7.1 The Hydrological Cycle

GEOL1340

Hydrologic Cycle

The continuous movement of water among Earth's atmosphere, surface, and subsurface reservoirs, driven primarily by solar energy and gravity.

Primary Driver of Surface Water Movement

Gravity, which pulls precipitation and surface water downslope toward tributaries and trunk rivers.

Surficial Process of Streams

Stream runoff acting as one of the most effective agents of weathering, erosion, and sediment transport across continental landmasses.

Drainage Basin / Watershed

The total land area that collects surface runoff and directs all precipitation into a specific river network.

Continental Divides

Topographic high points that determine which ocean or basin receiving drops of water will flow into (e.g., Snow Dome in Jasper National Park).

Longitudinal Profile

A cross-sectional view of a stream's elevation drop along its length, from its source (headwaters) to its mouth.

Concave-Up Curve

The natural profile shape of streams—steep gradients and narrow V-shaped channels near the headwaters, flattening out into gentler gradients and broad floodplains near the mouth.

Base Level

The lowest elevation to which a stream can cut down and erode its channel.

Ultimate Base Level

Sea level, representing the lowest overall limit for stream erosion worldwide.

Local (Temporary) Base Level

Lakes, reservoirs, or resistant rock ledges (such as waterfalls) that temporarily restrict downcutting upstream.

Raising Base Level Effects

A change like damming a river or sea level rise that reduces stream gradient and flow velocity, causing an increase in sediment deposition.

Lowering Base Level Effects

A change like a sea level drop or tectonic uplift that increases gradient and stream energy, causing the river to accelerate erosion and downcut.

Bevelling Topography

The process where rivers continuously wear down landforms toward a flat, graded relief matching ultimate base level over thousands to millions of years.

Continental Drainage Reversals

Tectonic plate movements and mountain-building events (orogeny) that can tilt landmasses and reverse major river systems over geological time (e.g., the Amazon and Mississippi rivers).

Earth's Unique Hydrological Setting

Earth being the only planet in our solar system with active, flowing surface water, making running water and fluvial processes the dominant drivers shaping the land surface.

Local Human River Context

The way major river networks dictate human settlement and regional development, such as Winnipeg's development centered around the Red River and Assiniboine River at The Forks.

Headwaters (Source)

The mountainous segment of a river characterized by steep gradients, high flow velocity, straight channels, and dominant headwater erosion.

Lowlands (Mouth)

The flat-gradient segment of a river characterized by lower flow velocity and wide meandering channels.

Urban Geomorphology Example (Winnipeg)

The University of Manitoba campus being built inside a major Red River loop situated directly on a point bar, and areas like Crescent Drive built on top of drained historical oxbow lakes and abandoned channels.

Residence Time

The average length of time a water molecule remains in a reservoir before being transferred elsewhere, calculated by dividing reservoir volume by the flux rate.

Atmospheric Water Volume

Approximately 13,000 cubic kilometres (km3) of water present in the air at any given time as water vapour and water droplets in clouds.

Ocean Water Volume Proportion

The oceans accounting for 97% of Earth's water volume (stored as salty water).

Freshwater Proportion

3% of Earth's water, of which two-thirds is stored as glacial ice, one-third is stored as groundwater, and about 0.03% is stored in lakes, streams, vegetation, and the atmosphere.