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

1. 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

2. 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.

3. 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

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

5. 100 km Fly Delta Satellite image from Google Earth Fly delta, at the outlet of the Fly River, which is a major sediment source for the Gulf of Papua.

6. Kikori delta 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

7. Modeling tidal discharges and channels 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 delta4. if the discharge is less than a critical value the channel is removed from the delta Delta channels Tidal discharge during flood

8. Model simulation

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

10. 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.

11. Simple model grid

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

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

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

15. 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).

16. Short-term sediment load scenarios

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

18. 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