Plots flow duration curves of flow data from a daily streamflow data set. Plots the percent time flows are equalled or exceeded. Calculates statistics from all values, unless specified. Data calculated using calc_longterm_stats() function then converted for plotting. Returns a list of plots.

plot_flow_duration(
data,
dates = Date,
values = Value,
groups = STATION_NUMBER,
station_number,
roll_days = 1,
roll_align = "right",
water_year_start = 1,
start_year,
end_year,
exclude_years,
complete_years = FALSE,
custom_months,
custom_months_label,
ignore_missing = FALSE,
months = 1:12,
include_longterm = TRUE,
log_discharge = TRUE,
include_title = FALSE
)

## Arguments

data Data frame of daily data that contains columns of dates, flow values, and (optional) groups (e.g. station numbers). Leave blank if using station_number argument. 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. Name of column in data that contains numeric flow values, in units of cubic metres per second. Only required if values column name is not 'Value' (default). Leave blank if using station_number argument. Name of column in data that contains unique identifiers for different data sets, if applicable. Only required if groups column name is not 'STATION_NUMBER'. Function will automatically group by a column named 'STATION_NUMBER' if present. Remove the 'STATION_NUMBER' column beforehand to remove this grouping. Leave blank if using station_number argument. 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. Default 1. 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 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 to use the first year of the source data. Numeric value of the last year to consider for analysis. Leave blank to use the last year of the source data. Numeric vector of years to exclude from analysis. Leave blank to include all years. Logical values indicating whether to include only years with complete data in analysis. Default FALSE. Numeric vector of months to combine to summarize (ex. 6:8 for Jun-Aug). Adds results to the end of table. If wanting months that overlap calendar years (ex. Oct-Mar), choose water_year_start that begins before the first month listed. Leave blank for no custom month summary. Character string to label custom months. For example, if months = 7:9 you may choose "Summer" or "Jul-Sep". Default "Custom-Months". 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 vector of month curves to plot. NA if no months required. Default 1:12. Logical value indicating whether to include long-term curve of all data. Default TRUE. Logical value to indicate plotting the discharge axis (Y-axis) on a logarithmic scale. Default FALSE. Logical value to indicate adding the group/station number to the plot, if provided. Default FALSE.

## Value

A list of ggplot2 objects with the following for each station provided:

Flow_Duration

a plot that contains flow duration curves for each month, long-term, and (option) customized months

calc_longterm_daily_stats

## Examples

if (FALSE) {

# Working examples:

# Plot flow durations using a data frame and data argument with defaults
flow_data <- tidyhydat::hy_daily_flows(station_number = "08NM116")
plot_flow_duration(data = flow_data,
start_year = 1980)

# Plot flow durations using station_number argument with defaults
plot_flow_duration(station_number = "08NM116",
start_year = 1980)

# Plot flow durations and add custom stats for July-September
plot_flow_duration(station_number = "08NM116",
start_year = 1980,
custom_months = 7:9,
custom_months_label = "Summer")

}
}