Downloaded from http://egsp.lyellcollection.org/ by guest on September 25, 2021 Chapter 1 Introduction J. Charman* & Engineering Group Working Party Cerne Abbas, Dorchester, Dorset, DT2 7JG, UK *Corresponding author (e-mail: [email protected]) framework of the Commission’s current multi-year work 1.1. Deserts programme, the third cycle in 2008 and 2009 focused on desertification and drought. With ongoing climate change, There are several, often conflicting, views of what is a desert. there is a projected shift in arid climatic zones north and In the 1973 edition of the Oxford English Dictionary its defi- south from the mid-latitudes into more populated regions. nition of deserts included the phrase ‘dry, parched, withered, This publication is, therefore, timely in bringing together hence uninteresting’. This somewhat belied the romantic current Earth science and engineering knowledge into a notions in the western world inspired by, among others, state-of-the-art review and handbook for the practitioner. Wilfred Thesiger and T. E. Lawrence. At about this time desert regions became very ‘interesting’, gaining a greater 1.1.1. Definitions significance with the rising price of oil fostering a develop- ment boom in many oil-rich countries, especially in the Many definitions have been proposed for the term ‘desert’ and Middle East. these are considered indetail inChapter 2.In general, most dic- During this period early western designed and controlled tionary definitions refer to regions that do not produce suffi- building and construction projects in the Middle East cient vegetation to support a human population. Many maps began to fall foul of a number of geotechnical hazards depict the location and extent of the deserts of the world. little understood by professionals whose previous experience Table 1.1 contains a list of the major, non-polar, deserts of had been gained in the temperate regions of the world. Tra- the world (after Goudie 2002) and the numbers shown in the ditional, locally developed techniques were neglected or table relate to the location shown on the map (Fig. 1.1). ignored, as had reported knowledge from valuable experi- While the location of, for example, the Sahara, Gobi and ence in the field (Bagnold 1941). Atacama deserts are well known, in reality they cover a Over the last 30 years considerable understanding and range of climatic conditions. For this report, which considers experience has been gained of the geomorphological pro- the physical characteristics of deserts and their influence on cesses and ground characteristics peculiar to desert engineering behaviour, a climatological definition has been regions, and their effects on design and construction. Many considered to be the most useful basis for the description innovative engineering techniques have been developed and identification of hot deserts. and employed, and information on these advances is now In detail, climate is unique to location and depends on the widely disseminated in the technical literature. local interaction of several factors, including temperature, The report of a Geological Society of London Working precipitation, relative humidity and wind. In any one geo- Party on Tropical Residual Soils (Fookes 1990, 1997) was graphically discrete desert, it is difficult to define transitions the first to consider a particular environment as the focus from typical desert conditions into other climatic regimes for an engineering geological handbook. As a natural succes- related to changes in latitude and elevation. sor in this approach, this Working Party report on engineer- Most scientific classifications rely on some combination ing works in Hot Desert regions, commissioned by the of the number of days of rainfall, the total amount of Engineering Group of the Geological Society, is intended annual rainfall, temperature, humidity or other factors. The to provide, under one cover, a practical handbook for the most widely accepted system, however, is probably that of practitioner, academic and student working in this sector Meigs (1953), dividing desert regions into three categories (see Text box 1.1). according to the amount of precipitation they receive. In 2003 the United Nations General Assembly, in its res- Meigs’ assessment used the Thornthwaite (1948) Moisture olution A/RES/58/211, declared the year 2006 as the Inter- Availability Index, and the Aridity Index as another measure. national Year of Deserts and Desertification. Combating These are explained more fully in Chapter 2. Typically, desertification and drought has been discussed by the UN extremely arid lands have at least 12 consecutive months Commission on Sustainable Development and, in the without rainfall, arid lands have less than 250 mm of From:M.J.Walker (ed.) Hot Deserts: Engineering, Geology and Geomorphology – Engineering Group Working Party Report. Geological Society, London, Engineering Geology Special Publications, 25, 1–6. http://dx.doi.org/10.1144/EGSP25.01 # The Geological Society of London 2012. