Contact

Bret M. Webb, Ph.D., P.E., D.CE
Professor
University of South Alabama
150 Jaguar Drive, SH3142
Mobile, AL 36688 USA
Phone: (251) 460-6174
Fax: (251) 461-1400
Email: bwebb@southalabama.edu

Research Positions

Currently seeking an MSCE student to perform research on groundwater impacts to coastal lagoons. A research assistantship is available. Contact me for more details.

Current Research Assistants

SE Students
Garland Pennison

 

MSCE Students
Patrick Hautau
Marshall Hayden
Kate Haynes
Jackie Wittmann

 

Undergraduate Students
Derek Kelly

Former Students

MSCE Students
Bryan Groza (2016)
Kari Servold (2015)
Chris Marr (2013)
Richard Allen (2013)
Miyuki Matthews (2012)

 

Post Docs
Jon Risinger
Jungwoo Lee

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I recently completed a document that introduces transportation professionals to coastal modeling. The guidance document, entitled A Primer on Modeling in the Coastal Environment, was written for the U.S. Department of Transportation Federal Highway Administration. It is now available for distribution. You can download a copy of the manual by clicking on the cover image at right. The document abstract/summary is provided below.

 

Document Summary

This manual provides an introduction to coastal hydrodynamic modeling for transportation engineering professionals. The information presented in this manual can be applied to better understand the use of numerical models in the planning and design of coastal highways.

Here, the term “coastal highways” is meant to generally capture the roads, bridges, and other transportation infrastructure that is exposed to, or occasionally exposed to, tides, storm surge, waves, erosion, and sea level rise near the coast. The hydrodynamic models that serve as the focus of this manual are used to describe these processes and their impacts on coastal highways through flooding, wave damage, and scour.

The primary audience for this manual is transportation professionals ranging across the spectrum of project delivery (e.g., planners, scientists, engineers, etc.). After reading this manual the audience will understand when, why, and at what level coastal models should be used in the planning and design of coastal highways and bridges; and when to solicit the expertise of a coastal engineer. This manual provides transportation professionals with the information needed to determine scopes of work, prepare requests for professional services, communicate with consultants, and evaluate modeling approaches and results.

The manual also provides guidance on when and where hydraulic and hydrodynamic models are used, and how they are used to determine the dependence of bridge hydraulics on the riverine or coastal design flood event.

The manual also gives recommendations for the use of models in coastal vulnerability assessments.

FHWA GI Pilot title slide... click for animation

We are wrapping up a one-year collaborative project between USA, the Mississippi Department of Transportation (MDOT), and the US Department of Transportation Federal Highway Administration (USDOT FHWA).  This was one of five pilot projects funded by USDOT FHWA to evaluate the use of green infrastructure for improving the resilience of coastal transportation systems. The pilot projects are an initial step in a more comprehensive effort by USDOT FHWA to develop an implementation guide for nature-based solutions that improve resilience. More information about that project is found at the following link {click here}.

 

Our pilot project with MDOT was focused on improving the resilience of a coastal bridge in Mississippi to hurricane hazards and future sea level rise. More specifically, our green infrastructure approach was designed to address the vulnerability of bridge approaches and low-elevation bridge spans. The causes of damage to the bridge during Katrina were determined through the use of hydrodynamic models. A hindcast simulation of Katrina was performed using the coupled ADCIRC+SWAN models. Those results were extracted and used to force a high-resolution, two-dimensional simulation using the XBeach model. An animation of some of those results is provided below.

 

To that end, a pair of vegetated berms were designed in order to mitigate storm damage now and in the future during extreme events.

 

An overview of the entire pilot project is available in a recorded webinar at the following link {click here for webinar}. Ours is the second presentation in the webinar recording (at about the 25-minute mark). Webinar recordings for all five pilot projects, as well as other presentations in an ongoing USDOT FHWA resilience series, can be found at the following link {click here for all webinars}. A brief animation of our presentation slides is available by clicking on the title slide image in this post.

 

Katrina Hindcast using XBeach, forced with ADCIRC+SWAN output…

XBeach animation

Hindcast of Katrina using XBeach: Terrain elevation contour colors correspond to the lower blue-green-brown-white color scale. Selected bathymetric contours are shown as dashed white lines on the surface. The animated water surface is contoured by significant wave height using the blue-white-red scale. Vectors represent the depth-averaged flow magnitude and direction, but only at every 1/10th grid cell for clarity.

