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,
custom_months,
custom_months_label,
complete_years = FALSE,
ignore_missing = FALSE,
months = 1:12,
include_longterm = TRUE,
log_discharge = TRUE,
log_ticks = ifelse(log_discharge, TRUE, FALSE),
include_title = FALSE
)
```

- data
Data frame of daily data that contains columns of dates, flow values, and (optional) groups (e.g. station numbers). Leave blank or set to

`NULL`

if using`station_number`

argument.- 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 or set to`NULL`

if using`station_number`

argument.- values
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.- groups
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.- 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. Default

`1`

.- 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'`

.- 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 or set well before start date (i.e.

`1800`

) to use from the first year of the source data.- end_year
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.- exclude_years
Numeric vector of years to exclude from analysis. Leave blank or set to

`NULL`

to include all years.- custom_months
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.- custom_months_label
Character string to label custom months. For example, if

`months = 7:9`

you may choose`"Summer"`

or`"Jul-Sep"`

. Default`"Custom-Months"`

.- complete_years
Logical values indicating whether to include only years with complete data in analysis. Default

`FALSE`

.- 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`

.- months
Numeric vector of month curves to plot.

`NA`

if no months required. Default`1:12`

.- include_longterm
Logical value indicating whether to include long-term curve of all data. Default

`TRUE`

.- log_discharge
Logical value to indicate plotting the discharge axis (Y-axis) on a logarithmic scale. Default

`FALSE`

.- log_ticks
Logical value to indicate plotting logarithmic scale ticks when

`log_discharge = TRUE`

. Ticks will not appear when`log_discharge = FALSE`

. Default to`TRUE`

when`log_discharge = TRUE`

.- include_title
Logical value to indicate adding the group/station number to the plot, if provided. Default

`FALSE`

.

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

```
if (FALSE) {
# Working examples:
# Run if HYDAT database has been downloaded (using tidyhydat::download_hydat())
if (file.exists(tidyhydat::hy_downloaded_db())) {
# 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")
}
}
```