About Amerisurv| Contact    
Magazine | Newsletter    
Flickr Photos | Advertise    
HomeNewsNewsletterAmerisurv DirectoryJobsStoreAuthorsHistoryArchivesBlogVideosEvents

Sponsored By

Software Reviews
Continuing Series
An RTN expert provides everything you need to know about network-corrected real-time GNSS observations.
Click Here to begin the series,
or view the Article PDF's Here
76-PageFlip Compilation
of the entire series
Test Yourself

Got Answers?
Test your knowledge with NCEES-level questions.
  Start HERE
Meet the Authors
Check out our fine lineup of writers. Each an expert in his or her field.
Wow Factor
Sponsored By

Product Reviews
Partner Sites







Spatial Media LLC properties




Home arrow Archives   The American Surveyor     

Vantage Point: Ankle Deep, Knee Deep, or Higher? Print E-mail
Written by Wendy Lathrop, PS, CFM   
Saturday, 02 August 2014

A 136Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

Hurricane Amanda and Tropical Storm Boris have already sloshed and wind-blasted their way through Central America. Amanda arrived a week before the official June 1 start of hurricane season, with Boris close behind. It's time to assess our storm surge prediction tools. While such storms generally cause most of their damage along our sea coasts, inland areas experience significant flooding from storm surge. What we all want to know is how much water might we expect? Which neighborhoods will be inundated first, and which roads will be impassable for evacuation or rescue?

If we can predict the direction of a storm and where it is likely to make landfall, we improve our opportunity to prepare for flooding events more realistically in relation to human safety and our built environment. Along large bodies of water such as the Great Lakes, the Atlantic and Pacific Oceans, and the Gulf of Mexico, additional height of water from air pressure changes and winds pushing water inland is called storm surge. But storm surge is not confined to those lands immediately along the waterfront. Through a model called Sea, Lake, and Overland Surges from Hurricanes (SLOSH), the National Oceanic and Atmospheric Administration (NOAA) calculates maximum potential impact and coastal inundation risk assessment based on storm intensity, path, and estimated storm size information from its National Hurricane Center (NHC).

The first difficulty is accurately predicting the storm's track and timing of its landfall. A slight shift can mean a different area will be impacted more severely, and a delayed or expedited arrival coincident with high tide can mean a whole lot more water is pushed inland than had been anticipated. A change in storm intensity affects air pressure, sucking water into low-pressure areas, while a variation in storm size influences how much area will be affected. This is not an easy set of variables to play with, so a series of many SLOSH runs creates a Probabilistic Storm Surge (P-Surge) estimate. Based on SLOSHbased simulations of impacts of each model run and relying on statistical analysis of past advisories' accuracy, P-Surge estimates are posted on the NHC website within half an hour of NHC's storm advisory.

Coastal areas are divided into SLOSH basins for computational purposes, and account for susceptibility related to dense population, low topography, and ports. Each basin is modeled to determine Maximum Envelope of Water (MEOW) by calculating SLOSH runs both left and right of the main storm track. By accounting for various uncertainties in storm forecasting, thousands of SLOSH runs yield MEOWs for worst-case scenarios to aid in evacuation planning. An analysis of all MEOWs for a basin will yield MOMs (Maximum of MEOW runs). Obviously in this short space, this generalized description omits many details of the variables and approaches. For instance, SLOSH does not account for rain flooding, normal river flow, or the impact of waves on top of storm surge. However, for fast model runs and its ability to resolve flows through particular situations, it is an invaluable tool.

But aside from all the math, we want to know the effect of storms on humans and our built and natural environments more directly. SLOSH Storm surge heights are referenced to a vertical datum, with all basins in the contiguous United States updated to NAVD88. Not everyone understands elevation, however, and so NHC forecasts storm surge as height above ground level. This year, NHC released an experimental Potential Storm Surge Flooding Map to help identify the areas where storm surge could cause inundation and what to what depth those areas could expect inundation. NHC calls this a "reasonable worst-case scenario for any given location", with the maps representing inundation levels with a 10% probability of being exceeded. The fourcolor coding system represents inundation levels up to 3 feet above ground, greater than 3 feet, greater than 6 feet, and greater than 9 feet above ground.

NHC anticipates releasing initial inundation mapping on its website when it issues its first hurricane or tropical storm watch (advising of a possible storm event) or warning (requiring immediate action as arrival of the storm is imminent) and will be updated every six hours, within about a half hour after running P-Surge. No GIS data from this model will be made available during the experimental phase of P-Surge while NHC seeks feedback and suggestions for improvements, need for modifications, and whether it should be integrated into NHC's regular operations.

