Morphodynamic relationships for ebb and flood delta volumes at Florida’s tidal entrances   总被引：1，自引：0，他引：1  

Mark A. Powell  Robert J. Thieke  Ashish J. Mehta 《Ocean Dynamics》2006,56(3-4):295-307

Tidal entrances constitute an important boundary condition for the coastal ocean regime. Based on data from 67 sandy entrances in Florida, morphodynamic relationships between tidal prism, entrance throat area, and ebb and flood delta volumes are revisited. The main source of sand in these deltas is the littoral zone as opposed to the river. It is found that, as a rule of thumb, the volume of a mature ebb delta is equal to one fifth of the prism at the spring range of tide. Data for the coasts of Florida taken together indicate that the volume of mature flood delta varies with one third power of the prism. The Atlantic Coast flood delta volumes by themselves do not show any correlation with the prism, presumably because entrance depths have been altered by dredging. A case study of the closure of a land barrier breach at Matanzas Inlet illustrates the application of the derived morphodynamic relationships between prism, throat area, and ebb delta volume. These relationships are useful for prediction of changes in the throat area and the ebb delta volume when morphologic changes occur over time scales consistent with the reestablishment of equilibrium.Responsible Editor: Alejandro Souza  相似文献   

Conditional resampling of hydrologic time series using multiple predictor variables: A K-nearest neighbour approach     

R. Mehrotra  Ashish Sharma 《Advances in water resources》2006

Unlike parametric alternatives for time series generation, non-parametric approaches generate new values by conditionally resampling past observations using a probability rationale. Observations lying ‘close’ to the conditioning vector are resampled with higher probability, ‘closeness’ is defined using a Euclidean or Mahalanobis distance formulation. A common problem with these approaches is the difficulty in distinguishing the importance of each predictor in the estimation of the distance. As a consequence, the conditional probability and hence the resampled series, can offer a biased representation of the true population it aims to simulate. This paper presents a variation of the K-nearest neighbour resampler designed for use with multiple predictor variables. In the modification proposed, an influence weight is assigned to each predictor in the conditioning set with the aim of identifying nearest neighbours that represent the conditional dependence in an improved manner. The workability of the proposed modification is tested using synthetic data from known linear and non-linear models and its applicability is illustrated through an example where daily rainfall is downscaled over 15 stations near Sydney, Australia using a predictor set consisting of selected large-scale atmospheric circulation variables.  相似文献   

Development of a numerical groundwater flow model using SRTM elevations     

Kyle C. Fredrick  Matthew W. Becker  L. Shawn Matott  Ashish Daw  Karl Bandilla  Douglas M. Flewelling 《Hydrogeology Journal》2007,15(1):171-181

Remotely-sensed elevation data are potentially useful for constructing regional scale groundwater models, particularly in regions where ground-based data are poor or sparse. Surface-water elevations measured by the Shuttle Radar Topography Mission (SRTM) were used to develop a regional-groundwater flow model by assuming that frozen surface waters reflect local hydraulic head (or groundwater potential). Drainage lakes (fed primarily by surface water) are designated as boundary conditions and seepage lakes and isolated wetlands (fed primarily by groundwater) are used as observation points to calibrate a numerical flow model of the 900 km² study area in the Northern Highland Lakes Region of Wisconsin, USA. Elevation data were utilized in a geographic information system (GIS) based groundwater-modeling package that employs the analytic element method (AEM). Calibration statistics indicate that lakes and wetlands had similar influence on the parameter estimation, suggesting that wetlands might be used as observations where open water elevations are unreliable or not available. Open water elevations are often difficult to resolve in radar interferometry because unfrozen water does not return off-nadir radar signals.  相似文献   

Ocean and atmospheric characteristics associated with the cyclogenesis and rapid intensification of NIO super cyclonic storms during 1981–2020     

Paul  Debashis  Panda  Jagabandhu  Routray  Ashish 《Natural Hazards》2022,111(1):261-282

Natural Hazards - Flooding events in the Lower Benue valley of Nigeria are often associated with huge damage to properties and loss of life in the adjoining communities. Specific objectives of this...  相似文献   

