Introduction to Physical Hydrology

Citation

Hendriks, M. R. (2010). Introduction to Physical Hydrology. Oxford University Press.

Chapter Summary

The book has about 330 pages: a short introduction, four long chapters on the four types of water named in the publisher's description (atmospheric water, groundwater, soil water and surface water), a brief epilogue, and three appendices: a Conceptual Toolkit on the mathematics used, ten Mathematics Toolboxes with derivations, and answers to the exercises. Groundwater takes up the largest share, roughly 90 of the main text's 275 pages.

Chapter 1: Introduction

The opening chapter sets up the framework for the rest of the book: the major water types, the hydrological cycle, the hydrological processes of a drainage basin, and the water balance that links them.

Chapter 2: Atmospheric water

The chapter moves from cloud formation and the generation of precipitation through precipitation types to the practical questions of measuring precipitation and estimating it over an area. Its second half deals with evaporation: the types of evaporation and how they are measured, and estimation with the Penman–Monteith equation.

Chapter 3: Groundwater

The longest chapter, with fifteen sections, several of them under informal titles ("Drilling a hole", "Bernoulli to the aid", "Brothers in science: Darcy and Ohm", "Keep it simple and confined", "Going Dutch"). Following the section headings, it builds from hydraulic head and Bernoulli's equation to aquifers, infiltration velocity and rate, Darcy's law, the refraction of groundwater flow, confined aquifers and the continuity equation, flow nets, groundwater flow regimes and systems, the fresh–saline interface described by the Ghijben–Herzberg relation, and groundwater hydraulics. The publisher's online resources include a test on Section 3.15 on groundwater hydraulics.

Chapter 4: Soil water

The unsaturated zone is introduced through negative water pressures and the determination of total potential. The chapter covers the soil moisture characteristic and hysteresis between drying and wetting, unsaturated flow, upward movement by capillary rise and evaporation, downward movement by infiltration and percolation, and preferential flow. The derivation of the Richards equation is placed in the Mathematics Toolboxes.

Chapter 5: Surface water

The final chapter returns to Bernoulli for open-channel flow, then covers measuring stage, water velocity and discharge, hydrograph analysis, conceptual rainfall–runoff models, and variable source area hydrology.

Appendices: Conceptual Toolkit, Mathematics Toolboxes, Answers to the exercises

The Conceptual Toolkit opens with a section titled "If you can't do the math" and summarises differentiation and integration with a quick reference to differentiation rules. The ten Mathematics Toolboxes work through horizontal and radial flow in confined and unconfined aquifers, a leaky aquifer, unconfined aquifers with recharge between canals and streams, two forms of the Richards equation, and open-channel flow. Answers to the exercises follow.

Key Concepts

Chapters 1–2: Introduction; Atmospheric water

• Water balance: the accounting of inputs, outputs and storage changes for a drainage basin.
• Areal precipitation: an estimate of precipitation over a whole area derived from point measurements.
• Penman–Monteith equation: the standard method for estimating evaporation from meteorological data.

Chapter 3: Groundwater

• Hydraulic head: the energy of groundwater per unit weight, the quantity whose gradient drives flow.
• Darcy's law: flow through a porous medium is proportional to the hydraulic gradient; the book draws an analogy with Ohm's law.
• Flow nets: graphical solutions of steady groundwater flow made of flow lines and equipotential lines.
• Ghijben–Herzberg relation: the relation between the height of fresh groundwater above sea level and the depth of the fresh–saline interface beneath it.

Chapter 4: Soil water

• Soil moisture characteristic: the relation between soil water pressure (suction) and moisture content.
• Hysteresis: the difference between that relation during drying and during wetting.
• Richards equation: the equation for unsaturated water flow, derived in the toolboxes.

Chapter 5: Surface water

• Hydrograph analysis: separating a river's discharge record into its components to understand how a catchment responds to rain.
• Variable source area: the idea that the parts of a catchment producing storm runoff expand and contract with wetness.

