Oct 05

Publication | Terrain-driven unstructured mesh development through semi-automatic vertical feature extraction

AWR_Figure2

M.V. Bilskie, D. Coggin, S.C. Hagen, S.C. Medeiros (2015). “Terrain-driven unstructured mesh development through semi-automatic vertical feature extraction.” Adv. Water Resources, doi:10.1016/j.advwatres.2015.09.020

Abstract: A semi-automated vertical feature terrain extraction algorithm is described and applied to a two-dimensional, depth-integrated, shallow water equation inundation model. The extracted features describe what are commonly sub-mesh scale elevation details (ridge and valleys), which may be ignored in standard practice because adequate mesh resolution cannot be afforded. The extraction algorithm is semi-automated, requires minimal human intervention, and is reproducible. A lidar-derived Digital Elevation Model (DEM) of coastal Mississippi and Alabama serves as the source data for the vertical feature extraction. Unstructured mesh nodes and element edges are aligned to the vertical features and an interpolation algorithm aimed at minimizing topographic elevation error assigns elevations to mesh nodes via the DEM. The end result is a mesh that accurately represents the bare earth surface as derived from lidar with element resolution in the floodplain ranging from 15 m to 200 m. To examine the influence of the inclusion of vertical features on overland flooding, two additional meshes were developed, one without crest elevations of the features and another with vertical features withheld. All three meshes were incorporated into a SWAN+ADCIRC model simulation of Hurricane Katrina. Each of the three models resulted in similar validation statistics when compared to observed time-series water levels at gages and post-storm collected high water marks. Simulated water level peaks yielded an R2 of 0.97 and upper and lower 95% confidence interval of ∼ ± 0.60 m. From the validation at the gages and HWM locations, it was not clear which of the three model experiments performed best in terms of accuracy. Examination of inundation extent among the three model results were compared to debris lines derived from NOAA post-event aerial imagery, and the mesh including vertical features showed higher accuracy. The comparison of model results to debris lines demonstrates that additional validation techniques are necessary for state-of-the-art flood inundation models. In addition, the semi-automated, unstructured mesh generation process presented herein increases the overall accuracy of simulated storm surge across the floodplain without reliance on hand digitization or sacrificing computational cost.

Permanent link to this article: http://www.mattbilskie.com/publication-terrain-driven-unstructured-mesh-development-through-semi-automatic-vertical-feature-extraction/

Jul 13

Presentation | University of Cambridge

MOM_Compare_MSAL

M.V. Bilskie, S.C. Hagen, K. Alizad, S.C. Medeiros, D.L. Passeri, J.L. Irish, & N. Plant, “Assessment of coastal flood risk in a changing climate.” University of Cambridge, Cambridge, UK, July 9, 2015

Last week, I had the opportunity to give a talk at the University of Cambridge to the Cambridge Coastal Research Unit (CCRU). Much thanks to Anna for organizing the event!

Abstract: Coastal regions around the world are susceptible to a variety of natural disasters causing extreme inundation. It is anticipated that the vulnerability of coastal cities will increase due to the effects of climate change, and in particular sea level rise (SLR). A novel framework has been developed to construct a physics-based storm surge model that includes projections of coastal floodplain dynamics under climate change scenarios. Numerous experiments were conducted and it was concluded that a number of influencing factors, other than SLR, should be included in future assessments of coastal flooding under climate change; e.g., shoreline changes, barrier island morphology, salt marsh evolution, and population dynamics. These factors can significantly affect the path, pattern, and magnitude of flooding depths and inundation along the coastline. Using these factors, a storm surge model of the northern Gulf of Mexico, U.S. (NGOM) representing present day conditions is modified to characterize the future outlook of the landscape. This adapted model is then used to assess flood risk in terms of the 100-year floodplain surface under various climate change scenarios. The collection of results facilitate the estimation and projection of potential future flood risk. This novel method to assess coastal flooding under climate change can be performed across any coastal region worldwide, and results provide awareness of regions vulnerable to extreme flooding in the future.

Permanent link to this article: http://www.mattbilskie.com/presentation-university-of-cambridge/

Jul 13

Conference | 36th IAHR World Congress

StaticvsDynamicM.V. Bilskie, S.C. Hagen & J. Irish, “Development of future tropical cyclone 100-year floodplains in a changing climate” 36th IAHR World Congress, Delft-The Hague, The Netherlands, June 28 – July 3, 2015.

