Calculates the long-term mean annual discharge (MAD) from a daily streamflow data set. Calculates statistics from all values, unless specified. Returns a tibble with statistics.

calc_longterm_mean(
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,
months = 1:12,
transpose = 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 include in analysis (e.g. 6:8 for Jun-Aug). Leave blank to summarize all months (default 1:12). Numeric vector of percents of long-term mean annual discharge to add to the table (ex. 20 for 20 percent MAD or c(5,10,20) for multiple portions of MAD). Leave blank for no values to be calculated. Logical value indicating whether to transpose rows and columns of results. Default FALSE.

## Value

A tibble data frame of numeric values of a long-term mean (and percent of long-term mean if selected) of selected years and months.

## Examples

# Run if HYDAT database has been downloaded (using tidyhydat::download_hydat())

# Calculate the long-term mean annual discharge (MAD) using only years with no missing data
calc_longterm_mean(station_number = "08NM116",
complete_years = TRUE)

# Calculate the long-term MAD and 5, 10 and 20-percent MADs using only years with no missing data
calc_longterm_mean(station_number = "08NM116",
complete_years = TRUE,
#>   STATION_NUMBER LTMAD 5%MAD 10%MAD 20%MAD
#> 1 08NM116         6.20   0.310    0.620     1.24