Bolivar Peninsula Research Articles

Damage Curves Derived from Hurricane Ike in the West of Galveston Bay Based on Insurance Claims and Hydrodynamic Simulations

Hurricane Ike, which struck the United States in September 2008, was the ninth most expensive hurricane in terms of damages. It caused nearly USD 30 billion in damage after making landfall on the Bolivar Peninsula, Texas. We used the Delft3d-FM/SWAN hydrodynamic and spectral wave model to simulate the storm surge inundation around Galveston Bay during Hurricane Ike. Damage curves were established through the relationship between eight hydrodynamic parameters (water depth, flow velocity, unit discharge, flow momentum flux, significant wave height, wave energy flux, total water depth (flow depth plus wave height), and total (flow plus wave) force) simulated by the model and National Flood Insurance Program (NFIP) insurance damage data. The NFIP insurance database contains a large amount of building damage data, building stories, and elevation, as well as other information from the Ike event. We found that the damage curves are sensitive to the model grid resolution, building elevation, and the number of stories. We also found that the resulting damage functions are steeper than those developed for residential structures in many other locations.

Eco-morphological evolution of the Bolivar Peninsula (Texas, U.S.A.) during the last 2,000 years: A multi-proxy record of coastal environmental changes

In the face of rapidly changing climate and increasing natural and anthropogenic disturbances, the long-term dynamics of coastal ecosystems in relation to hurricanes and human activities has become a focus of research for ecologists and geomorphologists across the Gulf of Mexico. This study integrates diatom, remote sensing, geochemical, and hydrodynamic analyses to document the ecological and morphological development of the barrier-island and estuary-wetland complex bordering Galveston Bay, Texas, from the late Holocene to the Anthropocene. The multi-proxy dataset revealed two major ecological shifts between 1320 and 840 cal yr BP and between 230 cal yr BP and 2008 AD in Galveston Bay. The first shift was driven by the landfall of a backdoor hurricane at ∼1000 cal yr BP in combination with the aperiodic and intense long-shore current that caused the barrier complex to retreat over fluvial deposits while the Bolivar Peninsula was growing toward the west. These morphological changes resulted in a narrower inlet, hence, restricting the marine influence from entering the bay and converting Galveston Bay to a wave-dominated estuary that was shallower and fresher. The second shift was caused by increasing modification to the waterway and infrastructures since 1800 AD. As a result, rapid sediment accretion was induced near the North Jetty, forming the current Bolivar Flats and setting the stage for mangrove colonization. The warming climate and hurricanes in recent decades acted as catalysts that accelerated mangrove expansion on the Bolivar Peninsula. Our results imply that the proposed coastal barrier system will likely increase the sediment deficit, alter the biogeochemical environment, and impact the primary productivity in the bay. However, on a regional scale, more and more mangrove stands are expected to appear around estuaries and lagoons, and along man-made jetties and barriers along the Gulf.

Physical modeling of progressive damage and failure of wood-frame coastal residential structures due to surge and wave forces

A physical model study was performed to examine the forces and response of 1:6 scale wood-frame coastal residential structures subjected to storm surge and waves. An on-grade and an elevated specimen were tested and exposed to regular waves with varying water depths and wave heights to simulate typical wave/surge conditions resulting from landfall hurricanes on low-lying barrier islands such as Hurricane Sandy that impacted the US East Coast in 2012 and Hurricane Ike that affected the US Gulf Coast in 2008. Results show that through careful design, wood-frame model specimens can be constructed to have similar strength and stiffness compared to full-scale structures. The two specimens were subjected to increasing surge and wave conditions, and the progressive damage was monitored using LiDAR. The on-grade specimen failed at a lower water level than the elevated specimen as expected. Both specimens showed failure modes consistent with the observed damage of residential structures in Ortley Beach, NJ, after Hurricane Sandy and on the Bolivar Peninsula, TX, after Hurricane Ike. The pressure distribution on the underside of the elevated structure and the resulting vertical forces on the on-grade structure were also examined in this study. The pressure distribution and the resulting vertical forces were significantly affected by water depth, wave height, and air gap. The results indicate that maximum vertical forces are positively correlated to wave height and water depth and negatively correlated to the air gap. The breaking type also affects vertical forces. Nonbreaking waves correlated to relatively small vertical forces, and waves breaking directly on the specimen correlated to peak vertical forces. Accelerometer data showed that the specimen decreased in stiffness during the tests due to progressive damage. An uplift pressure distribution equation was developed for an elevated residential structure as a function of wave height and air gap. The equation is generally conservative when compared to other data sets. The results and data presented in this study increase the current knowledge of the interaction between waves and residential structures, which may be useful to increase the resiliency of coastal communities.

