Derive hydraulic quantities from routed flow

Computes the family of time-and-motion quantities that a routed flood implies: peak flow velocity, time of concentration (by one or more methods), channel travel time, and the time-to-peak of the routed hydrograph. These are the layers a geographer maps alongside depth.

Usage

flood_hydraulics(
  x,
  length_m = 5000,
  overland_m = 100,
  retardance = 0.4,
  dt_hours = 24
)

Arguments

x

A flood_project whose route slot has been populated, or a flood_route object directly.

length_m

Representative flow-path (channel) length in metres, used for time of concentration and travel time. Default 5000.

overland_m

Overland flow length in metres for the Kerby component. Default 100.

retardance

Kerby retardance coefficient. Default 0.4.

dt_hours

Time step of the routed hydrograph in hours, used to convert the time-to-peak index into hours. Default 24 (daily).

Value

If x is a flood_project, the same object with its hydraulics slot populated. Otherwise a list of class flood_hydraulics with elements peak_velocity_ms, tc (a named vector of times of concentration in minutes by method: kirpich, kerby, kerby_kirpich, velocity), travel_time_min, and time_to_peak_hours.

Details

Velocity comes from Manning's equation at the routed peak depth. Time of concentration is available by the Kirpich channel method, the Kerby overland method, the combined Kerby-Kirpich sum, and a velocity-based travel time (flow-path length divided by peak velocity). Time-to-peak is read directly from the routed hydrograph.

See also

tc_kirpich, tc_kerby.

Examples

disc <- data.frame(
  date = seq(as.Date("2020-06-01"), by = "day", length.out = 15),
  Q_mm = c(0, 1, 3, 8, 18, 30, 22, 14, 8, 4, 2, 1, 0, 0, 0)
)
r <- flood_route(disc, method = "muskingum-cunge")
h <- flood_hydraulics(r, length_m = 4000, overland_m = 120)
h$tc
#>       kirpich         kerby kerby_kirpich      velocity 
#>        165.43         44.51        206.11         56.88 
h$peak_velocity_ms
#> [1] 1.172