=1= Storm Surge and Sea Rise

The series of 17 maps shows the relationship between storm surge and sea level rise along the Louisiana Gulf Coast. 

An explanation of how these maps fits into a larger research project is discussed here.


The map below shows the names of the parishes from which the study area was selected.

Map_01_Parishes_+_Gulf_1x0


The area selected for study is the area generally south of US highway 190, which traverses from the Texas to Mississippi borders as shown in the map below. The area comprises 29,008 square miles (18,565,363 acres)

Map_02_Parishes_+_Gulf_+_Big_study_area_1x0


A portion of the study was excluded due to being located in Louisiana state waters, an area with legal significance. Unlike other states, the waterways are owned by the state government under the tradition of napoleonic code, which was adopted during the French colonial period. The area excluded is shown in the map below.

Map_03_Parishes_+_Gulf_+_Excluded_study_area_+_land_1x0


A selection set of 93,600 random points were created as points to measure the elevation of sea level rise and storm surge levels. The points were selected such that no point could be closer than 750 feet from a mother point. The circular area within 750 is equal to 10.14 acres (π R²) = (3.14 * 375² ) = (441,786.47 Sq Ft) =   (441,786.47/ 43560 ft/acre) = 10.14 acres.

That is to say that a random point was selected approximately every 10 acres. The population to be sampled then is calculated as a circular area every 10.14 within an area of 18,565.44 acres. Thus, the population is 18,565.44 acres/ 10.14 acres = 1,830538.67. The sample size is 93,600.

Statistical samples are measured by two factors. The first is the confidence interval: the interval stated in a plus or minus value that a statistic varies within the sample. As in the case of polls, like support  for a particular candidate is stated as 45% plus or minus 2% from 43% to 47%. The confidence interval then is 2%. The second factor is the confidence level, usually stated as a percentage. If a sample level is 99%, then 99 samples out of 100 yield the same statistical results. 

The confidence interval for the selection set is 0.4042 with a confidence level of 99%. Both of these measures are extremely high because the selection set is very large within a very large population. Thus, the results are very reliable. The creation of the selection set took nearly 100 hours of processing on a robust desktop: 3.06 GHz 6-Core Intel Xeon Mac desktop with 12 cores and 64 gigabytes of RAM.   

Some points within the selection set were excluded because the points were located within the Louisiana state waters. The reason for exclusion is that the study examines the relationship between flooding and sea level rise on land rather than with open water.

The total number of excluded points were 30,611 or 32% of the sample. The remaining 62,989 points were shown in the land area on the following map.

Map_04_Parishes_+_Gulf_+_Excluded_study_area_+_land_1x0


The study area was divided into 117 major grids with each equal to 9,917.4 acres or 247.9 square miles.

Map_05_Excluded_study_area_+_Grid_1x0


In turn, each major grid was divided into 16 equal minor grids; each grid being equal to 9,917.4 acres or 15.5 square miles

Map_06_Excluded_study_area_+_Grid_Minor_1x0


The major grids are labeled with alphabetic rows and numeric columns. The northwestern most major grid is labeled as A-2 while the southwestern most major grid is labeled G-22.

Each grid is divided into 16 equal minor grids with numeric labeling from left to right and then top to bottom. The northwestern most minor grid is labeled as 1 while the  southwestern most grid is labeled 16.

Map_07_Excluded_study_area_+_Grid_Minor_Row_Column_1x0


Marsh Island is located south of Vermilion Bay in Vermilion Parish. The island is located approximately at the mid point between Texas and Mississippi along the Gulf Coast. The island is located in the southern half of major grid D-10.   

Map_08_Marsh_Island_Detail_1x0


The storm surge is shown in the following map along with the random points on Marsh Island as an example of the distribution of points and the degree of storm surge. The points measured the degree of storm surge from 1 to 21 feet for a category 3 storm at high tide.

