Figure 1.
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"State-of-the-beaches" of Alabama: 1998
by
Scott L. Douglass, Bradley Pickel, and Brian Greathouse
Civil Engineering Department
University of South Alabama
Mobile, AL 36688
College of Engineering Report No. 99-1
To
Coastal Programs Office
Alabama Department of Economic and Community Affairs
January 1, 1999
"Some of the fondest memories of many Alabamians are of trips to the beach."
Preface
This report was written for citizens interested in the scientific understanding of Alabama's Gulf beach erosion that has been developed over the past few years through research at the University of South Alabama. The report attempts to explain the analysis tools and results in a format for laymen. Some suggestions for future management decisions also are included at the end of the report. Most of these suggestions have already been made to the appropriate decision-makers and some of them have already been partially implemented.
This report was prepared under contract with the Coastal Programs Office of the Alabama Department of Economic and Community Affairs (ADECA). Funding for this research was provided by a grant from the National Oceanic and Atmospheric Administration, Office of Ocean and Coastal Resource Management (award #NA770Z0177). Mr. Phillip E. Hinesley, ADECA, was the technical monitor for the contract.
The report was written by Scott L. Douglass, Ph.D., P.E., Associate Professor of Civil Engineering; Bradley Pickel, graduate student in Marine Sciences; and Brian Greathouse, undergraduate student in Civil Engineering. Other University of South Alabama students that participated in collection of the data in this report included Wesley Price, Jennifer McClung, and Shawn Wozencraft. The air photo shoreline change database was initially developed by Ms. Tina Sanchez and updated by Mr. Scott Jenkins.
Summary
All of the Gulf of Mexico beaches of Alabama naturally fluctuate in width in response to the variable wave climate. The dry portion of the beach often builds wider when the waves are milder and gets narrower when the seas are stormier. Identifying the long-term trends in the midst of these fluctuations is a primary goal of this report.
About half (18 of the 38 miles measured) of Alabama's Gulf beaches have gotten narrower in the past three decades. Half of the beaches, while they fluctuated in width, did not have a trend in either direction. A few miles of beaches widened. Most of the beach width change trends are partially due to man's engineering. Figure 1 (also on the top of page) shows the general locations of these shoreline change trends. A more detailed breakdown of specific locations and rates of change is included in the report (Figure 3). The behavior of the beaches in 1998 generally was consistent with the trends of the past few years.
Hurricane Georges caused significant damages to beaches and beachfront buildings when it made landfall on September 28, 1998. The responses of the beach and dune system and the structural damages due to the hurricane were consistent with expectations based on prior storms and research models.
Suggestions for the future management of Alabama's beaches include complete sand bypassing at inlets, consideration of beach nourishment engineering, replacement of storm-overwashed sand, changes in the role of government, improved public access to the beaches, more appropriate beachfront building codes and practices, and future research focussed on addressing the critical management issues.
Introduction
"Golden is the sand"
The Robert Louis Stevenson poem with the line "golden is the sand" was not written with the Alabama beaches in mind - but it could have been! Alabama's Gulf of Mexico beaches are one of the greatest economic and environmental assets of the state. The tourist economy in south Baldwin County provides over 40,000 jobs and over $1 billion in revenue annually. All of this business ultimately rests on the thin strip of beach sand, the strand, along the Gulf of Mexico. Alabama citizens throughout the state consider the Gulf beaches to be one of the state's prettiest areas. Indeed, people from throughout the nation and the world acknowledge that the beauty of the white sand and gentle surf makes for some of the prettiest beaches in the world.
Development trends
The Alabama Gulf front properties have experienced tremendous development in the past few decades. The development trends of the state's beachfront lots is shown in Figure 2. The percentage of Gulf front lots with condominiums or hotels rose from 3% to 22% between 1970 and 1996. The percentage of condominiums will continue to increase as more single family houses are replaced with condominiums. The density of the housing of the beachfront properties is extremely high. Considered along the beach, these densities approach only several inches of coastline per person!
Figure 2.
This report
This "state-of-the-beaches" report presents data and analysis on the health of the narrow strip of beach sand between the buildings and the water. The report was initially prepared prior to Hurricane Georges but a special section was added that discusses the impact of the storm. Specific emphasis is placed on determining any trends in beach width and, where possible, explaining those trends in terms of the physical, coastal processes that are causing the changes. Notes are also made as to how well the trends and their causes are understood and where further research is warranted to improve our understanding of the "state of the beaches."
Individual reaches, or stretches, of beach are discussed in the "Beach by Beach" section of this report. The reaches are selected because these stretches of beaches, from 1 to 13 miles long, are generally behaving similarly. The extensive beach systems of the bays, sounds, and bayous of Alabama are not discussed in this report.
Terminology
The terms, "recession" and "accretion" are used in this report to describe the direction of shoreline movements. A "receding" or "recessional" shoreline is one where the beach is eroding and getting narrower. In other words, the location of the receding shoreline of the Gulf of Mexico is moving north. An "accreting" or "accretional" shoreline is one where the beach is gaining sand and getting wider. In other words, the location of the accreting shoreline of the Gulf of Mexico is moving south.
