289
9.3.2 Sample Statistics Distribution
Analytical methods to quantify the form, the size and the composition of sediments
are based on statistical assumptions that have been developed during the years.
However, the significant fact is that under the principle of characterization of the
grains of material a detailed study of their origin and form can be reached.
A statistical procedure is applied to problems where it is necessary to make the
classification of materials (composition and size), to establish mechanism that originated the beach and know the way how the sediments were deposited. The classification is made from the main statistical parameters of the sample and based on it, it
can determine whether the material dispersion or depositation was created by the
waves and/or the currents, as well as, to define which are the physical factor that
intervene in the configuration of the beach. This information is very relevant at the
moment to carry out the diagnosis and the analysis of agents that can generate erosion in a littoral system and to value the sediment interaction with physical processes in the coastal zone.
For the representation of the mechanical analysis of sediment, we have adopted
logarithmic functions. This gives a lot of practicality and relevance to the study,
allowing that the sample properties are expressed in terms of statistical deviations
from the normal distribution function. It is possible to express the frequency analysis from statistical and mathematical principles covering the entire distribution of
sample sizes, without practical or theoretical limitations, when are applied to the
full spectrum of sizes of sediment (Inman 1952). Parameters that depend on the
order statistics such as mean, median, standard deviation and asymmetry are applied
using different methodologies (moments, quartiles, logarithmic methods graphs,
etc.).
An adopted method for the analysis of size distribution of the sediment sample
consists in express the statistics though a logarithmic expression that describes the
diameter conversion (d) in millimetres to units phi (ϕ), using the equation ϕ = −
log 2 d (Krumbein 1936). In reaching this classification, and in the particular case of
sediments, measures of the central tendency of the mean and the median of the
samples diameter is taken into account, where one of these two variables can acquire
a greater importance than the other. In a normal distribution, the mean is the diameter value that represents the centre of gravity of the frequency distribution while
the median, from a geometric perspective, is the amount that divides systematically
the frequency curve (Inman 1952).
The influence of the median is relevant when it is about avoiding in the analysis
affections in the extremes at the moment to adjust the distribution; instabilities that
can potentially be originated by dispersions with respect to the mean for samples
that have a large number of sizes (Inman 1952). For its algebraic character, the central value of a large quantity of sediments samples can be obtained by means of the
analysed group, which reflects the average size that the sediment has in the source
where it was founded. Although, it must be remembered that it is more recommended for quantification porpoises the use of the arithmetic mean.
9 Physical and Morphological Changes to Wetlands Induced by Coastal Structures
9.3.2 Sample Statistics Distribution
Analytical methods to quantify the form, the size and the composition of sediments
are based on statistical assumptions that have been developed during the years.
However, the significant fact is that under the principle of characterization of the
grains of material a detailed study of their origin and form can be reached.
A statistical procedure is applied to problems where it is necessary to make the
classification of materials (composition and size), to establish mechanism that originated the beach and know the way how the sediments were deposited. The classification is made from the main statistical parameters of the sample and based on it, it
can determine whether the material dispersion or depositation was created by the
waves and/or the currents, as well as, to define which are the physical factor that
intervene in the configuration of the beach. This information is very relevant at the
moment to carry out the diagnosis and the analysis of agents that can generate erosion in a littoral system and to value the sediment interaction with physical processes in the coastal zone.
For the representation of the mechanical analysis of sediment, we have adopted
logarithmic functions. This gives a lot of practicality and relevance to the study,
allowing that the sample properties are expressed in terms of statistical deviations
from the normal distribution function. It is possible to express the frequency analysis from statistical and mathematical principles covering the entire distribution of
sample sizes, without practical or theoretical limitations, when are applied to the
full spectrum of sizes of sediment (Inman 1952). Parameters that depend on the
order statistics such as mean, median, standard deviation and asymmetry are applied
using different methodologies (moments, quartiles, logarithmic methods graphs,
etc.).
An adopted method for the analysis of size distribution of the sediment sample
consists in express the statistics though a logarithmic expression that describes the
diameter conversion (d) in millimetres to units phi (ϕ), using the equation ϕ = −
log 2 d (Krumbein 1936). In reaching this classification, and in the particular case of
sediments, measures of the central tendency of the mean and the median of the
samples diameter is taken into account, where one of these two variables can acquire
a greater importance than the other. In a normal distribution, the mean is the diameter value that represents the centre of gravity of the frequency distribution while
the median, from a geometric perspective, is the amount that divides systematically
the frequency curve (Inman 1952).
The influence of the median is relevant when it is about avoiding in the analysis
affections in the extremes at the moment to adjust the distribution; instabilities that
can potentially be originated by dispersions with respect to the mean for samples
that have a large number of sizes (Inman 1952). For its algebraic character, the central value of a large quantity of sediments samples can be obtained by means of the
analysed group, which reflects the average size that the sediment has in the source
where it was founded. Although, it must be remembered that it is more recommended for quantification porpoises the use of the arithmetic mean.
9 Physical and Morphological Changes to Wetlands Induced by Coastal Structures