Jeffrey G. Paine

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 (

Responses of Stable Bay-Margin and Barrier-Island Systems to Holocene Sea-Level Highstands, Western Gulf of Mexico

ABSTRACT The microtidal, wave-dominated coast of the western Gulf of Mexico displays a variety of Holocene geomorphic features indicating higher-than-present water levels that were previously attributed to storm processes while geoidal sea level was at its present position. Field and aerial-photograph examinations of bay margins, barrier islands, and beach-ridge plains following major hurricanes show that the elevated features are inundated periodically by high storm surge. Despite their inundation, these highstand features are not modified by modern storm processes. Instead, storm-related erosion and deposition are always seaward of and lower than the highstand features and are always limited to the extant shorezone, where elevations typically are less than 1.5 m above present sea level. Bay-margin and lagoonal highstand indicators include raised marshes and subtidal flats, wave-cut benches, abandoned wave-cut scarps with fringing marshes and/or beach ridges, and accretionary islands and recurved spits. Other emergent marine features include abandoned compound flood-tidal delta and washover fan complexes attached to barrier islands and anomalously high beach ridges within both the barrier-island complexes and beach-ridge plains. The highest beach ridges, raised marshes and flats, and erosional scarps and benches are manifestations of one or more rising phases and highstands in sea level, whereas the lower marshes and accretionary topography are mainly products of the falling phases and shoreface adjustment to present sea level. Different elevations of beach-ridge sets, discordant truncation of beach ridges, and elevated marine- and brackish-water faunal assemblages preserved in beach ridges, raised marshes and flats, and natural levees are compelling evidence of sea-level fluctuations of ±1 to 1.5 m from about 5500 to 1200 cal yr BP. Independent evidence from studies of geodynamic, climatic, and glacio-eustatic processes can explain the mid-Holocene highstands and late Holocene lowering of sea level that is observed in tectonically stable coastal regions far from former centers of glaciation.

Determining salinization extent, identifying salinity sources, and estimating chloride mass using surface, borehole, and airborne electromagnetic induction methods

[1] Using an example from an oil field in the semiarid Red River basin in Texas, we show that electromagnetic (EM) methods are useful in locating salinized soil and water, determining salinization extent, identifying likely salinity sources, and estimating the total mass of chloride within a saline-water plume. Each of these aspects assists in managing salinization and assessing its impact. We used ground EM instruments to establish salinization boundaries and determine the range of electrical conductivity, airborne measurements to locate potential sources and quantify the lateral extent and intensity of salinization, and borehole measurements and time domain EM soundings to determine salinization depth and relate ground conductivity to chloride content. We estimated infiltration volume and total chloride mass in the plume from EM data and an empirical, site-specific chloride:conductivity ratio established from well data. Because the measured conductivity of water strongly correlates with total dissolved solids concentration, mass estimation could be extended to any ionic constituent that covaries linearly with total dissolved solids concentration. EM methods owe their success to the large increase in electrical conductivity that occurs where highly conductive, saline water infiltrates geologic materials having naturally low conductivities. INDEX TERMS: 0694 Electromagnetics: Instrumentation and techniques; 1831 Hydrology: Groundwater quality; 1894 Hydrology: Instruments and techniques; KEYWORDS: salinization, electromagnetic induction, airborne geophysics, total dissolved solids, produced water, brine

Subsidence of the Texas coast: inferences from historical and late Pleistocene sea levels

