Description Usage Arguments Value See Also Examples
View source: R/compute_frequency_quantile.R
Performs a volume frequency analysis on annual statistics from a daily streamflow data set and calculates a statistic
based on the provided mean ndays 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
HECSSP. Returns a tibble with statistics.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20  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)
)

data 
A data frame of data that contains columns of events, flow values, and measures (data type). 
dates 
Name of column in 
values 
Column in 
station_number 
Character string vector of seven digit Water Survey of Canada station numbers (e.g. 
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
( 
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 
use_log 
Logical value to indicate logscale transforming of flow data before analysis. Default 
fit_distr 
Character string identifying the distribution to fit annual data, one of 
fit_distr_method 
Character string identifying the method used to fit the distribution, one of 
water_year_start 
Numeric value indicating the month ( 
start_year 
Numeric value of the first year to consider for analysis. Leave blank or set well before start date (i.e.

end_year 
Numeric value of the last year to consider for analysis. Leave blank or set well after end date (i.e.

exclude_years 
Numeric vector of years to exclude from analysis. Leave blank or set to 
months 
Numeric vector of months to include in analysis. For example, 
ignore_missing 
Logical value indicating whether dates with missing values should be included in the calculation. If

allowed_missing 
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 
A numeric value of the frequency analysis quantile, given the roll_days and return_period.
1 2 3 4 5 6 7 8 9 10 11  ## Not run:
# Working example:
# Compute the annual 7day 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)

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