The National Research Council's 2009 publication "Mapping the Zone: Improving Flood Map Accuracy" devoted a full chapter to the importance of appropriately communicating flood risk. The vast majority of the public understands an estimated level of inundation better than projected water surface elevation. While limited in scope of analysis, as many quick emergency forecast tools are, this new technology may be able provide a broadly understood straightforward advisory that more of the public will heed.

Wendy Lathrop is licensed as a Professional Land Surveyor in NJ, PA, DE, and MD, and has been involved since 1974 in surveying projects ranging from construction to boundary to environmental land use disputes. She is a Professional Planner in NJ, and a Certified Floodplain Manager through ASFPM.

A 136Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

< Prev   Next >

 American Surveyor Recent Articles
Thought Leader: Land is Too Important to Be Left to Land Specialists
A while back I was searching the Internet for an old treatise on land titles. A Google query yielded a book published in 1914. The author was Charles Claudius Kagey and the book was titled "Land Survey and Land Titles, a book for boys and girls, a reference volume for property owners, a text ....
Read the Article
Jason E. Foose, PS 
Decided Guidance: Wacker vs. Price - Irony in Sevenfold
This month's case takes us to Phoenix, Arizona in 1950. The Arizona Supreme Court went all guns-a-blazin' in Wacker vs. Price (216 P.2d 707 (Ariz. 1950)). Maybe it's just me, but I'm sensing plenty of irony and have taken license to point it out along the way. I like what the Court did with this case ....
Read the Article
Allen E. Cheves 
Around the Bend - A Visit to Carlson Software
The Ohio River is one of America's greatest, running near 1,000 miles between Pittsburgh and the Mighty Mississippi. Much of the coal and other products that fueled our nation's industrial expansion flowed between the shores of this maritime ....
Read the Article
Lee Lovell, PS 
Surveying & Mapping Economics Part 3 - Customers & Services
This article continues an inquiry into the economic conditions of the Surveying and Mapping industry (NAICS 541370) using data from the U.S. Census Bureau. This time we will look at customers and services. The data comes from the Economic Census conducted every 5 years on American ....
Read the Article
Jerry Penry, PS 
True Elevation: Black Elk Peak
Black Elk Peak, located in the Black Hills region of South Dakota, is the state's highest natural point. It is frequently referred to as the highest summit in the United States east of the Rocky Mountains. Two other peaks, Guadalupe Peak in Texas and ....
Read the Article
Larry Trojak 
Bringing The Goods - Mobile Scanning an Integral Component
When Jim Smith, Jerrad Burns and Charlie Patton left the Memphis division of a major construction company in 2015, they took with them the knowledge of how to get even the most complex jobs done and what equipment could best serve them in making that happen. So when they joined West ....
Read the Article
Lee Lovell, PS 
Test Yourself 41: Integers, Integers, and Integers
ABF is a 5:12:13 triangle, ACF is a 48:55:73 triangle, ADF is a 3:4:5 triangle, and AEF is a 7:24:25 triangle, all with integer sides and inscribed in a semi-circle. What are the lengths of BC, CD, and DE? ....
Read the Article
Wendy Lathrop, PS, CFM 
Vantage Point: Sunset or Sunrise?
While we often think of legislated government programs as static, they do change over time. Such evolution and opportunity for transformation are part of the dialogue in reauthorizing these programs. Every so many years there is a sunset on each government program, and this September is the ....
Read the Article


Amerisurv Exclusive Online-only Article ticker
Featured Amerisurv Events
List Your Event Here
contact Amerisurv


JAVAD Intros
Spoofer Buster

press [at] amerisurv.com
Online Internet Content


News Feeds

Subscribe to Amerisurv news & updates via RSS or get our Feedburn
xml feed

Need Help? See this RSS Tutorial

Historic Maps

post a job
Reach our audience of Professional land surveyors and Geo-Technology professionals with your GeoJobs career ad. Feel free to contact us if you need additional information.


Social Bookmarks

Amerisurv on Facebook 

Amerisurv LinkedIn Group 

Amerisurv Flickr Photos 

Amerisurv videos on YouTube 



The American Surveyor © All rights reserved / Privacy Statement
Spatial Media LLC
905 W 7th St #331
Frederick MD 21701
301-695-1538 - fax