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1 BASIC FLUVIAL GEOMORPHOLOGY GEOMORPHOLOGY 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

Basic Fluvial Geomorphology

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Page 1: Basic Fluvial Geomorphology

1

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

Page 2: Basic Fluvial Geomorphology

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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

Page 3: Basic Fluvial Geomorphology

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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

Page 4: Basic Fluvial Geomorphology

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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

Page 5: Basic Fluvial Geomorphology

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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

Page 6: Basic Fluvial Geomorphology

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VARIABLES RELATED TO THE PATTERN OF RIVERS

•Slope

•Discharge

•Slope

•Sediment load

PATTERN OF RIVERS

Bank materials

Page 7: Basic Fluvial Geomorphology

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EXAMPLES OF RIVER PATTERNS

Straight reaches: LATERAL CONTROLS

Meandering rivers

EXAMPLES OF RIVER PATTERNS

STABLE PATTERN

LOW SLOPE

Page 8: Basic Fluvial Geomorphology

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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

Page 9: Basic Fluvial Geomorphology

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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

Page 10: Basic Fluvial Geomorphology

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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

Page 11: Basic Fluvial Geomorphology

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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

Page 12: Basic Fluvial Geomorphology

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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:

Page 13: Basic Fluvial Geomorphology

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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

Page 14: Basic Fluvial Geomorphology

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POOLS AND RIFFLES

POOLS AND RIFFLES

Page 15: Basic Fluvial Geomorphology

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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

Page 16: Basic Fluvial Geomorphology

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DOMINANT DISCHARGE

FLUVIAL RESPONSE

Lane´s equation (1955) for predicting fluvial responses:

50** DQSQ s

Page 17: Basic Fluvial Geomorphology

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FLUVIAL RESPONSE

50** DQSQ s

50** DQSQ sFLUVIAL RESPONSE

Page 18: Basic Fluvial Geomorphology

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FLUVIAL RESPONSE INCISED CHANNELS

FLUVIAL RESPONSE INCISED CHANNELS

Page 19: Basic Fluvial Geomorphology

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Río Valderaduey

FLUVIAL RESPONSE

Meandering cutoffs in the Mississippi River

FLUVIAL RESPONSE

Page 20: Basic Fluvial Geomorphology

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FLUVIAL RESPONSE

FLUVIAL RESPONSE

Page 21: Basic Fluvial Geomorphology

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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