James C. Gibeaut

Regional controls on geomorphology, hydrology, and ecosystem integrity in the Orinoco Delta, Venezuela

Interacting river discharge, tidal oscillation, and tropical rainfall across the 22,000 km2 Orinoco delta plain support diverse fresh and brackish water ecosystems. To develop environmental baseline information for this largely unpopulated region, we evaluate major coastal plain, shallow marine, and river systems of northeastern South America, which serves to identify principal sources and controls of water and sediment flow into, through, and out of the Orinoco Delta. The regional analysis includes a summary of the geology, hydrodynamics, sediment dynamics, and geomorphic characteristics of the Orinoco drainage basin, river, and delta system. Because the Amazon River is a major source of sediment deposited along the Orinoco coast, we summarize Amazon water and sediment input to the northeastern South American littoral zone. We investigate sediment dynamics and geomorphology of the Guiana coast, where marine processes and Holocene history are similar to the Orinoco coast. Major factors controlling Orinoco Delta water and sediment dynamics include the pronounced annual flood discharge; the uneven distribution of water and sediment discharge across the delta plain; discharge of large volumes of water with low sediment concentrations through the Rio Grande and Araguao distributaries; water and sediment dynamics associated with the Guayana littoral current along the northeastern South American coast; inflow of large volumes of Amazon sediment to the Orinoco coast; development of a fresh water plume seaward of Boca Grande; disruption of the Guayana Current by Trinidad, Boca de Serpientes, and Gulf of Paria; and the constriction at Boca de Serpientes.

Meso-scale transfer of sand during and after storms: implications for prediction of shoreline movement

Abstract Monitoring beach volume changes of the Texas Coast following a major hurricane reveals the impact of storms on sand dispersal and shoreline movement at spatial and temporal scales encompassing tens of kilometers and decades. Beach volume histories at profile sites show the interdependence of sand exchange among adjacent sites and the spatial autocorrelation of sand movement. Beach volume histories also indicate periods when either longshore or cross-shore transport predominate and illustrate the long-term effects of coastal structures on beach mobility. This study confirms that net losses of sand from updrift barriers may not be directly linked with net gains of sand on adjacent downdrift barriers. Instead, sand dispersal within a coastal compartment may depend partly on the dynamics of shoals and temporary sand storage at the intervening tidal inlet. In our study, sand eroded from the updrift barrier (Galveston Island) is deposited in a terminal sand flat of the barrier, whereas sand accreted to the downdrift barrier (Follets Island) is derived from the intermediate ebb-tidal delta (San Luis Pass). Unlike continuous sand bypassing on some microtidal, wave-dominated coasts, sand bypassing at San Luis Pass is episodic, event driven, and inefficient, and sand is not transferred directly from one barrier to the next. p ]Because storms rapidly redistribute beach sediment, they can be the most important factor controlling short-term (

Mud volcanoes of the Orinoco Delta, Eastern Venezuela

Abstract Mud volcanoes along the northwest margin of the Orinoco Delta are part of a regional belt of soft sediment deformation and diapirism that formed in response to rapid foredeep sedimentation and subsequent tectonic compression along the Caribbean–South American plate boundary. Field studies of five mud volcanoes show that such structures consist of a central mound covered by active and inactive vents. Inactive vents and mud flows are densely vegetated, whereas active vents are sparsely vegetated. Four out of the five mud volcanoes studied are currently active. Orinoco mud flows consist of mud and clayey silt matrix surrounding lithic clasts of varying composition. Preliminary analysis suggests that the mud volcano sediment is derived from underlying Miocene and Pliocene strata. Hydrocarbon seeps are associated with several of the active mud volcanoes. Orinoco mud volcanoes overlie the crest of a mud-diapir-cored anticline located along the axis of the Eastern Venezuelan Basin. Faulting along the flank of the Pedernales mud volcano suggests that fluidized sediment and hydrocarbons migrate to the surface along faults produced by tensional stresses along the crest of the anticline. Orinoco mud volcanoes highlight the proximity of this major delta to an active plate margin and the importance of tectonic influences on its development. Evaluation of the Orinoco Delta mud volcanoes and those elsewhere indicates that these features are important indicators of compressional tectonism along deformation fronts of plate margins.

Barrier Islands: Coupling Anthropogenic Stability with Ecological Sustainability

Abstract Barrier islands provide a host of critical ecosystem services to heavily populated coastal regions of the world, yet they are quite vulnerable to ongoing sea level rise and a potential increase in the frequency and intensity of oceanic storms. These islands are being degraded at an alarming rate, in part because of anthropogenic attempts at stabilization. In this article, we outline a possible sustainability strategy that incorporates the natural degree of substrate instability on these sedimentary landscapes. We recommend placing the focus for managing barrier islands on maintaining ecosystem function and process development rather than emphasizing barrier islands as structural impediments to wave and storm energy.

