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Interaction of submarine canyons with the longshore driftInvestigations of sediment bypassing rates at canyons
Researcher : Hesam SanaeeSupervisor : Prof. J. A. RoelvinkExternal Supervisor : Edwin Elias, PhD, MScMentor : Ali Dastgheib , PhD, MSc
WSE-HECEPD 2011-2013
Content of Presentation
Introduction Research objective Research methodology Model setup in 2DH Forcing Model Simulation Analysis of residual current Analysis of the long shore rates Conclusion and recommendations
IntroductionArea of Study
Santa Barbara Littoral Cell
IntroductionTidal Information
A diurnal tide with a strong semi-diurnal distortionDiurnal Range = 1.64m Tidal velocities < 5 cm/s
IntroductionWave Climate
Wave directions range from 105°N to 345°N, No waves coming from 345N or more, due to the sheltering of Point Conception
More than 70% of waves within dataset originated from the west/north-western (270 - 345)
Wave heights ranging from 0.5 - 8.0m and waves higher than 7 m occurs rarely
IntroductionProblem Statement
Several large canyons connect to the SBLC coastal system and(are assumed) to cause a loss of sediment from the coastal zone
For a sustainable coastal management, it is necessary to:
– Understand the sediment transports around canyons
Main objective
To determine the quantity of littoral drift bypassing the submarine canyons versus the amount captured by the canyon
What is the role of sediment delivery due to the littoral sediment transport? What are the dominant processes in driving the hydrodynamics and sediment transport?
Process-based model consist of the following tasks
1. Hydrodynamic modelling; how do flow patterns in a canyon look like? 2. Sediment transport modelling; how do the sediment transports over a canyon look like?3. How does the canyon modify the wave propagation patterns? 4. What are the littoral drift rates along the coast with and without presence of the
submarine canyons?
Research objectives
In order to answer the objective of this research study, the following procedures was performed
o Using a 2DH model of SBLC Extending the sediment budget analysis to the point Mugu Investigating the effect of the Hueneme and Mugu canyons on the littoral drift Investigating the different geometries with and without canyons
o On a 3D model of Mugu submarine canyon Investigating the hydrodynamic patterns and processes Compare the Z-model with Sigma-Model
Research methodology
Model setup in 2DHDelft3D-Wave Module• Low resolution wave grid 180km x 90km +
High resolution grid at nearshore• Cross-shore resolution of 1100m -550 m
(nearshore)• Longshore resolution is about 1100 m• In total 22,800 grid points (151 in both M
and N direction)
Delft3D-Flow Module• Higher resolution flow grid 130km x12km• Cross-shore resolution of 550m(seaward
boundary) to 30 m (nearshore)• Longshore resolution is about 600 m
(western boundary) to 60m (eastern boundary)
• In total 60,965 grid points (M=685, N=89) • Neumann boundaries at Cross-shore
boundaries in combination of water level in offshore boundary
• Hydrodynamic time step = 15 seconds
ForcingInput reduction of the hydrodynamic forcing
• Schematization of tide A morphological tide (HW-LW cycle)
1.1x the mean tide
Constituent Description Amplitude [m]
Angular frequency
[deg/hr]
M2 Principal lunar semi-diurnal const. 0.5163 28.993289
K1 Lunisolar diurnal const. 0.3704 14.496644
O1 Lunar diurnal const. 0.2404 14.496644
Morphological tidal constituents with their adjusted amplitude and angular frequency
ForcingInput reduction of the hydrodynamic forcing
• Schematization of wave climate • Wave buoys data
3 years of wave record
