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Floods and Sandbars in the Grand Canyon



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INSIDE Vol 9 No 4 April 1999 GSA TODAY A Publication of the Geological Society of America Call for Papers Page D1 Electronic Abstract Submission Page D12 Registration Issue June GSA Today Floods and Sandbars in the Grand Canyon Ivo Lucchitta 6969 Snowbowl View Circle Flagstaff AZ 86001 Luna B Leopold 400 Vermont Avenue Berkeley CA 94707 ABSTRACT Erosion of sandbars and beaches in the Grand Canyon National Park downstream from Glen Canyon Dam has become a major problem that needs to be addressed Geomorphic and geologic mapping provide a link between sandbar elevations and discharge measurements This link allows an estimate of discharges that will deposit sand far enough above normal high water to prevent frequent depletions by erosion The sand is needed to protect habitats and archaeological sites and to maintain beaches used by recreationists It is proposed that when the Little Colorado is in flood discharge at Glen Canyon Dam be increased to bring the total discharge to the desired high value Analysis of the flow records show that such opportunities are presented on the average once in eight years suggesting that the proposal has a reasonable chance of success INTRODUCTION The Colorado River in the Grand Canyon section in Arizona once fluctuated greatly in its flow Year to year and seasonto season variability was large Peak discharges ranged from 300 000 cfs cubic feet per second to 19 200 cfs a difference of 16 times The amount of sediment transported as suspended load was very large Measurements carried out at the Grand Canyon for the period December 1940 to June 1941 show that at 50 000 cfs about 2 000 000 tons were moved per day during the rising stage of the flood 1 and 500 000 tons during the falling stage whereas almost 5 000 000 tons per day were moved during the peak of the flood Grand Canyon continued on p 2 1Sediment transported during the rising stage of a flood is much greater than that transported during the falling stage Leopold and Maddock 1953 Glen Canyon Dam at high discharge during the June 1983 flood The dam is 710 ft 216 m high The four jets of water issuing from near the lower right corner of the dam are from the outlet works Releases from the right spillway are hidden by the cloud of mist and spray near the lower left corner of the dam The left spillway whose exit is visible a short distance downstream from the outlet work jets was inactive when the photo was taken Discharge from the powerplant is below river level and not visible Photo courtesy of David L Wegner D E N V E R 1999 April 1999 Vol 9 No 4 GSA TODAY ISSN 1052 5173 is published monthly by The Geological Society of America Inc with offices at 3300 Penrose Place Boulder Colorado Mailing address P O Box 9140 Boulder CO 80301 9140 U S A Periodicals postage paid at Boulder Colorado and at additional mailing offices Postmaster Send address changes to GSA Today Membership Services P O Box 9140 Boulder CO 80301 9140 Copyright 1999 The Geological Society of America Inc GSA All rights reserved Copyright not claimed on content prepared wholly by U S Government employees within the scope of their employment Permission is granted to individuals to photocopy freely all items other than the science articles to further science and education Individual scientists are hereby granted permission without royalties or further requests to make unlimited photocopies of the science articles for use in classrooms to further education and science and to make up to five copies for distribution to associates in the furtherance of science permission is granted to make more than five photocopies for other noncommercial nonprofit purposes furthering science and education upon payment of a fee 0 25 per page copy directly to the Copyright Clearance Center 222 Rosewood Drive Danvers MA 01923 USA phone 978 750 8400 http www copyright com when paying reference GSA Today ISSN 1052 5173 Written permission is required from GSA for all other forms of capture reproduction and or distribution of any item in this publication by any means including posting on authors or organizational Web sites except that permission is granted to authors to post the abstracts only of their science articles on their own or their organization s Web site providing the posting includes this reference The full paper was published in the Geological Society of America s newsmagazine GSA Today include year month and page number if known where article appears or will appear GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide regardless of their race citizenship gender religion or political viewpoint Opinions presented in this publication do not reflect official positions of the Society SUBSCRIPTIONS for 1999 calendar year Society Members GSA Today is provided as part of membership dues Contact Membership Services at 800 472 1988 303 447 2020 or member geosociety org for membership information Nonmembers Institutions Free with paid subscription to both GSA Bulletin and Geology otherwise 50 for U S Canada and Mexico 60 elsewhere Contact Subscription Services Single copies may be requested from Publication Sales Also available on an annual CD ROM together with GSA Bulletin Geology GSA Data Repository and an Electronic Retrospective Index to journal articles from 1972 89 to GSA Members others call GSA Subscription Services for prices and details Claims For nonreceipt or for damaged copies members contact Membership Services all others contact Subscription Services Claims are honored for one year please allow sufficient delivery time for overseas copies up to six months STAFF Prepared from contributions from the GSA staff and membership Executive Director Donald M Davidson Jr Science Editors Suzanne M Kay Department of Geological Sciences Cornell University Ithaca NY 14853 Molly F Miller Department of Geology Box 117 B Vanderbilt University Nashville TN 37235 Forum Editor Bruce F Molnia U S Geological Survey MS 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