Abstract Changes in sea level observed at tide gauges are caused by actual changes in water level and by changes in elevation at the observing station. Recent research has focused on the relationship between climatic change and sea level, but vertical land movement can be just as important, particularly in subsiding sedimentary basins. The purpose of this study is to compare long-term rates of subsidence estimated from upper Pleistocene strata along the central Texas coast with historical subsidence rates from the same area obtained from geodetic surveys and tide gauge data. This comparison shows that historical subsidence rates are much greater than long-term averages and are equal or greater than actual sea-level change along the Texas coast south of Galveston Bay. Long-term (~ 10 5 yr) subsidence rates were estimated by establishing the extent of marine, marine-influenced, and nonmarine strata within the upper Pleistocene Beaumont Formation in the Copano Bay area of the central Texas coast, and comparing the maximum elevation of in-place, marine-influenced deposits with published maximum sea level estimates of 5–8 m above mean sea level (MSL) from correlative, well-dated coral terraces from stable and uplifted areas. In-place, shell-bearing horizons deposited at or below sea level occur no higher than 2 m MSL in the Copano Bay area, suggesting that there has been no more than 6 m of subsidence since the probable time of deposition during the Sangamon interglacial at ~ 120 ka. The long-term, average subsidence rate for this part of the Texas coast is thus 0.05 mm/yr or less. Historical subsidence rates were obtained by: 1. (1) calculating relative elevation changes between National Geodetic Survey first-order leveling surveys conducted in the early 1950s with those conducted in the late 1970s to early 1980s; 2. (2) normalizing the relative elevation differences between surveys to annual rates of change relative to an arbitrarily chosen benchmark; 3. (3) referencing these lines to sea level at three tide gauges; and 4. (4) comparing calculated rates of relative sea-level (RSL) rise along the lines with estimates of eustatic sea-level (ESL) rise. Rates of RSL rise for the Texas coast south of Galveston Bay were generally 4–8 mm/yr; locally, rates were as high as 23 mm/yr. These rates are significantly higher than global averages of ~ 1 mm/yr. Much of the difference is probably caused by subsidence of the Texas coastal zone at rates of 1–22 mm/yr, or 20–440 times the long-term average of 0.05 mm/yr. The highest subsidence rates were found locally where there has been historical water-level decline in shallow aquifers. Lower subsidence rates of 3–7 mm/yr occur regionally where groundwater decline is minimal or nonexistent. Increased subsidence over the long-term average in these areas may be caused by pressure decline in underlying oil and gas reseivoirs.

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.

Analysis of focused unsaturated flow beneath fissures in the Chihuahuan Desert, Texas, USA

Localized flow beneath fissures in arid settings has important implications for waste disposal in these regions. Fissures are surface features or gullies that are underlain by sediment filled fractures. The objectives of this study were to compare unsaturated flow beneath different fissures, investigate the vertical and lateral extent of increased flow associated with fissures, and examine different techniques for evaluating flow in zones containing fissures. Boreholes were drilled directly beneath four fissures and at horizontal distances of 10 and 50 m from the fissures. Physical parameters such as water content and water potential were analyzed in sediment samples and water potential was analyzed in plant samples. Environmental tracers such as Cl, 36ClCl, 3H, D, and 18O were analyzed in sediment samples. A trench was dug beneath one fissure for detailed sampling. Electromagnetic induction was used to measure apparent electrical conductivity in transects perpendicular to the fissures. Unsaturated flow is relatively higher beneath fissures, as evidenced by higher water potentials and lower chloride concentrations there than in surrounding sediments. The lateral extent of high water flux was restricted to the zone directly beneath one fissure but extended to profiles 10 m from two other fissures. The profiles 50 m from all fissures had low water fluxes, as indicated by low water potentials and high maximum chloride concentrations. The vertical extent of high water fluxes was restricted to the upper 10 to 20 m zone, as shown by water potential and chloride fronts within the upper 10 m zone beneath one fissure and by chloride fronts in the upper 20 m zone beneath and 10 m from another fissure. Additional evidence for localized water flux was provided by less enriched D and 18O, and higher plant water potentials in sediments beneath fissures relative to sediments adjacent to fissures. High tritium levels were found in all sampled profiles and cannot readily be explained. Apparent electrical conductivity was higher in two of the four fissures. Multiple independent lines of evidence indicate that subsurface water fluxes are higher at shallow depths beneath fissures; however, the various techniques differ in their effectiveness in delineating higher water fluxes beneath fissures. Multiple profiles drilled in one fissure indicate that there is large variability in flow along this fissure that is attributed to topographic variations and degree of ponding.

Identifying oil-field salinity sources with airborne and ground-based geophysics; a West Texas example

Salinization of soil and groundwater resources is a common problem in the central and southwestern United States where infiltration of saline water into the shallow subsurface impacts wildlife habitat, restricts or eliminates agricultural uses of land, and pollutes aquifers and surface water bodies. Public concern about the environmental effects of saline water has increased interest in identifying salinity sources and determining whether oil‐field brine has been introduced into the subsurface, where it has migrated, and whether it is the cause of specific problems on the land surface, in water wells, and in surface water bodies.

