Essential Hydrology and River System Terminology

Key Definitions in Hydrology and River Systems

River Features and Drainage Systems

River Channel: The bed and sides of a river form the river channel.

Drainage Basin: The area of land drained by a river.

Confluence: The point where a river and a tributary meet.

Tributary: A smaller river which joins a larger river.

Source: The starting point of a river.

Mouth: The end point of a river, where it enters the sea or a lake.

Watershed: A ridge of highland which determines to which drainage basin the water flows.

The Hydrological Cycle (Water Cycle Processes)

Hydrological Cycle: The continuous movement of water on, above, and below the surface of the Earth (the water cycle).

Evaporation: The change in state from a liquid (such as water) to a gas (such as water vapor) because of heating.

Condensation: The process by which a gaseous substance (such as water vapor) changes state into a liquid because of cooling.

Precipitation: Liquid and solid water particles that fall from the atmosphere to the Earth's surface. This includes:

• Rain and drizzle (liquid form)
• Snow and hail (solid ice)
• Sleet (partially melted ice or snow)

Transpiration: The process by which water absorbed by plants is evaporated into the atmosphere from the plant's leaf pores.

Ground Conditions and Water Storage

Unsaturated Ground: Ground that is dry or not holding the maximum amount of water.

Saturated Ground: Ground that is holding the maximum amount of water.

Water Table: The upper surface of groundwater stored in the rocks.

Surface Storage: Water stored on the surface (e.g., in puddles or lakes).

Soil Moisture Storage: Water stored within the soil layer.

Groundwater Storage: Water held within the spaces in porous, permeable rocks, underground.

Water Movement and Flow

Interception: The capture of rainwater by leaves. Some evaporates again, and the rest trickles to the ground.

Stemflow: When precipitation trickles along the stem of a plant.

Infiltration: The soaking of rainwater into the ground.

Percolation: The movement of water downwards through rock layers.

Surface Runoff: Rainwater that runs across the surface of the ground and drains into a river or body of water.

Overland Flow: The movement of water over the land, downslope toward a surface water body.

Throughflow: The flow of water within the soil layer. It takes place when the soil is completely saturated with water. It flows underground until it reaches a river, lake, or ocean.

Groundwater Flow: The movement of water that has infiltrated the ground and is discharged into a stream channel (contributing to streamflow).