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

`FALSE`

.- months
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`

).- percent_MAD
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 percentages). Leave blank or set to NA for no values to be calculated.- transpose
Logical value indicating whether to transpose rows and columns of results. Default

`FALSE`

.

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.

```
# Run if HYDAT database has been downloaded (using tidyhydat::download_hydat())
if (file.exists(tidyhydat::hy_downloaded_db())) {
# 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,
percent_MAD = c(5,10,20))
}
#> # A tibble: 1 × 5
#> STATION_NUMBER LTMAD `5%MAD` `10%MAD` `20%MAD`
#> <chr> <dbl> <dbl> <dbl> <dbl>
#> 1 08NM116 6.25 0.313 0.625 1.25
```