Trout at Transition
River Information
Upland rivers
Steep Gradients
Well oxygenated
Narrowed channel width – high proportion of water in contact with bed and channel sides
thus a lower cross sectional area
Valley type typically
V-Shaped – eroded by a river
U-Shaped – eroded by a glacier
Two forces happening in a river EROSIVE and TRANSPORTIVE
Lowland rivers
Reduced gradient
Wider channel width - lower proportion of water in contact with bed and channel sides thus
a lower cross sectional area
Flood plains
Three forces happening in a river EROSIVE, TRANSPORTIVE and DEPOSITION
Meanders increasing storage capacity
River Morphology
Channel patterns – straight, sinuous, meandering, braided
Thalweg – centreline of flow
From banking vantage point – describe the appearance of flow in terms of characteristics –
surface agitation, velocity of flow, depth. From this can you tell channel roughness, is it
eroding/transporting/depositing
Fluvial Processes
Erosion – 5 types
Cavitation-implosion of air bubbles causing fragments to move and impact each other
Pneumatic Action – turbulent water forcing air inside fissures & cracks weakening
structure
Attrition – two particles striking each other knocking small chips from them
Abrasion – rubbing or grinding together of two particles
Potholling / drilling – vertical vibration of a rock tool due to eddies
Transportation – 3 methods
Suspension – movement of particles away from bed when critical water velocity is
exceeded for that particle
Saltation – particle lifted up by water but its mass is such that it will fall again and may
bounce in downstream transport
Traction – particle cannot be lifted off of stream bed but can pushed along either
rolling or sliding.
Ideal Spawning Substrate Composition
Fine sand
Coarse Sand
Pebble (2.2 -22.2 mm)
Cobble (22.2 – 256mm)
0-3%
10-15%
40-50%
40-50%
Ideal Spawning Conditions
Water Velocity
Water Depth
Substrate Size
Dissolved Oxygen
Suspended Material
25-90 cm/s
17-76 cm
30-80 mm
8 mg/l (adult fish need 5 - 6.5 mg/l)
less than 5 mg/l
Factors Affecting Trout Redds and Adult Fish
1. Water Flow

High Flow
o floods can wash out redds (15cm depth required for minimum impact)
o Strand fish
o Flashy floods release more energy resulting in high rates of erosion and
washing out of smaller sediments
 Low Flows – fish and redds can become dry or stranded
2. Temperature

3-19 ○C
3. Water Chemistry

pH safe levels are >5 - <9.

Lethal lead level 1mg l-1
4. Dissolved Oxygen

5-5.5mg l-1
5. Mechanical Shock to redds
 high floods ‘jiggle’ the eggs when buried or can wash them out,
 compression of gravels from human ‘traffic’
6. Gravel Composition

Frequency and intensity of floods to
turn over and clean gravels of silt
wash away pollutants and debris
wash out spawning gravels
 Construction of reservoirs and structures across the rivers usually limits the
natural flux of gravel through the reach of the river immediately downstream of
the impoundment. Flow regulation prevents periodic natural floods which
loosen the river bed. As a consequence the river bed tends to degrade and to
coarsen. This leads to an evacuation of much finer spawning material and
compaction of the residual material. Excessive discharge can release high levels
of silt and wash out spawning habitats.
7. Siltation of redds
8. Hydrological manipulation

Straightening of channels – increase flow speed thus increase transportation of
sediments and washing our of rivers can occur leaving very little habitat
structure for fish and other river inhabitants
 Deepening of channels – channel diversity is reduced and bankings are eroded
quicker during floods due to vertical bank with no vegetation cover
 Culverting channels – no production or habitat
 Loss of riparian plants
o increased water transportation between land and river (run off)
o unstable bankings – increased erosion and siltation
9. Obstructions to migration
10. Riparian Land use

Erosion & collapse of river banks
o




Removal of riparian vegetation resulting in bank instability, leading to
under-cutting and collapse of bank. This will leave a un-vegetated bare
face which will erode very easily increasing siltation.
o As banking erodes river becomes wider and shallower. Braiding can
occur. No deeper water for fish and drying out or gravels and potential
spawning sites.
o Channel deviates from original course.
Grazing and loss of riparian zones
Trampling and Compaction
o Cattle grazing up to the channel edge can compress the upper layers of
the soil resulting in an impermeable layer through which percolation of
rainwater is inhibited resulting in greater run-off.
o Cattle hooves break up the banking increasing sedimentation and
erosion
o Cattle can compact and erode sediments within the river.
Tunnel Vegetation
o Lack of light penetration reduces primary production which directly
affect invertebrate production and therefore food availability for fish.
Urbanisation and Agriculture
o
o
o
o
o
Impermeable surfaces increase run-off and thus flooding
Urban run-off contains a cocktail of pollutants creating toxicity
problems.
Sewage input can result in eutrophication of rivers and increased
Biological Oxygen Demand reducing available dissolved oxygen.
Bare fields are easily eroded and run-off into rivers increases introducing
high levels of silt into the river.
Over spraying of arable fields and being washed into river.
Stream Ecology/Ecosystem


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Primary Plant Production
o 2 types
 Allochthonous – vegetable matter falling into the stream from
the riparian zone
 Autochthonous – in stream plants and algae
o Plant production is limited by several factors
 Light
 Temperature
 Nutrient availability
 Water Velocity
 Substrate type
 Litter retention
Invertebrate Communities
o Invertebrates feed in one of four ways
 Grazers – eat algae off of the surface of stones & plants
 Shredders – consume decomposing plant litter
 Filter Feeders – intercept fragments of litter or algae drifting in
the water
 Carnivores – eat other invertebrates
Physical Habitat Availability
o Different types of physical habitat dictate the animals and plants that
will be found there. Example. The mayfly Ephemera danica burrows into
sandy sediments whereas the mayfly Heptageniidae (stone clingers)
need pebbles.
Fish Production
http://www.geography.learnontheinternet.co.uk/
River Zones
Typical Stream Crossection