NRCEST 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) 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 transport q : sand source or sink D=Db (tidal variation)+Dc (closure depth)=total depth

5 GENESIS model longshore sediment transport Ozasa and Bramton, 1980: longshore gradient in wave height

6 GENESIS model Flow chart 1.Positions of some shorelines of different years 2.Setting parameters required 3.Model Calibration for K1 and K2 4.Prediction of futhure shoreline change

7 GENESIS model Example: I-Lan shoreline

8 GENESIS model Specified parameters Model Calibration

9 GENESIS model Model verification and prediction

10 Scales of modeling approach and users of GENESIS More than 1000

11 Discussion on GENESIS model JCR, 1997

12 Discussion on GENESIS model Limitations: 1.Inadequacy of data: waves 2.Closure depth 3.Permeability factor, transmission factors for detached breakwaters 4.Boundary conditions: later BC or end BC 5.Rigorous calibration and verifications: numbers of shorelines

13 Discussion on GENESIS model Restrictions 1.Predictive reliability 2.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 waves 5.Tools that can be misused and incorrect results are misinterpreted.

14 Discussion on GENESIS model Advices for users 1.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.

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

16 Modification on GENESIS model 1. Jetties and groins (sand bypassing and sand transmission)

17 Modification on GENESIS model 2. Detached breakwaters and Wave transmission (Kt)

Modification on GENESIS model 3. Cross-shore variation Shields Numbers

19 Modification on GENESIS model 4. Sediment transport by tidal (longshore)currents Bayram et al. (2006)

20 Modification on GENESIS model 5. Regional depth contour an open coast without structure or sources or sinks of sediment will 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.

21 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

22 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.

23 Recent study - I Four cross-shore profile models Ω : non-dimensional falling velocity (H/wT)

24 Recent study - I

25 Recent study - I

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

27 Recent study - I Calibration length vs. model hindcast for seasonally-dominated field

28 Recent study - I The design of coastal monitoring program must consider both the type of beach and the resources available.