FLUVIAL MORPHOLOGY: LANDFORMS MADE BY RUNNING WATER
Review and Study Guide
What is the most important geomorphic agent shaping earth’s physical landscape?
 Running Water – Stream flow
Where do streams get their water supply?
 Surface water runoff (often called storm flow)  sheet wash  rills  gullies  streams
 Groundwater (base flow)
What is the most common pattern made by streams?
 The most common pattern is dendritic
 Streams form a branched network – with a distinct stream order
 This is called a drainage system
What is a drainage basin?
 The total area drained by a river and its tributaries – also, watershed
 A drainage basin is defined by drainage divides
 Divides separate one drainage basin from another
What is the ultimate limit of stream erosion?
 The limiting level for a stream is base level
 Sea level is base level for most streams
 Sometimes a lake forms a local base level
What is the work of streams?
 Erosion
 Transport
 Deposition
What determines the ability of a stream to do work?
 Velocity -- Speed of flow
What determines the velocity?
 Gradient - Slope of the channel
 Channel shape and roughness - On straight sections, rivers flow fastest in the middle
 Sediment load - A stream’s velocity determines its competence to carry load
 Discharge - Amount of water flowing past a point in a given unit of time (cfs – cubic feet/second)
How do streams erode?
 Hydraulic action or scour (sheer force of water)
 Abrasion
 Dissolution
How do streams transport?
 In suspension (suspended load)
 In solution (dissolved load)
 By traction, rolling and dragging (bed load)
When do streams deposit their load?
 When the velocity decreases
 What would cause velocity to decrease?
 Reduced discharge
 Lower gradient
 Inside bend of a river
 Increased sediment load
How does a stream change as it approaches sea level?
 Discharge increases as tributaries join the stream
 Width and depth of channel increase
 Sediment load increases but particle size decreases
 Velocity increases slightly
Streams show three stages of gradation from mountains to the sea:
 Youth
 Maturity
 Old Age
Stream Stage 1 - Youth
Characteristics of Youthful Streams
 Steep irregular profile
 Waterfalls, rapids, and plunge pools
 River is deepening its channel
 Cutting into bedrock – Vertical erosion dominant
 Potholes
 V-shaped cross-section
Waterfalls
 Hard rock layers have not yet been smoothed away
 Potential Hydroelectric Power
Cutting into Bedrock
Large Boulders as Bed Load
Stream Stage 2 - Mature Valley
Characteristics of Mature Valley Streams
 Valley widening begins
 Meandering Stream
 Braided Streams – Sand bars and divided channels
 Floodplains
Lateral Erosion -- Valley Widening Begins
 Erosion is greatest on the outside bend – Cut-banks
 Deposition on the inside bend – Point bars
 Meanders
 Migrate downstream
 Widen the valley
 Form cutoffs
 Create oxbow lakes
Stream Stage 3 - Old Age
Characteristics of Old Age Streams
 Wide Alluvial Valley Stage
 Natural Levees
 Built by floods  (normal flooding is generally beneficial)
 Depositional feature
 Parallel to the stream channel on both banks
 Natural levees cannot contain floods
 Rivers drop their load when they enter the ocean or a lake and form a Delta
 Distributaries
 Typical delta – Nile Delta – Shaped like the Greek letter 
 Birdfoot delta – Mississippi Delta
 Ganges-Brahmaputra Delta – the largest and most densely populated
How do people change rivers?
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Deforestation
Channelization
Urbanization
Construction
Paving  e.g., Los Angeles River
Dam building
How do these changes affect rivers? How does development change streams?
 Stream Pollution