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BASIC FLUVIAL GEOMORPHOLOGYGEOMORPHOLOGY
Marta González del Tánago
E.T.S. Ingenieros de Montes
Universidad Politécnica de Madrid
•Interest of the FluvialGeomorphology in the river restoration projects
BASIC FLUVIAL GEOMORPHOLOGY
restoration projects
•Morphological analysis of the rivers
•The sediments in the fluvial processes
•The river in equilibrium: natural dynamics
•Dominant discharge concept
•Response of rivers to natural/human disturbances
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Why the Fluvial Geomorphology is important in river restoration
Use and abuse of rivers
•Physical degradation is one of the most important problems of river ecosystems, affecting their ecological status by means of:
- Lost of natural forms and processes
- Unwanted erosion and sedimentation processes
- Decrease of habitat quality and biodiversity
- Lost of environmental values of rivers
•The geomorphological analysis of rivers helps to:
Why the Fluvial Geomorphology is important in river restoration
g p g y p
•Identify problems related to the physical degradation
•Interpretate causes and consequences
•Propose alternatives for enhancing and restoring rivers
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Examples of physical degradation in rivers
Río Valderaduey Río Esgueva
Río Bernesga
Río Bernesga
Analysis of Fluvial Forms
FORMS:
• Longitudinal Profile
• Pattern and Sinuosity
• Hydraulic geometry
• Sediments and Bed forms
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LONGITUDINAL PROFILE
LONGITUDINAL PROFILE IN RIVERS
The longitudinal profile shows the slope of the river, which can be considered at different spatial scales
Watershed (Valley):
Geology and Relief
Fluvial segment:
Dams and local controlsDams and local controls
Fluvial reach:
Sediments and bed forms
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•The slope of the channel is one of the most important hydraulic variables, determining the hydraulic power and
VARIABLES RELATED TO THE LONGITUDINAL PROFILE OF RIVERS
channel stability
• The slope is related to the water velocity and the shear stress
•It is related to the sediment size:
6,0)(18d
S S: Slope (m/m)
Ad: Drainage area(milla 2))(18dA
S Ad: Drainage area(milla )
d: Medium diameter of sediments (mm)
PATTERN OF RIVERS
•Straight
•Meandering
•Braided
•Anastomosed
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VARIABLES RELATED TO THE PATTERN OF RIVERS
•Slope
•Discharge
•Slope
•Sediment load
PATTERN OF RIVERS
Bank materials
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EXAMPLES OF RIVER PATTERNS
Straight reaches: LATERAL CONTROLS
Meandering rivers
EXAMPLES OF RIVER PATTERNS
STABLE PATTERN
LOW SLOPE
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Braided rivers
EXAMPLES OF RIVER PATTERNS
UNSTABLE PATTERN
SEDIMENT LOAD, HIGH SLOPE
RELATIONSHIP BETWEEN SLOPE, SEDIMENT SIZE AND PATTERN
Selva de Oza
Valle glacial: Low slope, fine sediments, high sinuosity
Valle fluvial: High slope, coarse sediment, straight pattern (sinuous valley)
Tramo bajo del Tormes
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CROSS SECTIONS - HIDRAULIC GEOMETRY
•Base level
•Bankfull level, (dominio público hidráulico)
•Floodplain (riberas, llanura de inundación)
HIDRAULIC GEOMETRY
At-a-station:
cc
bb
aa
QCu
QCd
QCw
1
1
cba
CCC
wduQ
cba
34,0
40,0
26,0
c
b
a
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HIDRAULIC GEOMETRY
Downstream, at bankfull:
cc
bb
aa
QCu
QCd
QCw
1
1
cba
CCC
wduQ
cba
,
28,009,0
40,029,0
60,039,0
c
b
a
SEDIMENTS IN RIVERS
They come from watershed erosion or channel erosion and determine the turbidity of the water, the size of the substratum and the slope of the channel banks
Transport Origin
Wash load Suspension Watershed erosionChannel erosion (fine particles)
Bed load Siltation Channel erosion (coarse particles)Bed load Siltation ( p )Bed erosion
•Cohesive materials
•Non-cohesive materials•Sandy Rivers
•Gravel-bed Rivers
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SANDY RIVERS
SANDY RIVERS
Bed forms determine the roughness of the channel (Manning´s n), which varies according to the discharge
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GRAVEL-BED RIVERS
Gravel bars and islands modify the roughness of the channel and increase the diversity of hydraulic conditions (physical habitats)
GRAVEL-BED RIVERS
Bed forms according to the sediment size:
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CascadeSteps
GRAVEL-BED RIVERS
Bed forms according to the sediment size:
Plane bed
Pools and Riffles
Bed forms according to the sediment size:
GRAVEL-BED RIVERS
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POOLS AND RIFFLES
POOLS AND RIFFLES
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TYPES OF EQUILIBRIUM
More probable state:
•Uniform distribution of power
•Minimum work (minimum energy lost per unit length)
Mi i h d li•Minimum hydraulic power v*S
DOMINANT DISCHARGE
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DOMINANT DISCHARGE
FLUVIAL RESPONSE
Lane´s equation (1955) for predicting fluvial responses:
50** DQSQ s
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FLUVIAL RESPONSE
50** DQSQ s
50** DQSQ sFLUVIAL RESPONSE
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FLUVIAL RESPONSE INCISED CHANNELS
FLUVIAL RESPONSE INCISED CHANNELS
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Río Valderaduey
FLUVIAL RESPONSE
Meandering cutoffs in the Mississippi River
FLUVIAL RESPONSE
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FLUVIAL RESPONSE
FLUVIAL RESPONSE
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FLUVIAL DYNAMICS
•Watershed Hydrology
•Land uses
Human disturbance
•Channel forms
•Fluvial Processes
River Response
•Interest of the FluvialGeomorphology in river restoration projects
BASIC FLUVIAL GEOMORPHOLOGY
restoration projects
•Morphological analysis of the rivers
•The sediments in the fluvial processes
•The river in equilibrium: natural dynamics
•Dominant discharge concept
•Response of rivers to natural/human disturbances