Ch32.ppt - Ven Te Chow Hydrosyst

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					                  1D SEDIMENT TRANSPORT MORPHODYNAMICS
                              with applications to
                       RIVERS AND TURBIDITY CURRENTS
                                CHAPTER 32:
          INTRODUCTION TO FLUVIAL FANS AND FAN-DELTAS
Fluvial fans and fan-deltas form wherever rivers deposit sediment.
A fluvial fan is a completely terrestrial feature. The fan itself may be drained
at the downstream end by a river, or may not be drained at all.
A fluvial fan-delta is a fan that ends in standing water such as a lake, a
reservoir or the ocean.




    Copper Creek Fan, Death                    Fan-delta of the Mangoky
          Valley, USA.                         River, Malagasy Republic.
  Image courtesy Roger Hooke.                    Image from Internet.
                   1D SEDIMENT TRANSPORT MORPHODYNAMICS
                               with applications to
                        RIVERS AND TURBIDITY CURRENTS

        CHARACTERISTICS OF FLUVIAL FANS AND FAN-DELTAS

Fluvial fans and fan-deltas are depositional zones that are larger than the
rivers that create them.
Fluvial fans and fan-deltas spread out laterally. The river(s) on them access
the fan surface by migration and avulsion (channel jumping), so creating the
characteristic fan-shaped surface.
The long profile of a river on a fan is driven to be upward-concave by
sediment deposition.
Fluvial fans and fan-deltas tend to prograde outward in space as sediment
deposits.
Fans and fan-deltas tend to form in zones of tectonic subsidence.
Subsidence creates a “hole” that is filled with sediment.
Fan-deltas are strongly influenced by variations in the level of standing water
(base level).
1D SEDIMENT TRANSPORT MORPHODYNAMICS
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     RIVERS AND TURBIDITY CURRENTS
                    A LARGE FLUVIAL FAN

            The Kosi River flows southward from the
            Himalaya Mountains and deposits a large
            fan drained by the Ganges River.

            The fan is located within a subsiding
            foreland basin between the uplifting
            Himalaya Mountains to the north and the
            highlands of India to the south.

            Most of the sediment carried by the Kosi
            River deposits on the fan and never
            reaches the Ganges River.


             Kosi River and Fan, India (and adjacent
                           countries).
                       Image from NASA;
                    https://zulu.ssc.nasa.gov/mrsid/mrsid.pl
      1D SEDIMENT TRANSPORT MORPHODYNAMICS
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CHANNEL SHIFT ON A LARGE FLUVIAL FAN




                        Channel shift on the Kosi River was
                        introduced in Chapter 25. The map
                        makes clear the fan-shaped deposit
                        created by channel shift.




                          Channel shift on the Kosi Fan.
                       Adapted from Gole and Chitale (1966).
                                1D SEDIMENT TRANSPORT MORPHODYNAMICS
                                            with applications to
                                     RIVERS AND TURBIDITY CURRENTS
            CHANNEL SHIFT ON AND PROGRADATION OF A FAN-DELTA
The Yellow River Delta, China, is a muddy delta that subsides due to compaction
driven by the weight of its deposits. This subsidence acts to limit delta progradation.




                                              Channel shifting in the Yellow River Delta
   Yellow River Delta, China.
                                                  From Sun et al. (2002) based on
      Image from NASA;
   https://zulu.ssc.nasa.gov/mrsid/mrsid.pl               Pang & Si (1983).
            1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                               THE FAN AND ITS RIVER(S)
                          At any given time a fan may contain a single
                          river, or multiple distributaries. These rivers
                          may be meandering or braided.


                                                         The Kosi River
The river                                                 is braided in
                                                            its upper
                                                             reaches.

                The fan


                                                           The same river
                                                           is meandering
                                                             in its lower
                                                               reaches.
                   1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                  A FAN CREATED BY MEANDERING RIVER(S)
The Okavango River forms a large fan where it flows
into a graben (zone of subsidence associated with
extension of the continental crust) in Botswana, Africa.
                                    Meandering
                                   channel on the
                                   Okavango Fan.
                                  Image courtesy
                                     N. Smith.




                                  Satellite view
                                  of Okavango
                                      Fan.



