Depression-Breaching

Depressions, otherwise known as pits, are areas of a landscape wherein flow ultimately terminates without reaching an ocean or the edge of a digital elevation model.

Depressions, Pits, and Sinks

Depressions have been called by a variety of names. To clarify this mess, Lindsay (2016) provides a typology. This typology is followed here.

Original DEM

For reference, the original DEM appears as follows:

import richdem as rd
import numpy as np

beau    = rd.rdarray(np.load('imgs/beauford.npz')['beauford'], no_data=-9999)
beaufig = rd.rdShow(beau, ignore_colours=[0], axes=False, cmap='jet', figsize=(8,5.5))

(Source code, png, hires.png, pdf)

Complete Breaching

Depression-breaching is used to dig channels from the pit cells of a DEM to the nearest cells (in priority-flood sense) outside of the depression containing the pit. This resolves the depression as all cells in the depression now have a drainage path to the edge of the DEM.

The result looks as follows:

beau_breached    = rd.BreachDepressions(beau, in_place=False)
beaufig_breached = rd.rdShow(beau_breached, ignore_colours=[0], axes=False, cmap='jet', vmin=beaufig['vmin'], vmax=beaufig['vmax'], figsize=(8,5.5))

(Source code, png, hires.png, pdf)

We can visualize the difference between the two like so:

beau_diff    = beau_breached - beau
beaufig_diff = rd.rdShow(beau_diff, ignore_colours=[0], axes=False, cmap='jet', figsize=(8,5.5))

(Source code, png, hires.png, pdf)

Complete Breaching is available via the following commands:

Language	Command
Python	richdem.BreachDepressions
C++	richdem::BreachDepressions<Topology>()

Pros	Cons
Minimal Modifcations to DEM Simple	Slightly slower