MARGINSWS sept2006

Slide1: 

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: 

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: 

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

Slide4: 

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

Fly Delta: 

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

Slide6: 

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

Slide7: 

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

Slide8: 

Model simulation

Slide9: 

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: 

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: 

Simple model grid

Impact of tides on flow velocity: 

Impact of tides on flow velocity Constant flow velocity under ‘no tide’ scenario Continually changing flow velocity under ‘3m tide’ scenario

Impact of tides on suspended sediment transport: 

Impact of tides on suspended sediment transport More distinct delta plume in fluvial-dominated delta 2 to 3 channels are active sediment conduits under tide-dominated regine

Impact of tides on sedimentation: 

Impact of tides on sedimentation More elongated delta distributaries 2 channels remain active Mouth bar sedimentation

Human-induced change and extreme climatic events: 

Human-induced change and extreme climatic events 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).

Short-term sediment load scenarios: 

Short-term sediment load scenarios

Human impact on sedimentation: 

Human impact on sedimentation More erosion and scouring Evident: order of magnitude more sedimentation and progradation

Future Plans : 

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