Explosions and Fires at the Ports of Texas City and Houston: A Comparative Analysis of Waterside-Landside Crises, 1947–2019

Explosions and Fires at the Ports of Texas City and Houston:A Comparative Analysis of Waterside-Landside Crises, 1947–2019 Eric Pearson (bio) Click for larger view View full resolution The SS Amoco Virginia on fire at Hess Terminal, November 8, 1959. Photo courtesy of the Houston Fire Memorial. [End Page i] At one point during a confused nightmare of efforts to check the roaring flames and rescue the injured, Jesse Caveness, Harris County civil defense director, declared: "If this ship [Amoco Virginia] blows, it will be worse than Texas City." —"Fire Menaces Oil Tanks in Houston Area," Chicago Daily Tribune, Nov. 9, 1959. The Houston Ship Channel is one of the busiest seaports in the United States. It extends from a turning basin located approximately four miles east of downtown Houston to the Gulf of Mexico between Galveston Island and Bolivar Peninsula, a distance of fifty-two miles.1 The channel has been deepened and widened over the decades in order to accommodate increasingly larger vessels to keep pace with the needs of Texas industry. It measures forty feet in depth for much of its length and from three hundred to four hundred feet in width.2 In addition to general cargo facilities, the channel is home to major petrochemical plants. The heavy concentration of these oil and gas companies presents the potential danger of explosions and fires, as was seen in 1959 when a major gasoline fire engulfed the tanker Amoco Virginia and in 1979 when the tanker Chevron Hawaii exploded after being struck by lightning [End Page 1] while loading oil. These events caused concern that a chain reaction of explosions among the chemical and petroleum industries that line the ship channel could touch off a disaster similar to the one at Texas City that killed more than five hundred people in 1947—the worst industrial accident in the nation's history. Historians have not fully explored the links between these disasters and how the lessons learned from them were (or were not) applied toward industrial safety and public welfare. There were varying degrees of carelessness in many of these incidents. Certain questions need to be asked regarding the roles government and industry have played since the Texas City disaster and each of the succeeding explosions and fires at the Port of Houston. What impact did these accidents have on industrial safety, pollution control, and Texas industrialization? The Texas City disaster started with a Liberty cargo ship named the Grandcamp, which was built in Los Angeles in 1942 and originally named the Benjamin R. Curtis.3 The ship was rather small compared to today's cargo vessels, measuring a length of 423 feet and a gross tonnage (a nonlinear measure of a ship's overall internal volume) of 7,176 tons. The United States transferred ownership of the vessel after the war to the French government, which changed the ship's name. The Grandcamp loaded cargo such as twine, cotton, peanuts, and drilling equipment in Houston prior to arriving in Texas City on April 11, 1947, to load ammonium nitrate fertilizer.4 This could not be done in Houston because the loading of ammonium nitrate was banned by the Houston Port Authority.5 U.S. Coast Guard regulations did not prohibit the loading of the chemical compound in Texas City due to the fact ammonium nitrate was listed as a "dangerous cargo" and not as an "explosive."6 The Port of Texas City in 1947 was home to several large plants, including "the Monsanto Chemical Company, Humble Oil and Refining Co., Stone Oil Co., Republic Oil Refining Company, 11 warehouses, 9 piers, one grain elevator, and two thirds of the residential area of Texas City," according to a Coast Guard report.7 Many residential blocks stood adjacent [End Page 2] to the industrial complex and the nearby docks where the Grandcamp was moored. Click for larger view View full resolution SS Grandcamp. Moore Memorial Public Library, Texas City. The Texas City disaster began on April 16, 1947, when a small fire started in one of the cargo holds of the Grandcamp, which contained some two thousand tons of ammonium nitrate in one hundred...

