calc_annual_lowflows: Calculate annual low flows and dates

In fasstr: Analyze, Summarize, and Visualize Daily Streamflow Data

Calculate annual low flows and dates

Description

Calculates annual n-day minimum values, and the day of year and date of occurrence of daily flow values from a daily streamflow data set. Calculates statistics from all values, unless specified. Returns a tibble with statistics.

Usage

calc_annual_lowflows(
  data,
  dates = Date,
  values = Value,
  groups = STATION_NUMBER,
  station_number,
  roll_days = c(1, 3, 7, 30),
  roll_align = "right",
  water_year_start = 1,
  start_year,
  end_year,
  exclude_years,
  months = 1:12,
  transpose = FALSE,
  complete_years = FALSE,
  ignore_missing = FALSE,
  allowed_missing = ifelse(ignore_missing, 100, 0)
)

Arguments

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.
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).
transpose	Logical value indicating whether to transpose rows and columns of results. Default FALSE.
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.
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 'ignore_missing = FALSE' then it defaults to 0 (zero missing dates allowed), if 'ignore_missing = TRUE' then it defaults to 100 (any missing dates allowed); consistent with ignore_missing usage. Supersedes ignore_missing when used.

Value

A tibble data frame with the following columns:

Year	calendar or water year selected
Min_'n'_Day	annual minimum for each n-day rolling mean, direction of mean specified by roll_align
Min_'n'_Day_DoY	day of year for each annual minimum of n-day rolling mean
Min_'n'_Day_Date	date (YYYY-MM-DD) for each annual minimum of n-day rolling mean

Default columns:

Min_1_Day	annual 1-day mean minimum (roll_align = right)
Min_1_Day_DoY	day of year of annual 1-day mean minimum
Min_1_Day_Date	date (YYYY-MM-DD) of annual 1-day mean minimum
Min_3_Day	annual 3-day mean minimum (roll_align = right)
Min_3_Day_DoY	day of year of annual 3-day mean minimum
Min_3_Day_Date	date (YYYY-MM-DD) of annual 3-day mean minimum
Min_7_Day	annual 7-day mean minimum (roll_align = right)
Min_7_Day_DoY	day of year of annual 7-day mean minimum
Min_7_Day_Date	date (YYYY-MM-DD) of annual 7-day mean minimum
Min_30_Day	annual 30-day mean minimum (roll_align = right)
Min_30_Day_DoY	day of year of annual 30-day mean minimum
Min_30_Day_Date	date (YYYY-MM-DD) of annual 30-day mean minimum

Transposing data creates a column of 'Statistics' and subsequent columns for each year selected. 'Date' statistics not transposed.

Examples

# Run if HYDAT database has been downloaded (using tidyhydat::download_hydat())
if (file.exists(tidyhydat::hy_downloaded_db())) {

# Calculate annual 1, 3, 7, and 30-day (default) low flows with 
# default alignment ('right')
calc_annual_lowflows(station_number = "08NM116") 

# Calculate custom 3 and 7-day annual low flows with 'center' alignment
calc_annual_lowflows(station_number = "08NM116",
                     roll_days = c(3,7),
                     roll_align = "center",
                     start_year = 1980)
                     
}

fasstr documentation built on Sept. 30, 2024, 9:24 a.m.