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Almar R.,French National Center for Space Studies | Michallet H.,CNRS Laboratory of Geophysical and Industrial Flows | Cienfuegos R.,University of Santiago de Chile | Cienfuegos R.,National Research Center Para La Gestion Integrada Of Desastres Naturales | And 3 more authors.
Coastal Engineering

In the nearshore, describing the complex individual wave dynamics remains a key challenge. In this paper we test the ability of the Radon Transform to produce estimates of individual wave celerities and to separate incoming and outgoing waves conserving the temporal characteristics. The Radon Transform is a projection of a two-dimensional field into polar space. Oblique features such as propagating crests in a spatio-temporal space are identified with density peaks in the polar space. In this paper, the Radon Transform is applied to synthetic test cases including a wide range of beach slopes and wave conditions. The Radon Transform shows good skills at estimating individual celerity and separating incoming and outgoing components with a relative RMS error lower than 10%, even a standing wave node. The accuracy is fairly insensitive to wave characteristics whereas the main limitations rise from the sampling scheme and are the number and density of wave gauges. The distance between gauges should be less than one third of the shortest wavelength, while the set of gauges should cover more than one third of the longest wavelength. © 2014 Elsevier B.V. Source

Flores R.P.,Federico Santa Maria Technical University | Flores R.P.,University of Washington | Catalan P.A.,Federico Santa Maria Technical University | Catalan P.A.,National Research Center Para La Gestion Integrada Of Desastres Naturales | And 2 more authors.
Coastal Engineering

The spatial distribution of wave roller dissipation is derived from optical remote sensing observations in a laboratory setting and is used to estimate wave transformation and radiation stress forcing through the surfzone. The methodology relies on direct measurements of the size of individual wave breaking rollers in an irregular wave field via remote sensing. The wave roller measurements are used to calculate the roller energy, roller dissipation, and the roller component of the radiation stress. These hydrodynamic quantities then serve as input into the wave energy flux and cross-shore momentum balances in order to derive the wave height transformation and mean water level profiles. The accuracy of the methodology is shown to be very good through comparison with in situ data. In addition, the mean water level profile reproduces the transition zone lag and maximum water level at the most shoreward measuring point. Overall, it is demonstrated that the methodology can be successfully applied to irregular waves and can be used to estimate both wave transformation and radiation stress forcing through the surf zone. © 2016 Elsevier B.V. Source

Foy C.,313 Sherman St. | Arabi M.,Colorado State University | Yen H.,Texas AgriLife Research Center | Yen H.,U.S. Department of Agriculture | And 3 more authors.
Journal of Hydrologic Engineering

Hydrologic fluxes in mountainous watersheds are particularly important as these areas often provide a significant source of freshwater for more arid surrounding lowlands. The state of Colorado in the United States comprises a principal snow catchment area, with all major headwater river basins in Colorado providing substantial water flows to surrounding western and midwestern states. The ability to represent and quantify hydrologic processes controlling the generation and movement of water in headwater basins of Colorado therefore has significant implications for effective management of water resources in the western United States under varying climatic and land-use conditions. In the research reported in this paper, hydrologic modeling was applied to four snow-dominated, mountainous basins of Colorado [i.e., the river basins of (1) Cache la Poudre, (2) Gunnison, (3) San Juan, and (4) Yampa] to evaluate the relevance of specific hydrologic components (i.e., evapotranspiration, snow processes, groundwater processes, surface runoff, and so on) in the complex, high-elevation watersheds. The soil and water assessment tool (SWAT) model was calibrated and tested for multiple river locations within each basin using monthly naturalized flows over the 1990-2005 period. The model was able to adequately simulate streamflows at all locations within the four basins. Monthly patterns of precipitation, snowfall, evapotranspiration (ET), and total water yield were similar for all the basins, while subsurface lateral flow was the dominant hydrologic pathway, contributing between 64 and 82% to gross basin water yields on an average annual basis. Overall, results indicated the strong influence of snowmelt and groundwater processes on amounts and timing of streamflows in the study basins. Hence, enhanced representation of these processes may be essential to improve hydrological estimation using computer software in snowmelt-driven mountainous basins. In particular, examination of monthly streamflow residuals indicated that the normality and independence of model residuals, which are often assumed in parameter estimation and uncertainty analysis, were not always satisfied. © 2015 American Society of Civil Engineers. Source

Catalan P.A.,Federico Santa Maria Technical University | Catalan P.A.,National Research Center Para La Gestion Integrada Of Desastres Naturales | Catalan P.A.,Cctval Centro Cientifico Tecnologico Of Valparaiso | Haller M.C.,Oregon State University | Plant W.J.,University of Washington
Journal of Geophysical Research: Oceans

The microwave backscatter properties of surf zone waves are analyzed using field observations. By utilizing a preexisting, independent, water surface discrimination technique, the microwave returns were extracted along individual waveforms and the data from shoaling (steepening) waves, surf zone breaking waves, and remnant foam were separated and quantified. In addition, a wave tracking analysis technique allows the returns to be examined on a wave-by-wave basis as individual waves progress through the shoaling zone and break on a nearshore sand bar. Normalized radar cross sections (NRCS), polarization ratios, Doppler spectra, and scatterer velocities were collected using a dual-polarized, X-band radar operating at lower grazing angles than previously reported (1-3.5). The results indicate that the maximum NRCS levels are from the active breaking portions of the wave and were consistently about -20 dB, regardless of radar polarization, azimuth angle, wave height, or wind speed. In addition, breaking waves induce broadening of the Doppler spectra and mean scatterer velocities that correlate well with the carrier wave celerity. Analysis of the polarization ratios suggest that the active breaking portions of the wave are depolarized but that higher polarization ratios (>0 dB) are found on the leading edges shoreward of the active breaking portions of the waves, which indicates a clear distinction between two scattering regimes. These results are consistent with scattering from a very rough surface that is being mechanically generated by the breaking process, showing a good agreement with the expected grazing angle dependency of a Lambertian scatterer. Key Points Breaking waves scatter energetically, regardless of polarization, wave, or wind NRCS of active breaking correlates well with Lambertian scattering Only one breaking event suffices to broaden Doppler spectra © 2014. American Geophysical Union. All Rights Reserved. Source

Fernandez B.,Pontifical Catholic University of Chile | Gironas J.,Pontifical Catholic University of Chile | Gironas J.,National Research Center Para La Gestion Integrada Of Desastres Naturales
Drought: Research and Science-Policy Interfacing - Proceedings of the International Conference on Drought: Research and Science-Policy Interfacing

Chile has a wide variety of climates due to its geographical location, which covers over 4000 km from tropical regions in the north to the south Polar Regions. Drought of varying size and durations affecting different parts of the territory are commonly observed, including areas such as the arid Atacama Desert, the semi-arid central region, and the humid and very humid areas in the south. Despite the diversity of climates and weather conditions, the management of water resources in Chile is centralized. Thus, prior to making management decisions to cope with drought, the central water authority, must declare a drought as extraordinary. It is only after this declaration that the state can use public money to deliver aids, provide subsidies, allocate resources and implement other management tools. Recently the Standardized Precipitation Index (SPI) and the Standardized Runoff Index (SRI) were proposed as common indices to declare drought in the entire country. We studied the behavior of these indices throughout the territory for different durations (i.e., from 1 to 12 months), in order to identify the values that can be used to effectively declare extraordinary drought conditions in each region of the country. These indices were incorporated to the DGA's regulation for declaring drought in 2012, and have become common and objective tools to deal with drought in Chile. © 2015 Taylor & Francis Group, London. Source

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