105-120 120-135 135-150 150-165 165-180 180-195 195-210 210-225 225-240 240-255 255-270 270-285 285-300 300-315 315-330 330-3450,00 - 1,50 0.00098 0.00218 0.00738 0.02668 0.05485 0.06596 0.00467 0.00314 0.00216 0.00195 0.00319 0.01514 0.02835 0.03914 0.00887 0.00011 0.261,50 - 2,00 0.00008 0.00021 0.00078 0.00128 0.00187 0.00232 0.00277 0.00165 0.00150 0.00186 0.00368 0.02188 0.05631 0.10207 0.02323 0.00035 0.222,00 - 2,50 0.00008 0.00008 0.00008 0.00018 0.00016 0.00026 0.00059 0.00035 0.00066 0.00074 0.00271 0.02023 0.06377 0.09758 0.02034 0.00003 0.212,50 - 3,00 0.00000 0.00000 0.00016 0.00029 0.00010 0.00026 0.00030 0.00018 0.00021 0.00035 0.00133 0.01168 0.04511 0.06465 0.01388 0.00002 0.143,00 - 3,50 0.00000 0.00000 0.00005 0.00005 0.00005 0.00006 0.00013 0.00010 0.00018 0.00013 0.00048 0.00632 0.02606 0.04104 0.00699 0.00005 0.083,50 - 4,00 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00002 0.00000 0.00000 0.00002 0.00022 0.00351 0.01305 0.02103 0.00407 0.00000 0.044,00 - 4,50 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00002 0.00000 0.00000 0.00155 0.00619 0.01148 0.00229 0.00000 0.024,50 - 5,00 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00003 0.00086 0.00277 0.00563 0.00102 0.00000 0.015,00 - 5,50 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00002 0.00038 0.00134 0.00250 0.00050 0.00000 0.005,50 - 6,00 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00026 0.00098 0.00190 0.00030 0.00000 0.006,00 - 6,50 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00006 0.00013 0.00040 0.00112 0.00019 0.00000 0.006,50 - 7,00 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00003 0.00032 0.00034 0.00006 0.00000 0.007,00 - 7,50 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00008 0.00014 0.00003 0.00000 0.00000 0.007,50 - 8,00 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00003 0.00003 0.00000 0.00000 0.00000 0.00
SUM 0.00 0.00 0.01 0.03 0.06 0.07 0.01 0.01 0.00 0.01 0.01 0.08 0.24 0.39 0.08 0.00 1.00
Mean Wave Hight Hs (m) Wave direction sector (degrees w.r.t. North)
Probability of Occurance (%)
SUM
ForcingInput reduction of the hydrodynamic forcing
• Schematization of wave climate • Wave classification (116 wave conditions)
ForcingInput reduction of the hydrodynamic forcing
• Schematization of wave climate • Reduction of wave climate
• Opti Methodselects an optimum subset of wave conditions that contributes more to the
mean total sediment transport, only trough a number of predefined transects
• Energy Fluxselects an optimum subset of wave conditions that has equal energy with the
total wave record
ForcingInput reduction of the hydrodynamic forcing
ForcingInput reduction of the hydrodynamic forcing
116 simulations with different wave conditions
Each simulation has a certain influence on the long shore transport
ForcingInput reduction of the hydrodynamic forcing
• Opti-Method
Reduction116 ---> 24
RMS error < 5%
WC Hs (m) Tp (s) Dir (°) Old Weight New Weight
South/South-eastern
4 0.95 14.22 159.28 0.0267 0.0359
5 0.94 14.36 173.71 0.0549 0.0959
19 1.68 10.34 144.53 0.0008 0.0011
6 0.92 14.38 187.89 0.0660 0.1134
24 1.7 15.04 217.84 0.0016 0.0007
West/Northwest
25 1.71 14.37 233.39 0.0015 0.0029
11 1.21 12.96 263.5 0.0032 0.0044
27 1.75 13.3 263.81 0.0037 0.0072
12 1.27 12.03 278.58 0.0151 0.0256
85 4.21 14.6 279.21 0.0016 0.0028
28 1.77 12.78 279.27 0.0219 0.0264
80 3.71 14.68 280.23 0.0035 0.0021
45 2.25 12.83 293.58 0.0638 0.1248
73 3.23 13.92 293.79 0.0261 0.0129
81 3.72 14.12 293.99 0.0130 0.0075
14 1.31 9.32 308.08 0.0391 0.0415
82 3.73 12.3 308.14 0.0210 0.0282
60 2.74 11.02 308.18 0.0646 0.0693
74 3.23 11.69 308.22 0.0410 0.0752
87 4.22 12.24 308.35 0.0115 0.0066
46 2.24 10.11 308.41 0.0976 0.1925
101 5.75 13.07 308.96 0.0019 0.0032
83 3.74 10.99 319.18 0.0041 0.0046