Okavango Fan, Botswana, Africa.                         Image from NASA;
Image from Smith et al. (1997).                     https://zulu.ssc.nasa.gov/mrsid/mrsid.pl
                      1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                 FAN-DELTAS CREATED BY BRAIDED RIVERS
A sandur is a large fan or fan-delta created by a braided stream carrying sediment
from a glacier. The word is Icelandic in origin. The braided Kurobe River is confined
by dikes to protect the cultivated land on the fan.
       Skeithara Sandur, Iceland.
     Image courtesy H. Johannesson.




        Kurobe Fan-delta, Japan.
        Image courtesy S. Ikeda.
                 1D SEDIMENT TRANSPORT MORPHODYNAMICS
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             FANS AND FAN-DELTAS AT VARIOUS SCALES




                      Laboratory fan-delta, ~ 3 m.
Image taken at St. Anthony Falls Laboratory, University of Minnesota USA.
        1D SEDIMENT TRANSPORT MORPHODYNAMICS
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FANS AND FAN-DELTAS AT VARIOUS SCALES contd.




 Fan created by runoff from cultivated field; ~ 6 m.
 Image taken by author near Pigeon Point, California.
              1D SEDIMENT TRANSPORT MORPHODYNAMICS
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      FANS AND FAN-DELTAS AT VARIOUS SCALES contd.




Fan in Idaho, USA created by runoff from burned hillside, ~ 50 m.
       1D SEDIMENT TRANSPORT MORPHODYNAMICS
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FANS AND FAN-DELTAS AT VARIOUS SCALES contd.




   Copper Creek Fan, Death Valley, USA; ~ 10 km.
           Image courtesy Roger Hooke.
      1D SEDIMENT TRANSPORT MORPHODYNAMICS
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FANS AND FAN-DELTAS AT VARIOUS SCALES contd.




         Kosi River Fan, India; ~ 125 km.
              Image from Internet.
                        1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                             RIVERS AND TURBIDITY CURRENTS
                                      BAJADAS
A bajada is a set of closely-spaced fans that have amalgamated to form a single linear
morphology. Two examples are shown below.


     Bajada in western China




                                                               Bajada in Death Valley,
                                                                  California, USA
                       Images from NASA;
                    https://zulu.ssc.nasa.gov/mrsid/mrsid.pl
                       1D SEDIMENT TRANSPORT MORPHODYNAMICS
                                   with applications to
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                           FLOWS THAT CREATE FANS


Fans may be created by deposition from a) debris flows, b) sheet flows and c) river
    flows.
a) A debris flow is a dense flow that contains similar amounts by weight of water and
    sediment.
b) A sheet flow is a broad, unchannelized open channel flow that may cover a
    significant fraction of the fan (e.g. 30%) during a single flood.
c) A channelized flow is within a meandering or braided channel.
Debris flow and sheet flow fans tend to occur on slopes that are much steeper than
    fluvial fans created by channelized flows. The two do, however, have a range of
    overlap.
Here the case of fluvial fans created by channelized flows are considered in detail. It
    is of use, however, to view some debris flow fans before proceeding.
                          1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                            A DEBRIS FLOW (JAPAN)
      Double-click on the image to see the video. Video courtesy Paul Heller.




rte-bookjapandebflow.mpg: to run without relinking, download to same folder as PowerPoint presentations.
1D SEDIMENT TRANSPORT MORPHODYNAMICS
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         HARVEY CREEK FAN, PAPUA NEW GUINEA

       Harvey Creek Fan, Papua New Guinea is a fan
       dominated by debris flows created by the
       disposal of mine waste. It grades smoothly
       into a braided stream (Ok Mani) downstream.
        Mine disposal
            site

                                 Zone of
                                valley wall
                                 erosion

        Harvey Creek
            Fan               Braided Ok
                                 Mani


           Image courtesy Ok Tedi Mining Ltd.
     1D SEDIMENT TRANSPORT MORPHODYNAMICS
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HARVEY CREEK FAN, PAPUA NEW GUINEA contd.




             While the fan is mostly formed by debris flows,
             fluvial flow also plays a role. Bill Dietrich of the
             University of California Berkeley serves as
             scale.
                       1D SEDIMENT TRANSPORT MORPHODYNAMICS
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     A FAN-DELTA CREATED BY A DEBRIS
                 FLOW EVENT
A combination of debris flows and sheet flows
associated with the Vargas Disaster, Venezuela,
1999 destroyed
the town of
Carmen de
Uria.




