“You can't see them from sitting here”: Evaluating beach user understanding of a rip current warning sign

Rip current warning signs complement lifeguards and flags on many beaches globally to alert beach users to the danger of rip currents and to inform beach users about how to identify and avoid rip currents. Although rip current warning signs, such as the sign distributed by the U.S. National Oceanographic and Atmospheric Administration (NOAA), are an important part of any beach safety program, their effectiveness is unknown. Moreover, we do not know how beach users respond to or perceive the rip-current warnings represented graphically and textually. Here we report on a spatially and temporally randomized survey of 392 beach users from three heavily frequented public beaches in Texas (Galveston, Port Aransas, and Corpus Christi) at the height of the summer beach season in 2012. Beach users were asked to respond to the rip current warning sign developed in 2003–2004 by the U.S. Rip Current Task Force. Nearly half of respondents did not notice any warning sign when approaching the beach. When prompted by enumerators with the Task Force sign, 44.5% of beach users found the sign was “helpful” or “very helpful” to their ability to identify a rip current. However, more than half of beach users had difficulty translating the rip current image into a feature observable while standing or sitting on the shore. Many beach users will respond to a warning sign showing the rip current from the perspective of place, rather than the aerial view representing the ocean as space. This realization guides our specific suggestions for improving the current NOAA warning signs.     

Late Holocene dune migration on the south Texas sand sheet

There are a wide variety of vegetated, eolian depositional landforms associated with the south Texas sand sheet, attesting to the past dominance of eolian processes. Mapping identified two sets of parabolic dunes elongating with winds from the southeast and the northwest. Parabolic dunes elongated by northwesterly winds are older than ca. 200 years and may be associated with eolian depositional events ca. 2700 and/or 2000 years ago. The latest dune migration event, associated with southeasterly winds occurred ca. 200 years ago and at one site is inset into northwesterly-extended parabolic dunes. This period of dune migration may be coincident with particularly severe drought identified in the tree-ring record centered at AD 1790, when the Palmer Drought Severity Index was − 4. A threshold of dune movement may have occurred ca. in the 11th, 15th and 20th centuries when there are two or more consecutive years with a Palmer Drought Severity Index of < − 4, corresponding to 30–50% reduction in precipitation. Dune systems on Coastal Plain of Texas to reactivated repeatedly due to climate variability in the past 3000 years.     

GIS-based analysis of foundation repairs and soil conditions in the Dallas-Fort Worth region,Texas

The Dallas-Fort Worth region is subject to a severe expansive soils hazard, resulting in costly damage to many thousands of residential foundations each year. A GIS is used to examine relationships between a sample of approximately 10,000 foundation repair addresses and geologic and soil conditions. The study results show that foundation repairs are concentrated in areas underlain by bedrock, surficial deposits and soils that promote high shrink–swell potentials. A linear extensibility index, designed as an index of overall shrink–swell potential explains about 48% of the variation in the prevalence of repairs. Repairs are concentrated on soils that underlay many areas of new urban growth in the DFW region, suggesting that the incidence of foundation repairs in these areas will probably increase in the future. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Stability of tidal inlets—Pass Cavallo,Texas

Many tidal inlets are scoured in loose granular material, and the morphological changes in these inlets are discussed. The changes are the result of the predominantly fortnightly variations in the tide, the seasonal variations in storm activity and the occurrence of extreme meteorological events. The adjustment of an inlet to changes in the hydraulic environment and sudden changes in its morphology associated with extreme meteorological events is primarily via a change in the cross-sectional area. For a single-inlet bay system, the response of the inlet cross-sectional area can be determined using the stability analysis presented by Escoffier (1940). Rather than one inlet, many bays are connected to the ocean by several inlets. In this study, Escoffier's analysis is expanded to include the interaction of these inlets. In the analysis, the sediment carrying capacity of the inlet currents is characterized by the bottom shear stress. The stability analysis is applied to Pass Cavallo, Texas. Assuming the absence of future influences of tropical storms and hurricanes, the analysis shows that as a result of the opening of a companion inlet, Pass Cavallo ultimately will close.     