Permanent link to this article: http://www.mattbilskie.com/conference-36th-iahr-world-congress/

May 08

Publication | The dynamic effects of sea level rise on low gradient coastal landscapes: a review

SLR_EnchroachD.L. Passeri, S.C. Hagen, S.C. Medeiros, M.V. Bilskie, K. Alizad, D. Wang (2015). “The dynamic effects of sea level rise on low gradient coastal landscapes: a review.” AGU Earth’s Future, doi:10.1002/2015EF000298

Abstract: Coastal responses to sea level rise (SLR) include inundation of wetlands, increased shoreline erosion, and increased flooding during storm events. Hydrodynamic parameters such as tidal ranges, tidal prisms, tidal asymmetries, increased flooding depths and inundation extents during storm events respond non-additively to SLR. Coastal morphology continually adapts towards equilibrium as sea levels rise, inducing changes in the landscape. Marshes may struggle to keep pace with SLR and rely on sediment accumulation and the availability of suitable uplands for migration. Whether hydrodynamic, morphologic or ecologic, the impacts of SLR are interrelated. To plan for changes under future sea levels, coastal managers need information and data regarding the potential effects of SLR to make informed decisions for managing human and natural communities. This review examines previous studies that have accounted for the dynamic, nonlinear responses of hydrodynamics, coastal morphology and marsh ecology to SLR by implementing more complex approaches rather than the simplistic “bathtub” approach. These studies provide an improved understanding of the dynamic effects of SLR on coastal environments and contribute to an overall paradigm shift in how coastal scientists and engineers approach modeling the effects of SLR, transitioning away from implementing the “bathtub” approach. However, it is recommended that future studies implement a synergetic approach that integrates the dynamic interactions between physical and ecological environments to better predict the impacts of SLR on coastal systems.

Permanent link to this article: http://www.mattbilskie.com/publication-the-dynamic-effects-of-sea-level-rise-on-low-gradient-coastal-landscapes-a-review/

Apr 16

2015 LA ASCE Conference| Storm surge modeling in the northern Gulf of Mexico

M.V. Bilskie, S.C. Hagen, D.L. Passeri, K. Alizad, S.C. Medeiros, D. Coggin, J.L. Irish, N. Plant, A. Cox, C. Kaiser “Tide, wind-wave & hurricane storm surge modelling in the northern Gulf of Mexico under climate change.” 2015 ASCE Louisiana Section Spring Conference, Baton Rouge, LA, April 16-17, 2015.

Permanent link to this article: http://www.mattbilskie.com/2015-la-asce-conference-storm-surge-modeling-in-the-northern-gulf-of-mexico/

Apr 02

2015 ADCIRC User’s Group Meeting| Storm surge modeling in the northern Gulf of Mexico

M.V. Bilskie, S.C. Hagen, D.L. Passeri, K. Alizad, S.C. Medeiros, D. Coggin, J.L. Irish, N. Plant, A. Cox, “Tide, wind-wave & hurricane storm surge modelling in the northern Gulf of Mexico | climate change.” 2015 ADCIRC User’s Group Meeting, Silver Spring, MD, March 30-31, 2015.

Permanent link to this article: http://www.mattbilskie.com/2015-adcirc-users-group-meeting-storm-surge-modeling-in-the-northern-gulf-of-mexico/

Feb 23

Publication | Development and uncertainty quantification of hurricane surge response functions for hazard assessment in coastal bays

Taylor-2015-CoverPhoto

N.R. Taylor, J.L. Irish, I.E. Udoh, M.V. Bilskie, S.C. Hagen (2015). “Development and uncertainty quantification of hurricane storm surge response functions for hazard assessment in coastal bays.” Natural Hazards, doi:10.1007/s11069-015-1646-5

Abstract: Reliable and robust methods of extreme value-based hurricane surge prediction,
such as the joint probability method (JPM), are critical in the coastal engineering
profession. The JPM has become the preferred surge hazard assessment method in the
USA; however, it has a high computational cost: One location can require hundreds of
simulated storms and more than ten thousand computational hours to complete. Optimal
sampling methods that use physics-based surge response functions (SRFs) can reduce the
required number of simulations. This study extends the development of SRFs to bay
interior locations at Panama City, Florida. Mean SRF root-mean-square errors for open
coast and bay interior locations were 0.34 and 0.37 m, respectively, comparable with
ADCIRC errors. Average uncertainty increases from open coast, and bay SRFs were 10
and 12 %, respectively. Long-term climate trends, such as rising sea levels, introduce
nonstationarity into the simulated and historical surge datasets. A common approach to
estimating total flood elevations is to take the sum of projected sea-level rise (SLR) and
present day surge (static approach); however, this does not account for dynamic SLR
effects on surge generation. This study demonstrates that SLR has a significant dynamic
effect on surge in the Panama City area, and that total flood elevations, with respect to
changes in SLR, are poorly characterized as static increases. A simple adjustment relating
total flood elevation to present day conditions is proposed. Uncertainty contributions from
these SLR adjustments are shown to be reasonable for surge hazard assessments.