The maps shows that the level of inundation on Marsh Island varies from 8 to 14 feet, depending on the location of the random points.

The data set released by the US Dept. of Interior and posted on Environmental Research Services, Inc. (ESRI) server.  As stated by the National Hurricane Center, which is administered by NOAA:

“The Maximum of the Maximum Envelope of High Water (MEOW), or MOM, provides a worst case snapshot for a particular storm category under “perfect” storm conditions. Each MOM considers combinations of forward speed, trajectory, and initial tide level. These products are compiled when a SLOSH basin is developed or updated. As with MEOWs, MOMs are not storm specific and are available to view in the SLOSH display program for all operational basins. No single hurricane will produce the regional flooding depicted in the MOMs. Instead, the product is intended to capture the worst case high water value at a particular location for hurricane evacuation planning. The MOMs are also used to develop the nation’s evacuation zones.”

Map_09_Marsh_Island_Detail_Surge_1x0


The sea level rise is shown in the following maps along with random points on Marsh Island as an example of the distribution of points and the degree of sea level rise. The data set was released in 2016 by National Oceanic and Atmospheric  Administration (NOAA) and posted on the NOAA server. 

The US Academies of Science and Arts has studied the issue of rising sea levels and its relationship to atmospheric warming. Each  major industrialized and industrializing nation state has a similar institution that is provides technical information to the public as well as to government agencies for use in times of war and peace. Seventeen of the world’s leading academies formed a Intergovernmental Panel on Climate Change (IPCC) and issued a statement in US Academy’s publication, Science on 18 May 2001: 

There will always be some uncertainty surrounding the prediction of changes in such a complex system as the world’s climate. Nevertheless, we support the IPCC’s conclusion that it is at least 90% certain that temperatures will continue to rise, with average global surface temperature projected to increase by between 1.4° and 5.8°C (2.5 °and 10.44° Farenheit) above 1990 levels by 2100 (as reported in our working papers). This increase will be accompanied by rising sea levels; more intense precipitation events in some countries and increased risk of drought in others; and adverse effects on agriculture, health, and water resources.

The three maps posted below show sea level rise by 1, 5 and 9 feet. An one foot rise will nearly inundate Marsh Island while 5 and 9 feet rise will entirely submerge the island. 

Map_10_Marsh_Island_Detail_Sea_Rise_1ft_1x0

Map_11_Marsh_Island_Detail_Ses_Rise_5ft_1x0

Map_12_Marsh_Island_Detail_Ses_Rise_9ft_1x0


Each random point was measured for sea rise at three levels for each minor grid. The average counted the number of points inundated for a 1, 5, and 9 feet rise. The formula was:

(points at 1 ft * 1) + (points at 5ft * 5) + (points at 9 ft * 9)/ total points

Map_13_Average_Sea_Rise_1x0


Each random point was measured for storm surge each minor grid. The average counted the number of points inundated and the amount of surge at each point. The formula for each grid was:

Total surge for each point/ total points

Map_14_Average_Storm_Surge_1x0


Each random point was measured for storm surge within each minor grid for Marsh Island. The average counted the number of points inundated and the amount of surge at each point. The formula for each grid was:

Total surge for each point/ total points

Map_15_Marsh_Island_Detail_Surge_Average_1x0


Each random point was measured for sea rise at three levels for each minor grid for Marsh Island as an example. The average counted the number of points inundated for a 1, 5, and 9 feet rise. The formula for each minor grid was:

((points at 1 ft * 1) + (points at 5ft * 5) + (points at 9 ft * 9)/ total points)/total points

