TA2910 05 - Delta Coasts

8/10/2019 TA2910 05 - Delta Coasts

http://slidepdf.com/reader/full/ta2910-05-delta-coasts 1/49

Challenge the future

DelftUniversity ofTechnology

M.E. Donselaar

Delta deposits

8/10/2019 TA2910 05 - Delta Coasts

Sedimentary environments

• Continental: fluvial (braided, meandering)

aeolian

lacustrine

• Coastal: deltaslinear (clastic, carbonate)

• Marine: shelf

deep marine sands

pelagic

8/10/2019 TA2910 05 - Delta Coasts

Subdivision coasts

• Dominant sediment type:

- Clastic coasts

- Carbonate coasts

8/10/2019 TA2910 05 - Delta Coasts

Clastic coasts: Morphology

• Linear coasts

Nile deltaBarrier island - Alabama

• Delta coasts

http://www.geosci.unc.edu/faculty/glazner/Images/Coastlines/BarrierIslands/BogueBanks.jpg

8/10/2019 TA2910 05 - Delta Coasts

Delta evolution - 2

• Deposition bed load

sediment at river mouth:

mouth bars

• Mouth bars form obstacle

• River is forced to take

another course: Change of

river bed

• Suspension load spreads farout into sea

Dr. John Anderson Georgia Perimeter College, Dunwoody Campus

8/10/2019 TA2910 05 - Delta Coasts

Delta evolution - 3

• Continued supply of sediment

to river mouth creates delta

platform

• Delta expands seaward over

its delta platformdelta slope

pro-delta

delta platform

coastal plain

The Open University (1989)

8/10/2019 TA2910 05 - Delta Coasts

Delta morphology

• River dominated deltas

• Wave dominated deltas

• Tide dominated deltas

8/10/2019 TA2910 05 - Delta Coasts

Relation delta morphology - processes

8/10/2019 TA2910 05 - Delta Coasts

River dominated deltas

• Delta protrudes far into the

marine basin

• Weak tidal and wave action,

hence:

• Delta sediment is not re-

transported and

• Delta shape not modified

Mississippi delta

http://cass.jsc.nasa.gov/images/soce/soce_S29.gif

8/10/2019 TA2910 05 - Delta Coasts

Wave dominated deltas - 1

• Along-shore transport by wave-

generated currents of sediment

that reaches the delta mouth:

• Formation of spits on both

• Asymmetrical spits caused by

oblique approach of waves

(arrows)

• Delta protrudes into marinebasin

Ebro delta

8/10/2019 TA2910 05 - Delta Coasts

Wave dominated deltas - 2

• Waves transport delta

sediment laterally away from

distributary mouth

• Sediment deposited as beach

ridge complexes• Delta grows seaward by beach

ridge accretion

Wave-dominated Grijalva delta, Mexico

8/10/2019 TA2910 05 - Delta Coasts

Tide dominated deltas

• Strong tidal currents are

oriented perpendicular to the

coast and redistribute the

sediment

• Delta distributary channelsoriented parallel to each other

and perpendicular to the coast

• Delta does not protrude into

marine basin

http://www.escati.com/seasia_hi-def.htm

Irrawaddy river, Bay of Bengal

8/10/2019 TA2910 05 - Delta Coasts

Delta sub-environments - 1

distributarychannels

interdistributarybays

8/10/2019 TA2910 05 - Delta Coasts

Delta sub-environments - 2

interdistributarybay

crevasse splay

distributary channel

8/10/2019 TA2910 05 - Delta Coasts

Water density & sedimentation

• Depends on densities of river and sea water:

- Hypopycnal flow: density of river water < density of seawater

- Hyperpycnal flow: density of river water > density of seawater

- Homopycnal flow: density of river water = density of seawater

8/10/2019 TA2910 05 - Delta Coasts

• Water with lower density forms wedge overlying water withhigher density

• Boundary: turbulence and mixing of water, hence:

• Energy loss and sedimentation

http://www.ozestuaries.org/indicators/In_turbidity_f.html

8/10/2019 TA2910 05 - Delta Coasts

Hypopycnal flow - 1

Density of river water < density of sea water

8/10/2019 TA2910 05 - Delta Coasts

Hypopycnal flow - 2

8/10/2019 TA2910 05 - Delta Coasts

Hypopycnal flow – 3: sedimentation

• In sub-aqueous levees formed at the side of the jet, wherespeeds are slowed by mixing

