INTERNATIONAL HYDROLOGICAL PROGRAMME ____________________________________________________________ Hydrology of wadi systems IHP regional network on wadi hydrology in the Arab region In co-operation with the Arab League Educational, Cultural and Scientific Organization (ALECSO) and the Arab Centre for Studies of Arid Zones and Dry Lands (ACSAD) Edited by Howard Wheater and Radwan A. Al-Weshah _____________________________________________________________ IHP-V Technical Documents in Hydrology No. 55 UNESCO, Paris, 2002 The designations employed and the presentation of material throughout the publication do not imply the expression of any opinion whatsoever on the part of UNESCO concerning the legal status of any country, territory, city or of its authorities, or concerning the delimitation of its frontiers or boundaries. SC-2002/WS/33 ii TABLE OF CONTENTS Chapter One: Introduction …………………………………………………………...… 1 Howard S. Wheater and Radwan A. Al-Weshah PART 1 THE SCIENCE OF WADI SYSTEMS Chapter Two: Hydrological processes in arid and semi-arid areas ………………… 5 Howard S. Wheater Chapter Three: Applications of geochemical and isotopic methods:…………………… 23 A case study of Wadi Hawad, Sudan W. Mike Edmunds Chapter Four: Sediment and the vulnerability of water resources …………………… 37 Abdulaziz A. Alhamid and Ian Reid PART II OPERATIONAL WADI HYDROLOGY AND HYDROLOGICAL MODELLING Chapter Five: Data acquisition ………………………………………………………… 57 Jean Khouri Chapter Six: Rainfall-runoff analysis and modelling in wadi systems ……………… 87 Radwan A. Al-Weshah PART III MANAGEMENT OF WADI SYSTEMS Chapter Seven: Integrated development of wadi systems ……………………………… 113 Majid Benbiba Chapter Eight: Developpement integre de l'hydrologie des oueds (in French) ……… 123 Mohamed Ridha Kallel Chapter Nine: Sustainable management of wadi systems …………………………… 147 Abdin M. A. Salih and Ashraf H. M. Ghanem iii CHAPTER ONE INTRODUCTION Howard. S. Wheater1 and Radwan Al-Weshah2 1 Professor of Hydrology, Imperial College, London SW7 2BU, UK 2 Regional Hydrologist, UNESCO Cairo Office, Cairo, Egypt and Associate Professor of Hydrology and Water Resources Engineering, The University of Jordan, Amman, Jordan (on leave); e-mail: [email protected] Wadi Hydrology has emerged as a distinct scientific area within the last decade, due mainly to the initiative of a small number of individuals within and without the Arab region, and the active support of UNESCO, assisted by ACSAD and ALECSO. This has been due to the recognition that the hydrology of arid and semi-arid areas is very different from that of humid areas and raises important scientific, technical and logistical challenges, and that an improved science base is essential to meet current and future needs of water management. By definition, water is a scarce resource in arid regions, and most countries of the Arab region and other arid and semi-arid areas are facing severe pressures due to limited water resources. These pressures are expected to increase in the face of expanding populations and the increased per capita water use associated with economic development. Globally, projections are that by 2025, 5 billion people will live in countries experiencing moderate or severe water stress (WMO, 1997, Arnell, 1999); evidently conditions will be most severe for the driest regions of the world. In addition, there is growing recognition that climate change is a significant factor in water resource planning. While projections of future climate vary greatly between different models and emissions scenarios (IPCC, 1997), there is concensus that most of the arid and semi-arid regions of the world can expect an increase in water stress. Given these challenges, improved planning, development and management of scarce water resources is essential to maximise the available resource and balance competing uses, i.e. industrial, domestic and agricultural and the needs of the environment. And associated with the management of water quantity is the management of wastes and water quality, to protect natural systems and maintain the quality of available resources. However, appropriate development of water resources and their integrated management depends on an adequate scientific understanding of the hydrological processes. In addition, to achieve sustainable use of water resources requires a good understanding of the variability of hydrological processes in time, both within and between years. This publication has arisen from a UNESCO initiative to develop a programme in Wadi Hydrology for the Arab region, leading to an improved science base and appropriate decision support tools for the integrated management of wadi systems. This programme has been developed through a series of regional workshops, and has led, for example, to