Rivers are dynamic systems and primary geomorphic agents shaped by gravity, draining precipitation from their source to their mouth. They perform crucial fluvial processes (erosion, transportation, deposition) and are a key part of the hydrological cycle. They form networks of tributaries, distributaries, drainage basins, and watersheds, playing a central role in shaping landscapes and human settlements.

Drainage systems describe the pattern of river networks shaped by slope, structure, and geology. They are broadly classified into sequent drainage systems, which follow the land slope and structure, and insequent systems, which develop without regard to structure or slope, often on homogenous rocks.

Inconsequent (or Discordant) systems are river systems that do not follow (are 'in discord' with) the regional slope or geological structures, instead cutting right across them. They are classified into antecedent (which predate uplift) and superimposed (which were imposed on unrelated, buried rocks). Drainage patterns, on the other hand, describe the geometric arrangements of rivers (e.g., Dendritic, Trellis) which strongly reflect the underlying structure, rock type, and slope.

Rivers, as geomorphic agents, typically pass through three distinct stages – youth, mature, and old. Each stage is characterized by a dominant fluvial process (erosion, transportation, deposition), specific landforms, and the river’s changing relationship with its slope, velocity, and sediment load as it flows towards its base level (sea level).

River erosion, a key fluvial process, operates through mechanical (abrasion, attrition), chemical (solution), and hydraulic (hydraulic action) processes that shape landscapes over time. These processes create distinct landforms such as V-shaped valleys, gorges, canyons, waterfalls, potholes, plunge pools, river terraces, and meanders. The evolution of these features, especially terraces and incised meanders, provides crucial insights into a region's geomorphological and tectonic history (e.g., uplift or base-level changes).

Ox-bow lakes are crescent-shaped water bodies formed when a river abandons its meander loop, a process typical of the mature and old stages. In contrast, River Rejuvenation is the 're-energizing' of a river (often in its mature/old stage) when it regains vertical erosive power. This is usually caused by a fall in base level (sea level) or tectonic uplift of the land, leading to new, 'youthful' landforms like river terraces and incised meanders.

Rivers transport eroded material through four primary methods: rolling (traction), hopping (saltation), carrying within the water (suspension), and dissolving (solution). When the river's speed (velocity) decreases, it deposits these sediments, creating distinctive features like alluvial fans, fertile flood plains, raised levees, inner point bars, complex deltas, and braided channels.

Deltas are depositional landforms formed at the mouths of rivers where sediment accumulates faster than it can be removed by tides, currents, or waves. Think of a delta as a river's last effort to drop its load before reaching the sea. The shape of the delta—whether it's fan-like, foot-like, funnel-like, or pointed—depends entirely on the balance between the river's strength (sediment supply) and the sea's strength (waves and tides).

River deltas are depositional landforms formed at the mouths of rivers where sediment accumulates faster than it is removed. Think of the delta's shape as the result of a tug-of-war between the River's power (to deposit sediment) and the Sea's power (waves, tides, and currents, to remove or reshape it). This competition gives rise to the main types: arcuate, bird-foot, estuarine, and cuspate deltas.

Glaciers are massive, slow-moving bodies of ice that flow due to gravity. Their speed is fastest at the center and slowest at the bottom and edges due to friction. Glacial erosion is incredibly powerful, occurring mainly through two mechanisms: Plucking (where the ice rips out rock blocks) and Abrasion (where embedded rocks scrape and grind the bedrock). These processes combine to carve dramatic landscapes like U-shaped valleys.

Glaciers carve landscapes through powerful processes of Plucking (ripping out rock) and Abrasion (grinding rock). These processes create highly recognizable features in glaciated mountain regions. Key erosional landforms include the bowl-shaped cirque, the knife-edged arête, the pointed horn, and the asymmetrical rock masses like roche moutonnée and crag-and-tail.

Glaciers dramatically reshape pre-existing landscapes through erosion and transportation. They convert V-shaped river valleys into classic U-shaped glacial troughs. The differences in erosive power between main and tributary glaciers create hanging valleys. Where the ice erodes below sea level, the subsequent flooding forms deep, steep-sided coastal inlets called fjords.

Glaciers act as giant conveyor belts, transporting and depositing rock and soil. The material dropped by the melting ice (called till) and the meltwater (called outwash) forms unique landforms. These include ridges of debris like moraines, boat-shaped hills like drumlins, winding deposits like eskers, and lake basins like kettle lakes, all providing clues about past ice flow.

In deserts, wind is the primary force sculpting the land through three main actions: Abrasion (sandblasting), Deflation (lifting fine particles), and Attrition (particles colliding). These processes create distinct, often spectacular landforms such as Mushroom Rocks, wind-sculpted ridges called Yardangs, and massive depressions known as Blow-outs.

Wind transports material through three mechanisms: Suspension (carrying dust high up), Saltation (bouncing sand along the ground), and Creep (rolling larger grains). Deposition occurs when wind speed drops due to obstructions or a reduction in energy. This forms various landforms, most notably sand dunes (like Barchans and Longitudinal dunes) and the fertile, thick layers of silt called Loess.

In deserts and semi-arid regions, even limited running water causes intense erosion because there is little protective vegetation. The combined action of sudden flash floods and aridity creates distinctive landforms. Key erosional features include Wadis and Badlands, while major depositional features are the Bajada and the temporary salt lakes called Playas.

Groundwater acts primarily on rocks that are easily dissolved by slightly acidic water, such as limestone. The resulting landscape, known as Karst Topography, is created by two main processes: Solution (dissolving rock to form caves and sinkholes) and Deposition (precipitating minerals to form internal cave features like stalactites and stalagmites).

Wells are man-made structures used to access water stored underground (groundwater). The special geological feature known as an Artesian well allows water to rise to the surface automatically, often like a fountain, due to natural hydraulic pressure in a confined aquifer.

Springs are natural outlets where groundwater emerges at the surface. Their formation is fundamentally controlled by geological structure—specifically, the intersection of the water table with the land surface or the presence of faults and fissures. They are vital for water supply and categorized by their flow (perennial/intermittent) and temperature (cold/hot, including geysers).