Matching Items (6)

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2014 Yackulic, Yard, Korman and Van Haverbeke, A Quantitative Life History of Endangered Humpback Chub that Spawn in the Little Colorado River, Variation in Movement, Growth, and Survival

Description

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

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.

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Created

Date Created
  • 2014-01-16

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1998 Schmidt, Webb, Valdez, Marzolf and Stevens. Science and Values in River Restoration in the Grand Canyon

Description

Restoration of riverine ecosystems is often stated as a management objective for regulated rivers, and floods are one of the most effective tools for accomplishing restoration. The National Re- search

Restoration of riverine ecosystems is often stated as a management objective for regulated rivers, and floods are one of the most effective tools for accomplishing restoration. The National Re- search Council (NRC 1992) argued that ecological restoration means re- turning "an ecosystem to a close approximation of its condition prior to disturbance" and that "restoring altered, damaged, O f destroyed lakes, rivers, and wetlands is a high-priority task." Effective restoration must be based on a clear definition of the value of riverine resources to society; on scientific studies that document ecosystem status and provide an understanding of ecosystem processes and resource interactions; on scientific studies that predict, mea- sure, and monitor the effectiveness of restoration techniques; and on engineering and economic studies that evaluate societal costs and benefits of restoration.

In the case of some large rivers, restoration is not a self-evident goal. Indeed, restoration may be impossible; a more feasible goal may be rehabilitation of some ecosystem components and processes in parts of the river (Gore and Shields 1995, Kondolfand Wilcock 1996, Stanford et al. 1996). In other cases, the appropriate decision may be to do nothing. The decision to manipulate ecosystem processes and components involves not only a scientific judgment that a restored or rehabilitated condition is achievable, but also a value judgment that this condition is more desirable than the status quo. These judgments involve prioritizing different river resources, and they should be based on extensive and continuing public debate.

In this article, we examine the appropriate role of science in determining whether or not to restore or rehabilitate the Colorado River in the Grand Canyon by summarizing studies carried out by numerous agencies, universities, and consulting firms since 1983. This reach of the Colorado extends 425 km between Glen Canyon Dam and Lake Mead reservoir (Figure 1). Efforts to manipulate ecosystem processes and components in the Grand Canyon have received widespread public attention, such as the 1996 controlled flood released from Glen Canyon Dam and the proposal to drain Lake Powell reservoir.

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Created

Date Created
  • 1998-09

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1981 Geomorphology of the Colorado River in the Grand Canyon

Description

Sediment supplied to the Colorado River within the Grand Canyon has been sorted into distinct deposits of three grain size ranges. The major rapids are formed by boulder deposits from

Sediment supplied to the Colorado River within the Grand Canyon has been sorted into distinct deposits of three grain size ranges. The major rapids are formed by boulder deposits from side-canyon tributaries. As a result of a fourfold reduction in peak discharge when Glen Canyon Dam was closed in 1963, new fan debris may increase the gradient through some of the rapids by a factor of 1.8. Cobbles and gravel, transported only during flood stages, are preferentially deposited in the wider sections of the river as bars and riffles and are, for the most part, inactive during post-dam discharges. Fine-grain (largely sandy) terraces occur throughout the canyon, especially along the banks of the large reverse eddies above and below the rapids. The lower terraces are being reworked into beach-like shores by diurnally-varying, post-dam discharges. A slight net lateral erosion of the terraces has resulted. Prior to construction of the dam, sandy bed deposits underwent scour averaging about 1 m during spring floods, balanced by deposition from tributary sources during the summer. Downstream from rapids, decreased turbulence due to lower discharges has resulted in deposition averaging 2.2 m on the bed within the upper portions of the canyon. Differences in rock types along the river determine overall channel morphology. Rocks of low resistance result in a wide valley, a meandering channel, and abundant cobble bars and sand terraces. Narrow channels with rapids and deep pools are most frequent within the sections of the canyon where Precambrian crystalline rocks dominate.

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Agent

Created

Date Created
  • 1981-05

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Dams, Displacement, and Health: Reviewing Impacts of Large Dams on Displaced Communities

Description

This paper explores the impacts of dam-induced displacement on the health of populations. By the start of the 21st century, an estimated 40-80 million people worldwide were forced to resettle

This paper explores the impacts of dam-induced displacement on the health of populations. By the start of the 21st century, an estimated 40-80 million people worldwide were forced to resettle due to the construction of large dams. The process of displacement and resettlement is connected to numerous social impacts on communities such as decreases in household income, natural resources, and social connectivity, but less seems to be known about specific health impacts. Analyzing literature in a formal review allowed for increased understanding about what information already exists in published research regarding the connections between dams, displacement, and health. Some negative health impacts as a result of forced displacement were identified, including increases in infectious disease transmission, depression, and mortality rates as well as losses of food and water sources. However, the small amount of cases found in the literature review when compared to the massive scale of dam development worldwide indicates a gap in knowledge in the dam industry and research field specifically about the health of the vast majority of populations forcibly displaced by dams. Health impacts must be considered and systematically studied in dam projects involving displacement to fully understand the needs of resettled populations and move towards equitable processes in development projects worldwide.

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Agent

Created

Date Created
  • 2020-05

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Ebb and flow: preserving regulated rivers through strategic dam operations

Description

Fluctuating flow releases on regulated rivers destabilize downstream riverbanks, causing unintended, unnatural, and uncontrolled geomorphologic changes. These flow releases, usually a result of upstream hydroelectric dam operations, create manmade tidal

Fluctuating flow releases on regulated rivers destabilize downstream riverbanks, causing unintended, unnatural, and uncontrolled geomorphologic changes. These flow releases, usually a result of upstream hydroelectric dam operations, create manmade tidal effects that cause significant environmental damage; harm fish, vegetation, mammal, and avian habitats; and destroy riverbank camping and boating areas. This work focuses on rivers regulated by hydroelectric dams and have banks formed by sediment processes. For these systems, bank failures can be reduced, but not eliminated, by modifying flow release schedules. Unfortunately, comprehensive mitigation can only be accomplished with expensive rebuilding floods which release trapped sediment back into the river. The contribution of this research is to optimize weekly hydroelectric dam releases to minimize the cost of annually mitigating downstream bank failures. Physical process modeling of dynamic seepage effects is achieved through a new analytical unsaturated porewater response model that allows arbitrary periodic stage loading by Fourier series. This model is incorporated into a derived bank failure risk model that utilizes stochastic parameters identified through a meta-analysis of more than 150 documented slope failures. The risk model is then expanded to the river reach level by a Monte Carlos simulation and nonlinear regression of measured attenuation effects. Finally, the comprehensive risk model is subjected to a simulated annealing (SA) optimization scheme that accounts for physical, environmental, mechanical, operations, and flow constraints. The complete risk model is used to optimize the weekly flow release schedule of the Glen Canyon Dam, which regulates flow in the Colorado River within the Grand Canyon. A solution was obtained that reduces downstream failure risk, allows annual rebuilding floods, and predicts a hydroelectric revenue increase of more than 2%.

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Agent

Created

Date Created
  • 2010