HOW TO READ A RIVER

Colour The colour of a river is often dictated by the substrate across which it flows. There are a dozen or more “blackwaters” in the British Isles, all dark in appearance and invariably sourced in acidic, peaty soil. In contrast, the purifying aquifers that filter the water at the head of chalk streams create a course that is free from sediment and incredibly clear as a result. This allows greater penetration from sunlight and in turn an array of organisms and plants to thrive.

Riffles and glides A river bed is ever evolving, the water steadily smoothing rocks and shifting sediment, while a vicious spate might see trees uprooted and banks washed away. Riffles form where the river shallows, the surface dimpling like the bottom of an eggbox. A smooth surface usually indicates a steady depth and unobstructed riverbed, where the current is steady and the flow unhindered.

Bends and gullies The current slows on the inside of a bend, often creating a gentle back eddy where flotsam and sediment might collect. The bottom might be silted and a hazard to anybody wading. On the outside of a bend, the bank often becomes undercut due to the volume of water pressing against it. As the current here swirls, it may bore downwards to create a gully considerably deeper than the areas around it.

Slacks and creases Creases will form wherever two currents converge. As the two flows meet they create a distinctive line in the surface and fish will often be found sitting in the quieter water waiting for food items to whizz past their noses. Slacks will form behind rocks and fallen trees, and offer sanctuary to fish when the river level is high.

Patterns in the surface A river’s surface will often mirror the shape of the bed, particularly where the depth is relatively constant. A solid obstacle, such as a rock, will deflect the water to form a small peak, while the presence of weed might be evident from a variably broken surface as the fronds sway in response to the current. The language of water can seem easy to learn but is also ever changing and a flood may change the words completely.