Here we briefly describe the default model parameter values and settings for 'py_SBeLT'. Readers are directed to 'README.md' for information concerning the ranges of parameter values that have been testing using 'py_SBeLT'.
Default Value = 1000
We use a default value of 1000 for Iterations to allow users to explore 'py_SBeLT' in an efficient way without having to wait too long for results.
Default Value = 100
We use a default value of 100 for Bed_length. This length of bed was found to provide sufficient space to observe transport behaviors that are common to natural rivers, such as variable sediment particle residence times in the bed, spatially variable rates of transport, etc. The model was tested up to a Bed_length of 1000 millimeters are performed as expected. It is important to note however that the combination of Bed_length and Num_subregions in conjunction with Poiss_lambda control the intensity of transport simulated by 'py_SBeLT'. Therefore, if users change the parameter Bed_length, it may be useful to also consider changing the default values for Num_subregions and Poiss_lambda.
Default Value = 0.5
We use a default value of 0.5 for Particle_diam, with assumed units of length of millimeters. This default value provides a reasonable scale-- assuming a default bed_length of 100 millimeters--to view simulation results when plotted over the entire domain. This default value is also consistent with the grain sizes present on the bed surface of many low land rivers.
Default Value = 0.78
We use a default value of 0.78 for Particle_pack_den. This provides a surface coverage of 78% over the Bed_length. More or fewer particles on the surface can affect derived simulated behaviors such as how long particles sit in the mobile part of bed surface before mobilization occurs, or the availability of deposition locations in relation to the relative particle level, or stacking height.
Default Value = 4
We use a default value of 4 for Num_subregions, and in conjuction with the default Bed_length of 100 millimeters. If the user holds Bed_length and Poiss_lambda to the default values, increasing the Num_subregions will result in increased rates of particle transport up to the limit imposed by Particle_pack_den, and decreasing the Num_subregions will result in less transport.
Default Value = 3
We use a default value of 3 for Level_limit. This means that particles can stack 3 high in any region of the bed subject to particle availability, selected hop distances, etc. Using this default value provides for development of bed topography. As a result, model particles develop a unique history of age, or the duration between mobilization events. Using smaller values for Level_limit will depress bed topography, and truncate the distribution of particle ages.
Default Value = 5
We use a default value of 5 for Poiss_lambda to provide a relatively high rate of entrainment provided the default settings for Bed_length, Particle_pack_den and Num_subregions. Notably the value used for Poiss_lambda does not affect model behavior for the range of values tested for 'py_SBeLT' (see README.md), but it does influence how many iterations may be needed to achieve a relatively high number of total entrainment events, or particle passing events beyond internal and the downstream model boundary. These outcomes will influence interpretations of model results.
Default Value = 'False'
We use a default value of False for Guass. This means particle travel distances are sampled from a Lognormal continuous distribution, as opposed to a Normal distribution. We use the setting of False because this permits sampling from a distribution that can be skewed to longer distances, which is more consistent with experimental observations (see THEORY.md). Testing reveals however that use of a Normal distribution can yield behavior generally consistent with experimental results provided that values are truncated at zero and the mean, or central tendency, is positively offset from zero.
Default Value = 1
We use a default value of 1 for Gauss_mu. Depending on values selected for Gauss_sigma, a value of 1 for Gauss_mu provides a range of particle travel distances which scale from ~1 to 20 particle diameters (for the default Particle_diam setting), or more (accounting for the log transformation of X). More specifically, the value selected for Gauss_mu sets the median value for the distribution of all possible travel distances; in the default case this means that half of all possible sampled travel distances will scale as more than 5 particle diameters (accounting for the log transformation of X). Testing with 'py_SBeLT' reveals that this default setting generally avoids the development of isolated particle piles and model behavior which differs from experimental observations (see THEORY.md).
Default Value = 0.25
We use a default value of 0.25 for Gauss_sigma. For the default travel distance distribution setting (see Gauss), relatively large values for Gauss_sigma provide an increasingly skewed distribtuion to larger travel distances, and small values provide a distribution which tends to a Gaussian.
Default Value = 1
We use a default value of 1 for Data_save_interval. This default value will save model output every iteration.
Default Value = 'False'
We use a default value of False for Height_dependent_entr. This setting means that particles sitting at the height limit set by Level_limit are not automatically entrained during the next iteration. We use a default value of False because a setting of True removes the role of entrainment events variability in simulated behavior of transport. We provide the option to set this parameter to True to permit exploring how automatic entrainment may influence particle age distributions, or bed topography.
Default Value = '.'
We use a default setting of writing output to the active directory.
Default Value = 'sbelt-out'
We use a default setting of writing output to sbelt-out.