5 th Delft3D-OSS webinar Large scale long-term coastline modelling Using UNIBEST and Delft3D 14 March 2012
Aims Basic information on CL-models Model setup Trigger discussion > Delft3D = open source > UNIBEST = commercial software
Contents Introduction Theory Schematization Application > Delft3D & UNIBEST > Case Discussion
Introduction Why use it? Coastline model - Spatial scale (1-1000km) - Time scale (years to centuries) > Large spatial scales > Long term > Fast! > Robustness > Understanding (isolate wave-driven longshore transport) Delft3D model - Spatial scale (1-50km) - Time scale (days to years) Resolving effects of wave-driven currents!
Introduction Where to apply? What is it used for? > Uniform coasts > Long-term trends E.g. bar behaviour and dune erosion not resolved > Wave dominated > Nearshore zone Channels Shoals Wave driven currents
Theory How? 1. Represent the coast as a line 2. Transport along the coast dq No cross-shore transport l AQl Ql x t dx Cause : obliquely incoming waves alongshore transport gradients: dq eq.1: l V Ql ( Ql x) t dx Q l Q l Q l Erosion volume (V)
Theory How? 3. Profile shape is fixed Full profile moves instantaneously Profile change: eq.2: V xy h p dy dy h p
Theory How? 4. Coastline variation in time 5. Qs = f (Coastangle) Y dq t h dx 1 l p Coastline change: Transport: eq.3: Y dq t h dx 1 l p eq.4: dy Ql Ql,0 f dx
Theory How? 4. Coastline variation in time 5. Qs = f (Coastangle) Y dq 6. Diffusive behaviour t hp dx (Low angle waves) 1 l Coastline change: eq.5: y y Q 2 l K with K f 2 t x h p
Theory What? LT : Longshore sediment transport dy Ql Ql,0 f dx Wave data (shoals, islands, harbour moles) Profile + sediment characteristics Longshore currents (wind, tide & wave generated) CL : Coastline evolution Initial coastline 2 l K with K f 2 t x h p Type of coastline (sand, rock, availability of sand) Structures (breakwaters, groynes, revetments) Sources or Sinks (Rivers, estuaries, access channels) y y Q
Theory What? LT : Longshore sediment transport Wave data (shoals, islands, harbour moles) Qs = f (coast angle) Profile + sediment characteristics Longshore currents (wind, tide & wave generated) CL : Coastline evolution Initial coastline Type of coastline (sand, rock, availability of sand) Structures (breakwaters, groynes, revetments) dy Ql Ql,0 f dx 2 l K with K f 2 t x h p Sources or Sinks (Rivers, estuaries, access channels) y Coastline model y Q
Schematization Coastline definition Sediment transport (cross-shore rays) Environmental conditions Structures & nourishments Remarks!
Lausman et al., 2009 Large scale long-term coastline modeling Coastline definition > Parabolic Bay Shape Equation (PBSE) Headland Bay Beaches Static equilibrium Hsu et al. (2010)
Coastline definition > Cartesian based coastline models Not suitable for very curved coastlines Cross-shore coordinate (m) modified from Hsu et al. (2010) Longshore coordinate (m)
Coastline definition > Curvilinear coastline (UNIBEST) Defined by x,y coordinates and distance from coastline Possibility of a discontinues coastline Cross-shore distance x,y coordinates Coastline Reference line
Qs Sediment transport (rays) > Compute sediment transport every timestep > Use relation between sediment transport and coastangle Only an initial computation of sediment transport : Allows use of complex formulations! e.g. transport formulations like Bijker & Van Rijn 2004 and wave-current interaction models Qs Qs Qs Qs Coastline Qs Reference line
Sediment transport (rays) > Summed transport for each wave condition Bottom Profile Wave Height Longshore current Longshore Transport Wave Climate S L N waves i S L, i
Sediment transport (rays) > Qs=f() -> Lookup table for multiple orientations! S L (m 3 /yr) Equilibrium orientation Current coastline orientation Coastline orientation ( ) S c e 1 e c 2 2 e
Sediment transport (rays) > Application of : Qs=f(dy/dt) y (m) Waves Coastline Groyne Lookup table (S-Phi curve)
Sediment transport (rays) > Spatially non-uniform wave climate loc1 S1 loc2 S2 S1 S2 loc1 loc2
Sediment transport (rays) > Changes in time S1 S2 S1 S2 S1
Environmental conditions > Wave & Tide schematization > Location of offshore point > Temporal variation Structures & nourishments > Revetments > Groynes > Rivers > Nourishments
Remarks! > Profile moves instantaneously What part of the profile moves? Related to time scale Related to changes (erosion or sedimentation) > Sediment load in equilibrium Not the case if there are rocks Not suitable for cohesive sediments (settling lags) > Instant pick up of sediment Longshore current needs time and space to speed up! Suffices for larger spatial scales > Account for cross-shore losses! > Diffusive model approach Implicit assumption of dominance of low angle waves
Delft3D & UNIBEST Data OpenDAP / OpenEarth -> Bathymetrical data Get bathymetry data
Delft3D & UNIBEST Data OpenDAP / OpenEarth -> Bathymetrical data Google Earth -> Landboundary Conversion of KML to XY
Delft3D & UNIBEST Data OpenDAP / OpenEarth -> Bathymetrical data Google Earth -> Landboundary Wave bouys -> Wave climate (ORCA)
Delft3D & UNIBEST Data OpenDAP / OpenEarth -> Bathymetrical data Google Earth -> Landboundary Wave bouys -> Wave climate (ORCA) Delft3D-waves Grid + bathymetry Transform to nearshore
Delft3D & UNIBEST Data OpenDAP / OpenEarth -> Bathymetrical data Google Earth -> Landboundary Wave bouys -> Wave climate (ORCA) Delft3D-waves Grid + bathymetry Transform to nearshore Local climate UNIBEST Coastline definition Profiles Sediment transport comp s Structures
Delft3D & UNIBEST Data OpenDAP / OpenEarth -> Bathymetrical data Google Earth -> Landboundary Wave bouys -> Wave climate (ORCA) Delft3D-waves Grid + bathymetry Transform to nearshore Local climate UNIBEST Coastline definition Profiles Sediment transport rays Structures Post process
Case Lets give it a try!
Discussion Questions? Future of coastline models? Your applications? Suggestions
Next webinars: 11 th april 2012 : OpenDA by Martin Verlaan 9 th may 2012 : Delft Dashboard by Maarten van Ormondt 13 th june 2012 : Hurricane and tsunami modelling by Deepak Vatvani