Physics of desertification Physics of desertification Edited by FAROUK EL-BAZ ltek Optical Systems Lexington MA USA M.H.A. HASSAN University of Khartoum Khartoum, Sudan 1986 MARTINUS NIJHOFF PUBLISHERS a member of the KLUWER ACADEMIC PUBLISHERS GROUP DORDRECHT / BOSTON / LANCASTER Distributors for the United States and Canada: Kluwer Academic Publishers, 190 Old Derby Street, Hingham, MA 02043, USA for the UK and Ireland: Kluwer Academic Publishers, MTP Press Limited, Falcon House, Queen Square, Lancaster LAI lRN, UK for all other countries: Kluwer Academic Publishers Group, Distribution Center, P.O. Box 322, 3300 AH Dordrecht, The Netherlands Library of Congress Cataloging in Publication Data Papers of desertification. Papers presented at a workshop held in Trieste, Italy, Nov. 10-28, 1980, under the auspices of the International Center for Theoretical Physics. 1. Desertification--Congresses. 2. Geomorphology-- Arid regions--Congresses. 3. Arid regions--Congresses. 4. Arid regions agriculture--Congress€s. I. EI-Baz, Farouk. II. Hassan, M. H. A. III. International Centre for Theoretical Physics. GB611.P476 1986 551.4 86-762 ISBN-13: 978-94-010-8451-2 e-ISBN-13: 978-94-009-4388-9 001: 10.1007/978-94-009-4388-9 ISBN-13: 978-94-010-8451-2 Copyright © 1986 by Martinus Nijhoff Publishers, Dordrecht. Softcover reprint of the hardcover 1s t edition 1986 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publishers, Martinus Nijhoff Publishers, P.O. Box 163, 3300 AD Dordrecht, The Netherlands. PREFACE Deserts are parts of the Earth that receive little or no rain; 25 cm or less per year. The physical processes that act upon these parched lands are vastly different from those that shape the more humid parts of the terrestrial landmasses. In the desert, wind is a major agent of erosion and transportation. As the results of recent space missions have indicated, this is also true in the case of the planet Mars. Thus, our understanding of desert processes sheds light on fundamental planetary processes that may apply on any planetary body that is enveloped by a windy atmosphere. An understanding of the physical layout of arid lands, and the nature of processes that initiate changes therein is also fundamental to thoughtful utilization of these lands for the benefit of mankind. It is with this in mind that we prepared this book for publication. We believe that the collection of articles in this book will be useful to scientists who are interested in desert landforms and processes, and to planners of economic develop- ment of arid lands. The book also serves as a guide for students as to the state of our knowledge in this field as well as to the topics that require additional research. Special thanks are due to three staff members of the Smithsonian Institution's Center for Earth and Planetary Studies: Ellen Lettvin for her help in preparing the manu- script for publication; Rose Aiello for drafting the figures; and Donna Slattery for typing the manuscript. We are also indebted to the Itek Optical Systems Publications Department personnel for their help in preparing the manuscript. Farouk El-Baz M. H. A. Hassan v TABLE OF CONTENTS List of Contributors . . . . . . . . . . . . . . . . . . XI Report on Workshop on Physics of Desertification 1 M. H. A. Hassan Desertification of Arid Lands • • • • • • • • • • • • • • 4 H. E. Dregne Wind Versus Water Erosion in the Context of Desertification • • • • • • • • • • • 35 Michael M. Verstraete and Jean-Pascal van Ypersele The United Nations Organization and the Issue of Desertification 42 Michel M. Verstraete The Impact of Desertification on Land Productivity in Sudan • • • • 52 M. O. H. El-Karouri Desertification Problems in a Humid Region 59 Jens Tyge M~ller The Formation and Motion of Dunes and Sand Seas • • • • • 70 Farouk El-Baz Two-Dimensional Analysis of Dune Profile and the Effects of Grain Size on Sand Dune Morphology • 94 Haim Tsoar VII Stabilization and Afforestation of Sand Dunes Through Biosaline Culture Technique • 109 R. Ahmad Some Aspects of Sand Stabilization in Egypt • • • • • •• 118 S. S. Tag El Din Eco-Technique--Magic Formula for Reclaiming Desertified Semiarid Crop Land • • • • • 127 Hans-Joachim Spaeth Monitoring the Sand-Moving Desert Winds • • • • • • • •• 141 Farouk El-Baz Aeolian Activity as a Planetary Process • • • • • • • •• 159 Ronald Greeley On the Reddening of Quartz Grains in Dune Sand 191 Farouk El-Baz The Wind and Desertification Processes in the Saharo-Sahelian and Sahelian Regions 210 Monique Manguet The Advance Mechanism of Longitudinal Dunes • • • • • •• 241 Haim Tsoar Production of Dust 251 Dale A. Gillette Soil Erosion by Wind: An Overview • • • • • • • • • • • • 261 E. L. Skidmore Wind Erosion in the Interior Delta of the Niger in Mali ••••••••• • • • • • • • • 274 H. K. Barth Aeolian Processes and Features at Amboy Lava Field, California • • • • • • • • • • • • • 290 Ronald Greeley and James D. Iversen Aeolian Processes in the Environmental Wind Tunnel and in the Atmosphere •••••• 318 J. D. Iversen Threshold Velocities for Dust Production 322 Dale A. Gillette VIII Formation of Ripples, Dunes, and Antidunes in River Beds •.