Mapping coastal environments with lidar and EM on Mustang Island, Texas, U.S.

We explore whether lidar (light detection and ranging) and EM (electromagnetic induction) can improve the accuracy and resolution of wetland mapping that has historically been based chiefly on analysis of aerial photographs. Using Mustang Island on the central Texas coast as an example, we exploit (1) the known strong relationship between elevation and coastal habitat by comparing a lidar-derived digital elevation model (DEM) with existing wetland maps and detailed vegetation transects, and (2) another known strong relationship between soil and water salinity and coastal habitat by collecting and comparing EM-derived conductivity data with elevation and vegetation type across the island.

Assessment and Monetary Valuation of the Storm Protection Function of Beaches and Foredunes on the Texas Coast

ABSTRACT Taylor, E.B.; Gibeaut, J.C.; Yoskowitz, D.W., and Starek, M.J., 2015. Assessment and monetary valuation of the storm protection function of beaches and foredunes on the Texas coast. Beaches and dunes dampen wave energy and protect against storm surge. This protection is not uniform and varies according to geomorphic characteristics along the coast. Barrier island communities should identify the protection afforded by beaches and dunes to better assess their vulnerability and inform decision making regarding management alternatives. Our study presents a classification identifying a theoretical level of protection that beaches and foredunes could provide against overwash resulting from a tropical storm or hurricane along Mustang and North Padre Islands, Texas. In addition, a monetary valuation of this protective function is estimated at a site level. The theoretical level of storm protection was determined by assessing the response of representative beach-dune profiles to a set of synthetic storms and identifying the storm level at which profiles were overwashed. A monetary value was then assigned to the storm protection function of beach-dune profiles using a replacement cost approach. The level of protection afforded by beaches and foredunes varies across the islands. Some areas are more vulnerable to overwash and inundation during low-intensity storms. About 50% of the assessed beach-dune profiles provide overwash protection against at least a 100-year storm. Areas with the highest protection levels (100 and 200 y) share the following characteristics: (1) they have high dunes (>4 m in elevation), (2) they are in largely undeveloped areas or where buildings are at least 150 to 200 m landward of the line of vegetation, and (3) they generally have a wider beach–foredune complex width. The total annual value of the storm protection function of beaches and foredunes is estimated to be

Multisensor classification of wetland environments using airborne multispectral and SAR data

141.4 million (USD 2013, replacement cost equivalent).

Modeling wetland vegetation using polarimetric SAR

Near concurrent airborne data were acquired over the wetlands of the Bolivar Peninsula on the Texas coast by the NASA/JPL AIRSAR (June 28, 1996) and NASA/Stennis Space Center Calibrated Airborne Multispectral Scanner (CAMS) (July 3, 1996), both at 4 m spatial resolution. Several approaches which utilize information from both sensors are investigated for classifying the landcover in these data sets. Differences in statistical characteristics of the data necessitate individual parametric models for observations from each sensor, so data are initially classified separately, then a final classification is obtained by combining results from the statistical models using different multisensor integration techniques. These integrated results are compared to single-sensor classification results, as well as to a multisensor classification based on artificial neural networks.

Modeling SAR backscattering response to coastal inundation

Airborne polarimetric synthetic aperture radar (SAR) data are investigated for their potential in mapping herbaceous coastal wetlands. The subenvironments of coastal wetlands have very distinct vegetation cover and surface properties. Qualitative analysis of the SAR images reveals the relative importance of surface and vegetation scatter in these subenvironments. Furthermore, sampled SAR data distinctly separate the subenvironments, indicating that classification techniques could be used to discriminate among them. Although wetland environments are typically too vegetated to use empirical surface models to explain the SAR return, discrete scatterer models can be used to account for the scattering due to the vegetation. A discrete scatterer model fitted to a coastal wetland site on Bolivar Peninsula near Galveston, Texas provides insight into the dominant scattering mechanisms, and may aid in the accurate mapping of coastal wetlands.

COMBINING EM AND LIDAR TO MAP COASTAL WETLANDS: AN EXAMPLE FROM MUSTANG ISLAND, TEXAS

Synthetic aperture radar (SAR) data are investigated for their potential to detect the presence of inundation in a coastal marsh. Polarimetric SAR data were acquired by the NASA/JPL AIRSAR sensor over the coast of Texas, USA during dry conditions in 1995 and again during wet conditions in 1996. Some environments discernable in the L-band data from 1995 are not discernable in the data from 1996. A microwave scattering model is developed to simulate the SAR response. An increase in the double-bounce component of the model indicates the presence of inundation.