A holistic approach to evaluating dune cores

As population density increases in coastal counties, shoreline stabilization efforts continue to gain momentum to protect infrastructure. Although protection techniques vary from ‘soft’ to ‘hard’ engineering, this paper focuses on a ‘hybrid’ technique utilizing geotubes as artificial dune cores. Previous literature presents conflicting results on the efficacy and potential impacts of dune cores on a beach-dune system. Here we evaluate and quantify the geomorphic impacts following dune core installation and investigate their economic feasibility. This was completed by comparing five case studies: Sea Isle City, NJ; Bolivar Peninsula, TX; Grand Isle, LA; Santa Rosa Beach, FL; and Nantucket Island, MA. An economic assessment was completed to compare dune core installation costs and repairs to alternative shoreline hardening methods. LiDAR data were used to compare dune slope, beach width, and beach volume between digital transects adjacent to and in front of the dune core installations. Digital elevation models (DEMs) were generated to provide a holistic view of geomorphic change and to assess whether erosion occurred landward of the dune core. Results indicate that dune cores are an economically feasible option compared to alternative methods. Limitations include UV exposure, wave influence, and heavy winds. Morphologically, beach width was 29.1% wider in adjacent transects and dune slope was 39.1% steeper in front of the dune core. Beach volume was lower by an overall average of 23.4%. The findings from this study suggest that dune cores are a ‘hard’ or ‘grey’ protection method.

Responses by Atlantic Ghost Crab (Ocypode quadrata) Populations to Hurricane Impacts on a Texas Beach: A 10-Year Study

The Atlantic ghost crab (Ocypode quadrata) is a widely distributed predator and scavenger along Atlantic Ocean and Gulf Coast beaches. A long-term study was initiated on the Bolivar Peninsula of Texas in 2006 to assess the impact of human activity on ghost crabs. Line transects were used to determine crab burrow arrangement at a high-impact site and a low-impact site. Differences were found between the two sites in number of active burrows per transect, burrow density, the diameter of burrow openings, burrow distance to the high-water line, and nearest-neighbor distances. In Fall 2008, Hurricane Ike struck the study sites. Re-examinations of the sites in 2010 showed changes in ghost crab burrows. The high-impact site experienced a decline in human activity – beach width increased by > 50%, the number of burrows/transect tripled, and nearest-neighbor distances decreased by one-third. The hurricane also reshaped the low-impact site on the western tip of the peninsula as beach width decreased by two-thirds, burrow density increased by sevenfold, and nearest-neighbor distances decreased by one-half. Sampling in 2012, 2014, and 2016 show that some of the physical characteristics of the beach gradually returned to near pre-hurricane status. However, reduced beach space at the low-traffic site remained, with higher burrow density and reduced crab size persisting 8 years after the hurricane, and the post-storm reduction in human traffic in the high-impact site has maintained higher burrow density there even as traffic increased. Monitoring the ecological impact of hurricanes is of growing importance as global climate change could lead to increased frequency and severity of tropical storms.

SMALL BUILDING PERFORMANCE IN HURRICANE IKE ON THE BOLIVAR PENINSULA

Hurricane Ike made landfall on the U.S. Gulf of Mexico coast on September 13, 2008 over the Galveston Bay Entrance in Texas (Edge, 2013). The Bolivar Peninsula is a barrier island/peninsula on the east side of the Entrance that received peak overland storm surge and wave heights in the right front quadrant of the hurricane. Prior to the storm Bolivar had been developed with 6000+ buildings, primarily low-density, single-family houses elevated on piling foundations. Over 2000 buildings were destroyed during the storm.

