SURA Super-Regional Testbed on Coastal Inundation – Tropical Storm Harry V. Wang, Derek Loftis, Yi-cheng Teng and Yanqiu Meng Virginia Institute of Marine Science The College of William & Mary Greate Road, Gloucester Point, VA SURA super-regional testbed on coastal inundation

Outline 1.SELFE model 2.Analysis Tides Results for V2.0 Spin-up time effect 2D results 3D results 3. Preliminary results for storm surge during Hurricane Ike

- SELFE (Semi-Implicit, Eulerian Lagrangian, Finite Element) - SELFE (Semi-Implicit, Eulerian Lagrangian, Finite Element) Unstructured mesh (w or w/o orthogonal), no Unstructured mesh (w or w/o orthogonal), no coordinate transformations in x-, y-, or z-directions coordinate transformations in x-, y-, or z-directions Stable and robust semi-implicit, finite-difference/ finite- volume/ finite element methods Stable and robust semi-implicit, finite-difference/ finite- volume/ finite element methods Efficient computational algorithms (semi-Lagrangian advection scheme); time step: 3 minute, used for 30 m resolution grid Efficient computational algorithms (semi-Lagrangian advection scheme); time step: 3 minute, used for 30 m resolution grid Capable of simulating flooding using semi-implicitCapable of simulating flooding using semi-implicit wetting-and-drying scheme wetting-and-drying scheme The unstructured grid model using semi-implicit semi-Lagragian schemes The unstructured grid model using semi-implicit, semi-Lagragian schemes Reference: Reference: 1. An advanced piecewise-linear iterative solver recently developed (2008) by Brugnano and Casulli, 1. An advanced piecewise-linear iterative solver recently developed (2008) by Brugnano and Casulli, SIAM, J. Sci. Comp. Vol. 30, No. 1, pp SIAM, J. Sci. Comp. Vol. 30, No. 1, pp A high-resolution wetting and drying algorithm for free-surface hydrodynamics (2009) by Vincenzo 2. A high-resolution wetting and drying algorithm for free-surface hydrodynamics (2009) by Vincenzo Casulli, Int. J. Numer. Meth. Fluids 2009; 60:391–408 Casulli, Int. J. Numer. Meth. Fluids 2009; 60:391–408

I. Results Analyses Plan for the Inundation Testbed v2.0 - Tropical Domain Tides: Datum adjustment = m Forcing: 8 constituents (M2, N2, S2, K2, O1, K1, P1, Q1) provided by UND Runs: (METADATA TEMPLATE INCLUDED) 1. 2D spatially varying Mannings n provided by UND 2. 3D run, 11 vertical layers, bottom friction using z0 from UND Mannings n to z0 conversion 3. 3D run, 11 vertical layers, bottom friction using z0=0.01m Analysis: amplitude, phase for 10 constituents (forcing + M4, M6) Skill: table & summary graphs of model vs observed using 6 metrics for 59 stations Model Model Comparisons table and summary graphs from skill assessment

Set Up for 2D and 3D mode SELFE model Model domains: Gulf of Mexico, a domain with nodes and elements Tidal boundary conditions: M2, K1, O1, S2, N2, K2, Q1, P1 provided by UND Time step = 180 s, total run time = 75 days (spin up for 15 days plus 30 days to reach steady state) The equilibrium tidal potential was included For 2D, Spacial varying Manning n was used (provided by UND). For 3D, Vertical 11 S-layers were used; constant Z 0 equals 0.01 m and spacial varying roughness height derived from manning coefficient** were used. Tidal constituents were generated for 59 stations and the statistics for modeled tidal constituents compared with observation were generated. ** Bretschneider C.L., H. J. Krock, E. Nakazaki, and F.M. Casciano ( 1986): Roughness of typical Hawaiian Terrain for Tsunami run-up calculations. J.K.K. Look report, University of Hawaii, Honolulu.

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The effect of spin-up (for 30 days versus for 75 days) on tidal constituents

The effect of 2D spatial varying n, 3D fixed z0, and 3D spatial varying z0

Hurricane Ike: Datum + sterric adjustment = m Forcing: gridded Ike wind / pressure fields & 8 constituent tidal BCs provided by UND – Runs: 1. 2D no waves, spatially varying Mannings n provided by UND 2. 3D no waves, 11 vertical layers, bottom friction using z0 from UND Mannings n to z0 conversion 3. 3D no waves, 26 vertical layers, bottom friction depend on sediment stratification Analyses: model elevation time series at 218 stations provided by UND, currently hydrographs from 169 stations are on the SURA server in IMEDS format, still performing QA / QC on this data. II. Results Analyses Plan (Con ’ t)

The Use of Gulf of Mexico and Atlantic model domain for storm surge 1. Forcing field: wind (OWI+ H*wind) and pressure field (provided by UND) 2. Eddy viscosity: calculated by 2 nd order closure and the empirical wave mixing 3. Note: SELFE obtain erroneous results using Gulf of Mexico-only domain with the tidal boundary condition at Florida and Yucatan Straits. The boundary condition was forced at the Atlantic coast with 6 tidal constituents

Effect of Suspended Sediment Stratification on Bottom Boundary Layer

3d with Flux Rif 3d with fixed z0 3d with Flux Rif 3d with fixed z0 3d with Flux Rif 3d with fixed z0

Lower Cd allows larger Ekman transport both in terms of velocity magnitude and the veering angle Higher Cd induced smaller Ekman transport z z Amerada Pass

Lesson learned Tidal time series and constituent comparisons were conducted for 59 stations in the Gulf of Mexico domain. Sufficient spin up is needed in order to be free from inertia wave. Overall, the skill assessment of the model results are reasonable; M2 tide is good, less satisfactory for O1. 2D and 3D tidal results yield similar results. For simulating Hurricane Ike, preliminary results showed that the model is much more sensitivity to the bottom friction parameter with wind forcing. A 3D test was conducted to consider sediment stratification effect (Adams and Weatherly, 1981). It was shown that reduction of bottom friction due to sediment stratification can yield results for fore-runner via cross-shore Ekman transport.