ABSTRACT Carvalho, A.M.; Lima Jr., S.B.; Maia, L.P.; Claudino-Sales, V.; Gastão, F.G.C.; Eduardo, L.M.; Pinheiro, L.S., and Silva, M.V.C., 2021. Understanding polydirectional aeolian cross-strata architecture in a coastal unidirectional wind regime. Journal of Coastal Research, 37(2), 364–379. Coconut Creek (Florida), ISSN 0749-0208. Crescentic dune fields along the NE coast of Brazil were analyzed to justify processes associated with the wide range of cross-strata dip directions in aeolian deposits found in a unidirectional wind regime. Multiple spatial and temporal field-based methodologies were employed, including trenching, ground penetrating radar (GPR), and photogrammetry. Wind dynamics, coastline morphology, bounding surface developing processes, and dune migration patterns were also considered. Analysis revealed a relationship between small- and large-scale morphologies of the crescentic dune field. The interactions of crescentic dune crests, in association with the superposition of multiple superposed dunes, explain the majority of cross strata and dip directions found in dune trenches and GPR sections. This study provides convincing evidence that microscale structures observed within trenches and GPR sections are compatible with the macroscale slipface position observed within the dune field. Small-scale changes in wind direction, caused by the dune crest morphologies themselves, explain much of the supposedly unexpected strata dip directions that arc through from 90° to 180°. The presence of near-surface water tables supports the formation and preservation of aeolian cross-strata sequences.

ABSTRACT Carvalho, A.M.C.; Ellis, J.T.; Lamothe, M., and Maia, L.P., 2016. Using wind direction and shoreline morphology to model sand dune mobilization. This paper aims to establish a relationship between wind direction, shoreline position, and aeolian transport directions. Ceará State in NE Brazil, which mainly comprises barchans, barchanoids, parabolic dunes, and large flattened composed dunes was used to formulate and test a dune transport model that can be applied to north and east facing beaches. The headland-bay beaches of Ceará progressively increase in angle from E to W. This is accompanied by a corresponding change in the near-beach dune migration direction. A significant change in the wind pattern for the northern portion of Ceará was found, which resulted in a shift in dune migration from E-W to ENE-WSW as the shoreline orientation changed from NW-SE to W-E. The different aeolian transport conditions along the stretches of the headland-bay beach gradually shifted from transport parallel to the shoreline to unimpeded aeolian transport that moves sediments inland. Beach feeding occurs from headland bypass as dunes occupy the area landward of the headland. A zone of composite wind transport directions, winds carrying sand directly from the beach and those transporting sediment landward of the headland, was identified. This variation of wind transport conditions is confirmed by the dune morphology and influenced by the relationship between shoreline position and wind angle approach. The proposed model uses the sine of the angle between wind direction and shoreline orientation to predict aeolian transport and determines the volume of sediment transported by the wind. This model identifies stretches of shoreline under different aeolian transport directions and exhibits compatibility with measured dune migration.

ABSTRACT da Silva Dias, F.J.; Valente Marins, R., and Parente Maia, L., 2013. Impact of drainage basin changes on suspended matter and particulate copper and zinc discharges to the ocean from the Jaguaribe River in the semiarid NE Brazilian coast. This study aims to understand the fluvial contribution to the estuary and thence to the ocean and the behavior of the suspended particulate matter (SPM) and particulate Cu and Zn during spring tide cycles and during the dry and rainy seasons in 2005, 2006, and 2008, at the Jaguaribe River Estuary, NE Brazil. The distribution of metals concentrations in SPM during dry and rainy seasons suggests a lithogenic origin of aluminum (Al), iron (Fe), and copper (Cu), as a result of erosion and leaching of soils in the drainage basin due to anthropogenic drivers, such as urbanization, shrimp farming, and agriculture. Anthropogenic drivers also affect Zn flows associated with SPM during the dry season. The highest discharges of SPM and particulate metals occurred during rainy periods due higher freshwater volumes observed in the estuarine channel. The results strongly suggest that the high variability of discharges typical of semiarid drainage basins can be underestimated with the use of secondary data, showing the necessity of obtaining data in situ .

ABSTRACT Sherman, D.J., Houser, C., Ellis, J.T., Farrell, E.J., Li, B., Davidson-Arnott, R.G.D., Baas, A.C.W., and Maia, L.P., 2013. Characterization of aeolian streamers using time-averaged videography. In : Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.) Aeolian streamers are common in prototype saltation systems. Streamers are elongate, flow-aligned features within which the concentrations of saltating grains are large relative to a spanwise average concentration. The occurrence of streamers introduces substantial spatial and temporal variability in local sand transport rates. There have been few studies to attempt to characterize the scales of streamers, and the results of those studies have been constrained because they use Eulerian approaches to measure an inherently Lagrangian process. We describe the results from a field experiment designed to address this methodological problem. Field experiments were conducted at Jericoacoara, Ceará, Brazil, in October, 2011. The wind field was measured with ultrasonic anemometers and ruggedized thermal probes. Transport rates were measured using Miniphones, Wenglor Particle Counters, and hose traps. A set of three video cameras, deployed in a triangular array, was used to capture images of streamers. The field of vision for the central, upwind-facing camera was a minimum of about 15 m, expanding to more than 100 m in the middle distance. Video images were time-averaged over a number of intervals, ranging from 1 – 64 seconds, to establish characteristic path lengths and spatial and temporal scales. The results of these analyses show that this methodological approach is technically sound. Streamer characteristics are center-to-center spacings of about 1 m, length-scales exceeding 50 m and time scales of individual streamers exceeding 64 s.