Permanent link to this article: http://www.mattbilskie.com/development-and-uncertainty-quantification-of-hurricane-surge-response-functions-for-hazard-assessment-in-coastal-bays/

Dec 20

2014 AGU Fall Meeting | Assessment of coastal flood risk in a changing climate along the northern Gulf of Mexico

FWJ_159stormsM.V. Bilskie, S.C. Hagen, D.L. Passeri, K. Alizad, “Assessment of coastal flood risk in a changing climate along the northern Gulf of Mexico.” 2014 AGU Fall Meeting. San Fransisco, CA, December 15-19, 2014.

Abstract: Coastal regions around the world are susceptible to a variety of natural disasters causing extreme inundation. It is anticipated that the vulnerability of coastal cities will increase due to the effects of climate change, and in particular sea level rise (SLR). We have developed a novel framework to construct a physics-based storm surge model that includes projections of coastal floodplain dynamics under climate change scenarios. Numerous experiments were conducted and it was concluded that a number of influencing factors, other than SLR, should be included in future assessments of coastal flooding under climate change; e.g., shoreline changes, barrier island morphology, salt marsh migration, and population dynamics. These factors can significantly affect the path, pattern, and magnitude of flooding depths and inundation along the coastline (Bilskie et al., 2014; Passeri et al., 2014).

Using these factors, a storm surge model of the northern Gulf of Mexico (NGOM) representing present day conditions is modified to characterize the future outlook of the landscape. This adapted model is then used to assess flood risk in terms of the 100-year floodplain surface under SLR scenarios. A suite of hundreds of synthetic storms, derived by JPM-OS (Joint Probability Method – Optimum Sampling), are filtered to obtain the storms necessary to represent the statistically determined 100-year floodplain. The NGOM storm surge model is applied to simulate the synthetic storms and determine, for each storm, the flooding surface and depth, for four SLR scenarios for the year 2100 as prescribed by Parris et al. (2012). The collection of results facilitate the estimation of water surface elevation vs. frequency curves across the floodplain and the statistically defined 100-year floodplain is extracted. This novel method to assess coastal flooding under climate change can be performed across any coastal region worldwide, and results provide awareness of regions vulnerable to extreme flooding in the future.

Permanent link to this article: http://www.mattbilskie.com/agu14-assessment-of-coastal-flood-risk/

Dec 10

Multiple-thread gzip

I was recently backing up some very large datasets and became impatient with the typical time it takes from creating *.tar.gz archives. During one backup session I started searching for a possible method to utilize multiple threads. I came across pigz, which is basically a parallel implementation of gzip. I came across an interesting thread on linuxquestions.org discussing how to implement pigz with tar, instead of gzip with tar (http://bit.ly/1zPFbHS).

Here was one of the recommended solutions by user dru8274.
To compress:
tar -I pigz -cf out.tgz in/

To extract:
tar -I pigz -xf out.tgz in/

I performed a non-scientific benchmark test on a 5.0 GB directory with an 4-core (8-thread) Intel Xeon 3.70 3.7 Ghz. The directory contains a good mix of MS documents, ASCII text files and images. The typical tar -xzf command took 6 minutes, while using pigz instead of gzip resulted in a wall time of 3 minutes. This is a significant time saver!

Permanent link to this article: http://www.mattbilskie.com/multiple-thread-gzip/

Oct 29

High performance computing of oceanic and nearshore hydrodynamic processes

NGOM_512DecompInvited Presentation

M.V. Bilskie, S.C. Hagen, D.L. Passeri, K. Alizad, S.C. Medeiros, “High performance computing of oceanic and nearshore hydrodynamic processes.” HPC User Group of Orlando Meeting, October 28, 2014.

Permanent link to this article: http://www.mattbilskie.com/high-performance-computing-of-oceanic-and-nearshore-hydrodynamic-processes/

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