Flow Exceedance Curves

A nice and simple flow duration curve figure that anyone can use for analyzing probability. These figures display discharge vs. percent of time that a particular discharge. This information can become particularly useful to show how frequent particular discharges may occur or exceed some percentage of time (e.g., 25% and 75%) The area under the curve dictates the average daily flow, while the median daily flow is at 50% in the case above over a 74 year period utilizing average daily flows.

library(tidyverse)
library(dataRetrieval)
source('logtickmarks.r') #function for specifying logarithmic y-axis breaks  
options(scipen=999) #removing scientific notation 
TRENTONFlow <- readNWISdv(siteNumber='01463500',parameterCd=c("00060")) #Importing USGS average daily flow values for Trenton, NJ 
​
#Attached below is a specific function for outputting a logarithmic tick mark/grid. 
​#Developing ggplot2 theme format 
themebox <- function(base_family = "sans", ...){
  theme_bw(base_family = base_family, ...) +
    theme( plot.title = element_text(size = 18,  face = "bold"),
      axis.ticks.length = unit(-0.05, "in"),
      axis.title = element_text(face="bold", size=18),
      axis.text.x=element_text(margin=unit(c(0.3,0.3,0.3,0.3), "cm"),colour="black", size = 18),
      axis.text.y=element_text(margin=unit(c(0.3,0.3,0.3,0.3), "cm"),colour="black", size = 18),
      axis.line = element_line(size=0.5, colour = "black"),
      #axis.ticks.x = element_blank(),
      aspect.ratio = .8,
      legend.background = element_rect(color = "black", fill = "white") )
}

TRENTONFlow %>% 
  mutate(my_rank = 1 - percent_rank(X_00060_00003)) %>%     #transforming flow values into a ranked percentage 
  mutate(my_rank = if_else(my_rank == 0.01, 1, my_rank)) %>%   
  ggplot(aes(my_rank,X_00060_00003)) +
  geom_line(size=2) +
  ggtitle("Trenton New Jersey - Flow Duration Curve") +
  scale_y_log10(name = 'Predicted daily flows (cfs)',
                breaks = logTicks(n = 10), #1,2,4,10,100, etc. outline how many major base pair ticks marks
                    minor_breaks = logTicks(n=100))+  #outline how many minor base pair ticks marks; keep in mind logarithmic
  scale_x_continuous(name = 'Percentage of time flow exceeded')+
  themebox()

flow_exceedance_curve.zip
File Size:	214 kb
File Type:	zip

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