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Water Resources
Lecture 4
The River Environment (2)
Problems with generic zoning of a river:
• Many rivers are different – they occur in different
geological and climatic regions.
• Different rivers have different transitions along
their profiles.
• Rivers do not often undergo a gradual transition
along their profile:
– What about rejuvination at a nick-point?
– What happens when a tributary with very different
characteristics joins the main stream?
– What happens when a river is dammed along its
Hiererarchical Classification of
River Systems
• Proposed by Frissel et al, 1986.
• Adapted to a geomorphological classification for
Southern Africa by Rowntree and Wadeson, 1999.
• Basic Principle:
River System
River Zones
Morphological Units
Hydraulic Biotopes
Frissel et al
Definitions (Frissel)
• Stream System:
– All surface waters in a Watershed (catchment).
• Segment System:
– Portion of a stream system flowing through a
single bedrock type, and bounded by tributary
junctions or major waterfalls.
Definitions: Frissel
• Reach System:
– A length of stream segment lying between
breaks in a channel slope, local side-slopes,
valley floor width, riparian vegetation, and
bank material.
• Pool or riffle system:
– A subsystem of a reach having characteristic
bed topography, water surface, slope, depth and
velocity patterns
Classification of Rowntree and
Hydraulic Biotopes
• A mosaic of small patches of uniform
condition within the wetted perimeter of a
• Delineated by discontinuities in either flow
or substratum.
Hydraulic Biotopes
Substrate Types
Flow Types
• Bedrock
• Boulder
• Large Cobble
• Pebble
• Gravel
• Sand
• Silt/Mud
• No flow
• Barely perceptible flow
• Smooth boundary turbulent
• Ripple surface
• Slow and fast riffle flow
• Undular standing wave
• Broken standing wave
• Cascade
• Chute
• Free fall
• Boil
The Rive Continuum Concept
(Vannote et al, 1980)
• 4 dimensions to change in a river system.
• RCC Deals with longitudinal change:
Basic Principle:
Rivers possess a continuous gradient of physical and
chemical conditions that are progressively and
continuously modified modified downstream.
Driving variables
Response variables
Davies and
Day, 1998.
• Essentially all components of a river, at any
point along its length, are dictated by
abiotic and chemical conditions and
modified by gradients of biological
variables and processes that occur upstream
of the point of consideration.
Criticism of RCC:
It does not focus on all 4 dimensions
of change.
E.g: Junk et al, 1989: Flood Pulse Concept.
From Davies and
Day 1998
Davies and Day, 1988
Frissel et al, 1986
Rowntree and Wadeson 1999
Vannote et al, 1980
Junk et al, 1989
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