calc_ldc: Calculate load duration curve
In TxWRI/ldc: Calculate and Plot Pollutant Load Duration Curves

Description Usage Arguments Details Value Examples

View source: R/calc_ldc.R

Calculates the period of record load duration curve from a data frame that includes mean daily flow and associated point measurements of pollutant concentration.

calc_ldc(
  .tbl,
  Q = NULL,
  C = NULL,
  allowable_concentration = NULL,
  breaks = c(1, 0.8, 0.4, 0),
  labels = c("High Flows", "Medium Flows", "Low Flows"),
  estimator = 6
)

`.tbl`	data frame with at least two columns Q (discharge or flow) and C (associated pollutant concentration).
`Q`	variable name in .tbl for discharge or flow. This must have unit set, typically "ft^3/s".
`C`	variable name in .tbl for associated pollutant concentration at a given flow value. This must have a unit set, typically "mg/L" or "cfu/100mL".
`allowable_concentration`	an object of class `units` specifying the allowable pollutant concentration.
`breaks`	a numeric vector of break points for flow categories. Must be of length of labels + 1. defaults to `c(1, 0.8, 0.4, 0)`.
`labels`	labels for the categories specified by breaks.
`estimator`	numeric, one of `c(5,6,7,8,9)`. `6` is the default method correponding to the Weibull plotting position. Further details are provided in `stats::quantile()`.

The exceedance probability is calculated from the descending order of Daily Flows. By default, the Weibull plotting position is used:

p = P(Q > q_i) = \frac{i}{n+1}

where q_i, i = 1, 2, ... n, is the i-th sorted streamflow value.

object of class tibble. Includes variables in .tbl and Daily_Flow_Volume (discharge volume), Daily_Load (pollutant sample volume), P_Exceedance (exeedance probability), Flow_Category (as defined by breaks and labels).

# Basic example using built in Tres Palacios data
library(dplyr)
library(units)
# Format data
install_unit("cfu")
df <- as_tibble(tres_palacios) %>%
  ## filter data so this run quicker
  filter(!is.na(Indicator_Bacteria)) %>%
  ## flow must have units, here is is in cfs
  mutate(Flow = set_units(Flow, "ft^3/s")) %>%
  ## pollutant concentration must have units
  mutate(Indicator_Bacteria = set_units(Indicator_Bacteria, "cfu/100mL"))
# Calculate LDC

## specify the allowable concentration
allowable_concentration <- 126
## set the units
units(allowable_concentration) <- "cfu/100mL"
df_ldc <- calc_ldc(df,
                   Q = Flow,
                   C = Indicator_Bacteria,
                   allowable_concentration = allowable_concentration)
df_ldc

## cleanup
remove_unit("cfu")