 

Title slide image for ASBPA 2017 presentation

I recently presented the results of a year-long research project on synthesizing the capacity of natural and nature-based features (NNBF) to reduce coastal storm hazards. The presentation was given in the Living Shorelines session at ASPA 2017 in Fort Lauderdale, Florida in October. The project, and presentation, were a collaboration between researchers at USA, the Dauphin Island Sea Lab, Northeastern University, the City College of New York, and the US Army Corps of Engineers Engineer Research and Development Center who funded the project.

 

More than 200 published research papers were identified, evaluated, and synthesized in this work. The synthesis focuses on the ability of marshes, mangroves, maritime forests, seagrasses, reefs, beaches, and dunes to attenuate waves, storm surge, flooding, and erosion. With very few exceptions, the literature does not contain unified methods for analyzing and describing these capabilities, and the range of values describing their performance is broad. Regardless of the uncertainty in published values, there is literature that supports the capacity of each of the NNBF considered to provide some measurable reduction of coastal storm hazards. A logical next step is to perform a detailed meta-analysis on values reported in these publications in order to determine average performance values and characterizations of their uncertainty.

 

A short animation of the presentation can be viewed by clicking on the title slide shown here. Please contact me for a full copy of the presentation.

 

Suggested citation below…

Webb, B. M., Scyphers, S., Cebrian, J., Gittman, R., Sharma, S., Rosati, J. 2017. Evaluating the capacity of natural and nature-based features to reduce coatal storm hazards. American Shore & Beach Preservation Association National Coastal Conference. Fort Lauderdale, FL Oct. 24-27.

Pres-cover-pageThe latest study out of our ACES center (Applied Coastal Engineering & Science) is now available. The study, entitled “Lake Forest Mapping: Analysis of Shoaling and Pool Volumes,” was recently completed for the Lake Forest Property Owner’s Association and the City of Daphne with contracting support provided by the Mobile Bay National Estuary Program. The goals of the study were to determine how much sediment has accumulated in the Lake Forest lake (reservoir) since the time of dam construction in 1973/1974, where the largest accumulations of sediment have occurred, and what the remaining normal pool volume is within the lake.

We collected over 12,000 new elevation measurements within and around the lake to map the sediment elevations and also analyzed eight (8) shallow sediment push cores from the lake bed. The results of the study show that over 300,000 cubic yards of medium to coarse grained sediments have accumulated, or shoaled, within the present-day lake shoreline since 1973/1974. Approximately 80% of the lake has shoaled by some measurable amount since the time of dam construction, with some areas accumulating over ten (10) feet of sediment! As a result, the pool volume of the lake has decreased by about 60% due to the accumulation of sediments. The remaining volume could perhaps accommodate another 90 years of sediment input at the current reported rate of 7800 tons per year (as per Cook & Moss, 2008[1]), but the margin for error is quite large.

I presented these study results at a recent Mobile Bay National Estuary Program’s Project Implementation Committee Meeting. A copy of that presentation [2] can be downloaded {here}.  A copy of the final study report [3] can be downloaded {here}.  Please include proper attribution and/or citation [2,3] when reusing these data, results, graphics, and/or figures.

[1] Cook, M., and Moss, N. 2008. Analysis of Water Quality, Sediment Loading Rates, Biological Resources, and Impacts of Land-Use Change on the D’Olive and Tiawasee Creek Watersheds, Baldwin County, Alabama, 2008. Geological Survey of Alabama, Open File Report 08-11: 92 pp.

[2] Webb, B.M. 2016. Lake Forest Mapping: Analysis of Shoaling and Pool Volumes. Mobile Bay National Estuary Program Project Implementation Committee Meeting. August 18, 2016. Presentation.

[3] Webb, B.M. 2016. Lake Forest Mapping: Analysis of Shoaling and Pool Volumes. University of South Alabama, Center for Applied Coastal Engineering and Science, Technical Report No. 16-002F. 41 pp.

 

Fig07 for web site

Our manuscript entitled “Spatial Variability of Hydrodynamic Timescales in a Broad and Shallow Estuary: Mobile Bay, Alabama” has been published by the Journal of Coastal Research. The manuscript is currently available online as a pre-print. The final version with color will be available in the coming months. Please {click on this link} for access to the manuscript.

The results presented in this new manuscript by Webb and Marr (2016) were initially developed as part of Chris Marr’s thesis research back in 2013. This new manuscript presents a much more narrow focus of his work and some new analyses as well. For more information about this work please review the {thesis} by Marr and/or this previous {blog post}.