pkg/R/PEC_sw_drift_NL.R


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# Copyright (C) 2016  Johannes Ranke
# Contact: jranke@uni-bremen.de
# This file is part of the R package pfm

# This program is free software: you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation, either version 3 of the License, or (at your option) any later
# version.

# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
# details.

# You should have received a copy of the GNU General Public License along with
# this program. If not, see <http://www.gnu.org/licenses/>

#' Calculate predicted environmental concentrations in surface water due to drift
#'
#' This is a basic, vectorised form of a simple calculation of a contaminant
#' concentration in surface water based on complete, instantaneous mixing
#' with input via spray drift.
#'
#' @param rate Application rate in units specified below
#' @param applications Number of applications for selection of drift percentile
#' @param drift_percentages Percentage drift values for which to calculate PECsw
#' @param water_depth Depth of the water body in cm
#' @param rate_units Defaults to g/ha
#' @param PEC_units Requested units for the calculated PEC. Only µg/L currently supported
#' @return The predicted concentration in surface water
#' @export
#' @author Johannes Ranke
#' @examples
#' PEC_sw_drift_NL(100)
PEC_sw_drift_NL <- function(rate, 
                            applications = 1,
                            water_depth = 30, 
                            drift_percentages = c(1),
                            rate_units = "g/ha",
                            PEC_units = "\u00B5g/L")
{
  rate_units <- match.arg(rate_units)
  PEC_units <- match.arg(PEC_units)
  water_volume <- 100 * 100 * (water_depth/100) * 1000   # in L (for 1 ha)
  PEC_sw_overspray <- rate * 1e6 / water_volume          # in µg/L
  PEC_sw_drift <- PEC_sw_overspray * drift_percentages / 100
  names(PEC_sw_drift) <- paste(drift_percentages, "%")
  return(PEC_sw_drift)
}