•.•.••..•.•... 327 J¢rgen Freds¢e Saltation Threshold Mechanics • • • • • • • • • • • • • • 344 J. D. Iversen Dust Production by Wind Erosion: Necessary Conditions and Estimates of Vertical Fluxes of Dust and Visibility Reduction by Dust • • • 361 Dale A. Gillette The Aeolian Wind Tunnel--Saltation Similitude • • • • • • 372 J. D. Iversen Shape and Dimension of Dunes in Open Channel Flow • • • • • • 385 J¢rgen Freds~e The Stability and Propagation of Sand Ripples and Dunes • • • • •• •••• 398 I. A. Eltayeb and M. H. A. Hassan Turbulent Flow Over Topography With Applications to Sand-Wave Development ••••••••••••••• 435 K. J. Richards INDEX ••••••••••••••••••••••••••••••••• • •• " ••••••.••••• . • . 46 3 IX LIST OF CONTRIBUTORS Professor R. Ahmad Dr. I. A. Eltayeb Faculty of Science School of Hathematical University of Karachi Sciences Karachi 32, Pakistan University of Khartoum Khartoum, Sudan Dr. Hans Karl Barth Universitaet Bremen Dr. J~rgen Freds~e FB1-Schewertukt Geographie Institute of Hydrodynamics Post Fach 330440 and Hydrolic Engineering D-2800 Bremen 33 Technical University Federal Republic of Germany of Denmark KD-2800 Lyngby Denmark Professor Harold E. Dregne International Center for Arid and Semi-Arid Land Studies Dr. Dale A. Gillette Texas Tech University Cires Program P. O. Box 4260 University of Colorado Lubbock, Texas 79409 USA Boulder, Colorado 80307 USA Dr. Farouk El-Baz Dr. Ronald Greeley Itek Optical Systems Department of Geology 10 Haguire Road Arizona State University Lexington, Hassachusetts 02173 Tempe Arizona 85281 USA USA Dr. H. H. A. Hassan Dr. M. O. H. El-Karouri School of Hathematical Agricultural Research Council Sciences P. O. Box 6096 University of Khartoum Khartoum, Sudan Khartoum, Sudan XI Dr. J. D. Iversen Dr. Hans-Joacnim Spaeth Aerospace Engineering Department of Geography Department University of Oklahoma 304 Town Engineering Building at Norman Iowa State University Norman, Oklahoma 73069 USA Ames, Iowa 50010 USA Dr. S. S. Tag EI Din Professor Monique Mainguet Desert Institute Laboratoire de Geographie Al-Matreya, Cairo Physique Zonale at d'Etudes Arab Republic of Egypt des Pays ages en Roches Sedimentaires Universite de Reims Dr. Haim Tsoar 57, rue Pierre Taittinger Department of Geography 51100 Reims, France Ben-Gurion University Beer-Sheeva 84105, Israel Jens Tyge M~ller Institute of Geology Dr. Michel M. Verstraete c/o Institute of Physics Desertification Unit Bygning 521 United Nations Environmental Langelandsgade Programme DK 8000 Aarhus C P. O. Box 47074 Denmark Nairobi, Kenya Dr. K. J. Richards Jean-Pascal van Ypersele Department of Applied Desertification Unit Mathematics and United Nations Environmental Theoretical Physics Programme University of Cambridge P. O. Box 47074 Silver Street Nairobi, Kenya Cambridge, United Kingdom Dr. E. L. Skidmore U. S. Department of Agriculture Wind Erosion Research Unit Room 204, East Waters Hall Kansas State University Manhatten, Kansas 66506 USA XII REPORT ON WORKSHOP ON PHYSICS OF DESERTIFICATION By M. H. A. Hassan BACKGROUND AND OBJECTIVES: Al though deserts and arid lands comprise nearly one-third of the Earth's land surface, the physical processes taking place in these regions are far from being fully understood. In certain places these processes result in severe degradation of soil and lead to desertification and human suffering. It is estimated that nearly 80 million people are threatened by desertification, particularly those living near desert bound- daries and around oases that are surrounded by active sand dunes. In recent years and particularly after the Sahelian drought and famine, the problems of arid lands have received wide international attention. Most of this attention, however, has been directed towards ecological, socioeconomic, and management problems. It is now generally accepted that a fundamental understanding of the problems of deserts and arid regions can only be achieved through a broadly based interdisciplinary approach. In this approach, it is essential to consider the desertification mechanism as a complicated combination of both physical and ecological processes--a clear understanding of which must be based on physical and mathematical modelling. A workshop on the Physics of Desertification was held in Trieste, Italy, from the 10th to the 28th of November 1980, under the auspices of the International Center for Theoretical Physics. The workshop was attended by approximately 80 scien- 1