Groundwater models [antikvár]

I. IMTROEUGTIOM 1. Purpose The main purpose of this manual is to describe the development of the use of the digital computer for groundwater models and to present detailed instructions for preparing a Fortran programme for any selected groundwater basin. The manual is divided into seven chapters. In Chapter I a brief history is given, the relationship of the groundwater model to other models is outlined, and the role of groundwater basins in overall water resources management is introduced. In Chapter II the general subject of groundwater models is reviewed. In Chapter III the geologic, hydrologio and mathematical relations involved in groundwater model development are discussed. Chapter IV describes the translation of raw data into the final polygonal network digital computer programme. Chapter V summarises the use of the finite difference digital programmes. Chapter VI briefly describes an interesting electronic circuit analysis approach. Chapter VII is a brief discussion of groundwater models as a part of the overall water planning process. Chapters IV and V with the annexes are really the manual and experienced hydrogeologists, groundwater hydraulics experts and others will find nothing new in the first three parts of the manual. It is hoped, however, that Chapter I will be read by those not interested in details and that Chapters II and III will be of use to those who want more baokground in hydrogeology and groundwater hydraulics. In Chapters IV and V there is of necessity considerable reference to Fortran (meaning Formula Translator), a computer programme language widely used for scientific and engineering purposes. It is not possible to provide a complete background on Fortran, but the elements of the language are summarised in Annexe I and selected source books explaining Fortran are included there. When the compilation of geologic and hydrologio data has reached the stage where a computer programme is to be written, access to a professional programmer is desirable. However some actual programmes are included in the appendixes to provide as much detailed guidance as possible to a person with little or no experience in the use of Fortran language. It will become apparent that learning of Fortran will be a real benefit to users of the programmes. 2. Baokground Mathematical models of groundwater basins and aquifers have been used in solving hydrologio problems for many years by using equations of groundwater flow. Each equation is valid for particular boundaiy and flow conditions, and new equations are being continually developed for other boundary and flow conditions. These equations are extremely useful and are well documented in the literature on this subject. For solving problems in large areas with complex geologic and hydrologio factors, the special mathematical equations are not adequate. For such problems various types of model (reviewed briefly in Chapter II) have been evolved, including scale models (substituting sand or other materials in an attempt to duplicate the aquifer properties) and analogue models. Scale models are perhaps the older, a lairge variety having been used since Darcy (I856) published results of his famous experiments. Analogue models attempt to simulate groundwater flow by using thin plates (Hele-Shaw models) or by several varieties of electrical conducting model. These models may conduct electricity through resistant fluid, through solid conducting sheets or most commonly through networks of electrical resistors and capacitors. An interesting variation is the use of a thin, stretched rubber sheet to model the equipotential for certain kinds of steady state condition. The electrical models are described in many books, among them Todd (1959) and Walton (1970). This manual does not attempt to judge which of the many methods are best for any particular purpose. However, most of the models mentioned above require laboratory facilities and equipment. The rapid development of large, fast and complex digital computers has made available relatively inexpensive computer services in many cities of the world. For those agencies which do not have laboratory facilities the use of these computer services can provide extremely useful analysis of groundwater basins.