed the analysis of the joint leads, it was not the only method by which a preferred alternative was selected. The selection of a preferred alternative was based on the full EIS analysis and considerations relating to qualitative and quantitative evaluations of impacts. Public comment, socioeconomic considerations, AMWG stakeholder input, and other factors were all considered in this decision. See Appendix C of the FEIS for a final report on the Structure Decision Analysis.

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