PATTERNS OF GASTROPOD MOLLUSK PREDATION ON BIVALVE MOLLUSKS ALONG THE UPPER TEXAS GULF COAST

Abstract Predation on bivalve mollusks by gastropod mollusks is common in coastal regions of the United States; however, few previous studies have examined whether drilling gastropods exhibit prey selection. In 2016, shells with small holes drilled by as many as two gastropod predators were collected at three sites separated by 30 km along the Texas Upper Gulf Coast on the Bolivar Peninsula (29° 40′N, 94° 90′W). The likeliest predators in these waters are the southern oyster drill (Stramonita haemastoma Linnaeus 1767) and the moon snail (Neverita duplicate Say 1822). Collected shells were identified to species and measurements were taken to examine statistical relationships between predators and prey species. These measurements included drill-hole diameter, shell thickness, drill-hole completeness, number of drill attempts, and collection site. Across the three locations, 17 different species of shells with drill holes were collected; of these, we focused on the ten most abundant species (n = 277 shells). The sample showed high variation in drill-hole diameter, shell thickness, and drill-hole completeness. Both the total number of holes and mean drill-hole diameter differed significantly among prey species (ANOVA, both P < 0.0001). In addition, drill-hole diameter correlated directly with prey shell thickness (P < 0.0001). Shells whose drill holes were complete were significantly thinner than shells with incomplete holes (P < 0.0001). Mean prey shell thickness, mean drill-hole diameter, and mean number of drill holes all differed significantly by collection site (all P < 0.0001). Ecological and morphological implications related to gastropod predation on mollusks are discussed.

A graph-based approach for assessing storm-induced coastal changes

ABSTRACTHurricanes and tropical storms are severe threats to coastal properties, settlements, and infrastructure. Airborne light detection and ranging (lidar) surveys conducted before and after storm events allow detailed analysis of coastal geomorphologic and sediment volumetric changes and have been proved very useful in the study of coastal changes. Traditionally, most studies use the pixel-based differencing method to quantify the spatial extent and magnitude of coastal changes based on sequential lidar surveys. This research presents a graph theory-based approach and associated software tools for representing and quantifying storm-induced damages to buildings, beaches and sand dunes, coastal vegetation canopy, and infrastructure. Generation of elevation difference grids, construction of local contour trees, and derivation of semantic properties are key components of the new algorithm for change object detection and extraction. An ontology and taxonomy are proposed to classify change objects into different types of coastal damages in terms of their semantic properties. This method has been successfully applied to assess damages of Hurricane Ike to the Bolivar Peninsula on the Texas Gulf Coast based on pre- and post-storm airborne lidar data and colour infrared aerial photographs.

Shoreface ravinement evolution tracked by repeat geophysical surveys following Hurricane Ike, Bolivar Peninsula, Texas, 2008–2013

We have investigated the impact of Hurricane Ike on the shoreface of the Bolivar Peninsula, Texas, using three near-surface marine geophysical surveys during a five-year span following the storm, which made landfall in September of 2008. Multibeam bathymetry, sidescan backscatter, and CHIRP subbottom reflection data were collected during each survey. The first survey, in November, 2008, discovered the presence of an erosional, landward-facing scarp across a broad of the barrier spit shoreface at approximately 3.5-m water depth. The erosion incised into a shallow reflection horizon interpreted as the Holocene shoreface ravinement, exposing lag deposits that were truncated at the scarp and forming a thin high-backscatter anomaly. Up to 1.0 m of material was excavated shoreward of the scarp, including up to 0.5 m of shoreface sand above the shoreface ravinement, and another 0.5 m of indeterminate lithology below, consisting of easily erodible material. A second survey, in May 2010, found that the scarp had migrated seaward by up to 100 m and the depth of erosion indicated by the scarp had reduced to approximately [Formula: see text]. In a May 2013 survey, the scarp was no longer in evidence. The initial erosional event is interpreted to be caused by the ebb flow of the storm surge across the peninsula compounded by high-wave orbital velocities in the waning storm. This erosional event and its subsequent evolution demonstrate an impact on the shoreface lasting for years post-storm, as the shoreface gradually adjusted to a new equilibrium profile. These results document that an advancement of a shoreface ravinement can be caused by a single large event (e.g., tropical storm or hurricane) in this microtidal, relatively low wave energy setting. This process, tracked with near-surface geophysical techniques, was a key but seldom-observed component of the back stepping of barrier islands during sea-level rise.