Satellite remote sensing of the geographical distribution of suspended particle size in an energetic shelf sea

Natural and created Spartina brackish marsh habitats in the Guadalupe Estuary, adjacent to the Aransas National Wildlife Refuge, Texas, USA were surveyed during spring, summer, and fall 2004 to evaluate the equivalence of nekton assemblages in an old (>30 years) created marsh. During each season, six replicate samples were collected in each marsh type using a 1-m² drop sampler. Multivariate analysis revealed significant differences in nekton assemblage structure among marsh type, both within and across seasons. Species richness was significantly higher in the natural marsh in spring and summer but not in fall. Several species that were dominant in the natural marsh but rare or absent in the created marsh had strong correlations with the presence of oyster substrate that was only encountered in natural marsh samples. Although cumulative richness was greater in the natural marsh, eight species were collected only from the created marsh. Shrimp and fish biomass was significantly higher in natural marsh. Analysis of the density, biomass and size structure of three commercially important crustaceans indicated that the created marsh supported similar biomass of some species (white shrimp, blue crab); however, the size structure of some populations was variable among marshes (blue crab, brown shrimp). We conclude that lower substrate complexity (specifically oyster) and soil organic content in the created marsh reduced measures of nekton similarity and recommend that these features be addressed in future restoration efforts.     

The effect of urbanization on stream hydrology in hillslope watersheds in central Texas

This study examined the effect of urbanization on stream hydrology in hillslope watersheds. Ten streams (seven in hillslope and three in gentle slope watersheds) around Austin, Texas were selected for analysis. For each stream, we compared parameters of transfer function (TF) models estimated from daily rainfall and streamflow data collected in two study periods (October 1988–September 1992 and October 2004–September 2008) representing different degrees of watershed urbanization. As expected, the streams became more intermittent as the watersheds were more urbanized in all the study streams. However, the effect of urbanization on peakflow differs between hillslope and gentle slope watersheds. After watershed urbanization, peakflow increased in gentle slope watersheds, but decreased in hillslope watersheds. Based on the results of the TF models, we found that urbanization made stream not flashier but drier in hillslope watersheds. Overpumpage of aquifer has been recognized as a problem that leads to the stream dryness in the study area. However, the overpumpage alone cannot explain the differences in hydrological changes between the two types of watersheds. We attributed the reduced peakflow and stream dryness in the hillslope watersheds to land grading for construction forming stair‐stepped or terraced landscape. Compared with natural hillslope, a stair‐stepped landscape could infiltrate more stormwater by slowing down surface runoff on tread portions of the stair. Our findings suggest that a watershed management scheme should take into account local hydrogeologic conditions to mitigate the stream dryness resulting from urbanization in hillslope watersheds. Copyright © 2010 John Wiley & Sons, Ltd.     

Using hydrologic and hydraulically derived geometric parameters of perennial rivers to determine minimum water requirements of ecological habitats (case study: Mazandaran Sea Basin—Iran)

This paper studies one of the most important problems of dry countries that are confronted with water deficit and the competition of rivals to allocate water. Some common methods have been investigated for computing the minimum water requirement to save a river's biological activity. After a discussion of the currently used method in Iran (the Tenant Method), the application of some other methods, which are known as Hydraulic and Hydrological Methods, is illustrated. The case study is a river in the northern part of Iran and this research addresses the critical situation of this river in near future regarding the planned anthropogenic alteration and its consequences. It has been shown that the application of environmental water allocation methods that have no background in a region could be misleading. The first proposed method is the Texas Method, in which flexibility in water allocation helps to develop an integrated river management paradigm in the study area. The second preferred method is a Hydraulic Method, by which the implementation of morphological parameters or flow geometrical properties could sustain physical habitat within an acceptable range in terms of depth, width, velocity, and bed shear stress. In the case study, the Maximum Curvature Method was superior to the Slope Method. The investigation revealed that using a widely recommended slope of 1 for the discharge‐wetted perimeter function can lead to an overestimated and unacceptable discharge. The Tenant Method in respect to minimum environmental flow requirement yielded the weakest result, and it has been illustrated that its application might impose irrecoverable shock to the ecosystem. The Flow Duration Curve Method (the Q₉₅ Method), in spite of its subjectivity, showed more compatibility with the river's condition in comparison with the Tenant Method. Copyright © 2011 John Wiley & Sons, Ltd.     

