flooded
Map floodplains from an elevation model and a stream network.
flooded maps floodplains from terrain: the low, gently sloping ground beside streams. It reads
terrain rather than modelling flood flows, so it is quick to run over large areas for screening and
planning. From a 30 m elevation model it maps the valley floors of a whole watershed group, as in
the map below. From 1 m lidar it also picks out raised ground across a valley floor, such as road
and rail grades, dykes and fill, that can cut a floodplain off from its river.
Floodplain (flood factor 4) of the Parsnip River watershed group, BC, from the 30 m MRDEM-30
elevation model, modelled on streams of order 3 and up that bull trout can reach according to the
default configuration of link.
How it works
The Valley Confinement Algorithm (US Forest Service; Nagel et al. 2014) finds unconfined valley
bottoms: valley floors wide and flat enough for a river to spread out and build a floodplain, as
opposed to reaches held between valley walls. flooded ports it to R from BlueGeo and bcfishpass.
Ground counts as floodplain where it is:
- gently sloped (9% or less by default);
- close to a stream, both in a straight line (1 km by default) and in a distance that counts
steep ground as farther;
- below a water level set at a multiple of bankfull depth above nearby streams. Bankfull depth
comes from each stream's upstream area and mean annual precipitation (Hall et al. 2007).
That multiple is the flood factor. Three presets run from the active channel (2) through the
functional floodplain (4) to the valley bottom (6). Small gaps are then filled and small patches
dropped, and lakes and wetlands can be added. Each part of a shared floodplain can be assigned to
the streams it belongs to, carrying reach flags such as fish habitat onto the ground beside each
reach.
What it needs
- Elevation. flooded fetches an elevation model for an area of interest, by default
Natural Resources Canada's MRDEM-30 (30 m, all of Canada, no login). Any elevation raster on a
projected grid in metres works, such as 1 m provincial lidar DEMs from
stac-elevation-bc, or a DEM built at any
resolution from the LidarBC point clouds in
stac-pointcloud-bc.
- Streams. Stream lines with upstream contributing area in hectares. In BC,
fwapg adds it to the Freshwater Atlas; the atlas as
published in the BC Data Warehouse does not carry it. Elsewhere, any network with upstream area
works.
- Precipitation (optional). Mean annual precipitation over each stream's upstream area. In BC,
fwapg carries it on every segment from ClimateBC. Without it, bankfull
depth comes from upstream area alone.
Installation
pak::pak("NewGraphEnvironment/flooded")
Functions still change between releases (NEWS),
so pin a version for repeatable work: pak::pak("NewGraphEnvironment/[email protected]").
Example
A 5 km reach of the Bulkley River ships with the package. Its floodplain at the default flood
factor (6), by stream:
library(flooded)
dem <- terra::rast(system.file("testdata/dem.tif", package = "flooded"))
streams <- sf::st_read(system.file("testdata/streams.gpkg", package = "flooded"), quiet = TRUE)
valleys <- fl_valley_confine(
dem, streams,
area_field = "upstream_area_ha",
precip = fl_stream_rasterize(streams, dem, field = "map_upstream")
)
by_river <- fl_valley_attribute(valleys, streams, group = "gnis_name", dem = dem)
by_river$area_ha <- round(as.numeric(sf::st_area(by_river)) / 1e4)
sf::st_drop_geometry(by_river)[, c("gnis_name", "area_ha")]
#> gnis_name area_ha
#> 1 Bulkley River 264
#> 2 Cesford Creek 112
#> 3 Richfield Creek 130
#> 4 Robert Hatch Creek 50
#> 5 <NA> 99
Floodplain shared by two streams counts toward both, so the rows add up to more than the 287 ha
total.
Learn more
Ecosystem
| Package | Role |
|---|
| fresh | Stream network modelling engine: segment, classify, cluster, aggregate |
| link | Intrinsic habitat models: develop, test and communicate |
| wet | Stream flow and water temperature for BC's Freshwater Atlas |
| flooded | Delineate floodplain extents from DEMs and stream networks (this package) |
| drift | Track land cover change within floodplains over time |
| floodplains | Floodplain and land cover change modelling for BC watershed groups |
| stac_floodplains_bc | STAC catalogue of floodplain land cover change in BC, 2017-2023, by watershed group |
| cd | Climate departure analysis from ERA5-Land reanalysis |
| fly | Estimate airphoto footprints and select optimal coverage for a study area |
Land cover change: fresh (network) → flooded (floodplains) → drift (land cover change)
→ floodplains (watershed groups) → stac_floodplains_bc (published)
Data and methods it builds on
- Code adapted from BlueGeo (Devin Cairns, MIT) and
bcfishpass (Simon Norris, Apache 2.0), following the
USDA VCA Toolbox.
Parameters and flood levels: methodology.
What the output can be used to claim: floodplain interpretation.
- fwapg (Simon Norris): the BC Freshwater Atlas in
PostgreSQL, with upstream area, ClimateBC mean annual precipitation
and channel width on its stream segments.
- NRCan's MRDEM-30
elevation model.
- Bundled data: BC's 25 m TRIM DEM, the Freshwater Atlas, stream access and habitat modelled by
link (which applies bcfishpass's barrier and habitat
override tables), ClimateBC precipitation and BC lidar, with licences in
inst/NOTICE.md.
Citation
Cite flooded from CITATION.cff, or with "Cite this repository" on GitHub.
License
MIT (see LICENSE). Adapted code is credited in LICENSE.note;
data licences are in inst/NOTICE.md.
