The Glen Canyon Dam Final EIS analyzed baseline impacts of dam operations on downstream environmental and cultural resources from 1963 to 1990, and compared those baseline impacts to possible alternative operations of Glen Canyon Dam, including three alternatives that would provide steady flows from the dam and six alternatives that would provide various levels of fluctuating flows. The EIS team and the cooperating agencies identified a preferred alternative called: the Modified Low Fluctuating Flow Alternative. This EIS served as the culmination of the Glen Canyon Environmental Studies launched in the early 1980s to document the effects of Glen Canyon Dam on downstream resources, fulfilling one of the mandates of the Grand Canyon Protection Act of 1992.
ABSTRACT: Recovery of imperiled fishes can be achieved through suppression of invasives, but outcomes may vary with environmental conditions. We studied the response of imperiled desert fishes to an invasive brown (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) suppression program in a Colorado River tributary, with natural flow and longitudinal variation in thermal characteristics. We investigated trends in fish populations related to suppression and tested hypotheses about the impacts of salmonid densities, hydrologic variation, and spatial–thermal gradients on the distribution and abundance of native fish species using zero-inflated generalized linear mixed effects models. Between 2012 and 2018, salmonids declined 89%, and native fishes increased dramatically (∼480%) once trout suppression surpassed ∼60%. Temperature and trout density were consistently retained in the top models predicting the abundance and distribution of native fishes. The greatest increases occurred in warmer reaches and in years with spring flooding. Surprisingly, given the evolution of native fishes in disturbance-prone systems, intense, monsoon-driven flooding limited native fish recruitment. Applied concertedly, invasive species suppression and efforts to mimic natural flow and thermal regimes may allow rapid and widespread native fish recovery.
While the ecology and evolution of partial migratory systems (defined broadly to include skip spawning) have been well studied, we are only beginning to under- stand how partial migratory populations are responding to ongoing environmen- tal change. Environmental change can lead to differences in the fitness of residents and migrants, which could eventually lead to changes in the frequency of the strategies in the overall population. Here, we address questions concerning the life history of the endangered Gila cypha (humpback chub) in the regulated Colorado River and the unregulated tributary and primary spawning area, the Little Colorado River. We develop eight multistate models for the population based on three movement hypotheses, in which states are defined in terms of fish size classes and river locations. We fit these models to mark–recapture data col- lected in 2009–2012. We compare survival and growth estimates between the Col- orado River and Little Colorado River and calculate abundances for all size classes. The best model supports the hypotheses that larger adults spawn more frequently than smaller adults, that there are residents in the spawning grounds, and that juveniles move out of the Little Colorado River in large numbers during the monsoon season (July–September). Monthly survival rates for G. cypha in the Colorado River are higher than in the Little Colorado River in all size classes; however, growth is slower. While the hypothetical life histories of life-long resi- dents in the Little Colorado River and partial migrants spending most of its time in the Colorado River are very different, they lead to roughly similar fitness expectations when we used expected number of spawns as a proxy. However, more research is needed because our study period covers a period of years when conditions in the Colorado River for G. cypha are likely to have been better than has been typical over the last few decades.
ABSTRACT: This book is a response to the USGS’s call for a research design that could be used as a framework for prioritizing cultural resources in the Colorado River ecosystem below Glen Canyon Dam. Changing River includes summaries of current environmental conditions and previous research and brings together diverse archaeological opinions about Grand Canyon’s human story. It then presents a theoretical basis for using a landscape approach to organize future research efforts in the canyon. The research presented here explores the geophysical, paleoclimatic, and biological parameters that have shaped the canyon landscape and influenced choices made by humans as they attempted to adapt to this ecosystem. It then focuses on the distribution of cultural materials and patterns using several archaeological approaches, and investigates natural and cultural realms as mutually reinforcing and interacting components of an integrated ecosystem to which humans have applied meaning and value over time.
ABSTRACT: As called for in its operational plan, the Cultural Program of the Grand Canyon Monitoring and Research Center convened a Protocol Evaluation Panel (PEP). The Bureau of Reclamation co-sponsored this PEP. In 1994, a Programmatic Agreement (PA) was developed by the Advisory Council on Historic Preservation with the following parties: Bureau of Reclamation, National Park Service, Arizona State Historic Preservation Office, Havasupai Tribe, Hopi Tribe, Hualapai Tribe, Kaibab Paiute Tribe, Navajo Nation, San Juan Southern Paiute Tribe, Shivwits Paiute Tribe, and Zuni Pueblo. The Havasupai Tribe and the San Juan Southern Paiute Tribe have not signed the PA as of this report’s completion. The PEP was structured to address four topical areas: monitoring and compliance, archaeology, Native American issues, and geomorphology. Overall recommendations were developed by the full panel, based on the results of subpanel reports on the four topical areas.
ABSTRACT: This document establishes the Adaptive Management Work Group (AMWG), a federal advisory committee functioning as part of the Glen Canyon Dam Adaptive Management Program (GCDAMP). The 1992 Grand Canyon Protection Act directs the Secretary of the Interior to operate Glen Canyon Dam in such a manner as to protect, mitigate adverse impacts to, and improve the values for which Grand Canyon National Park and the Glen Canyon National Recreation Area were established, including but not limited to natural and cultural resources and visitor use. The Act also calls for implementation of long-term monitoring programs and activities that will ensure Glen Canyon Dam is operated to that end. As part of long-term monitoring, the Secretary’s Record of Decision mandates development and initiation of the GCDAMP, which provides for monitoring the results of the operating criteria and plans adopted by the Secretary and changes to those operating criteria and plans. GCDAMP includes the AMWG, which will facilitate the GCDAMP, recommend suitable monitoring and research programs, and make recommendations to the Secretary as required to meet the requirements of the Act.
Modified Low Fluctuating Flow Alternativeinitiated the Glen Canyon Dam Adaptive Management Program (GCDAMP) by establishing the Adaptive Management Work Group (AMWG) under the Federal Advisory Committee Act (FACA). AMWG’s stipulated purpose was to develop “a long-term monitoring, research, and experimental program” to evaluate the continuing effects of dam operations and to propose additional modifications when warranted.
ABSTRACT: This is the original cultural resources compliance document that was prepared in conjunction with the 1996 Environmental Impact Statement on the operations of Glen Canyon Dam. Broadly, it stipulated that cultural resources along the Colorado River corridor would be identified and evaluated for National Register eligibility, a Monitoring and Remedial Action Plan would be developed that would guide future monitoring activities and remedial actions necessary to address any adverse effects to historic properties that was identified through the monitoring. Finally, a Historic Preservation Plan was to be developed that would guide the long-term management of the historic properties under the 1994 PA. This document would incorporate all of the previous actions.
ABSTRACT: This study assesses the impact of Glen Canyon Dam releases on rafting (white-water boating and day-use rafters) and angling recreationists in Glen Canyon and Grand Canyon National Park using attribute and contingent valuation surveys. Several sources of information were utilized in this study: knowledgeable people (fishing quides, rafting guides, resource managers, and GCES researchers), seven formal surveys (including attribute surveys), and contingent valuation survey to quantify, in dollars, the effects of dam releases on the recreational exoerience. The goal of the study was to assess the impact of alternative annual flow release patterns for Glen Canyon Dam on recreationists in the aggregate. Flow regimes combining high constant flows in the summer months with moderate or low flows during the remainder of the year would be likely to produce the largest recreational benefits. Extreme high or low flows will adversely affect all river recreation, with flows below approximately 5,000 cubic feet per second and above 35,000 cubic feet oer second to both boaters and anglers.