                                                  December,
               March, 1999                          1999


   Images courtesy José Lopez, Universidad Central de Venezuela, Venezuela.
                 1D SEDIMENT TRANSPORT MORPHODYNAMICS
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    A FAN-DELTA CREATED BY A DEBRIS FLOW EVENT contd.




Image courtesy José Lopez, Universidad Central de Venezuela, Venezuela.
1D SEDIMENT TRANSPORT MORPHODYNAMICS
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    FLUVIAL FAN-DELTAS

           Fluvial fan-deltas occur where rivers meet
  1938     lakes (e.g. reservoirs) or the ocean, creating a
           depositional environment. The example here
           is that of a fan-delta prograding into a
           reservoir. The image from 1938 is from before
           dam installation. The circle denotes a fixed
           point that allows tracking of progradation.
             Lake Altoona, Eau Claire River, USA.

                                         1988
  1951
                       1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                 DEPOSITIONAL STRUCTURE OF FAN-DELTAS

The deposits of fan-deltas can be divided into three zones: a coarse-grained
aggradational topset emplaced by fluvial deposition, a coarse-grained progradational
foreset emplaced by avalanching and a fine-grained aggradational bottomset
emplaced by plunging turbidity currents or rain from surface plumes. Subsidence may
limit or stop progradation.                                 The foreset may be at or
                                                          near the angle of repose
                     topset                               (in which case it is called a
                                                          Gilbert delta), but is usually
                                                          well below this angle. In a
                                                          sand-bed stream, the
                                         foreset          topset and foreset are
                                                          sandy and the bottomset is
  antecedent                                              muddy. In a gravel-bed
     bed                                                  stream the topset and
                                                          foreset are often composed
        coarse-grained
                                                          of gravel and coarse sand,
                     fine-grained        bottomset        and the bottomset of finer
                                                          sand and mud.
              1D SEDIMENT TRANSPORT MORPHODYNAMICS
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AN EXAMPLE: SEDIMENTATION IN LAKE MEAD, COLORADO RIVER, USA
         (based on an original from Grover and Howard, 1937)
                            1D SEDIMENT TRANSPORT MORPHODYNAMICS
                                        with applications to
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EMPLACEMENT OF THE TOPSET BY BRAIDED STREAMS IN AN EXPERIMENTAL
      FAN-DELTA UNDERGOING SUBSIDENCE (Cazanacli et al., 2002)
              Double-click on the image to see the video clip.




rte-bookXESbasinsurfflow.avi: to run without relinking, download to same folder as PowerPoint presentations.
                           1D SEDIMENT TRANSPORT MORPHODYNAMICS
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 EMPLACEMENT OF COARSE-GRAINED TOPSET AND FORESET AND FINE-
GRAINED BOTTOMSET IN A LABORATORY FLUME (Kostic and Parker, 2003a,b)
                      Double-click on the image to see the video clip.




rte-bookmudsanddelta.mpg: to run without relinking, download to same folder as PowerPoint presentations.
                   1D SEDIMENT TRANSPORT MORPHODYNAMICS
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DELTAS AND FAN-DELTAS ARE OFTEN THE SITES
           OF RIVER DISASTERS




 Bridge on Skeithara Sandur, Iceland        Approach to bridge on
destroyed by Jokullhaup flood of 1996.    Boundary Creek Fan, New
   Image courtesy H. Johannesson         Zealand, destroyed by flood.
                                         Image courtesy S. Coleman.
1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                  OR DISASTERS WAITING TO
                          HAPPEN




                   Image from FEMA website,
                             USA
                     1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                     THE MISSISSIPPI DELTA PROBLEM

                                           The Mississippi River forms a fine-
                                           grained fan-delta as it approaches the
                                           Gulf of Mexico. The delta subsides
                                           by compaction under its own weight.




    Image from NASA;
https://zulu.ssc.nasa.gov/mrsid/mrsid.pl
          1D SEDIMENT TRANSPORT MORPHODYNAMICS
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      THE MISSISSIPPI DELTA PROBLEM contd.

