Baseflow separation
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Introduction
Chapman (1999) gives an excellent overview of baseflow separation techniques. Recursive digital filters are easiest to automate. Below are a few R implementations of the filter equations listed on the site:
NOTE: this is work in progress - the scripts have not yet been thoroughly tested and may contain bugs!
Filter equations
One-parameter algorithm
Chapman (1999) equation 8:
bf_oneparam <- function(discharge, k){
bf <- rep(discharge[1],length(discharge))
for(i in 2:length(discharge)) {
bf[i] <- (k*bf[i-1]/(2-k)) + ((1-k)*discharge[i]/(2-k))
if(bf[i] > discharge[i]) bf[i] <- discharge[i]
}
return(bf)
}
Parameter k is the recession constant during periods without direct runoff.
Boughton two-parameter algorithm
Chapman (1999) equation 9:
bf_boughton <- function(discharge, k, C){
bf <- rep(discharge[1],length(discharge))
for(i in 2:length(discharge)) {
bf[i] <- (k*bf[i-1]/(1+C)) + (C*discharge[i]/(1+C))
if(bf[i] > discharge[i]) bf[i] <- discharge[i]
}
return(bf)
}
IHACRES three-parameter algorithm
Chapman (1999) equation 11:
bf_IHACRES <- function(discharge, k, C, a){
bf <- rep(discharge[1],length(discharge))
for(i in 2:length(discharge)) {
bf[i] <- (k*bf[i-1]/(1+C)) + (C*(discharge[i] + a*discharge[i-1])/(1+C))
if(bf[i] > discharge[i]) bf[i] <- discharge[i]
}
return(bf)
}
References
- Chapman, T., 1999. A comparison of algorithms for stream flow recession and baseflow separation. Hydrol. Process. 13, 701-714