The steep gradient and fast-flowing water in the upper course of a river provide significant erosive power. Hydraulic action (the force of the water dislodging material) and abrasion (rocks and sediment carried by the river grinding against the bed and banks) are the dominant processes. This leads to the formation of deep, narrow valleys with steep sides, often referred to as gorges or canyons. The characteristic 'V' shape is due to the river's vertical erosion and the subsequent collapse and removal of material from the valley walls by weathering and mass movement.

Waterfalls are steep, vertical drops formed when a river flows over a resistant cap rock overlying a less resistant rock layer. The softer rock erodes more quickly, undercutting the cap rock, which eventually collapses, causing the waterfall to retreat upstream. Rapids are similar but less dramatic, characterized by turbulent, fast-flowing water over a series of small, irregular drops caused by uneven erosion of alternating hard and soft rocks.

Potholes are formed by the abrasive action of pebbles and stones, held in swirling eddies of water, grinding against the riverbed. Over time, this continuous grinding action carves out smooth, cylindrical depressions. They are most common in areas with hard, resistant rock and sufficient sediment load.

Meanders develop in the middle and lower courses where the river gradient is gentler and the river channel is wider. The flow of water is faster on the outer bank of a bend, causing erosion (cut bank), while it is slower on the inner bank, leading to deposition (slip-off slope). This process causes the meanders to migrate laterally and become more pronounced over time.

As meanders continue to develop, they can become so pronounced that the neck of land between two adjacent meanders is cut through by the river, especially during floods. The river then adopts a straighter course, abandoning the old meander loop, which becomes filled with water, forming an oxbow lake.

Floodplains are formed by the deposition of alluvium (silt, sand, and gravel) carried by the river during periods of flooding. As the river overflows its banks, its velocity decreases, and it deposits its sediment load. Over time, repeated flooding and deposition build up a broad, flat area of fertile land.

When a river floods, the water spreads out over the floodplain. The velocity of the water decreases rapidly at the river's edge, causing the coarser, heavier sediment (like sand and gravel) to be deposited there. This deposition builds up a ridge or embankment parallel to the river channel, known as a natural levee.

As a river approaches its mouth, its velocity significantly decreases upon entering a larger, calmer body of water. This causes the river to drop its sediment load, which accumulates and builds up to form a delta. The shape of a delta is influenced by factors such as sediment load, wave action, and tidal currents.