The relationship between inlets and beaches
Most of the dramatic shoreline change in Alabama is near the tidal passes or inlets. Some of this shoreline change is probably in response to natural inlet fluctuations. And, man's engineering has influenced much of it. Alabama has 3½ tidal inlets: Perdido Pass, Little Lagoon Pass and Mobile Pass break through the barrier island system of the state. Petit Boit Pass is at the western end of Dauphin Island and straddles the Mississippi-Alabama border. Each of the three passes in the state has a significant impact on the beaches in the vicinity of the pass. Each of the passes has engineered jetty or seawall structures and regular dredging to maintain adequate water depths. The sand that is dredged from these passes is sand that came off the adjacent beaches. It is also sand that was on its way back to the beaches before it was removed by dredging operations. That sand is part of the same littoral system as the sand on the beaches. The details of our understanding of the relationship between the beaches and passes are discussed below.
Littoral drift
Along the Alabama Gulf beaches, the dominant direction of longshore sand transport, or littoral drift, is from east to west. However, often and for sustained periods of time, significant amounts of sand move toward the east. The dominant processes, or mechanism, for moving sand in the littoral system is longshore sand transport. Longshore sand transport is the wave-driven movement of sand along the coast. As waves approach a beach at an angle, they break and move sand in that direction. Thus, when waves approach the beach from the other direction, the longshore sand transport direction reverses. Some of the long-term shoreline change trends in Alabama can be explained in terms of changes in longshore sand transport.
Data and Analysis
Two types of data were used to measure the beaches: aerial photography and beach profile surveying. Aerial photography allows for an estimate of the dry beach width at that moment in time. However, because of cross-shore sand transport mechanisms such as sand bar migration, the dry beach is only a small portion of the complete littoral system. The sand underwater immediately offshore of any sandy beach is also part of the beach system since it breaks wave energy and feeds sand to and from the dry beach. Surveyed beach profiles measure the underwater portion of the littoral system as well as the elevations of the dry beach and dune system.
The University of South Alabama's air photo shoreline change database was used to calculate average annual erosion rate. The data are shoreline positions based on 13 sets of air photos spanning the 1970 to 1997 period. Five of the 13 sets of air photos were taken during the 1970's and 80's. Eight sets of air photos were taken annually, in late September, in the 1990's by the ADECA Alabama Coastal Programs offices. None of the photos used in this analysis were post-storm photos. The air photos are part of the Alabama Coastal Shoreline Archives that is housed in the College of Engineering at the University of South Alabama. The archives contain these and other air photos as well as most of the historic coastal charts and surveys of the Alabama coast.
Beach width was measured at 92 fixed locations from arbitrary but consistent points (e.g. the corner of a house, the centerline of a road) to the visible wetline. The measurements were adjusted for the actual scale on a photo-by-photo basis using Global Positioning System (GPS) technology. Sources of error include those due to interpretation of the wetline; water level fluctuations due to tides, winds, barometric pressure, and waves; and photogrammetric errors of tilt and lens distortion.
The data were evaluated using linear regression analysis to determine the shoreline change trend. Confidence intervals, at the 80% and 95% level, were computed for the trend. These confidence intervals can be considered to be analogous to the "margin of error" that typically is presented with polling data.
The results, the annual shoreline change rate in feet per year, are shown in Figure 3. The vertical bars represent the shoreline change trend at each location. They range from an accretion rate of over 20 feet/year at one location on Dauphin Island (on an accreting bulge on the golf course) to a recession rate of over 20 feet/year at another location on Dauphin Island (near the Coast Guard facility). Positive trends indicate shoreline accretion: i.e. the beach was getting wider. Negative trends indicate shoreline recession: i.e. the beach was getting narrower.
Figure 3.
Figure 3 only includes that data through 1997. Data were collected for 1998 prior to Hurricane Georges using a GPS. These data were not included in the statistical analysis. However, inspection of the 1998 data indicated that the behavior of the beaches in 1998 was generally consistent with the data of the past few years.
It is obvious from Figure 3 that the answer to the question "is the beach eroding" depends greatly on which Alabama beach is being considered. The interpretation of the locations of the bars with the open star (80% confidence interval includes zero) is that there is no trend. The beaches fluctuate but there is no trend. Some exceptions to this interpretation are appropriate at places where, because of man's manipulations, the changes are not linear.
The general summary Figure 1 was generated from the data in Figure 3 using three basic assumptions. One, that there is no trend in the data if the 80% confidence interval for the trend included 0 feet/year. Two, a single location with a significant trend is ignored if the adjacent locations showed no trend. Three, the beaches behaved consistently between data locations.
The report also contains a few beach profiles. 22 beach profiles in the state have been surveyed repeatedly since the early 1990's (see Figure 4 for locations). Some older beach profiles are available for Dauphin Island. The beach profile data were obtained using standard surveying techniques. Elevations along a line perpendicular to the shoreline are surveyed from a fixed benchmark across the dunes, beach, into the water and out to and sometimes across the sand bar (for an example, see Figure 7).
Figure 4.
Beach by Beach results
The following discussion summarizes the results of the monitoring data described above on a beach by beach basis. The individual beach reaches discussed are shown on Figure 5. The discussion also attempts to explain the results in terms of the authors' understanding of the coastal processes of that area based on a decade of research on the Alabama coast and general principles of coastal science and engineering. There is an incomplete understanding of the Alabama coastal processes because of the short duration and limits of our research. We do have a better understanding, through site-specific research, of the coastal processes affecting some portions of the Alabama coast than others. For example, the causes of the dramatic changes on the east end of Dauphin Island are fairly well understood due to several years of focussed research. We do not have as clear of an understanding of the coastal processes of Perdido Pass, which have a great influence on the beaches of Orange Beach. Also, relatively little is known about the coastal processes of the Gulf Shores beaches.