Critical Analysis

Strengths

• Mathematics taught, not assumed. The publisher stresses a class-tested learning framework of examples, exercises and Mathematics Toolboxes, and the contents bear this out: a Conceptual Toolkit for readers who "can't do the math", step-by-step derivations moved out of the main text, and answers to the exercises printed in the book, which makes it usable for self-study.
• Physical principles built step by step. The groundwater chapter in particular proceeds in small sections from Bernoulli's equation and hydraulic head to Darcy's law, continuity, flow nets and aquifer hydraulics, and the surface water chapter returns to Bernoulli, so the same principles carry through the book.
• Endorsed by teaching hydrologists. Comments printed by the publisher come from Hubert Savenije (Delft University of Technology), who praises the examples, the exercises and the treatment of mathematics; Roger Thunvik (Royal Institute of Technology, Sweden), who singles out the mathematical tools and boxes; and Ian Maddock (University of Worcester), who highlights the boxed case studies and the exercises with answers. The book was also the subject of a research resource review by Joan Estrany in Progress in Physical Geography (2011).
• Extra practice online. The publisher lists interactive spreadsheets, multiple-choice questions and the groundwater hydraulics test as student resources.

Limitations

• Narrow, physics-centred scope. The structure follows the four water types. Snow and ice, water quality and solute transport, and hydrological modelling beyond conceptual rainfall–runoff models do not appear in the contents, and evaporation is covered within the atmospheric water chapter.
• Weighted towards groundwater. About a third of the main text is groundwater, and two section titles ("Going Dutch", the Ghijben–Herzberg relation) reflect the Dutch setting in which the author teaches; surface water gets a chapter of similar length but only five sections.
• A single 2010 edition. No second edition is listed, so measurement technology and research since the late 2000s are not reflected.

Where It Fits in the Course

The course pairs hydrology with geomorphology. Among its books, Hendriks and S. Lawrence Dingman's Physical Hydrology are the two dedicated hydrology texts. Dingman is a larger quantitative textbook that treats hydrology as a geoscience of the land phase of the water cycle, including snow, evapotranspiration, groundwater and runoff, and how water and energy budgets are measured and modelled. Hendriks is the gentler starting point: it develops the same physical principles with more mathematical support and printed answers, and is best read first, with Dingman used afterwards for breadth and depth.

On the geomorphology side, Goudie and Viles's Landscapes and Geomorphology: A Very Short Introduction gives a quick overview of landscape processes, while Huggett and Shuttleworth's Fundamentals of Geomorphology and Bierman and Montgomery's Key Concepts in Geomorphology are broad textbooks that work through the process domains, rivers among them. Hendriks's chapters on soil water and surface water provide the hydrological basis for those chapters, and Anderson and Anderson's quantitative Geomorphology: The Mechanics and Chemistry of Landscapes builds on the same habit of reasoning from conservation laws.

How to Use This Book

The book is a university textbook by an associate professor who teaches hydrology and physical geography at all levels at Utrecht University, and it suits students coming to hydrology from physical geography or earth science. Its treatment is explicitly mathematical, but the Conceptual Toolkit covers the differentiation and integration it uses.

• Start with Chapter 1 and the Conceptual Toolkit. Check the toolkit before Chapter 3 if calculus is rusty.
• Core sequence: Chapter 3 (groundwater) and Chapter 4 (soil water) form the heart of the book, and Chapter 4 picks up infiltration, which Chapter 3 introduces; read them in order and work the exercises before checking the answers.
• Use the toolboxes selectively. The Mathematics Toolboxes on aquifer flow and the Richards equation can be left for a second reading or for courses with a stronger quantitative emphasis.
• Chapters 2 and 5 can be read alongside a course's practical work on rain gauges, evaporation estimates, discharge measurement and hydrograph analysis.
• Supplement for breadth. For snow, water quality, global water resources or more recent methods, use Dingman's textbook or current review articles.