international 1 training programmes, a recent international conference (Sharm el Sheikh, 2000), and the formulation of an international Wadi Hydrology Network to provide high quality data and a test-bed for the development of appropriate tools for modelling and analysis. The aim of this publication is to summarise the scientific, technical and management issues associated with the integrated management of Wadi systems. The individual contributions are as follows: PART 1 THE SCIENCE OF WADI SYSTEMS In Chapter 2, Wheater reviews the scientific understanding of arid and semi-arid hydrological processes, focussing particularly on rainfall variability in space and time, runoff processes, and transmission losses from ephemeral wadi flows, and discusses the implications of this process understanding for rainfall-runoff and water resource modelling. Groundwater is a vital resource for the region, and the estimation of groundwater recharge one of the most difficult aspects in defining sustainable rates of groundwater abstraction. In Chapter 3 Edmunds presents a case study from Sudan which demonstrates the potential of geochemical and isotopic methods to give quantitative insight into groundwater systems and surface water-groundwater interactions. Sediment transport is a major practical issue in considering sustainability of surface water management, whether for floods or water resources, and data and desgn guidance are extremely limited. The state-of-the-art is reviewed by Alhamid and Reid in Chapter 4. PART II OPERATIONAL WADI HYDROLOGY AND HYDROLOGICAL MODELLING Data are essential to underpin both scientific advancement and effective management of wadi systems, yet the harsh environment and infrequent nature of hydrological events pose major problems for instrumentation and operational management, and the complex nature of the processes means that networks must be carefully designed for a given purpose. In Chapter 5, Khouri discusses the essential issue of data acquisition. Specific aspects covered include data needs, and the development and design of surface water and groundwater networks. Hydrological modelling is a powerful tool to support hydrological and water resource design and management, yet few methods have been developed and validated for arid areas. In Chapter 5, Al-Weshah describes commonly-applied methods of rainfall-runoff analysis and modelling in wadi systems. He points the way forward to research needs and future developments, and review selected computer models that can be applied to arid regions. A case study was presented at the end of this chapter. PART III MANAGEMENT OF WADI SYSTEMS This final section draws on extensive operational experience from the region to discuss the context for water resource management. In Chapter 7, Benbiba discusses constraints on water resources development, the assessment, planning and management of water resources, legislative aspects and the needs for research and training. 2 In Chapter 8, Kallel presents an integrated view of hydrological management, including the development of hydrological services, the development of monitoring infrastructure, methods of analysis, process understanding and provision of technical support. Finally, in Chapter 9, Salih and Ghanem provide the context of sustainable management, including the challenges of integrating technical, socio-economic, environmental and institutional and legal aspects, drawing on case study experience from Saudi Arabia. This study is implemented by UNESCO Cairo Office under the activities of the Arab Network in Wadi Hydrology established in 1996 in cooperation with ALECSO (Arab Leaguge Educational, Cultural, and Scientific Organization), and ACSAD (Arab Center for Studies of Arid Zones and Dry Lands). All articles presented in this book peer reviewed. The efforts of Dr. Abdin Salih and his successor Dr. Radwan Al-Weshah, as a regional hydrologist in UNESCO Cairo Office, to this publications are highly appreciated. REFERENCES Arnell N.W., 1999b, “Climate change and global water resources”, Global Environmental Change 9, pp. S31-S49, Elsevier Science Ltd. IPCC, 1997, “An Introduction to Simple Climate Models used in the IPCC Second Assessment Report”, (ed.) Houghton J.T., Filho L.G.M., Griggs D.J., and Maskell K., IPCC Working Group I, Web Site: http://www.ipcc.ch World Meteorological Organisation, 1997. Comprehensive Assessment of the Freshwater Resources of the World. WMO, Geneva, 34pp. 3 CHAPTER TWO HYDROLOGICAL PROCESSES IN ARID AND SEMI ARID AREAS Howard S. Wheater Professor of Hydrology, Department of Civil and Environmental Engineering, Imperial College of Science, Technology and Medicine, London SW7 2BU, UK 2.1 INTRODUCTION The arid and semi-arid regions of the world are under severe and increasing pressure