Map_16_Marsh_Island_Detail_Sea_Rise_Average_1x0


There is a relationship between storm surge and sea level rise along the Louisiana Gulf coast. The Cajun prairies are typically well drained by bayous flowing south to the Gulf of Mexico. The Cajun prairies are protected by the low lying lands along the Gulf, much of which is a marsh, a submerged prairie with grass lands traversed by natural waterways and artificial drainage introduced by the oil industry to move heavy equipment into inland wetlands areas. A third area is the Atchafalaya Swamp, an area with a large cypress and tupelo forests that was mostly clear cut and harvested beginning in the later 19th century. A fourth area is along the Mississippi River, an area in which large levees were constructed after the 1927 flood, which devastated the entire Mississippi River Valley. The levees prevented catastrophic floods, but funneled the sediment into the Gulf from a drainage area from the Rocky Mountain in Colorado to the Appalachians in Pennsylvania. That sediment was used to extend the river delta. A fifth area is the state waters in the Gulf of Mexico, which adjoins the land created by  Mississippi River. Although with muddy water, it is a area with great productivity for fish and shrimp forming one of the major areas where seafood is spawned. It is one of the most productive fish habitats in North America, which is to say one of the great habitats of the world.

As a result of the land use changes, the buffer between the Gulf and the settled areas was damaged. In general, these settled areas are marked by the key populated points as shown on the map below. The bayous in the prairies were prevented in many cases from absorbing tidal flow by locks. The marsh was cut by artificial canals allowing the accumulated sediment to flow into the Gulf. Likewise, the Atchafalaya Basin, without its massive trees, no longer held water as a natural overflow from the Mississippi River in times of flood. The Mississippi no longer deposited its rich alluvial soils as was the case with the bayous, the marsh, and the basin. The Gulf turned muddy and absorbed the nitrogen deposited from manure and artificial fertilizer used in the Mississippi River Valley, creating enormous algae blooms that kill fish.

The distribution of the relationship between storm surge and sea rise varies by the five areas as shown in the map below.

The prairies are shown in yellow to red grids as generally marked by the population centers of Lake Charles, Lafayette, Eunice, and Abbeville.

These population centers and their major grids are farther from the Gulf being higher in elevation. And so, the storm surge is higher as well. In these elevated areas, surge is positively correlated with sea rise. If an area is subject to storm surge as in Lake Charles, then a corresponding sea level rise is predicted. It is important to note that the color does not measure the elevation, but rather the degree of relationship between storm surge and sea rise. Although Lake Charles is relatively high, it is located along an arterial ship channel that allows from from the Gulf to reach a previously unfolded area.

The areas shown in blue and green comprise the marsh, Atchafalaya Basin, and the Mississippi.

The marsh area is generally marked by Cameron, Grand Chenier, Pecan Island, Weeks Island, Cocoderie, and Dulac.

The Atchafalaya Basin is largely unpopulated except by fisherman and trappers, but is edges can be marked by Morgan City, Thibodaux and Houma.

The Mississippi River area is marked by New Orleans, Yscloskey, Bohemia, Grand Isle, and Venice

In these blue and green areas, the relationship between surge and rise is negatively related. If an area is subjected to high levels of surge, then the least amount of sea rise results in flooding. This can be demonstrated by the Village of Cameron, located south of City of Lake Charles. Because the village is along the coast and is low-lying, the slightest storm causes high levels of storm surge. As a result, the slightest sea level rise results in flooding. Again, the colors do not represent elevation, but the relationship between storm surge and sea rise.     

The area shown in grey is Louisiana state waters. Port Fouchon is shown in grey as land loss has been significant in this locale. The port provides significant support to offshore petroleum production platforms and drilling rigs as well as the Louisiana Offshore Oil Port pipeline. The high replacement costs in infra-structure associated regulatory issues to protect fisheries make the port difficult to abandon.  

The area was excluded from the measurement of sea rise and storm surge. The purpose of the exclusion is that correlation between in areas shown in green would be increased because the storm surge would not be prevented from occurring by land, but would respond directly to predicted rise and predicted surge.

The equation for the correlation coefficient as calculated in Microsoft Excel is for Pearson’s r

Equation

 

Map_17_Correlated_Grid_Surge_to_Rise_1xo