Figure 5.
Perdido Key
The western two miles of Perdido Key are in Alabama. The analysis of the air photos, Figure 3, shows no significant trend. Figure 6 shows an example of the full database on Gulf shoreline position at a location opposite the bridge to Ono Island. There are significant fluctuations, over 150 feet, in shoreline position. However, there is no significant trend in the data. The slope of the trendline is -0.2 feet per year +/- 2 ft. Thus, the 80% confidence interval, analogous to margin of error, includes no trend. The beach profile data (not shown) here also have no trends.
Figure 6.
There are two major engineering projects that are important to the long-term health of the Perdido Key beaches. The jetties at Perdido Pass were built in 1968-69 immediately before the beginning of the air photo database used in this report. The jetties successfully "stabilized" the inlet. Prior to construction, the inlet had migrated along a stretch of coastline extending about 4 miles to the east of its present location in the past several hundred years. The present-day locations of all of the beaches of Alabama on Perdido Key were in the water of Perdido Pass at some point during the last two hundred years. The shoreline position just east of Perdido Pass is essentially fixed in place by the eastern Perdido Pass jetty. The eastern jetty has a low weir section that allows sand to pass over the rocks into a deposition basin in the pass when sand is moving westward in the wave-driven littoral current of Perdido Key.
A large beachfill was placed in Florida at the eastern end of Perdido Key in the early 1990's. A 400 foot wide beach was built along several miles of the Johnson Beach unit of the Gulf Islands National Seashore and even more sand was placed offshore in a constructed sand bar. It is possible that some of that sand may move out of the area to the developed Florida beaches of Perdido Key and eventually to Alabama in the future.
Alabama Point
Immediately west of Perdido Pass (for about 1 to 1½ miles) is one of only two beaches in the state that has gotten significantly wider since 1970. The western jetty, built in 1968-69 just before the beginning of the air photo database used in this report, is a high, rock jetty designed to keep sand from moving back east into the pass. Figures 1 and 3 show the beaches for about a mile west of the pass have accreted since 1970. Figure 3 shows annual trends of up to 13 feet per year of accretion adjacent to the western jetty.
This deposition of sand adjacent to the western jetty is called a "fillet" by analogy with a fillet weld in the corner of two pieces of metal. The sand fillet formed as the beach planform (shape of the beach as viewed from above) moved toward a new equilibrium position adjacent to the jetty. When waves are approaching the Alabama coast from the southwest and the longshore sand transport is to the east, sand is free to move off the beaches of Orange Beach into this area. However, when waves are approaching the Alabama coast from the southeast and the longshore sand transport is to the west, the sand in this area is partially sheltered by both the rock jetty itself and the shoals around the mouth of Perdido Pass. Essentially, this sand is partially, permanently trapped in this fillet.
The sand fillet is also the location of the disposal area for the sand-bypassing operation at Perdido Pass. Most of the sand dredged from the deposition basin and main channel during the past thirty years has been placed on the beaches within several hundred yards of the jetty or immediately offshore of these beaches. The beaches have fluctuated dramatically in response to sand bypassing episodes. Further research into the correlation of these fluctuations and the dredging/sand-bypassing history is warranted. The bypassed sand has helped the fillet reach its new equilibrium planform or shape since the jetties were built. All of the sand in the fillet is sand that would otherwise have moved east into the channel or west to the other beaches of Orange Beach. Thus, the engineering project has probably permanently widened these beaches but, as explained below, perhaps at the partial expense of the beaches to the west.
West Orange Beach
The beaches of the western portion of Orange Beach appear to be receding from 1970 to 1997 (see Figures 1 and 3). This recessional reach extends roughly from the west end of Cotton Bayou to the western city border at the main unit of the Gulf State Park.
This recession may be due to the engineering of Perdido Pass. In particular, this recession may be due to the sand trapped in the fillet on the west side of the pass. As mentioned above for the wider beaches, this trapping can be explained as an expected response of beaches to construction of a jetty on a coast that has a variable wave climate. When waves are approaching the Alabama coast from the southwest and the longshore sand transport is to the east, sand is free to move off these beaches to the east. However, when waves are approaching the Alabama coast from the southeast and the longshore sand transport is to the west, that sand is partially sheltered by both the jetty and the shoals around the mouth of Perdido Pass. Thus, the beaches farther to the west of the pass are starved.
Long-term erosion due to jetties typically is displaced some distance downdrift of the jetties due to the fillet formation as described above. At other jettied inlets of comparable size, the downdrift erosion occurs as far as 1 to 4 miles or more from the jetty. Essentially, the formation of an equilibrium shoreline and new ebb-tidal shoal after jetty construction traps large amounts of sand in the inlet vicinity and starves the downdrift beaches.
The pattern of accretion near the jetty and recession farther downdrift (Figures 1 and 3) is consistent with the signature patterns of erosion caused by jetties. Further research is needed to determine the amount of sand trapping by the Perdido Pass system and its effect on the beaches of west Orange Beach. A better, scientifically based, understanding of the coastal processes of the Perdido Pass area would be useful input to future decisions about the best location for disposal of dredged sands. Perhaps the sand bypassing operations could be modified to reduce the cost of dredging and maximize the help to the Orange Beach beaches.
East Gulf Shores
The beaches of the eastern, developed portion of Gulf Shores, from the western border of Gulf State Park to just west of the main beach area, show varying levels of recession mixed with areas that show no trend (see Figure 3). It should be noted that this analysis does not include any 1998 data.
