River banks erode in bursts. A clay bank can hold its shape for months, then lose half a metre in one winter spate. That is what makes measuring erosion so interesting, and so awkward: you are trying to capture a slow, uneven process with kit that fits in a rucksack and a morning to spare. The methods beginners actually need are simple — a tape, a few pegs, a notebook and the patience to stand back and look properly. What follows is how to use them without getting wetter than you intended.
Five minutes of looking will tell you more than an hour of guessing. Walk the stretch and note how the bank is failing, because different processes need different measurements. Look for an undercut toe where the river has scooped material out from below; a clean, near-vertical face suggests fluvial erosion is dominant. Look for tension cracks parallel to the bank top, slumped blocks and a jumble of soil at the toe — that is mass failure, where the bank has become too steep to stand up and has collapsed under its own weight. Exposed roots, a soil line on tree trunks and bare soil under overhanging turf all signal recent loss.
Also check what else is at work. Livestock poaching on a farmed stretch, footpaths along the crest, land drains, and boat wash can all drive erosion harder than the river itself. Note where the channel bends: outer bends erode, inner bends build. Marking those observations on a sketch map gives your later numbers something to sit against.
In England and Wales, riverbanks are usually private land and there is no general right to wander along them, so ask the landowner or the angling club first. In Scotland the right of responsible access is broader, but you still need to respect farmland, closed gates and wildlife. Sites designated for their geology or wildlife — SSSIs, nature reserves, local wildlife sites — may need consent from the relevant conservation body, and digging pits or pinning banks can count as damage. Ask. It takes one email.
Then apply the first rule of river fieldwork: never stand on the thing you are measuring. An eroded bank may be undercut, so the surface you are standing on has no support beneath it. Work from the stable bank top, from a gravel bar, or from a vantage point a few metres back. Avoid working directly downstream of weirs and sluices, where recirculating water can hold you under, and steer clear of steep, muddy entry points that you would have to climb out of.
Drive a metal or hardwood rod, 30–50 cm long, into the bank until its top sits a set distance above the surface — 5 cm is a workable standard. Record both the pin's position along the bank (measured with a tape from a fixed landmark such as a fence post or a large tree) and its grid reference. On each visit, measure the distance from the top of the pin down to the bank surface with a steel rule. If that distance grows, the bank has eroded; if it shrinks, sediment has been deposited. Use a bright washer or a band of tape near the top so you can find the pin again after a spate.
To see where loss is happening, run a transect from a fixed point at the bank top down towards the water. Stretch a tape between two ranging rods and use a line level and a second tape to measure the vertical offset between them. Take readings at set intervals — every 50 cm along the transect works well — and record the horizontal distance and the drop each time. Repeat the same transect on every visit and plot the profiles on the same axes. The result often surprises people: banks rarely retreat evenly, and a profile shows whether the toe is being scoured while the top stays put.
Cheap, quick and very persuasive. Choose a photo point you can return to — a marker post, a distinctive boulder — and stand in the same place each time, framing the same length of bank. Include something of known scale, such as a ranging rod with painted bands or a tape held vertically against the face. Photographs catch slumping events that pins between visits might miss.
Erosion on the bank is only half the story; the material has to go somewhere. Suspended sediment is the fine fraction carried in the flow. A simple sample — a clean bottle filled just below the surface, left to settle — lets you compare the depth of sediment in the base of the bottle, as a proportion of the total, between sites and visits. It is crude, but if you always sample at the same spot, in the same way, the comparison is still useful.
Bedload is the coarser material that rolls, slides and bounces along the bed. A pebble count is the standard beginner exercise: stretch a tape across a riffle, and at fixed intervals pick up the clast under your fingertip and measure its intermediate axis with callipers. Recording a hundred clasts gives a picture of what the river is moving. You can also mark a batch of pebbles with paint or numbered tags and see how far they travel after a spate. Anything you place in the channel must be recoverable and must not create a hazard for other river users.
Consistency matters far more than sophistication. For every visit, record the site name and grid reference, the date and time, the observers, the weather over the preceding days, and the river level or flow. A photograph of the gauge or a mark on a stable post at the water's edge lets you compare like with like. If you measure a bank in July low flow and again after a February flood, you will not know whether the change came from the flood or the season.
Write measurements in the same units every time, note the method used, and add a quick sketch of the site. Note anything that might have disturbed the site — livestock, dredging, a fallen tree upstream. And keep a backup: photograph your notebook pages at the end of the day.
The real value of this kind of fieldwork comes from repetition, not from clever equipment. Pick a short stretch — 20 or 30 metres is plenty — set out your fixed landmarks, pins and photo points, and commit to returning at the same stage of flow every month or two. Add the readings to a simple spreadsheet with one row per visit and one column per measurement, and plot the profiles or pin lengths as you go.
After a year you will have something genuinely useful: a record of how one bend behaves through wet and dry seasons, with photographs and notes to explain the odd jumps. That is real geomorphology, done with a rucksack and a notebook. Take your time, stay off the edge, and let the river do the dramatic part.
