fasstr: compute_frequency_quantile – R documentation

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compute_frequency_quantile

Calculate an annual frequency analysis quantile

Description

Performs a volume frequency analysis on annual statistics from a daily streamflow data set and calculates a statistic based on the provided mean n-days and return period of the statistic, defaults to minimum flows. For example, to determine the 7Q10 of a data set, set the roll_days to 7 and the return_period to 10. Function will calculate using all values in 'Values' column (no grouped analysis), unless specified. Analysis methodology replicates that from HEC-SSP. Returns a tibble with statistics.

Usage

compute_frequency_quantile(
  data,
  dates = Date,
  values = Value,
  station_number,
  roll_days = NA,
  roll_align = "right",
  return_period = NA,
  use_max = FALSE,
  use_log = FALSE,
  fit_distr = c("PIII", "weibull"),
  fit_distr_method = ifelse(fit_distr == "PIII", "MOM", "MLE"),
  water_year_start = 1,
  start_year,
  end_year,
  exclude_years,
  months = 1:12,
  ignore_missing = FALSE
)

Arguments

`data`	A data frame of data that contains columns of events, flow values, and measures (data type).
`dates`	Name of column in `data` that contains dates formatted YYYY-MM-DD. Only required if dates column name is not 'Date' (default). Leave blank if using `station_number` argument.
`values`	Column in `data` that contains numeric flow values, in units of cubic metres per second. Default `'Value'`.
`station_number`	Character string vector of seven digit Water Survey of Canada station numbers (e.g. `"08NM116"`) of which to extract daily streamflow data from a HYDAT database. Requires `tidyhydat` package and a HYDAT database. Leave blank if using `data` argument.
`roll_days`	Numeric value of the number of days to apply a rolling mean. Required.
`roll_align`	Character string identifying the direction of the rolling mean from the specified date, either by the first (`'left'`), last (`'right'`), or middle (`'center'`) day of the rolling n-day group of observations. Default `'right'`.
`return_period`	Numeric vector of the estimated time interval, in years, between flow events of a similar size, inverse of probability, used to estimate the frequency statistic. Required.
`use_max`	Logical value to indicate using maximums rather than the minimums for analysis. Default `FALSE`.
`use_log`	Logical value to indicate log-scale transforming of flow data before analysis. Default `FALSE`.
`fit_distr`	Character string identifying the distribution to fit annual data, one of `'PIII'` (Log Pearson Type III) or `'weibull'` (Weibull) distributions. Default `'PIII'`.
`fit_distr_method`	Character string identifying the method used to fit the distribution, one of `'MOM'` (method of moments) or `'MLE'` (maximum likelihood estimation). Selected as `'MOM'` if `fit_distr ='PIII'` (default) or `'MLE'` if `fit_distr = 'weibull'`.
`water_year_start`	Numeric value indicating the month (`1` through `12`) of the start of water year for analysis. Default `1`.
`start_year`	Numeric value of the first year to consider for analysis. Leave blank to use the first year of the source data.
`end_year`	Numeric value of the last year to consider for analysis. Leave blank to use the last year of the source data.
`exclude_years`	Numeric vector of years to exclude from analysis. Leave blank to include all years.
`months`	Numeric vector of months to include in analysis (e.g. `6:8` for Jun-Aug). Leave blank to summarize all months (default `1:12`).
`ignore_missing`	Logical value indicating whether dates with missing values should be included in the calculation. If `TRUE` then a statistic will be calculated regardless of missing dates. If `FALSE` then only those statistics from time periods with no missing dates will be returned. Default `FALSE`.

Value

A numeric value of the frequency analysis quantile, given the roll_days and return_period.

Examples

## Not run: 

# Working example:

# Compute the annual 7-day flow value with a 1 in 10 year return interval
compute_frequency_quantile(station_number = "08NM116",
                           roll_days = 7,
                           return_period = 10)
                            

## End(Not run)

fasstr

Analyze, Summarize, and Visualize Daily Streamflow Data

v0.3.2

Apache License 2.0

Authors

Jon Goetz [aut, cre] (<https://orcid.org/0000-0002-4993-1119>), Carl James Schwarz [aut], Robin Pike [ctb], Province of British Columbia [cph]

Initial release