It should also be noted that this portion of the coast has the narrowest beaches in the state. For example, in the September 1995 photos used in this study, the beach widths, defined as the distance between the buildings or bulkheads and the high water line, averaged about 70 feet and varied from 0 to 130 feet along the central 2.5 miles of Gulf Shores beaches. They average over 200 feet and varied from 120 to 700 feet in the rest of Baldwin County. The narrow beaches in Gulf Shores may be due to encroachment of the buildings more than erosion. To the citizen or the tourist, the result is the same… the beaches are narrower.
It is possible that the bulkheads and narrow beaches in this area have slightly biased the analysis used in this report. When water is adjacent to the wall, the beach width is measured at the wall instead of some landward or narrower location. It is known from observations that there are days with no dry beach seaward of the bulkheads in this area. It is not known if the frequency of occurrence of this condition is greater than it has been historically. Further research, including more detailed surveys of the full beach profile, is recommended to develop a better understanding of the beach sand volume and processes for future management decisions.
Repetitive surveys of a beach profile are shown in Figure 7. Sand elevations in front of the aluminum bulkhead at the Main Beach (the "Hangout" area at the south end of Highway 59) at different times since 1992 are shown. Most of the surveys are near the end of the summer when the beaches are typically at their widest. The figure shows that there is a tremendous amount of sand in the profile that is stored in the sand bar that is offshore.
Figure 7.
Lagoon Pass area
The engineering of the pass has impacted the beaches around Lagoon Pass for at least a mile on either side. The inlet was stabilized by jetty construction in 1981. There was no sand bypassing system put into place. In a classic response to jetty construction, the beaches accreted on the eastern side and receded on the western side for about a decade. In the early 1990's a lawsuit settlement included the nourishment of the western beaches and the shortening of the jetties. With the shortening of the jetties, dredging is now needed on a fairly regular basis (about 6 times per year) to maintain depths in the pass. The dredged sand is disposed of on the beaches to the immediate west. Essentially, the current operations are a form of sand bypassing. The coastal engineering has worked. The beaches have been widened on the western side of the pass and the pass has remained open.
West Gulf Shores
The western beaches of Gulf Shores, from Lagoon Pass to the end of West Beach Boulevard, have been recessional since 1970. The extent of the recession, shown in Figures 1 and 3, includes almost all of the beaches to the west of Lagoon Pass. Of particular interest is the recession near the west end of Little Lagoon. Figure 8 shows the detailed shoreline change analysis at one location. The trend is one of recession of about 5 feet per year. The 80% confidence interval for the slope of the trend is plus or minus about 2 feet/year. This is analogous to the margin of error commonly used to present polling results as discussed earlier. One interpretation of the statistics is that the recession rate is somewhere between 3 and 7 feet/year. It is clear that there is a significant recessional trend.
Figure 8.
The causes of this recession are unclear and require further research. Part of the recession may be due to the engineering at Lagoon Pass. Another possible cause of the erosion along these beaches is the removal of sand from the beach system that occurs when a large storm hits the area. For example, when Hurricane Opal brushed this coast in 1995 on its way to Pensacola, the storm surge crossed over the barrier island allowing waves to move sand from the beaches and dunes across the road and into Little Lagoon. A layer of sand up to several feet deep was deposited on the lots and West Beach Boulevard at the end of the storm. Little of this overwashed sand was returned to the beaches from which it came. Hurricane Georges resulted in similar overwash. Some portion of the overwashed sand was returned to the beaches but the portion that was on private property, or in Little Lagoon after the storm, was not returned to the beach. Thus, there was a significant removal of sand from the beach and dune system. The volume of sand removed from these beaches via this overwash process during Opal and Georges was very roughly equivalent to 20 to 30 feet of permanent beach width.
West Baldwin County
Most of beaches of western Baldwin County, from the west end of Little Lagoon to the end of Fort Morgan Peninsula, have no shoreline change trends for the past thirty years. Figures 1 and 3 show that most of these beaches have no significant trend. There has been some serious speculation that these beaches may be growing over the past century. These data however do not show any significant accretion in the past three decades. The beach widths along some of these beaches are the widest in the state because the construction was set back so far. The perception of healthy beaches may be partially because they are so wide as measured from the construction line. When the waterline is 300 feet from the buildings, shoreline fluctuations of plus or minus 100 feet are hardly noticeable.
Figure 3 shows that a few locations have recessional trends. The western tip of Fort Morgan Peninsula, in the state park, in particular has extremely large recession rates. These recession rates are probably related to the dynamics of Mobile Pass. The elevations of the shoals offshore of this area have decreased. Part of this decrease may be natural fluctuations but part of it is probably also due to the removal of sand from the outer bar of Mobile Pass. The same problem is influencing the beaches of Dauphin Island.
East Dauphin Island
The beaches of the east end of Dauphin Island have experienced some of the most dramatic shoreline recession in the United States in the past 20 years. The shoreline recession is over 500 feet in the vicinity of the Coast Guard R&R facility. Several studies have shown that the location and elevation of the ebb tidal delta of Mobile Pass influence these beaches. Sand or Pelican Island as well as Dixie Bar are part of the ebb-tidal delta.
Shoreline change analysis shows that roughly the easternmost mile of the island is receding while the next mile of beaches to the west is accreting! This pattern is due to a shift of sand from the easternmost mile to the next mile to the west. This pattern of sand shift is consistent with one due to wave driven longshore sand transport along the beaches.
