Description Usage Arguments Value Author(s) Examples

Calculates a suite of statistics describing flood characteristics, such as the timing, frequency and duration of events. The event threshold can be defined as a flow quantile (e.g. upper 90th percentile [default]) or a specific threshold volume (e.g. ML/day).

For the purpose of deriving annual flood statistics, the function can also be applied based on the hydrologic year. This is advisable where the high flow season spans years, such that prolonged spells may span years. Setting the parameter hydro.year=TRUE uses the hydro.year function to determine the appropriate hydrologic year for each record, which is then used for deriving annual spell characteristics.

It is possible for there to be multiple days with the same annual maximum flow value (although less likely than for low flows). In estimating the average timing (and sd of timing) of minimum flows, the function calculates the average day of year (DOY) of minimum flows in each year first, before calculating the average across years. Circular functions are used to address the proximity between days toward the beginning and end of the year.

Missing values are allowed for convenience (NA's are removed and the time-series is concatenated before functions are applied), but may lead to biased results. For the purpose of the annual statistics years with fewer than 350 days of available record are ignored.

When used with ddply to compute outputs for multiple gauges or time periods simultaneously, results, icluding graphs are produced for each factor level, including graphs. Note the funtion will return warnings if annual stats are calculated when year is used as a factor.

1 2 3 4 |

`flow.ts` |
Dataframe with date and discharge data in columns named "Date" and "Q" respectively. Date must be in POSIX format (see ts.format). If a third column exists then this is assumed to provide a vector of years for the purpose of calculating annual spell statistics based on a predetermined hydrologic year. |

`quant` |
Percentile/quantile to use for defining event magnitude (default 0.9). A value of 0.9 is the upper 90th percentile (i.e. a volume exceeded 10% of the time), and corresponds to Q90. |

`threshold` |
A user supplied threshold for defining spells. This would typically be derived from hydraulic models or similar knowledge pertaining to a gauge site. |

`ind.days` |
Periods between spells of less than ind.days (default 5) are considered to be 'in spell' for the purpose of further calculations. A value of 0 means spells 1 day apart are considered indpedendent. |

`duration` |
logical. Should statistics describing spell duration be returned? |

`volume` |
logical. Should statistics describing spell volumes be returned? Note that for days considered 'in-spell', the returned values have the threshold volume subtracted first, and hence reflect the amount of water that was flowing past the gauge above threshold. This is most useful in water planning scenarios. |

`plot` |
logical. Should the time-series be plotted? Data points considered 'within spell' are identifed using red circles and the threshold is identified with a horizontal line. |

`ignore.zeros` |
logical. If TRUE, days below a user defined cease-to-flow threshold (default 0.1) will be excluded when estimating the spell threshold for a given percentile. This is primarily of interest in highly ephemeral rivers, where flow may only occur for a small fraction of the time. In such cases, the inclusion of zeros will skew estimates of high flow events downwards, which may be undesirable. |

`ctf.threshold` |
values below this threshold are treated as zero for the purpose of percentile based calculations (see ignore zeros). |

`ann.stats` |
logical. If TRUE, the function returns results describing the annual maximum series (i.e. that describing the characteristics of the largest flood event in each year of the time-series). The duration of each annual high.spell is defined as the number of days above the smallest annual maximum for the largest (and longest) high.spell event in each year. |

`ann.stats.only` |
logical. If TRUE, statistics describing the annual series only are returned. |

`inter.flood` |
logical. If TRUE, statistics describing inter-flood spell characteristics are reported. |

`hydro.year` |
logical. If TRUE, each record is first assigned to a hydrologic year based on the timing of minimum flows. See |

A dataframe with the following columns.

flood indices

`high.spell.threshold ` |
The high spell threshold applied in the analysis) |

`n.events ` |
The number of events in the series greater than or equal to the high.spell.threshold |

`spell.freq` |
The frequency of spell events (no. per year) |

`ari` |
Average Recurrence Interval of events in years (1/spell.freq) |

`min.high.spell.dur` |
Minimum duration of spell events |

`avg.high.spell.dur` |
Average duration of spell events |

`med.high.spell.dur` |
Median duration of spell events |

`max.high.spell.dur` |
Maximum duration of spell events |

`avg.spell.volume` |
Average spell volume (volumes above the threshold only) |

`avg.spell.peak` |
Average spell peak |

`sd.spell.peak` |
Standard deviation of spell speaks |

`avg.rise` |
Average absolute rate of daily rise during spell events |

`avg.fall` |
Average absolute rate of daily fall during spell events |

interflood indices

`average.interval` |
The average time between spells (years) |

`min.interval` |
The mininum time between spells (years) |

`max.interval` |
The maximum time between spells (years) |

Annual flood statistics

`avg.max.ann` |
The average annual maximum flow |

`cv.max.ann` |
The coefficient of variation of annual maximum flows |

`flood.skewness` |
The average annual maximum / mean daily flow |

`ann.max.timing` |
The average day of the year (0-366) on which maximum flows occur |

`ann.max.timing.sd` |
circular standard deviation of the average timing of annual maximum flows |

`ann.max.min.dur` |
Minimum duration of the annual maximum spells (always equal to 1) |

`ann.max.avg.dur` |
Average duration of the annual maximum spells |

`ann.max.max.dur` |
Maximum duration of the annual maximum spells |

`ann.max.cv.dur` |
The coefficient of variation of the duration of annual maximum spells |

Nick Bond <n.bond@latrobe.edu.au>

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | ```
data(Cooper)
Cooper<-ts.format(Cooper)
high.spells(Cooper, quant=0.9)
high.spells(Cooper, quant=0.9, ann.stats=FALSE, plot=FALSE)
high.spells(Cooper, quant=0.9, ann.stats=FALSE, ignore.zeros=TRUE)
high.spells(Cooper, quant=0.9, ann.stats=FALSE, ignore.zeros=TRUE, hydro.year=TRUE)
require(plyr)
Cooper$year<-strftime(Cooper$Date, format="%Y")
ddply(Cooper, .(year), function(x) high.spells(x, ann.stats=FALSE))
Cooper$time.period <- ifelse(Cooper$year<1980,"pre_1980","post_1980")
ddply(Cooper, .(time.period), function(x) high.spells(x, ann.stats=FALSE))
``` |

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