Using statistical and artificial neural network models to forecast potentiometric levels at a deep well in South Texas

Reliable forecasts of monthly and quarterly fluctuations in groundwater levels are necessary for short- and medium-term planning and management of aquifers to ensure proper service of seasonal demands within a region. Development of physically based transient mathematical models at this time scale poses considerable challenges due to lack of suitable data and other uncertainties. Artificial neural networks (ANN) possess flexible mathematical structures and are capable of mapping highly nonlinear relationships. Feed-forward neural network models were constructed and trained using the back-percolation algorithm to forecast monthly and quarterly time-series water levels at a well that taps into the deeper Evangeline formation of the Gulf Coast aquifer in Victoria, TX. Unlike unconfined formations, no causal relationships exist between water levels and hydro-meteorological variables measured near the vicinity of the well. As such, an endogenous forecasting model using dummy variables to capture short-term seasonal fluctuations and longer-term (decadal) trends was constructed. The root mean square error, mean absolute deviation and correlation coefficient (R) were noted to be 1.40, 0.33 and 0.77 m, respectively, for an evaluation dataset of quarterly measurements and 1.17, 0.46, and 0.88 m for an evaluative monthly dataset not used to train or test the model. These statistics were better for the ANN model than those developed using statistical regression techniques.     

Structure of the Texas Orocline beneath the sedimentary cover (southeast Queensland,Australia)

The New England Orogen in eastern Australia is characterised by orogenic-scale curvatures (oroclines). The largest and most prominent curvature in this system is the Texas Orocline, but its subsurface geometry is still poorly constrained. A large component of the orocline is covered by post-oroclinal sedimentary rocks, which obscure deeper sections of the orocline and make it difficult to understand how the structure is connected to other segments of the New England Orogen. Here, we present geophysical data that elucidate the structure of the Texas Orocline below the sedimentary cover. Using 2D seismic, aeromagnetic TMI (total magnetic intensity) and Bouguer gravity datasets, in combination with outcrop and well data, we identified the depth to the New England ‘basement’ and significant faults intersecting it. We also traced the strongly contorted subsurface continuation of the Peel-Yarrol Fault System, which is characterised by local gravity and magnetic anomalies associated with isolated serpentinite outcrops. Constraints on the timing of oroclinal bending were obtained from the interpretation of seismic transects, which showed that early Permian sedimentary rocks of the Bowen Basin were deposited in a subtrough that deviates from the general north–south trend of the Bowen Basin. The subtrough is oriented approximately parallel to the western limb of the Texas Orocline, thus suggesting that the orocline formed during and/or after early Permian rifting. Our analysis indicates that initial bending occurred contemporaneously with the development of the early Permian rift basins, most likely in the backarc region of a retreating subduction zone. Subsequently, phases of strike-slip and contractional deformation have further tightened the pre-existing curvatures.     

The tectonic significance of lower Permian successions in the Texas Orocline (Eastern Australia)

The Texas Orocline is a prominent orogenic curvature that developed during the early Permian in the southern New England Orogen. Outliers preserving lower Permian sedimentary successions (Bondonga, Silver Spur, Pikedale, Terrica, Alum Rock and Ashford beds) approximately outline the oroclinal structure, but the tectonic processes responsible for the development of these basinal successions, and their relationships to the Texas Orocline, are unclear. Here we address this shortcoming by providing new U–Pb detrital and primary zircon ages from these successions, as well as detailed stratigraphic and structural data from the largest exposed succession (Bondonga beds). Field observations and U–Pb geochronological data suggest that the lower Permian successions in the Texas Orocline are remnants of a single, formerly larger basin that was deposited after ca 302 Ma. Time constraints for formation of this basin are correlative with constraints from the lower Permian Nambucca Block, which was likely deposited in response to regional back-arc extension during and/or after the development of the Texas Orocline. The conclusion that the lower Permian sedimentary basins in the Texas Orocline belong to this back-arc extensional system supports the suggestion that oroclinal bending in the New England Orogen was primarily controlled by trench retreat and associated overriding-plate extension.