In this chapter we discuss the basics of good monitoring design. ‘Design’ here means the stipulation of where, when and how many observations or sampling units are taken to provide the data from which we will make inferences against some specified objectives. We discuss here the underlying principles that we consider central to good design, and present an ideal case. In the interests of establishing an understanding of why elaborate designs are often presented, we ignore for the moment the ubiquitous compromises that are necessary for logistic, social or economic reasons. We do not focus here on particular variables (chapter 10), what sorts of changes are considered important (chapter 11) or the specifics of natural systems in the interests of presenting the general principles that underlie good monitoring for most variables in almost any system. Nor do we discuss here the analytical tools used to refine or optimize designs or analyse the resultant data (chapters 7–13). This chapter should be read, therefore, as a conceptual overview of the design principles that motivate us and which will be expanded in operational detail throughout later chapters.

We recognize that ‘ideal’ designs will rarely, if ever, be feasible (for a variety of reasons) and discuss in later chapters what compromises are most likely to be precipitated by the characteristics of streams (chapter 8) or because of accidents of history, money etc. In beginning here with an outline of the concepts behind an ‘ideal’ case, we seek to establish the principle that all these inevitable compromises are just that – compromises.