R/compute_frequency_quantile.R
compute_frequency_quantile.Rd
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.
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,
allowed_missing = ifelse(ignore_missing, 100, 0)
)
A data frame of data that contains columns of events, flow values, and measures (data type).
Name of column in data
that contains dates formatted YYYY-MM-DD. Only required if dates column name is not
'Date' (default). Leave blank or set to NULL
if using station_number
argument.
Column in data
that contains numeric flow values, in units of cubic metres per second. Default 'Value'
.
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.
Numeric value of the number of days to apply a rolling mean. Required.
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'
.
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.
Logical value to indicate using maximums rather than the minimums for analysis. Default FALSE
.
Logical value to indicate log-scale transforming of flow data before analysis. Default FALSE
.
Character string identifying the distribution to fit annual data, one of 'PIII'
(Log Pearson Type III)
or 'weibull'
(Weibull) distributions. Default 'PIII'
.
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'
.
Numeric value indicating the month (1
through 12
) of the start of water year for
analysis. Default 1
.
Numeric value of the first year to consider for analysis. Leave blank or set well before start date (i.e.
1800
) to use from the first year of the source data.
Numeric value of the last year to consider for analysis. Leave blank or set well after end date (i.e.
2100
) to use up to the last year of the source data.
Numeric vector of years to exclude from analysis. Leave blank or set to NULL
to include all years.
Numeric vector of months to include in analysis. For example, 3
for March, 6:8
for Jun-Aug or
c(10:12,1)
for first four months (Oct-Jan) when water_year_start = 10
(Oct). Default summarizes all
months (1:12
).
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
.
Numeric value between 0 and 100 indicating the percentage of missing dates allowed to be
included to calculate a statistic (0 to 100 percent). If 'ignore_missing = FALSE'
then it defaults to 0
(zero missing dates allowed),
if 'ignore_missing = TRUE'
then it defaults to 100
(any missing dates allowed); consistent with
ignore_missing
usage. Supersedes ignore_missing
when used.
A numeric value of the frequency analysis quantile, given the roll_days and return_period.
if (FALSE) {
# 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)
}