Near surface geophysics: Investigating the dynamic coastal environment — Introduction

The coastal zone is a habitat for much of the world’s population, a key economic driver for fishing, shipping, recreation and tourism, and a critical wetlands ecology. However, the coastal zone is also a dynamic setting undergoing significant change at many different time scales. Large storms, for example, can restructure coastal morphology on the scale of hours or days. Rising sea level or changes in sediment supply will alter the coastline over decades to centuries and longer. These are human-relevant time scales, and such changes can have major impacts on coastal infrastructure, habitability, and ecology. Human activity also impacts the coast; e.g., hardening of coastlines and inlets, reduction in sediment supply due to damming, artificial beach replenishment, extraction of ground water for human consumption and agriculture, and the introduction of pollutants. Both land- and marine-based near-surface geophysical methods can play a significant role in understanding the many processes that impact …

Impacts of Hurricane Ike on the beaches of the Bolivar Peninsula, TX, USA

Hurricane Ike caused substantial beach erosion along the coast of the Bolivar Peninsula, TX. Much of the erosion was caused by the offshore (ebb) flow of the ca. 5m storm surge that formed spatially discrete scour features. Using aerial photography and repeat LiDAR data, we identify five types of scour features and describe the alongshore distribution in four flow environments. Type 1 scours are relatively small and compact features associated mainly with flow off a wide, vegetated (grasses, shrubs, trees) surface across a wide beach. Type 2 scours are large and branching forms associated mainly with flow that was channeled by streets or gaps between structures. Type 3 scours are large and blocky features associated with flow off a marsh surface, across a highway, which removed almost all beach sands from the surface. Type 4 scours are elongated, shore perpendicular channels associated with the same flow characteristics as Type 3 scours. Type 5 scours are elongated, shore-perpendicular features, sometimes branching, associated with flow through gaps in a destroyed shore protection structure. Repeat imagery indicates that many of the features persisted for at least seven months. Recent aerial photography indicates that aspects of some features remained evident more than three years after Ike's landfall.

Marine Archeological Survey of the Proposed Bolivar Ferry Dredge Spoil Pile Expansion Area, Galveston County, Texas

Archeologists from AmaTerra Environmental, Inc. (AmaTerra) and Southeastern Archaeological Research, Inc. (SEARCH; collectively the Team) conducted intensive underwater archeological remote sensing survey on behalf of the Texas Department of Transportation (TxDOT) on a proposed dredge spoil expansion area south of the Bolivar Peninsula at the mouth of Galveston Bay, Galveston County, Texas. The survey was required for compliance with the National Historic Preservation Act of 1966, as amended, due to dredge permits to be issued by the US Fish and Wildlife Service, and the Antiquities Code of Texas, due to its location on lands owned by a political subdivision of the State of Texas (the Texas General Land Office). Completed under Antiquities Permit 6272, the survey area includes the 51-acre dredge spoil expansion footprint and the original 16-acre dredge spoil pile (67 acres total). The archeologists utilized towed marine magnetometer and side-scan sonar survey along 12 parallel, 20-meter-interval transects to assess the full archeological Area of Potential Effects. The survey area was found to be littered with isolated modern metallic debris. Side-scan sonar imagery revealed a submerged surface that was generally flat with no indications of shipwrecks and a large oyster reef along the southwestern quarter. One large metallic feature located within the survey area (Anomaly M1) was identified as a fallen modern navigational sighting marker tower. None of the archeological survey data, sensor readings, or imagery from the proposed expansion area is consistent with expected signatures of historic-age shipwrecks. Archeologists did re-identify the previously-documented magnetic anomaly M44 that was recommended for avoidance or testing within the original dredge pile area. If the avoidance zone continues to be observed, it will not be impacted by the current undertaking. As such, the project is recommended to proceed with no Historic Properties, State Archeological Landmarks, or archeological sites impacted in accordance with guidelines outlined in 36 CFR 800 and 13 TAC 26. No sites were identified and no artifacts were collected during the course of the survey. Accordingly, all project-generated notes, forms, and other materials will be permanently curated at AmaTerra’s office in Austin, Texas and SEARCH’s office in Pensacola, Florida.

