Simulic
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River Processes and Landforms – Source to Mouth

GeographyEarth's Structure & LandformsAges 15–16

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The long profile of a 100 km river, divided into upper, middle and lower course. Drag the survey site along the river to read discharge, width, depth, velocity and bedload size and roundness (the Bradshaw model), see the valley and channel cross-section, and use the Hjulström curve to tell which particle sizes are eroded, transported or deposited. Run time to watch landforms develop: V-shaped valley and interlocking spurs, a waterfall retreating to form a gorge, migrating meanders cut off into ox-bow lakes, levees and floodplain built by floods, and a delta or an estuary.

Lesson: River processes (erosion, transportation, deposition) and river landforms

What it shows

A river changes from source to mouth. In the steep upper course it erodes downwards, cutting a V-shaped valley between interlocking spurs; where hard rock lies over soft rock a waterfall forms and retreats upstream, leaving a gorge. In the middle course lateral erosion widens the valley and meanders migrate until a neck is cut off as an ox-bow lake. In the lower course floods build levees and a floodplain, and the river ends in a delta or an estuary. The Bradshaw model and the Hjulström curve explain these changes.

How to use

Drag the orange site along the long profile, or use Survey site, to read the table and the eight Bradshaw charts. Pick a landform tab (V-shaped valley, Waterfall and gorge, Meanders and ox-bows, Floodplain and levees, River mouth) and choose a Speed. Press Big flood to raise velocity on the Hjulström curve and trigger floods. Change Discharge at mouth, Source height and Rock type.

Parameters you can change

  • Discharge at the mouth (bankfull) 20–1000 m³/s
  • Height of the source (sets the gradient) 200–2500 m
  • Rock type Band of hard rock over soft rock (waterfall), Soft rock throughout, Hard rock throughout
  • Survey site (distance from the source) 0–100 km
  • Type of river mouth Delta (weak tides, high sediment load), Estuary (strong tides)

Questions to explore

  1. Why does mean velocity increase downstream even though the gradient decreases?
  2. Why is clay harder to erode than sand, according to the Hjulström curve?
  3. What sequence of processes makes a waterfall retreat and leave a gorge behind?

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