About 400,000 cubic yards of sand shifted from the easternmost mile of Gulf beaches to the next mile of beaches to the west between 1984 and 1996. The probable cause of this shift is a change in longshore sand transport rates due to changes in the wave climate caused by the northwestward migration of Sand/Pelican Island and the loss of elevation of the shoals around the outer portion of the ebb-tidal delta.
A wave-driven longshore sand transport model has been used to evaluate the sensitivity of the beach shift to the shoal elevations. The beaches of Dauphin Island were found to be so sensitive to the sheltering afforded by the shoals that a two-foot increase in the elevation of the shoals would have reduced the longshore sand transport rate, and thus the erosional shift of sand along the beach, to roughly 50% of what was experienced. The implication of those model results is that some of the landward recession is attributable to the removal of sand from those shoals for maintaining the ship channel to Mobile. Over 16 million cubic yards of sand have been removed from the outer bar of the ebb-tidal delta and dumped offshore in the past 25 years.
West Dauphin Island
The west end of Dauphin Island, from the little red schoolhouse to the end of the road, has been receding since 1970. The data analysis for this study stopped at the west end of Bienville Road and did not include the undeveloped portion of the island. The recession rate has averaged 2 to 3 feet per year. The cause of this recession is not as well understood as that at the east end. Clearly, storm overwash during Hurricane Frederic and Elena moved sand from the beach and dune system to the sound. This removal of sand may be contributing to the recession.
Consideration of the natural sand transport paths indicates that another probable cause of the recession of the west end beaches is the removal of sand from the outer bar of Mobile Pass several miles to the east. Sand apparently naturally moves via wave driven processes along the outer edge of the ebb-tidal delta (Sand/Pelican Island) from the area near the lighthouse towards the fishing pier. It then naturally moves from Sand Island to the beaches of Dauphin Island in the form of migrating sandbars between the pier and the general vicinity of Ponchatrain Street. From there, the sand is moved west via wave driven longshore sand transport toward the west end of Dauphin Island. Thus, the "river of sand" that feeds the beaches of the west end of Dauphin Island is being interrupted by the dredging removal of sand several miles to the east. The beach erosion currently being experienced by these beaches is consistent with erosion experienced miles downdrift of other navigation projects that remove sand from the littoral system.
The impact of Hurricane Georges
This section is a brief summary overview of the response of the beaches to Hurricane Georges based primarily on limited beach profile surveying immediately before and after the storm and on-site visits to some of the coast immediately after storm passage.
On September 28, 1998 Hurricane Georges made landfall just west of the Alabama barrier island beaches. Alabama was exposed to the more severe side of the storm including waves driven by onshore hurricane force winds and storm surges that varied up to roughly +10 feet (elevations are referenced to the National Geodetic Vertical Datum) which is about 8 feet higher than the mean high tide. The storm caused erosion of the Gulf beaches throughout the state. The storm also caused significant property damage to beachfront structures throughout the state.
The response of the beaches to the storm was about what was expected. The types, locations, and magnitude of both the storm-induced beach erosion and structural damage that occurred had been fairly well predicted by available analysis tools and knowledge of typical storm damage. Some general observations are as follows:
A. Damage to structures during Hurricane Georges was related to 4 things:
1. Distance from the water - the closer to the water at the beginning of the storm, the more damage. Examples of damage were the west end of Dauphin Island and eastern Gulf Shores. Both areas had extremely narrow beaches immediately before the storm and suffered serious property damage. Counter examples are the Gulf State Park Convention Center and Phoenix V condos. Both of these areas had fairly wide beaches before the storm and suffered relatively minor or no wave damage. At the time of the publication of this report, three months after the storm, some Gulf front businesses in the areas with the narrowest beaches immediately before the storm hit were still not open. Businesses that were behind wide beaches were open within days after the storm. Another example is the comparison between the main pavilion and the 2nd St. beach access facilities in Gulf Shores. The former were damaged were as the latter were not. The 2nd St. structures were setback farther from the water. There were many more similar examples. A primary reason for coastal construction setbacks in Alabama is to provide for a "buffer zone" between the waves and structures to account for the natural variability in beach width from week to week to protect the beach. A secondary effect of this "buffer zone" is that in storms, this buffer zone can work to protect structures too. This "buffer zone" concept was validated in Georges.
2. Elevation of construction - the higher the elevation, the less damage. Examples of damage are the condos on Perdido Key that were built with a base floor elevation at about +8 ft. Most of them suffered severe losses in the lower floor units. Counter examples can be found at the Windrift condo also on Perdido Key and at many sites throughout Baldwin County. Houses and condos elevated above +13ft suffered much less damage.
3. Amount of sand reservoir in the beach and dune system in front of development -the more sand in the reservoir, the less the damage. Examples of very little sand are the west end of Dauphin Island and eastern Gulf Shores. Examples of much sand are the condos on Fort Morgan Peninsula that are set behind the sand dunes. These condos suffered no wave damage from the storm and were open for business within days.
4. Construction methods - pilings and tie downs work. The slab failure of a condo on Perdido Key is an example of why slabs do not work well on the beach. Post-storm inspection indicated the structure failed because the waves and storm surge removed the underlying sand. Pile supported structures throughout the area survived better than slabs. The exception to this finding was on the west end of Dauphin Island. Some pile-supported houses that were adequately elevated collapsed. It appears that the local pile-depth penetration practices need to be re-evaluated on Dauphin Island because some of the houses apparently failed due to vertical scour of the sand around the base of the piles. Perhaps a better local practice could be based on some rational design analysis that combines coastal engineering estimates of storm-induced scour with structural and geotechnical engineering considerations.
