DDF99 {UKFE}

FEH99 depth duration frequency precipitation model

Description

Estimation of design rainfall depths, and the rarity of observed rainfall

Usage

DDF99(Duration, RP, pars, Depth = NULL, disc = NULL)

Arguments

Duration

numeric. The duration of interest (in hours)

RP

return period

pars

a numeric vector of length six. The six catchment parameters for the DDF model in the order of: c, d1, d2, d3, e, f

Depth

a user supplied rainfall depth for the duration under question

disc

converts from the sliding duration to fixed duration estimate. Choices are "hourly" or "daily"

Details

The depth duration frequency rainfall model is detailed in the Flood Estimation Handbook (1999), volume 2. A note about the discretisation: The user can choose between "daily" or "hourly" for the sliding duration to fixed duration conversion. If the 'Depth' argument is used, it overrides the return period (RP) argument and provides RP as a function of depth. However, if both the 'Depth' and the 'disc' arguments are used, the sliding duration depth is provided as a function of the user input depth. This resulting depth can then be used without the 'disc' argument to determine the sliding duration RP.

Value

the rainfall depth or rainfall return period

Author(s)

Anthony Hammond

Examples

#Examples from FEH volume 2
#The parameters for these examples are from FEH v2
#What is the 2-day rainfall with return period 100-years for Norwich.
DDF99(Duration = 48, RP = 100, pars = c(-0.023, 0.273, 0.351, 0.236, 0.309, 2.488))
#What is the 4-hour rainfall with return period 20 years for a typical point in the Lyne catchment
DDF99(Duration = 4, RP = 20, pars = c(-0.025, 0.344, 0.485, 0.402, 0.287, 2.374))
#How rare was the rainfall of 6th August 1978 at Broughshane, County Antrim?
DDF99(Duration = 5, Depth = 47.7, pars = c(-0.022, 0.412, 0.551, 0.276, 0.261, 2.252))