• in a distributary mouth bar, where a combination ofspreading and mixing reduce speed and competence

• Finer sediment is carried farther out and is deposited fromsuspension. It may be carried and distributed by offshorecurrents and is eventually deposited as prodelta muds. Thisresults in lower depositional slopes and more extensivedeposits

8/10/2019 TA2910 05 - Delta Coasts

Hyperpycnal flow - 1

Density of river water > density of sea waterForming of turbidity currents common. Mainly concerns small rivers

with a high sediment load during peak run-off

8/10/2019 TA2910 05 - Delta Coasts

Hyperpycnal flow - 2

• Where the river inflow is more dense than the basinal water(e.g., due to sediment concentration), sediment movesalong the base of the basin. It is usually deposited quiterapidly, but the finer portions may move farther as

sediment gravity (turbidity) flows. These are generallyassociated with coarser sediment loads, and resulting deltasare small, elongate and generally steeply dipping

8/10/2019 TA2910 05 - Delta Coasts

Homopycnal flow - 1

Density of river water = density of sea (or lake) water

Rapid mixture of two water types, and formation of Gilbert-type

deltas. Mainly concerns rivers that end in lakes with a low salinity

8/10/2019 TA2910 05 - Delta Coasts

Homopycnal flow - 2

8/10/2019 TA2910 05 - Delta Coasts

Delta shape in cross-section

Selley (1985)

normal to coast

parallel to coast

8/10/2019 TA2910 05 - Delta Coasts

Sedimentary sequences

• Seaward progradation of

delta:

• Delta platform deposits

gradually cover delta slope

and pro-delta deposits

• Coarsening upward successiondelta slope

pro-delta

delta platform

coastal plain

8/10/2019 TA2910 05 - Delta Coasts

Sequences - 1

• Vertical sequence varies with

location in the delta

environment

• Vertical sequence varies with

delta type (river-, wave- ortide-dominated)

Selley (1985)

8/10/2019 TA2910 05 - Delta Coasts

• Log response also varieswith location in the delta

Coleman & Prior (1982)

Sequences - 2

8/10/2019 TA2910 05 - Delta Coasts

Prograding delta succession

8/10/2019 TA2910 05 - Delta Coasts

Delta switching - 1

• Delta sediments build positive relief

• Sediment stack forms obstacle

• Entire delta switches to new position by upstream avulsion

• Accommodation increase in time: delta may return to(subsided) former position, hence:

• Autocyclic sequences

8/10/2019 TA2910 05 - Delta Coasts

Delta switching - 2

• Example: Mississippi delta

switching from positions 1-7

• Total time: 5000 y

http://www.utdallas.edu/research/fyi/060106/images/figure1.jpg

8/10/2019 TA2910 05 - Delta Coasts

Compulsory reading

• Nichols - Chapter 12:

• Sections 12.1 – 12.3

• Sections 12.4.5 – 12.4.7

Sections 12.5 – 12.7

TA2910 05 - Delta Coasts

Documents

Transcript of TA2910 05 - Delta Coasts

FifthGlobalConferenceonOceans,Coasts,andIslands ... · FifthGlobalConferenceonOceans,Coasts,andIslands GLOBALOCEANSCONFERENCE2 010 ENSURINGSURVIVAL,PRESERVINGLIFE,IMPROVINGGOVERNANCE

Coasts : Flooding Coasts / Causes and Consequences of Rising Sea Levels

Coasts in Crisis - University of Mississippi · Coasts in Crisis, Types of Coasts Types of Coasts Coasts are the dynamic junction of water, air, and land. Winds and waves, tides and

Coasts Part1

Tectonic Classification of Coasts Tectonic effects on coastal …fbuon/PGEOG_334/Lecture... · 2007-02-06 · 2. Trailing Edge Coasts Neo-trailing edge coasts Afro-trailing edge coasts

Coasts 2 Features

tgaw, coasts, exam

Coasts Intro Test

Coasts Intro Homework

Estuaries and Coasts

TA2910 08 - Shelf Sediments

COASTS. Theme Overview COASTS COASTAL PROCESSES COASTAL LANDFORMS COASTAL MANAGEMENT.

Primary Coasts Young coasts Terrestrial influences dominate Types –Land erosional coasts –Built out by land processes –Fault Coasts.

Coasts Introduction

Coasts revision booklet

TA2910 03 - Aeolian Sediments

Lithosphere Coasts

Crowded Coasts

Coasts – Human Activities

primary coasts