B. The beach and dune erosion was what would be expected from a storm such as Hurricane Georges. The dune erosion model methodology recommended by the University of South Alabama appears to be an appropriate tool. Specifically, the eroded profiles after Georges looked very similar to the erosion model results. The general shape of the profiles in the high dune areas had an upwardly concave profile to a dune scarp just as predicted by Kriebel's EDUNE model. One example is shown in Figure 9. Similar results were found at every site surveyed that was backed by a high dune. At Cotton Bayou, the pre-storm dune had a wide crest at about +13 ft. This dune receded over 30 feet north during the storm. About 4 to 5 feet of vertical beach elevation was lost between the original waterline and the post-storm dune scarp. Also note that interpretation of the beach width based on water line is not clear. In other words, the actual waterline may not have moved much but the beach and dune above the waterline were severely eroded. The post-storm profile was not extended offshore to a closure depth but focused on the dune portion of the profile.
Figure 9.
Beach and dune erosion similar to that shown in Figure 9 undermined many beachfront structures. More condos would have been undermined if condo developers, at the request of the Alabama Department of Environmental Management, had not been recently siting the condos up to 60 feet north of the construction control line on the basis of dune erosion model predictions.
C. Some of the sand eroded from the beach and dune system was overwashed onto (and in some cases across) the barrier island but some of it was pulled offshore into the sand bar system. The existing sandbars were pulled farther offshore during the storm. Figure 10 shows the beach profile changes at a location along the west end of Dauphin Island. This location is in the area with no north/south roads about halfway between the schoolhouse and the west end. The profile begins near the front of the houses. There was obvious overwash of sand from the beach and dune system to the north at this location. A lens of sand between 1 and 2 feet thick buried the roadway.
Figure 10.
The pre-storm profile (the dashed line on Figure 10) was Friday before the storm and the post-storm profile (the solid line on Figure 10) was Friday after the storm. Before the storm, the dune field was significant and had an elevation of about 8 feet. Also, note that the profile "closes" in the offshore. In other words, it appears that all of the significant vertical change in the beach system is accounted for in the survey (except the overwash fan).
The survey shows that there was much sand volume moved offshore beyond the pre-storm sand bar location (400 ft). This created an extremely wide flat area from 200 to 500 feet offshore that was essentially neck deep water. The sand in the area between 400 and 600 feet offshore was 1 to 4 feet deeper immediately after the storm. The volume of sand added to this offshore bar is roughly 300 cubic feet/foot of beach. This is roughly half the sand volume lost from the beach (0 to 300 ft). This indicates that the remaining 300 cubic feet/foot of beach was overwashed north of the house line. Extrapolated per mile of beach, this is very roughly 50,000 cubic yards of sand overwashed to the north per mile of beach. Essentially, this was a significant withdrawal of sand from the sediment budget of the beach. At a unit cost of $10/cy this is a half a million dollars of sand per mile moved from the beach!
D. The beaches were recovering immediately after the storm. Throughout the state, onshore sand transport was evident the next few days after the storm. For example, on the Cotton Bayou and Dauphin Island profiles, there is a small sand bar near the water's edge. This is probably sand that was pulled offshore during the storm and was already moving back onshore as a sand bar.
Structures specifically designed and engineered for the Alabama coastal environment survived. Examples are the many beachfront condos that were operating within days after the storm, the interstate bayway, the Dauphin Island bridge, the revetment at the Mobile County Park in Alabama Port, and the headland beach/breakwater system that was just built by the University of South Alabama at Gulf Pines Gulf Course on Mobile Bay. Counter examples are condos that were damaged, the causeway to Dauphin Island (which was exposed to the same wave conditions as the park revetment that survived), and Bayfront Road in Mobile. There are many other examples.
What can be done to improve the health of the future beaches
Some of the fondest memories of many Alabamians are of trips to the beach. Alabama has some of the prettiest beaches in the world today but many citizens would argue that they were prettier twenty years ago. The real issue is… how pretty will they be twenty years or fifty years from now?
This section of the State-of-the-beaches report presents suggestions for the management of Alabama's beaches based on the technical findings presented above. The present day state-of-the-beaches has been influenced by management decisions made along the coast during the past several decades. Likewise, the future state-of-the-beach will be influenced by management decisions made in the next few years. The philosophy underlying these suggestions is that beach management and development decisions should be made either:
- to work with the natural coastal processes, or
- with an understanding of the costs of working against the natural coastal processes.
Successful management strategies are not based on technical information alone. They are based on value judgements of the policy-makers and the decision-makers. The technical information provided by this report is one input to the decision-making process. Thus, the technical input can be used to come to different management conclusions. The suggestions are based on a blend of an understanding of the technical results and the authors' perceptions of what is most important to Alabama at this time. These suggestions are based on treating the beach sands of the state as a valuable resource. They deal with technical and management issues. The technical issues are:
- bypass sand at inlets
- beach nourishment engineering
- return overwashed sand
The management issues are:
- role of government in beach management
- public access
- beachfront building codes and practices
Bypass sand at inlets
Sand dredged from inlets should be placed either on the adjacent beaches or in a location where it will migrate rapidly to the beaches. This practice, called artificial sand bypassing, is a common engineering tool to minimize the impact of inlet dredging on adjacent beaches. Essentially, sand bypassing just replaces the natural process that channel dredging interrupts. Sand bypassing is vital to the future health of the beaches of Alabama. The state should consider legislation that requires this. Most of the shoreline recession in the state is due in part to inlet engineering. At present, bypassing of some limited form is occurring at Perdido Pass and Lagoon Pass. However, the operational decisions regarding the bypassing are primarily driven by the need to maintain adequate depths of water in the passes. Bypassing schemes should be adopted which also directly consider the adjacent beach widths.