15 1.29 8.49 319.56 0.0089 0.0012
ForcingInput reduction of the hydrodynamic forcing
• Schematization of wave climate • Energy Flux
ForcingInput reduction of the hydrodynamic forcing
• Schematization of wave climate • Reduction of wave climate
• Energy flux
WC Hs (m) Tp (s) Dir (°) Occ (%) Total %
South/South-eastern
9 1.53 13.04 157.6 1.11
2 0.8 14.1 160.2 3.735 1.08 14.44 161.1 2.03
1 0.79 14.07 182 3.87
7 1.45 14.49 182 1.114 1.05 14.59 182.1 2.13
3 0.93 14.33 195.1 2.736 1.44 14.91 206.1 1.1
14 2.13 14.48 211.1 0.52 18.33
West/Northwest
8 1.49 13.38 255.8 1.1515 2.25 13.8 259.1 0.49
20 3.29 14.03 260.2 0.22
10 1.88 12.72 284.4 11.6922 4.23 14.75 285.5 1.99
16 2.86 13.91 285.6 4.63
17 2.97 13.33 297.6 4.4712 1.99 11.82 297.6 11.29
21 4.21 13.94 298 2.12
13 1.99 10.07 306.2 13.1719 3.04 11.75 306.2 4.86
23 4.35 12.7 306.4 2.19
24 4.39 11.74 315 2.3218 3 10.28 315.1 5.69
11 1.95 8.98 315.2 15.38 81.66
ForcingInput reduction of the hydrodynamic forcing
• The energy flux method resembles better percentage of the total target
24 wave cases from WEF are the reduced wave climate
Model simulationModel simulations was performed separately for each wave condition(24 wave conditions from selected wave cases) -On Deltares cluster
Delft3D = Version 5.01.00.2163
Run time = over one tidal cycle of 1490 minutes
Transport formula = Van Rijn 1993 by default
Bed updating = Turned off (maximum longshore transport)
Analysis of residual current
Residual current is determined by Fourier analysis of the velocity field
Accounting for both effect of tides and waves
Residual current results from the weighted average of the mean velocities of all 24 wave cases
Analysis of residual current Section 1
Analysis of residual currentSection 3
Analysis of the longshore ratesLongshore drift rates
Less than 10% error in annual dredging rates for two bench mark
Transect 12 Santa Barbara harbor
Transect 24 Ventura harborCanyons
Analysis of the longshore ratesIndividual wave case contribution to the annual sediment transport
Longshore sediment transport is a function of wave height and direction (according to the CERC formula)
Analysis of the longshore ratesLittoral drift rates along the coast with and without canyons
Analysis of the longshore ratesLittoral drift rates along the coast with and without canyons
Potential sediment lost to the canyons
? Canyons
Analysis of the longshore ratesIndividual wave case contribution to the annual sediment transport
With canyons
Southern Swells
Analysis of the longshore ratesLittoral drift rates along the coast without canyons
Wave case 4 ( Dir 182 degree)
Analysis of the longshore ratesLittoral drift rates along the coast without canyons
Wave case 4 ( Dir 182 degree)
Analysis of the longshore ratesLittoral drift rates along the coast without canyons
• Effect of each canyon
Conclusion The quantity of littoral drift bypassing the submarine canyons vs. the amount captured by the canyon
The dominant processes in driving the hydrodynamics and sediment transport• Dominant westerly swells induce a net increasing eastward sediment transport, except
upcoast of the Hueneme canyon due to coastline orientation and presence of the Hueneme canyon
• Southern waves drives the sediment transport westward and net sediment transport along the up coast of the canyons increases due to the refraction over the canyons
The role of sediment delivery due to the littoral sediment transport• The longshore sediment transport analysis estimates the potential lost to the canyons
Recommendations
• Using a real forces could validate the observed hydrodynamic data (in between two canyons)• The 3D Model of each canyons could resolve the sediment movement in the canyons
Thank you and
Questions ?