River Processes, Profiles & Landforms
A River’s Three Lives
A river changes character along its course. Geographers split the journey from source to mouth into three sections: upper course (high energy, narrow valley, vertical erosion); middle course (more discharge, gentler gradient, lateral erosion); lower course (lots of water, almost flat, deposition dominates). Each section produces its own landforms, but the same processes — erosion, transport and deposition — do all the work, just in different proportions.
The Four Erosion Processes
Rivers erode in four ways. Hydraulic action uses the sheer force of the water to dislodge material, especially in cracks. Abrasion uses the river’s sediment as sandpaper, scraping at the bed. Attrition rounds and smashes the load itself as pebbles collide. Solution dissolves slightly soluble rocks like limestone. The mix changes downstream: hydraulic action and abrasion dominate in the upper course where boulders are tumbled by fast flow; attrition is most visible in the middle course where rounded pebbles signal long transport; solution operates everywhere but is invisible to the eye.
Going downstream: width increases, depth increases, gradient decreases, velocity actually increases (less friction in a wider, deeper channel), discharge increases, sediment size decreases and rounding increases.
Upper-Course Landforms
In the steep upper course, the river has limited water but high energy because of gradient. Vertical erosion cuts down hard, producing a narrow V-shaped valley with interlocking spurs — ridges that the young river weaves around because it lacks the power to cut through them.
A waterfall forms where a band of hard rock lies above softer rock. The softer rock erodes faster and is undercut, leaving the hard cap unsupported. Eventually the cap collapses; the waterfall retreats upstream, leaving a steep-sided gorge behind. High Force on the River Tees and Aysgarth Falls in Yorkshire are classic UK examples. River cliffs — small, steep banks — appear at the outside of bends even in upper courses.
Middle-Course Landforms: Meanders & Floodplains Begin
As the gradient eases, the river begins to swing sideways. Where flow is slightly stronger on the outside of a bend (deeper, faster water), erosion creates a river cliff; where flow is slower on the inside (shallower, less energy), deposition builds a point bar of sediment. Repeated cycles deepen the curve into a full meander. Over decades the meander migrates across the valley floor, widening the floodplain.
Lower-Course Landforms: Floodplains, Levees & Oxbow Lakes
In the lower course the river is wide, deep and full of fine sediment. Each flood spreads water across the broad floodplain, and as that water slows on the flat ground it drops its load — coarsest first, then finer particles. This builds raised banks called levees immediately next to the channel and gradually deepens the fertile floodplain soil beyond. Oxbow lakes form when a meander becomes so pronounced that the river cuts through its own narrow neck during a flood; the abandoned curve becomes a crescent-shaped lake that slowly silts up.
The Bradshaw model shows how channel and discharge variables change downstream. As you move from source to mouth: discharge, width, depth, average velocity and load quantity all rise; gradient, sediment size and channel roughness fall. Many textbooks then add: load roundness rises (from angular boulders to smooth pebbles); valley shape changes from V to broad U; cross-profile shifts from steep banks to wide floodplain. Edexcel may show you part of the model and ask you to predict the missing variable — learn the directions, not the exact numbers.
A storm hydrograph plots rainfall (bars) and river discharge (line) over time after a storm. The lag time is the gap between peak rainfall and peak discharge — short lag = flashy river, long lag = slower response. UK upland catchments with steep slopes and impermeable rock have short lag times; lowland catchments with permeable chalk, vegetation and large floodplains have long lag times. Urbanisation shortens lag times because impermeable concrete sends rainwater straight into drains.
Meanders form because flow is fastest on the outside of a bend (eroding) and slowest on the inside (depositing). Repeating this widens the curve until a flood breaks across the neck, creating an oxbow lake.