#' Function to return the DH24 hydrologic indicator statistic for a given data frame
#'
#' This function accepts a data frame that contains a column named "discharge" and a threshold value obtained
#' using the peakdata and peakthresh functions and calculates
#' DH24; Flood-free days. Compute the flood threshold as the flow equivalent for a flood recurrence of 1.67 years.
#' Compute the maximum number of days that the flow is below the threshold for each year. DH24 is the mean
#' (or median-Use Preference option) of the maximum yearly no-flood days (days-temporal).
#'
#' @param qfiletempf data frame containing a "discharge" column containing daily flow values
#' @param thresh numeric containing 1.67-year flood threshold calculated by getPeakThresh
#' @return dh24 numeric containing DH24 for the given data frame
#' @export
#' @examples
#' qfiletempf<-sampleData
#' dh24(qfiletempf, 1158)
dh24 <- function(qfiletempf, thresh) {
lfcrit <- thresh
noyears <- aggregate(qfiletempf$discharge, list(qfiletempf$wy_val),
FUN = median, na.rm=TRUE)
colnames(noyears) <- c("Year", "momax")
noyrs <- length(noyears$Year)
dur <- data.frame(Year = rep(0,nrow(qfiletempf)), dur = rep(1,nrow(qfiletempf)))
max_yr <- rep(0,noyrs)
for (i in 1:noyrs) {
subsetyr <- subset(qfiletempf, as.numeric(qfiletempf$wy_val) == noyears$Year[i])
flag <- 0
pdur <- 0
nevents <- 0
for (j in 1:nrow(subsetyr)) {
if (subsetyr$discharge[j]<lfcrit) {
flag <- flag+1
nevents <- ifelse(flag==1,nevents+1,nevents)
pdur <- pdur+1
} else {
if (flag > 0) {
dur$dur[nevents]<-pdur
dur$Year[nevents]<-subsetyr$wy_val[j]
}
flag <- 0
pdur <- 0
}
}
dur_sub <- dur$dur[dur$Year==subsetyr$wy_val[j]]
max_yr[i] <- ifelse(length(dur_sub)>0,max(dur_sub),0)
}
max_yr[max_yr==0]<-NA
dh24 <- mean(max_yr,na.rm=TRUE)
return(dh24)
}
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.