Combining airborne electromagnetic induction and hydrochemistry to quantify salinity contributions to a large basin stream, Colorado River, Texas, USA

We combined multifrequency airborne electromagnetic induction (EM) measurements of apparent ground conductivity with chemical analyses of surface water to delineate natural and oilfield salinity sources that degrade surface water quality by elevating total dissolved solids, chloride and sulphate concentrations along several hundred kilometres of the Colorado River (western Texas, USA). To reduce the cost of airborne geophysical surveying over such large areas, we used a helicopter to tow an EM instrument at low altitude along the stream-axis and measure the apparent electrical conductivity of the ground at multiple frequencies, examined results in the field to identify salinized stream segments and optimal water sampling locations and then flew more detailed surveys over these limited areas rather than over the entire basin as is typical in salinization studies. Minimally processed stream-axis EM data (including apparent conductivities measured at single frequencies and multifrequency ‘spectrograms’ along the stream-axis) helped identify salinized streambed segments, discriminate between surface and subsurface sources of salinity and determine water sampling locations upstream and downstream from each segment. We integrated EM, streamflow and hydrochemical data to calculate salinity loads, identify specific natural and oilfield salinity sources and guide and implement remediation efforts. Stream-axis flight lines offer the advantage of rapidly acquiring high-resolution subsurface conductivity data along long stream segments where traditional gridded flight-line surveys and waterborne measurements are impractical or prohibitively expensive. They also overcome difficulties associated with topographic effects when surveying deeply incised streams. Such surveys provide valuable information on location, extent and type of salinization and can guide water sampling and more intensive ground or airborne measurements.

STREAMBED INDUCTION LOGS: AN AIRBORNE APPROACH TO IDENTIFYING SALINITY SOURCES AND QUANTIFYING SALINITY LOADS

We delineated natural and oil-field salinity sources that degrade water quality in the upper Colorado River (west Texas) and Petronila Creek (Texas coast) by combining multifrequency airborne EM measurements of apparent ground conductivity with chemical analyses of surface water at key stream locations. To reduce the cost of high-resolution airborne surveying over such large areas, we first flew along the stream axes and then examined preliminary results in the field to identify likely salinized stream segments. We then flew more detailed surveys over these areas rather than over the entire basin. Stream-axis EM data also helped identify water-sampling locations upstream and downstream from each salinized segment. We used these data to calculate salinity loads, discriminate among possible natural and oil-field salinity sources, and more effectively implement best-management practices to optimize remediation efforts. We acquired stream-axis airborne EM data along the upper Colorado River using a Geophex GEM-2A instrument operating at five frequencies between 450 Hz and 39 kHz. Increases in chloride, sulfate, and total dissolved solids loading in the upper Colorado River basin occur along eleven segments of elevated apparent conductivity identified from airborne EM data. Each segment encompasses areas of baseflow salinity contributions to the stream from natural dissolution of evaporite minerals in the Permian basin, from oil-field produced water, or both. Analyses of surface water confirm increases salinity loading associated with each segment. Airborne EM data acquired on the coast along Petronila Creek revealed three stream segments with elevated ground conductivity. Increases in chloride, sulfate, and total dissolved solids loading are attributed to shallow baseflow contributions. Using airborne EM and hydrochemistry data, we interpret the dominant salinization mechanism to be historic discharge of produced water into unlined drainage ditches and pits, infiltration into sandy Pleistocene channel deposits, lateral migration as far as several kilometers, and discharge into the stream.

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

We combined airborne lidar and ground-based EM induction measurements with vegetation surveys along two transects across Mustang Island, a barrier island on the Texas coast, to examine whether these methods can be used to map coastal wetlands and associated geomorphic environments. Conductivity varied inversely with elevation along both transects. Elevation and conductivity profiles correlated reasonably well with habitat mapped in the largely imagery-based 1992 National Wetland Inventory (NWI), but they possessed greater detail and identified misclassified habitat. Detail achievable with elevation and conductivity data was similar to that achieved in on-the-ground vegetation surveys. Lowest elevations and highest conductivities were measured in saline environments (marine and estuarine units, forebeach, salt marsh, and wind-tidal flats). Highest elevations and lowest conductivities were measured in nonsaline environments (upland and palustrine units, dunes, vegetated-barrier flats, and fresh marsh). Elevation and conductivity data allow better discrimination among coastal wetland and geomorphic environments than can be achieved from image interpretation alone. Future work should include evaluating the effect of vegetation density on lidar-beam penetration, quantifying seasonal change in ground conductivity in fresh and saline coastal environments, examining the geographic variability of elevation and conductivity statistics, and evaluating the use of airborne EM sensors to measure ground conductivity at multiple exploration depths.