recession: Recession Constant

In lfstat: Calculation of Low Flow Statistics for Daily Stream Flow Data

Description

Does recession analysis using either the MRC (Master recession curve) or IRS (individual recession segments) method.

Usage

recession(lfobj,
          method = c("MRC", "IRS"),
          seglength,
          threshold,
          peaklevel = 0.95,
          seasonbreakdays = NULL,
          thresbreaks = c("fixed", "monthly","seasonal"),
          thresbreakdays = NULL,
          plotMRC = TRUE,
          trimIRS = 0, 
          na.rm = TRUE) 

Arguments

lfobj	An object of class "lfobj"
method	"MRC" or "IRS"
seglength	The length of the duration segments - see the WMO-manual and use seglenplot to choose a good value.
threshold	The threshold level (70 means Q70)
peaklevel	A level between 0 and 1 or a logical vector, see details.
seasonbreakdays	A vector of breakdays. Needed if the recession constant should be calculated individually for different seasons, see details.
thresbreaks	"fixed" uses a fixed threshold level, "monthly" calculates the threshold for every month separately, "seasonal" calculates thresholds for every season defined using "thresbreakdays".
thresbreakdays	Needed if "thresbreaks = 'seasonal'" to define the periods for which separate thresholds should be calculated, see details
plotMRC	logical, if TRUE and "method = 'MRC'" a plot like figure 5.4 in the manual is given.
trimIRS	Should a trimmed mean be used for calculating the IRS-constant? (0 means no, 0.1 means trim by 10 %)
na.rm	Should NAs in the series be ignored?

Details

For recession analysis it is necessary to define flood discharge peaks in the hydrograph. Peaklevel defines a day to be a discharge peak, if peaklevel * flow > flow[day before] and peaklevel * flow > flow[day after]. Use recessionplot to find a good level or hand a logical vector where TRUE means rainpeak.

If thresbreakdays or seasonbreakdays is a single day, e.g. "01/06", the start of the hydrological year is taken as the second breakday. If more than two seasons are to be specified, a vector of all breakdays is needed.

Value

The overall recession rate in days. If seasons are defined a rate for every season is calculated.

Author(s)

Daniel Koffler and Gregor Laaha

References

Gustard, A. & Demuth, S. (2009) (Eds) Manual on Low-flow Estimation and Prediction. Operational Hydrology Report No. 50, WMO-No. 1029, 136p.

See Also

seglenplot, recessionplot

Examples

## Not run: 
data(ngaruroro)
recession(ngaruroro,method = "MRC",seglen = 7,threshold = 70)

## End(Not run)

Example output

Loading required package: xts
Loading required package: zoo

Attaching package: 'zoo'

The following objects are masked from 'package:base':

    as.Date, as.Date.numeric

Loading required package: lmom
Loading required package: lattice
[1] 19.80968

lfstat documentation built on May 2, 2019, 6:07 p.m.