lfstat (version 0.9.12)

recession: Recession Constant

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)

Value

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

Arguments

lfobj

An object of class 'lfobj'

method

'MRC' or 'IRS'

seglength

The length of the duration segments - see the WNO-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 break days. 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?

Author

Daniel Koffler and Gregor Laaha

Details

For recession analysis it is necessary to define flood discharge peaks in the hydrograph. Argument 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 rain peak.

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

References

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

See Also

seglenplot, recessionplot

Examples

data(ngaruroro)
recession(ngaruroro,method = "MRC",seglen = 7,threshold = 70)