                                The river has a bed of fine sand,
                                but carries copious amounts of
                                mud. The river has gradually
                                avulsed eastward across its fan-
                                delta since the end of the last
                                glaciation (Fischetti, 2001).

                                The surface of the fan subsides
                                under compaction by its own
                                weight. Without replacement of
                                this sediment, shoreline must
                                trangress, or move inland. In the
                                fan-delta’s natural state, the
                                sediment was replaced by
                                overbank deposition as the river
                                flooded and the channel avulsed,
                                so that net progradation
Image courtesy C. Paola         (regression) resulted.
                       1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                   THE MISSISSIPPI DELTA PROBLEM contd.
Dikes all along the Mississippi River prevent overbank deposition of both mud and
sand. As a result, the river now aggrades within its levees, and the surrounding fan
surface is rapidly subsiding under compaction without replacement.




    Mississippi River and levees               Subsiding fan-delta surface
   downstream of New Orleans.              behind levees south of New Orleans.
                        1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                    THE MISSISSIPPI DELTA PROBLEM contd.
The river has aggraded to the point that it is poised to avulse into the Atchafalaya
River through the Old River. It is prevented from doing so by the structure shown
below.


                                           Mississippi River
  Red River




                        Old River




    Atchafalaya River
                       The Old River Control Structure, Louisiana
                       1D SEDIMENT TRANSPORT MORPHODYNAMICS
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                     THE MISSISSIPPI DELTA PROBLEM contd.
Subsidence rates are now so high that the shoreline is rapidly moving landward. The
entire delta, and the city of New Orleans in particular, are now at risk. It has been
predicted that by 2090 the seashore will have advanced to New Orleans (Fischetti,
2001). The city may be destroyed by a hurricane well before this time.


                                                                       New Orleans




                                                       Zone of rapid shoreward
                                                          coastline advance

                                                       Satellite image from the
        Image courtesy L. Quezergue                            Internet.
                             1D SEDIMENT TRANSPORT MORPHODYNAMICS
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A BEAUTIFUL IMAGE IN CLOSING:
THE FAN-DELTA OF THE SELENGA
 RIVER AT LAKE BAIKAL, RUSSIA
       Image from NASA;
    https://zulu.ssc.nasa.gov/mrsid/mrsid.pl
                          1D SEDIMENT TRANSPORT MORPHODYNAMICS
                                      with applications to
                               RIVERS AND TURBIDITY CURRENTS
                             REFERENCES FOR CHAPTER 32

Cazanacli, D., Paola, C. and Parker, G., 2002, Experimental steep, braided flow: application to
    flooding risk on fans, Journal of Hydraulic Engineering, 128(3), 1-9.
Gole, C. V. and Chitale, S. V., 1966, Inland delta building activity of the Kosi River, Journal of
    Hydraulic Engineering, ASCE, 92(2), 111-126.
Grover, N.C., and Howard, C.L., 1937, The passage of turbid water through Lake Mead,
    Transactions, American Society of Civil Engineers, 103, 720-732.
Kostic, S. and Parker, G., 2003a, Progradational sand-mud deltas in lakes and reservoirs. Part
    1. Theory and numerical modeling, Journal of Hydraulic Research, 41(2), 127-140.
Kostic, S. and Parker, G., 2003b, Progradational sand-mud deltas in lakes and reservoirs. Part
    2. Experiment and numerical simulation, Journal of Hydraulic Research, 41(2), 141-152
Pang, J. & Si, S., 1983, Fluvial Process of the Yellow River Estuary, Proceedings, International
    Symposium on River Sedimentation, Beijing, China, March 24-27, 1980, Guanghua Press,
    417-425 (in Chinese).
Fischetti, M., 2001, Drowning New Orleans, Scientific American, October.
Smith, N. D., McCarthy, T. S., Ellery, W. N., Merry, C. L. & Ruther, H., 1997, Avulsion and
    anastomosis in the panhandle region of the Okavango Fan, Botswana, Geomorphology, 20,
    49 – 65.
Sun, T., Paola, C., Parker, G. and Meakin, P., 2002, Fluvial fan-deltas: Linking channel processes
    with large-scale morphodynamics, Water Resources Research, 38(2),
    doi:10.1029/2001WR000284.

				
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