Glen Canyon Dam Adaptive Management Program Administrative History

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.

An ecological survey of the riparian zone of the Colorado River from Lees Ferry to the Grand Wash Cliffs, Arizona, was initiated between 1 June 1974 and 30 June 1976. The purposes of this study were:

First, to describe vegetational changes as a result of the controlled water release from Glen Canyon Dam, second, preparation of a vegetation map from river level up to the 500 foot contour level, third, to describe population densities, home ranges, and demography of important vertebrates, fourth, to inventory insects of the riparian zone, fifth, to describe the distribution and impact caused by feral burros, and sixth, to describe the interrelationships of humans with the biota.

The major findings include the following: (1)The construction of Glen Canyon Dam has permitted the development of a new riparian community. This community is characterized by salt cedar, arrowweed, coyote willow, desert broom, and seep willow. (2) Botanical investigations in the riparian and adjacent habitats discerned the presence of 807 species of vascular plants representing 92 families. Also, two species, previously undescribed, Flaveria mcdougallii and Euphorbia rossii, are presented. (3) An accessment of important vertebrates and insects revealed: a) rodent communities on beaches tend to be less productive and less stable than those rodent communities of the terrace areas, b) Peromyscus eremicus appears to be the most successful small mammal in the riparian zone, c) rodent survivorship is very low and suggests a nearly annual population turnover, d) 178 species of birds utilize the riparian zone, of these 41 breed there, e) the most common bird species is the Lucy's Warbler, f) over 12,000 insect specimens in 20 orders and 247 families were collected and prepared, g) insect production on the exotic salt cedar fluctuate dramatically in comparison to insect production on dominant native plants. (4) Feral ass distribution was found to be greater than previously believed. It has been determined that the expanding feral ass populations are systematically destroying riparian and desert habitats within the study area and their immediate removal is suggested. (5) Human impact seems to be a function of visitor activities and the specific biotic sensitivity of the use area rather than a function of the total number of users. (6) In 1974, 395 different campsites were reported between Lees Ferry and Pierce's Ferry. In 1975, 350 different campsites were used. (7) Establishment and maintenance of an inner canyon trail system, the removal of all future human fecal waste material and education of river users may be the means to minimize habitat destruction rather than just setting a user-day limit.