Book review: Estimating Groundwater Recharge, by Richard W Healy (Cambridge University Press, 2010)

Abstract

Estimating Groundwater Recharge by Richard W. Healy (Healy 2010, with contributions from Bridget R. Scanlon) is an excellent addition to the growing knowledge base of groundwater science and technology. Understanding groundwater recharge is a prerequisite for the meaningful simulation of groundwater flow and transport, and, hence, successful management of renewable water resources. By placing an emphasis on method, this book provides clear concepts of the recharge process and associated methods that stem from more than 800 peer-reviewed references. Estimating Groundwater Recharge is organized into nine relatively concise chapters. It begins with descriptions of the conceptual framework of groundwater recharge and ends with an example of the USA to illustrate how the conceptual models are applied in reality. Chapters 2 through 8 deal with various methods. Theoretical models are combined with cases studies, drawn largely from the research projects undertaken in developed countries. Chapter 2 discusses water-budget methods, a foundation of following methods. Chapter 3 is about the modelling approach, while chapter 4 introduces the methods related to surface-water data. The physical, chemical and heat-tracer methods form chapters 5 through 8, which acknowledge the differences between applications for both the unsaturated and saturated zones. For instance, chapter 5 is dedicated to the physical methods as applied in the unsaturated zone, whereas chapter 6 discusses the same methods but in the saturated context. The organization of chapters in the book does, in some respects, resemble Groundwater Recharge in a Desert Environment: The Southwestern United States edited by Hogan et al. (2004). Perhaps due to the common authorship, some similarities exist. However, Healy’s book offers a comprehensive yet focused treatment in both theoretical and practical aspects through a wealth of cited references. The approach helps to reinforce theoretical concepts and therefore gives it a more modern feel. Introduction of recharge terminology in section 1.2 of the book is helpful, not only for its use as an academic text but also for practical clarity for those who are not necessarily groundwater practitioners. ‘Recharge’ is defined in the book as the downward flow of water reaching the water table, adding to groundwater storage. In fact, adding storage should be seen as an innate part of water arrival at the water table. Depending on the rate of groundwater discharge, the build up of the groundwater storage due to recharge may not necessarily be observed as this storage is conditioned by other factors apart from recharge. Healy rightly points out that the definition excludes water flow to an aquifer from an adjoining groundwater system, which is referred to as interaquifer flow or groundwater underflow. Another interesting term that is expanded upon is ‘base flow’, which is sometimes understood differently between groundwater and surface-water professionals. The groundwater camp would insist that base flow is water that has been discharged from the saturated zone. This is the stated definition in many groundwater books, including this one. In the opposing camp, base flowmay be regarded as all streamflow that is not derived directly from surface runoff. Without proper clarification of the terminology used, confusion may arise as has been experienced during the assessment of the role of base flow in the instream flow requirements required by the national Water Act in South Africa. The conceptual clarification of base flow made in section 4.1.2 of this book is practically valuable for multi-disciplinary research. Like many other hydrogeological phenomena, recharge varies both spatially and temporally, dependent upon the combination of influencing factors such as climate, soils, geology, geomorphology, hydrology, vegetation and land use. Based on the source of data, its availability and the nature of the parameters considered, etc., the book comprehensively documents some 40 methods that can be applied for estimating groundwater recharge in a range of hydrogeological scenarios. A distinction is made between point and integrated values of recharge estimation. Diffuse and focused recharges are also highlighted throughout the text for the readers’ consideration. The concepts used are consistent with those given by popular Received: 24 May 2011 /Accepted: 4 July 2011 Published online: 21 July 2011