Validation of a satellite-based cyclogenesis technique over the North Indian Ocean     

Suman Goyal  M Mohapatra  Ashish Kumar  S K Dube  Kushagra Rajendra  P Goswami 《Journal of Earth System Science》2016,125(7):1353-1363

Indian region is severely affected by the tropical cyclones (TCs) due to the long coast line of about 7500 km. Hence, whenever any low level circulation (LLC) forms over the Indian Seas, the prediction of its intensification into a TC is very essential for the management of TC disaster. Satellite Application Centre (SAC) of Indian Space Research Organization (ISRO), Ahmedabad, has developed a technique to predict TCs based on scatterometer-derived winds from the polar orbiting satellite, QuikSCAT and Oceansat-II. The India Meteorological Department (IMD) has acquired the technique and verified it for the years 2010–2013 for operational use. The model is based on the concept of analogs of the sea surface wind distribution at the stage of LLC or vortex (T1.0) as per Dvorak’s classifications, which eventually leads to cyclogenesis (T2.5). The results indicate that the developed model could predict cyclogenesis with a probability of detection of 61% and critical success index of 0.29. However, it shows high over-prediction of the model is better over the Bay of Bengal than over Arabian Sea and during post-monsoon season (September–December) than in pre-monsoon season (March–June).  相似文献   

Evaluating global reanalysis datasets for provision of boundary conditions in regional climate modelling     

Ditiro B. Moalafhi  Jason P. Evans  Ashish Sharma 《Climate Dynamics》2016,47(9-10):2727-2745

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Evaluating spatio-temporal representations in daily rainfall sequences from three stochastic multi-site weather generation approaches     

R. Mehrotra  Ashish Sharma 《Advances in water resources》2009

Many hydrological and agricultural studies require simulations of weather variables reflecting observed spatial and temporal dependence at multiple point locations. This paper assesses three multi-site daily rainfall generators for their ability to model different spatio-temporal rainfall attributes over the study area. The approaches considered consist of a multi-site modified Markov model (MMM), a reordering method for reconstructing space–time variability, and a nonparametric k-nearest neighbour (KNN) model. Our results indicate that all the approaches reproduce adequately the observed spatio-temporal pattern of the multi-site daily rainfall. However, different techniques used to signify longer time scale observed temporal and spatial dependences in the simulated sequences, reproduce these characteristics with varying successes. While each approach comes with its own advantages and disadvantages, the MMM has an overall advantage in offering a mechanism for modelling varying orders of serial dependence at each point location, while still maintaining the observed spatial dependence with sufficient accuracy. The reordering method is simple and intuitive and produces good results. However, it is primarily driven by the reshuffling of the simulated values across realisations and therefore may not be suited in applications where data length is limited or in situations where the simulation process is governed by exogenous conditioning variables. For example, in downscaling studies where KNN and MMM can be used with confidence.  相似文献   

Role of basic rheological models in determination of wave attenuation over muddy seabeds     

Mamta Jain  Ashish J. Mehta 《Continental Shelf Research》2009

Among rheological models for estimating the rate of dissipation of non-breaking waves in muddy seabeds, those representing viscoelastic and poroelastic behaviors are used widely. In that regard, the dependence of the wave attenuation coefficient derived from basic rheological representations of mud behavior is examined on a cursory basis. For wave attenuation due to viscoelastic muds, results based on a semi-analytical model incorporating the effects of typically thin mud layers are summarized. This and an existing model for poroelastic beds are tested against selective laboratory data. Relying on these tests, it is emphasized that fluid-like mud should be modeled as a viscoelastic fluid medium, and that only non-fluid beds can be modeled as poroelastic media. Mechanisms for energy dissipation depend on bed compactness specified by the solids volume fraction, porosity or density, and on a characteristic Péclet number defined in terms of particle size, permeability and wave frequency. Due to the role of the latter parameter, for simulation of wave attenuation the chosen rheological model for a bed of given compactness must be applicable over the expected range of wave frequency.  相似文献