NRCEST

Shoreline model - GENESIS

Chang Hsien Kuo

國立交通大學土木工程學系中華民國 102年 5月 16日

2

One-Line model

Shoreline change: 1-D (One-Line)

Constant shape: (Dean Profile)

Bathymetric change: 2-D

3

One-Line model

Hanson and Kraus (1989) – Generalized model for simulating shoreline change, GENESIS

Variation of longshore sediment transport Constant beach profile

4

One-Line model

Hanson and Kraus (1989) – Generalized model for simulating shoreline change, GENESIS

Q(x) : longshore sediment transportq : sand source or sink

D=Db (tidal variation)+Dc (closure depth)=total depth

5

GENESIS model

longshore sediment transport

SPM (1984), W:Numerical factor

Ozasa and Bramton, 1980: longshore gradient in wave height

~0.5 >>

breaking waves predicted

6

GENESIS model

Flow chart1. Positions of some shorelines of

different years2. Setting parameters required3. Model Calibration for K1 and K2 4. Prediction of futhure shoreline

change

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GENESIS model

Example: I-Lan shoreline

12 3 4

5

新城溪

利澤突堤

清水護岸

永鎮

蘭陽溪大福

竹安溪

烏石港

外澳

蔀後

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GENESIS model

GENESIS模式參數 參數值

時間間格 t （hr） 1

灘線間格 x （m） 50

終端水深 CD （m） 4.4

漂砂至陸側最大高程 BD （m） 3

底床有效粒徑 10D (mm) 0.13

Specified parameters

0.99910.9991

0.99920.9992

0.9993

0.99

93

0.99

940.

9994

0.99

950.

9995

0.99

96

0.9996

0.99

97

0.9997

K1

K2

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.9991

0.9992

0.9993

0.9994

0.9995

0.9996

Model Calibration

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GENESIS model

Model verification and prediction

0 0.5 1 1.5 2 2.5 3

x 104

0

2500

5000

7500

10000

Longshore Distance(m)

Offs

hor

e D

ista

nce

(m)

2012四月光達實測資料2012 GENESIS四月 模擬結果

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Scales of modeling approach and users of GENESIS

More than 1000

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Discussion on GENESIS model

JCR, 1997

1. Offshore waves: regular wave or observed/calculated waves , H(t), T(t), θ(t)

2. Engineering Structures and activities Ex: Beach profile; Gated boundary of structures : tip of the structure

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Discussion on GENESIS model

Limitations:1. Inadequacy of data: waves2. Closure depth3. Permeability factor, transmission factors for detached

breakwaters4. Boundary conditions: later BC or end BC5. Rigorous calibration and verifications: numbers of

shorelines

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Discussion on GENESIS model

Restrictions1. Predictive reliability2. Not applicable to simulating randomly fluctuating beach

(e.g. Strom-induced cross-shore sediment)3. Experience (trained individuals): complexity of beach

processes. 4. Potential errors also are involved in the hindcast of

incident waves5. Tools that can be misused and incorrect results are misinterpreted.

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Discussion on GENESIS model

Advices for users1. It should be kept in mind that the assumptions are

idealizations of complex processes and therefore have limitations

2. In light of profound variability of coastal processes, it is clear that a single answer obtained with a deterministic simulation model must be viewed as a represnetative result that has smoothed over a large number of unknown and highly variable conditions.

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Modification on GENESIS model

This paper reviews the 25-plus year history of significant developments of the GENESIS shoreline response model

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Modification on GENESIS model

1. Jetties and groins (sand bypassing and sand transmission)

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Modification on GENESIS model

2. Detached breakwaters and Wave transmission (Kt)

Modification on GENESIS model

3. Cross-shore variation

Shields Numbers

: Nondimenional falling velocity

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Modification on GENESIS model

4. Sediment transport by tidal (longshore)currents

Bayram et al. (2006)

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Modification on GENESIS model

5. Regional depth contour an open coast without structure or sources or sinks of sedimentwill evolve to a straight line if a standard shoreline response model is run a sufficiently long time. This limitation can be remedied by specifying a fixed representative contour which is appended to the feed-back contour associated with local changes in the shoreline.

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Modification on GENESIS model

6. Interaction between beach berm and dune

Davidson-Arnott et al. (2005): sand transport to the dune is related to the width of the berm up to some distance over which equlibrium conditions have developed between the wind and the sand surface.

Larson (2004): The erosion rate due to dune impacted by waves’ run-up

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Recent study - I

The ability to robustly predict future shoreline position under the influence of changing waves and sea-level rise is a key challenge to scientists and engineers alike. This contribution outlines from 1 to 10 years at wo distinct beach types: a storm-dominant site and the second exhibiting a large seasonal variability.

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Recent study - I

Four cross-shore profile models

Ω : non-dimensional falling velocity (H/wT)

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Recent study - I

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Recent study - I

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Recent study - I Impact of temporal sampling (dt:day) < 30days

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Recent study - I

Calibration length vs. model hindcast for seasonally-dominated field

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Recent study - I

The design of coastal monitoring program must consider both the type of beach and the resources available.