INUNDATION AND DESTRUCTION ON THE BOLIVAR PENINSULA DURING HURRICANE IKE

Hurricane Ike was one of the most destructive storms in US history, and caused catastrophic damage to the Bolivar Peninsula, Texas, with over 4.7m measured surge at the Gulf of Mexico shoreline. This surge began unusually early, reaching 2.5m at 25 hours before landfall while winds were both weak and shore-parallel. The strong forerunner surge resulted from Coriolis effects on the wind-driven alongshelf current, and occurred previously in the similarly destructive 1900 and 1915 Galveston Hurricanes. In onshore areas with strong wave action, damage was near-total to buildings whose flooring systems could be reached by wave crests, while slightly more elevated buildings survived almost unscathed. There was much less of a correlation between survival and elevation in areas with small waves.

Transgressive Ravinement versus Depth of Closure: A Geological Perspective from the Upper Texas Coast

Abstract The upper Texas coast is one of the most populated areas along the Gulf of Mexico. Three dynamic barriers along this section of coastline (Bolivar Peninsula, Galveston Island, and Follets Island) have a well-documented history of shoreline change. Numerous engineering studies incorporating both sedimentological data and numerical models have been established for this system to understand sediment fluxes. However, rarely have previous studies examined sediment fluxes for the upper Texas coast in light of certain fundamental concepts of coastal geology. Here, we discuss the current theory and understanding of barrier island dynamics from a geologic standpoint as they relate to sediment budgets for the upper Texas coast. From sediment cores, we quantify both shoreface and washover sand fluxes, which previously were not incorporated as sand sinks into sediment budgets for this system. Shoreface sand fluxes represent a sizable portion of the total budget, whereas modern washover sand fluxes are minima...

Storm surge propagation in Galveston Bay during Hurricane Ike

We studied Hurricane Ike's storm surge along the Texas–Louisiana coast using the fully nonlinear Finite-Volume Coastal Ocean Model (FVCOM, by Chen et al., 2003) with a high-resolution unstructured mesh. The model was validated with USGS surge data collected during Hurricane Ike. This study focused on 1) how the surge wave propagates into and within Galveston Bay and 2) the importance of the bay's barrier system. Ike's coastal surge propagated alongshore due east towards Louisiana, partly because of Bolivar Peninsula, which, together with Galveston Island, provided a barrier protecting the bay. In the upper bay, a west–east oscillation of water surface gradient of about 0.08 m/km was found and studied. We then varied Bolivar Peninsula's topography for different simulations, examining the role of barrier islands on surge propagation into the bay. Results suggest that when the Peninsula's height (or volume) was reduced to about 45% of the original, with two breaches, the bay was exposed to dangerously high water levels almost as much as those if the Peninsula was leveled to just 0.05 m above the Mean Sea Level, underlining the nonlinear nature of this bay-barrier system.

Building Destruction from Waves and Surge on the Bolivar Peninsula during Hurricane Ike

The Bolivar Peninsula in Texas was severely impacted by Hurricane Ike with strong winds, large waves, widespread inundation, and severe damage. This paper examines the wave and surge climate on Bolivar during the storm and the consequent survival and destruction of buildings. Emphasis is placed on differences between buildings that survived (with varying degrees of damage) and buildings that were completely destroyed. Building elevations are found to be the primary indicator of survival for areas with large waves. Here, buildings that were sufficiently elevated above waves and surge suffered relatively little structural damage, while houses at lower elevations were impacted by large waves and generally completely destroyed. In many areas, the transition from destruction to survival was over a very small elevation range of around 0.5 m. In areas where waves were smaller, survival was possible at much lower elevations. Higher houses that were not inundated still survived, but well-built houses at lower elevations could also survive as the waves were not large enough to cause structural damage. However, the transition height where waves became damaging could not be determined from this study.

