The first morning of our shoreline survey began with a table full of neat plans. We would measure the same stretch of beach at regular intervals, mark each result on a chart and compare the figures at the end of the week. I had drawn a line along the coast in my notebook. It looked reassuringly straight.

By midday, the tide had reached the marker posts before we finished our measurements. The water pushed across the sand, and our carefully spaced points disappeared beneath it. We packed the equipment and watched the empty beach from the path. I felt that the day had produced nothing.

The next morning, our leader suggested that we stop treating the tide as an interruption and record its movement as part of the survey. We set a timer and noted where the water reached at each interval. The method was less tidy than my chart: some readings were taken on wet sand, others from the path, and the line in my notebook grew into a series of marks.

At first, I missed the clean rows of numbers. Then the notes began to show something the original plan could not: the water did not return to the same point at the same pace. One reading was smudged by a drop of water, so I wrote beside it, “check next time”, rather than pretending it was exact. When we returned the following day, we started at a different time and watched the pattern unfold again.

At the end of the week, our notebook looked less like the plan I had imagined and more like a record of what had actually happened. We had not made every measurement in the same way. We had learned to ask better questions of the changing shore. The straight line in my first drawing was still there, faint beneath the new marks.