Tidal Landforms in the Gulf of Papua:Sediment Transport and Morphology

Sergio Fagherazzi1, Irina Overeem2

Department of Geological Sciences, Florida State University

INSTAAR, University of Colorado

Outline

• Objective within S2S

• Simple approach to modeling tidal velocities and tidal channel morphology.

• Short-term modeling to identify sedimentation patterns in a tide-dominated delta.

• Short-term modeling to asses sediment storage in the tide-dominated delta system.

• Future plans.

Objective

Develop a simple routine for an existing stratigraphical 3D model (SedFlux3D) to model tide-dominated delta evolution.

The Fly Delta was a missing link: predict storage of sediment in the deltaic part of the sedimentary system

Different tidal deltas are present along the Gulf of Papua, with a fan-like shape or dendritic distributaries

Gulf of Papua

100 km

Fly Delta

Fly delta, at the outlet of the Fly River, which is a major sediment source for the Gulf of Papua.

Satellite image from Google Earth

The Kikori delta represents an end member of tidal deltas, with the tidal component much stronger than the

fluvial one

The delta channels are in competition for the river discharge and the tidal prism. At the same time the channels contribute to the total tidal prism.

Tidal fluxes flush the channels preventing infilling and creating tidal loops that are characteristic of

tidal deltas

Kikori delta

Delta channels Tidal discharge during flood

Our simplified model consists of four steps:

1. the original channel is built in the domain.

2. a new channel, created by avulsion, is added to the network (in this simplified version the new path is randomly chosen)

3. The tidal discharge is calculated for the entire delta

4. if the discharge is less than a critical value the channel is removed from the delta

Modeling tidal discharges and channels

Model simulation

Fly delta:The same mechanism is regulating the fine structure of the tidal network in the islands and nearby coastal plains

Short-term Delft3D modeling

• Physics-based hydraulic and morphological modeling developed at Delft Hydraulics

• Input data: • Bathymetry, tidal measurements, sediment

discharge, river discharge

• For this project: Flow module• Main assumption: Wave influence neglible• Simulation Time: max. 1 year, dt = 5 min.

Simple model grid

Impact of tides on flow velocity

Constant flow velocityunder ‘no tide’ scenario

Continually changing flow velocityunder ‘3m tide’ scenario

Impact of tides on suspended sediment transport

More distinct delta plumein fluvial-dominated delta

2 to 3 channels are active sediment conduits under tide-dominated regine

Impact of tides on sedimentation

More elongateddelta distributaries

2 channels remain active

Mouth bar sedimentation

Human-induced change and extreme climatic events

Human impact on sediment flux of the Fly River, PNG

8

115

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20

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60

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Qs Pre-human Qs modern day

mln

to

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discharge of Fly River, PNG

0500

100015002000250030003500400045005000

mean year El Nino' march97-jan98

dis

char

ge

in m

3/se

c

Sediment load +1400% ?

Mining and deforestation in the upstream drainage area of the Fly River is thought to have 14 times increased the sediment flux (Syvitski et al., 2005).

Water discharge -400%

El Nino of March 1997-Jan 1998 caused decrease of cloud cover and extreme drought, discharge of the Fly is thought to have been 4 times reduced (Glantz et al., 2000).

Scenario

Sediment load (kg/m3)

River discharge(m3/s)

Remarks

Sand Clay

A 0.0058 0.058 1500 “Pre-human”(Syvitski, 2005)

B 0.083 0.083 1500 “Modern”(Syvitski, 2005)

Short-term sediment load scenarios

Human impact on sedimentation

More erosion and scouring

Evident: order of magnitude more sedimentation and progradation

Future Plans

• Integrate simplified tidal discharge model into SedFlux3D by using parametrizations for erosion and sedimentation derived from short-term experiments with Delft3D.

• Use real-world data to further constrain the model experiments: bathymetry, sediment load, sedimentation rates are on shopping list, modeling river flux with HydroTrend otherwise.

Avulsions of channels driven by tidal dynamics

Scouring of abandoned channels