River Systems and Hydrological Cycle: Key Concepts and Processes

Watershed

The area of land that drains water into a river system

Source

The starting point of a river

Mouth

The end of a river where it flows into the sea, lake, or another river

Drainage Basin

The area drained by a river and its tributaries

Confluence

The point where two rivers meet

Channel Network

The system of interconnected river channels within a drainage basin

Drainage Density

The total length of all rivers in a basin divided by the area of the basin

Hydrological Cycle

The continuous movement of water between the atmosphere, land and oceans

Evaporation

Liquid water turning into water vapour due to heat

Transpiration

Water vapour released from plants

Infiltration

Water soaking into the soil

Percolation

Water moving down through soil and rock

Throughflow

Water moving sideways through soil toward a river

Groundwater Flow

Water moving slowly through rock underground

Overland Flow / Surface Runoff

Water flowing over the land surface into a river

Stores

Places where water is held in the hydrological cycle

Flows

Movements of water between stores

Upper Course

The steep, high-energy part of a river near its source

Middle Course

The section where lateral erosion and transportation dominate

Lower Course

The flat, low-energy part of a river near its mouth

Landforms

Natural physical features created by river processes

Erosion

The wearing away of rock by the river

Hydraulic Action

Erosion caused by the force of water

Abrasion

Erosion caused by river load scraping the bed and banks

Attrition

Rocks colliding and breaking into smaller pieces

Solution

Erosion where minerals dissolve in water

Transportation

Movement of material by the river

Traction

Large rocks rolled along the river bed

Saltation

Small stones bouncing along the river bed

Suspension

Fine material carried within the water

Solution (transport)

Dissolved material carried by the river

Deposition

The dropping of material when a river loses energy

Channel Shape

The form of the river channel

Velocity

The speed of river flow

Discharge

The volume of water passing a point per second

Channel Roughness

The amount of friction caused by bed and banks

Hydraulic Radius

The ratio of cross-sectional area to wetted perimeter

Wetted Perimeter

The length of the channel bed and banks in contact with water

Bradshaw Model

A model showing how river characteristics change downstream

River Pollution

Contamination of a river by harmful substances

River Pollution Causes

Industrial waste, sewage, agriculture, urban runoff

River Pollution Impacts

Ecosystem damage, unsafe water, loss of biodiversity

River Pollution Management

Laws, treatment plants, monitoring, education

Case Study - Shanghai's Suzhou Creek

Example of river pollution and management

Physical Causes of Flooding

Heavy rainfall, relief, geology, snowmelt

Human Causes of Flooding

Urbanisation, deforestation, building on floodplains

Impacts of Flooding

Loss of life, property damage, economic loss, disease

Management of Flooding

Hard engineering, soft engineering, planning

Hazards of Living Near a River

Flooding, erosion, pollution

Opportunities of Living Near a River

Water supply, transport, fertile land, energy

Case Study - Mississippi River 2019

Example of river flooding, impacts and management