A sampling plan and monitoring programme - how to design it
The most common mistake in monitoring is to start with the measurements rather than with the plan. Yet it is the plan that decides whether the data will be representative, comparable and useful - or whether you will be left with a set of readings from which it is hard to conclude anything. Before you head into the field, it is worth answering a few questions.
Why we measure - the aim
It all begins with the aim: assessing status, detecting changes, controlling a discharge, responding to an event, scientific research. The aim decides everything else - trend monitoring requires different points and frequency than early warning.
The next decisions of the plan - where, how often, what to measure - follow directly from the aim. The same river needs an entirely different plan depending on why it is being studied:
| Aim of monitoring | Where you put the points | How often | Range of parameters |
|---|---|---|---|
| Status assessment / trend | representative, fixed sites on a typical reach | less often, but over years, on fixed dates | broad, unchanging set |
| Discharge control | above and below the source, in the same session | according to the variability of the discharge; more often if it is irregular | parameters characteristic of the discharge + oxygen |
| Early warning | at the point of greatest risk, not the most convenient one | continuously (a probe) or densely during the risk period | a narrow set of fast ones: oxygen, temperature, conductivity |
| Response to an event | along the plume, downstream, plus a reference point above | every few hours or days, as long as it lasts | depending on the suspicion; always plus oxygen and pH |
| Scientific research | according to the study design (replicates, controls) | according to the hypothesis | according to the hypothesis |
⚠️ The point “above the source” is part of the measurement, not an extra. Without a reference upstream there is no way to tell the influence of a discharge from the natural background of the catchment - and that is the commonest gap in plans made in a hurry.
Where - measurement points
- Representativeness - a point should reflect what you want to assess (the current, not a stagnant pocket; a typical reach, not an exception).
- Constancy - the same, unambiguously described sites, so that results can be compared over time.
- The logic of the layout - e.g. above and below a potential source, on the inflows and the outflow of a lake.
When and how often
- Frequency is matched to the aim and the dynamics of the phenomenon: a trend - less often, but for a long time; events (blooms, floods) - more densely, in periods of risk.
- Seasonality - many indicators have an annual rhythm; the plan should cover the right times.
- A fixed time within the day where the daily rhythm matters (e.g. oxygen).
What we measure - the range of indicators
Match the indicators to the aim - from the basic field ones (oxygen, pH, conductivity, temperature) to the biological and laboratory ones (nutrients, priority substances). The logic of the elements of status assessment can be helpful.
Resources and feasibility
The best plan is one that can be delivered: a realistic number of points, equipment, people and time. It is better to have fewer sites run consistently than an ambitious plan abandoned after a season.
Sources
- Sampling programmes and techniques: ISO 5667-1:2023 Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and sampling techniques (adopted as EN ISO 5667-1:2023; the previous edition, based on ISO 5667-1:2020, was withdrawn in October 2023).
- Rivers and streams: ISO 5667-6:2014 (Part 6: Guidance on sampling of rivers and streams).
- Lakes and reservoirs: ISO 5667-4:2016 (Part 4: Guidance on sampling from lakes, natural and man-made).
(Editions verified on 18 August 2026. The standards are paid documents - they are cited here as the address of the methodology, not as a text to copy.)
In practice
It is worth recording the plan and keeping it together with the data. In LimnoLog the structure of a project (stations, sessions, indicators) reflects your plan, and the sampling planner helps you keep to the schedule. On how to present the results later, we write in the article A monitoring report.
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