recession {lfstat}

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)

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?

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.

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, WNO-No. 1029, 136p.

See Also

seglenplot, recessionplot

Examples

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