dsd-int 2015 - uniqueness and generality of delta morphologoy - liang li

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Uniqueness and generality of

delta morphology The effect of initial bathymetry perturbations on long-

term morphological modeling

Liang Li Helena van der Vegt Joep Storms Dirkjan Walstra

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Introduction Validity of Process-based long-term

models

Long-term: Unknown initial and boundary conditions

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Introduction Uncertainties

1. Model assessment

2. Sensitivity analysis

3. Geometry population

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Introduction Objective

1. Develop a series of indicators for Delft3d models to calculate the geometry of the morphological patterns.

2. Quantify the effect initial bathymetry perturbations on the delta morphology

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Indicators Why

Ombrone system, Italy Frontera system, Tabasco, Mexico

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Indicators Compare delta morphologies

Point-wise metric Pattern

recognition Short time scale

Long time scale

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Indictors List

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Indictors Channel network, delta plain geometry

Delta plain Channel network

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Model setup Model grid and bathymetry

Model parameters Value Unit

Manning 0.03 1

3s m

Sand diameter 0.00025 m

Sand dry density 1600 3kg m

Clay falling velocity 0.0015 1ms

Clay dry density 500 3kg m

Critical shear stress for clay erosion 0.5 2N m

Morphological acceleration factor 30 [ - ]

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Model setup Initial bathymetry perturbations

1. 1cm perturbations 2. 1000 m3 river discharge 3. 1 m wave height 4. 1 m tidal amplitude

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Morphology Initial bathymetry noise

Unperturbed

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Results Delta plain

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Mean

b 0.16%

c -0.22%

d 0.13%

Mean

b 0.2%

c 2.6%

d 2.7%

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Results Channel networks

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Mean

B 5%

C 7%

D 7.6%

Mean

B 24%

C 33%

D 24%

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Conclusions(1)

1. The difference induced by small perturbations does not increase in time.

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Conclusions(2)

1. The uncertainty range induced by small perturbations varies for different scale of indicators. 1. Small: delta plain 2. Large: channel network