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Analysis of Variance Applied to Measures of Central Tendency and Dispersion in Sediments
Wayne C. Isphording
Two problems that frequently confront researchers' performing routine sediment analysis involve: (1) the choice of which mathematical technique to use in order to evaluate the size frequency distribution and (2) the number of sieves needed to insure sufficient accuracy for the size analysis.
To investigate this, samples of recent beach and river sediments were collected and were sieved using a 0.5 and 1.0 phi sieve interval. Mean diameters, standard deviation, skewness and kurtosis were calculated using (1) the central moment measure equations, (2) Folk and Ward's equations and (3) Inman's equations. The results obtained with the central-moment measure equations, and the 0.5 phi sieve data, were assumed to provide the most accurate estimates of the various parameters. These values were then compared with those obtained with Folk and Ward's and Inman's equations for both 0.5 and 1.0 phi sieve data to determine what differences resulted. Comparisons were made by both graphical plots and standard analysis of variance F and T tests to determine if statistically different resu ts were obtained using the three different methods.
The results of this study indicated that: (1) no significant differences result when mean diameters and standard deviations are calculated by the three methods, if a 0.5 phi sieve interval is used, (2) only minor differences are found between the three methods if the mean diameter of beach and river sediments are derived using 1.0 phi sieve data, (3) noticeable loss of accuracy results if the standard deviation of either beach or river sediments is computed, using 1.0 phi data, (4) significant differences from the central-moment estimates occur if skewness and kurtosis are calculated for well sorted sediments using Folk and Ward and Inman's equations, especially if 1.0 phi sieve data is used, (5) neither Folk and Ward nor Inman's equation can be used to reliably determine kurtosis, re ardless of whether 0.5 or 1.0 phi sieve data is used.
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