The Colorado River ecosystem in lower Glen Canyon and throughout Marble and Grand Canyons was greatly altered following closure of Glen Canyon Dam in 1963, as flood control and daily fluctuating releases from the dam caused large ecological changes. Ecosystem research was conducted from 1983 through 1990, and intensively from 1990 through 1995 when dam releases were modified both for scientific purposes and protection of the river ecosystem. High flows (e.g., beach/habitat building flows) were included in the Glen Canyon Dam Environmental Impact Statement (EIS), which identified a preferred strategy for dam operations and protection of the downstream ecosystem. Use of high flows partially fulfills recommendations of many river and riparian scientists for return of more natural flows, as part of initial efforts in river restoration. In 1996, a seven-day experimental controlled flood was conducted at Glen Canyon Dam to closely study the effects of a high flow event equivalent to those proposed for future dam management. It is an example of modification of operations of a large dam to balance economic gains with ecological protection. Limited to 1274 m 3 /s, the test flood was lower than pre-dam spring floods. The experiment was conducted to (1) test the hypothesis that controlled floods can improve sediment deposition patterns and alter important ecological attributes of the river ecosystem without negatively affecting other canyon resources and (2) learn more about river processes, both biotic and abiotic, during a flood event. Along with an explanation of the planning and background of this flood experiment, this paper summarizes expected and realized changes in canyon resources studied during the flood. Responses of specific resources to the flood are synthesized in the following compendium papers.

Environmental Environmental externalities externalities re-resulting sulting from from the the construction construction and and operation operation of of a a number number of of hydropower hydropower plants plants are are now now being being re-reexamined. examined. The The focus focus of of many many recent recent analyses analyses is is on on identifying identifying new, new, often often more more restrictive, restrictive, opera-operational tional regimes regimes which which will will improve improve downstream downstream environmental environmental conditions. conditions. These These new new regimes regimes may may create create significant significant market market and and nonmarket nonmarket benefits benefits but but constraints constraints on on hydropower hydropower opera-operations tions frequently frequently lead lead to to economic economic costs. costs. This This pa-paper per introduces introduces an an hourly hourly constrained constrained optimiza-optimization tion framework framework for for estimating estimating the the short-run short-run costs costs of of restricting restricting hydropower hydropower operations. operations. Glen Glen Can-Canyon yon Dam, Dam, on on the the Colorado Colorado River River in in Arizona, Arizona, is is used used as as a a case case study. study. Newly Newly available available market-marketbased based prices prices are are employed. employed. (JEL (JEL Q25) Q25) I. I. INTRODUCTION INTRODUCTION Hydropower Hydropower plants plants produce produce electricity electricity without without burning burning fossil fossil fuels fuels and and producing producing air air pollution pollution and and are are sometimes sometimes thought thought of of as as environmentally environmentally benign. benign. In In fact, fact, large large hy-hydropower dropower facilities facilities have have blocked blocked the the spawn-spawning ing of of anadromous anadromous and and migratory migratory aquatic aquatic species, species, eliminated eliminated the the downstream downstream transport transport of of sediment, sediment, fundamentally fundamentally altered altered the the sea-seasonal sonal hydrograph, hydrograph, affected affected water water chemistry, chemistry, and, and, changed changed the the downstream downstream temperature temperature regime regime (Collier, (Collier, Webb, Webb, and and Schmidt Schmidt 1996). 1996). Furthermore, Furthermore, the the daily daily operations operations of of these these units, units, particularly particularly units units used used to to produce produce peaking peaking power, power, may may have have a a number number of of ad-adverse verse effects effects on on aquatic aquatic and and riparian riparian commu-communities nities (Nilsson, (Nilsson, Jansson, Jansson, and and Zinko Zinko 1997). 1997). The The environmental environmental externalities externalities resulting resulting from from the the construction construction and and operation operation of of a a number number of of hydropower hydropower plants plants are are now now being being reexa...

The Colorado River ecosystem in lower Glen Canyon and throughout Marble and Grand Canyons was greatly altered following closure of Glen Canyon Dam in 1963, as flood control and daily fluctuating releases from the dam caused large ecological changes. Ecosystem research was conducted from 1983 through 1990, and intensively from 1990 through 1995 when dam releases were modified both for scientific purposes and protection of the river ecosystem. High flows (e.g., beach/habitat building flows) were included in the Glen Canyon Dam Environmental Impact Statement (EIS), which identified a preferred strategy for dam operations and protection of the downstream ecosystem. Use of high flows partially fulfills recommendations of many river and riparian scientists for return of more natural flows, as part of initial efforts in river restoration. In 1996, a seven-day experimental controlled flood was conducted at Glen Canyon Dam to closely study the effects of a high flow event equivalent to those proposed for future dam management. It is an example of modification of operations of a large dam to balance economic gains with ecological protection. Limited to 1274 m 3 /s, the test flood was lower than pre-dam spring floods. The experiment was conducted to (1) test the hypothesis that controlled floods can improve sediment deposition patterns and alter important ecological attributes of the river ecosystem without negatively affecting other canyon resources and (2) learn more about river processes, both biotic and abiotic, during a flood event. Along with an explanation of the planning and background of this flood experiment, this paper summarizes expected and realized changes in canyon resources studied during the flood. Responses of specific resources to the flood are synthesized in the following compendium papers.

Many fish and wildlife management agencies expend a large proportion of their fishery management budgets to provide catchable‐size trout for the creation and maintenance of put‐and‐take fisheries. Increasingly, this practice has been called into question. This study examines the economic issues involved and compares the economic costs of providing catchable rainbow trout Oncorhynchus mykiss in two Colorado streams with anglers' willingness to pay for them. The apparent discrepancy between the economic costs of providing catchable trout and their economic benefits suggests that the Colorado catchable trout program and those in other states should be reviewed on efficiency grounds.

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