lfstat (version 0.9.4)

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)

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?

Value

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

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.

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)