At Mobile Pass, bypassing is not occurring. Millions of cubic yards of sand are being permanently removed from the littoral system by the dredge disposal practices used to maintain the Mobile Ship Channel. From 1974 to 1997, over 16 million cubic yards of sand was permanently removed from the littoral system of the state and dumped offshore in deep water. This is enough sand to widen the beaches of Dauphin Island over 1000 feet. The removal of this sand from the littoral system has contributed to the beach erosion on Dauphin Island, both on the east end and the west end, and possibly to the beach erosion on Fort Morgan Peninsula. The removal of this sand from the littoral system is not a sustainable development practice if the future of Dauphin Island is considered.
In 1995, the National Research Council made specific recommendations concerning the use of beach quality sand from federal navigation projects for beach nourishment. In 1998, the American Coastal Coalition proposed a new national coastal policy that directly calls for "statutory language in the Water Resources Development Act that directs the placement of beach quality sand dredged from a navigation project on nearby beaches unless such disposal is not environmentally sound." It is suggested that these recommendations be adopted by the federal government to protect the beaches of Alabama from further degradation due to inlet engineering. Consideration could also be given to restoring to the beaches the sand that has been historically removed by man through dredging.
Beach nourishment engineering
Beach nourishment, or fill, is the direct placement of sand on the beach to widen the beach. Beach nourishment can successfully widen beaches and decrease damages due to storms. The lessons learned from beach nourishment engineering nationwide in the past decade, and the very limited experience with beach nourishment in Alabama, indicates that it is a technically feasible way to widen the Alabama beaches. It is suggested that beach nourishment engineering be considered where wider beaches are desired in Alabama. Beach nourishment might be the appropriate solution along all of heavily developed portions of the Alabama coast experiencing erosion including Gulf Shores, Orange Beach, and Dauphin Island.
Return overwashed sand
Sand that is overwashed onto the barrier island during large storms should be returned to the beaches. After passage of hurricanes such as Opal and Georges, deposits of sand must be removed from parking lots, roadways, driveways, and drainage ditches. Beach profile analysis has shown that this sand comes from the beach and dune area. All of this sand should be returned directly south to the beaches. There is essentially a cottage sand-mining industry along the Alabama coast after storms. Entrepreneurial bulldozer operators throughout the southern half of the state converge on the coast and get paid to remove sand from parking lots and roads. Prior to Hurricane Georges, they commonly moved the sand to other private property on the barrier island or hauled it completely off the island to stockpiles. Local and state officials have partially changed this practice to one of returning the sand to the beaches at a few locations. Further efforts along these lines are suggested.
Sand that is partially contaminated with debris can be sifted with commercially available sifters. None of this sand should be moved off the island. Institutional and jurisdictional obstacles including questions of the use of state highway moneys to put sand on private beach property should be addressed now prior to the next storm. Adoption of this suggestion will minimize the long-term adverse impacts of future storms on the beaches of Alabama.
Role of government in beach management
There is no government agency in Alabama with overall responsibility for beach management to which a citizen with a beach erosion problem can turn for assistance. Yet, because of the natural littoral system where others can cause erosion problems at different locations, the citizen has little recourse to address the problem without the assistance of government. A task force on shoreline erosion reported to the 1996 Alabama legislature on the role of government in beach management. The summary report is included here in its entirety:
"Whereas Alabama's Gulf and bay shorelines are valuable to the coastal citizens and the entire state for their economic, environmental and quality of life benefits; and whereas effective erosion solutions are rarely feasible on a lot-by-lot basis because of the natural littoral, sand-sharing system; we believe that shoreline erosion management is an appropriate role for state government in close cooperation with coastal county and municipal governments. Therefore, we recommend that the Alabama legislature give legal authority and funding for shoreline erosion management to the state's existing coastal zone management program. The recommended adequate level of funding is $300,000 to $500,000 for carrying out three tasks:
- monitoring the sand resource at a level adequate for selecting appropriate erosion responses
- funding and implementing solutions to site-specific erosion problems and developing area-specific inlet or beach management plans with local governments. The allocation of this funding should be based on maximizing the benefits to all the state's residents with specific requirements for public access. It could be set up, in part, as a pool of money for matching by local units of government.
- Representing the state's beach related interests when the sand resources are manipulated, whether naturally or artificially.
The state's shoreline erosion management effort should continue to be advised by a board with a similar composition of this task force with representatives from the coastal county and municipal governments."
The recommendations of the task force should be implemented by state government for the future health of the Alabama beaches. Most importantly, it is suggested that the Alabama Legislature give legal authority and funding for beach erosion management to someone in the executive branch of government.