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://egsp.lyellcollection.org/ by guest on September 25, 2021 Distibution of the major non-polar deserts of the world (after Goudie 2002). The numbers relate to the list of locations shown in Table 1.1. Fig. 1.1. Downloaded from http://egsp.lyellcollection.org/ by guest on September 25, 2021 2 INTRODUCTION Text box 1.1. Terms of Reference of the Working Party (1) These Terms of Reference are as agreed by the Desert Working Party (DWP) and committee of the Engineering Group of The Geological Society of London. (2) The DWP has been established by the Engineering Group of the Geological Society and comprises officers and specialist participating members who will act as chapter authors or co-authors. The participating members may be assisted by any number of corresponding members based in the UK and, occasionally, overseas. (3) The DWP will produce a report to complement the earlier report on Tropical Residual Soils produced by an earlier Working Party of the Engineering Group, first published in 1990 and re-published in book format in 1997. It is currently envisaged that the report will be in book format, but this will be kept under review in recognition that major change is taking place within the publishing industry. (4) It is intended that the report will be a comprehensive, state-of-the-art, review on hot deserts and their materials. Primarily, the report will cover conditions and materials in modern hot deserts, but there will be some coverage of unmodified ancient desert soils that exhibit engineering behaviour that is in many respects similar to modern desert materials. (5) The aim of the DWP is to produce a report that will act as an essential reference handbook for professionals as well as a valuable textbook for students and others. The style will be concise and digestible by the non-specialist, yet be authoritative, up to date and extensively supported by data and collations of technical information. The use of jargon will be minimized and necessary specialist terms will be defined in an extensive glossary. There will be copious illustrations, many of which will be original, and many good-quality photographs. (6) The content of the report will embrace a full range of topics, from the latest research findings to practical appli- cations of existing information. There will be an endeavour to identify likely directions of future research and to predict future development. The report will be based on worldwide experience in hot desert terrain, and will draw upon the experience of its members and publications on hot desert conditions. (7) There will be collective responsibility for the whole report. Although each participating member will be the draft- ing author or co-author of one or more chapters, all members will be expected to review and contribute to the chap- ters drafted by other members. annual rainfall, and semi-arid lands have a mean annual pre- that are relevant to such deserts today. In these regions, the cipitation of between 250 and 500 mm (Table 1.2). influence of surface water is mainly experienced only in An initial subdivision can be made into ‘cold’ and ‘hot’ ‘rare’ events, such as flooding. The effect of moisture move- deserts. In ‘cold deserts’, in the higher latitudes, the prevail- ment is generally limited to those areas with near-surface ing low temperature and the low moisture availability are the groundwater, such as inland drainage basins and coasts. causes of the lack of vegetation. In ‘hot deserts’, in the mid- Nevertheless, it is essential that in these areas the process latitudes around the tropical belts, the lack of vegetation is be clearly understood to ensure the safety and durability of the result of a combination of high temperature and aridity, new structures. where evaporation is largely in excess of precipitation and In semi-arid and dry sub-humid deserts, the role of moist- overgrazing. The word ‘desert’ can cover, therefore, a ure increases; for example, in the formation of pedogenic range of climatological conditions from arid to dry sub- soils. Indeed, many features of present-day hot deserts are humid and from hot to cold. This raised the conundrum for relict, and are the result of moisture movement processes the Working Party of where to focus this report since it more active in the mild semi-arid and dry sub-humid con- was considered that to attempt cover the complete range of ditions that have occurred repeatedly in the fluctuating cli- conditions could weaken its application. To avoid this it matic cycles (glaciations) of the Quaternary. Similarly, the was decided to concentrate the Working Party’s efforts on present-day cool, cold or polar deserts also encompass pro- hot desert regions. cesses of a periglacial, or even glacial, nature. These con- ditions often make significant differences to local materials and the engineering approach. 1.1.2.