Offshore transport of sediment during cyclonic storms: Hurricane Ike (2008), Texas Gulf Coast, USA

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Cultural Resource Assessment and Archival Research for the Proposed Galveston-Bolivar Causeway Galveston County, Texas

In 2008, following a cultural resources remote-sensing survey for the Proposed Galveston-Bolivar Causeway Project, PBS&J was contracted by the Texas Department of Transportation to perform three studies as supplements to the original investigation. These studies comprised a hydraulic probing investigation at the Old Port Bolivar slip in the area of a charted historic shipwreck; a review of historic maps and aerial photography of the Area of Potential Effect (APE); and an assessment of a collection of abandoned hulks at the northwestern tip of Bolivar Peninsula. All three studies were completed between June and August 2008. The hydraulic probing investigation at the Old Port Bolivar slip located the remains of a potential submerged shipwreck site measuring approximately 40 x 11 feet at a depth of 17–18 feet below the water surface. PBS&J also examined over 40 historic maps from the collections of the National Archives in Washington, D.C. The investigation of historic maps isolated at least 12 shipwrecks within the APE. Historic Tobin aerial photos of the APE acquired by PBS&J were limited to the sets available from 1930 and 1956. One shipwreck anomaly discovered during the 2007 Galveston-Bolivar Causeway remote-sensing survey was captured in the 1956 aerial. The incomplete coverage area of the 1930 photography prevented a review of other known targets. An investigation of the abandoned hulks at Bolivar Peninsula determined that 16 barges are arranged in three primary groups. These barges have either ferrous or wooden hulls; most of the hulks are submerged. Research did not discover parallels for the types of barges examined by PBS&J, but review of barge construction history indicates many of these hulks could likely predate World War II.

Holocene Evolution of the East Texas Coast and Inner Continental Shelf: Along-Strike Variability in Coastal Retreat Rates

ABSTRACT The low gradient east Texas coast and inner-continental shelf, from Sabine Lake at the Texas-Louisiana border to the western end of Galveston Island, experienced extreme along-strike variations in rates of Holocene coastal retreat. Around 7.7 ka a barrier shoreline was located approximately 55 km offshore. Toward the western end of Galveston Island, the shoreline retreated 55 km, occupying a position on the lagoon side of the Island by about 5.3 ka. Toward the Texas-Louisiana border, the shoreline retreated more gradually, occupying a position seaward of Sabine Bank by 5.3 ka. Between 4.7 ka and 2.8 ka the shoreline at Sabine Bank retreated 30 km, while Galveston Island prograded seaward. Bolivar Peninsula began to accrete around 1.5 ka. Heald and Sabine banks, located on the inner continental shelf above terraced fluvial deposits of the Trinity-Sabine incised valley, are the only preserved remnants of these former shoreline positions. Fluctuating rates of sea-level rise were not the forcing mechanism behind episodes of rapid shoreline retreat because these events were localized. Rather, along-strike variations in the rate of transgression were caused by the variable inner-shelf gradients, which increase towards the west, and the orientation of the Sabine incised valley and associated terraced fluvial deposits, which trend northeast-southwest (parallel to shore). As shorelines retreated over fluvial deposits, these served as local sand sources that enabled barrier islands to persist Figure 1. Map of the east Texas inner shelf showing locations of Sabine, Heald, and Shepard banks. Paleotopographic map of the Pleistocene surface (thin contours; Siringan 1993) delineates the Trinity-Sabine incised valley, which formed during the last lowstand of sea level (Thomas and Anderson 1994). Bathymetric contours are shown as thick lines with bold numbers. Dots are core locations. End_Page 405------------------------ offshore, out of equilibrium with sea level. Once these sand sources became depleted, and/or sea level reached some critical threshold, barrier shorelines became stranded offshore as banks, and new shorelines formed landward. The geologic setting of coastal areas, specifically antecedent topography, plays a primary role in controlling coastal evolution. To accurately forecast long-term (centennial to millennial) coastal evolution, it is essential that impacts associated with variations in the underlying geology of coastal areas be incorporated into coastal forecasting models.