Public Access
Public access to the Alabama Gulf beaches is limited. There are long stretches of beach that have no public access today. Several decades ago, this was not true. Anecdotal evidence indicates that access across private property was common several decades ago but is severely blocked by parking restrictions and fences today. As property values continue to increase, and people from out of the area buy more of this property, Alabama citizens will have less and less access to their own beaches. In the words of the syndicated columnist Rheta Grimsley Johnson in a series of columns about the coast in 1998,
"Used to be, eccentrics eddied up to the shore; now it's rich people who relish rules"
"It's the same story again and again, especially if there is a beach involved. We create a traffic jam getting there, raise buildings that block public access and jealously guard the limited turf"
The limited public access is an insidious threat to the future health of the Alabama beaches. Because of the interconnectedness of the natural littoral system, the most cost-effective solutions to beach erosion problems require government action. The political consensus needed for such proper action will be much harder to obtain when the general public perceives that its access to the beaches is limited. A reasonable analogy is highway construction. Highways are the best solution to many transportation needs, they are usually paid for with public moneys, and they are accessible to all citizens.
Unless public access to Alabama's beaches is improved, it is likely that the best solutions will not be politically possible and the beaches of the state will continue to deteriorate for another generation. Methods of increasing public access include requiring beachfront condo developers to provide public access ways, constructing parking access, and acquiring beachfront property by state and local governments.
Beachfront building codes and practices
The Alabama coast has experienced a disproportionate share of property damage caused by hurricanes. Alabama has experienced 5 of the 25 most damaging U.S. hurricanes this century in terms of property damage. By contrast, Alabama has experienced none of the 25 most deadly U.S. hurricanes this century. Major property damage has been sustained due to Frederic, Elena, Opal, and Georges in the last few decades.
The official Federal Emergency Management Agency 100-year flood plain maps for the Baldwin County Gulf coast are wrong. The base flood elevations are underestimated and therefore the maps underestimate the flood areas. The maps and elevations are based on the results from a numerical model study in 1984 that estimated the 100-year flood elevations are about +8 feet. This water level has been exceeded, on the barrier island where the buildings are, at least 4 times in the last 30 years. It appears that the proper 100-year flood elevation on the barrier island is about +13 feet. The result of the inaccurate maps is that buildings are being built at elevations such that they sustain major damage in minor hurricanes. Local governments can adopt more stringent floodplain codes and maps than the federal guidance.
Another part of the damage problem is the building construction. Building techniques that produce buildings easily damaged during hurricanes, such as slab on grade construction instead of pile-supported foundations and construction as close to the water as legally possible, have been built recently along the Alabama coast. The proper engineering of hurricane resistant structures is well established. Principles include designs and techniques for avoiding or resisting the extremely severe wind, water level and wave environment during hurricane landfall. If these engineering and design recommendations were followed, a significant reduction in damages would occur.
Two suggestions for local governments are:
- Raise the minimum building "flood" elevations to the true 100-year flood level (probably about 12-13 feet).
- Adopt more stringent building codes for the beachfront properties and other high hazard areas that require hurricane resistant structures.
Adoption of these suggestions would save millions of dollars of damage in future storms. They are probably the two most effective steps that could be undertaken to mitigate future damages along the Alabama coast.
Setting construction of hard structures (bulkheads, buildings, etc) farther back from the water is suggested. Allowing the beach to fluctuate in width without hitting such structures is an excellent approach to insuring adequate beach width. The existing construction control setback lines provide for a small "buffer zone" to accommodate shoreline fluctuations. These should be considered minimal distances. At several locations, these lines could be re-evaluated and perhaps moved north. Local governments and individual developers should consider greater setbacks. Part of the problem is that individual developers attempt to maximize the number of condo units per lot by pushing the buildings as far south as possible to meet local parking ordinances. The beaches are more valuable to the community than parking spaces.
Beach nourishment, suggested above, is a viable alternative to setting construction farther back. A successfully engineered beach will accomplish many of the same goals as a construction setback. For the portions of the coast that have large condominiums on narrow beaches, beach nourishment is an attractive alternative.
Future research
Suggestions to federal, state and local government for future coastal research that will have the most impact on the management of the Alabama beaches are in three directions:
- Better documentation of Hurricane Georges impacts and damages. The issues raised above including the relationships between beach width and damage, elevation and damage, sand reservoir volume and damage, and construction technique and damage could be better documented. Also, the dune erosion modeling methodology could be improved by using Georges data as a calibration data set.
- Local coastal processes studies. Both Gulf Shores and the Perdido Pass area need more detailed, local coastal processes studies. Our understanding of the technical issues related to the coastal processes is best at Dauphin Island. Several studies of the island have quantified the erosion and its causes. Understanding the beach dynamics better at Gulf Shores and Perdido Pass will be valuable input to decision-makers.
- Continued and improved monitoring of the state's beaches. The data used in this report are the results of limited funding for monitoring. This level of monitoring, annual low altitude air photos with sparsely spaced beach profiles, can be considered a bare-bones approach. It should continue and be augmented. Suggested modifications to the monitoring program include more densely spaced survey information about the behavior of the beaches and some measure of the forces, primarily waves, causing the behavior. Also, the behavior of any project that adds sand to the beach and dune system should be monitored to develop an improved understanding of the overall impacts of engineered beach nourishment along the Alabama coast.
The response of the beaches to Hurricane Georges essentially confirmed that the Alabama Coastal Programs management efforts are based on proper concepts. Before the storm, the state's management efforts were based on our best understanding of the complex interactions between the natural and constructed systems. This understanding was developed with input from a decade of focussed, applied coastal research. Future management decisions can be positively influenced by sound research input.
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