Title of Manuscript:

• Computing water flow through complex landscapes, Part 2: Finding hierarchies in depressions and morphological segmentations (doi: 10.5194/esurf-2019-34)

Previous Manuscripts:

• Computing water flow through complex landscapes – Part 1: Incorporating depressions in flow routing using FlowFill (doi: 10.5194/esurf-7-737-2019)

Subsequent Manuscripts

• Computing water flow through complex landscapes, Part 3: Fill-Spill-Merge: Flow routing in depression hierarchies (doi: 10.5194/esurf-9-105-2021)

Authors: Richard Barnes, Kerry Callaghan, Andrew Wickert

Corresponding Author: Richard Barnes (richard.barnes@berkeley.edu)

Code Repositories

• Author's GitHub Repository

This repository contains a reference implementation of the algorithms presented in the manuscript above, along with information on acquiring the various datasets used, and code to perform correctness tests.

Depressions – inwardly-draining regions of digital elevation models – present difficulties for terrain analysis and hydrological modeling. Analogous "depressions" also arise in image processing and morphological segmentation where they may represent noise, features of interest, or both. Here we provide a new data structure – the depression hierarchy – that captures the full topologic and topographic complexity of depressions in a region. We treat depressions as networks, in a way that is analogous to surface-water flow paths, in which individual sub-depressions merge together to form meta-depressions in a process that continues until they begin to drain externally. The hierarchy can be used to selectively fill or breach depressions, or to accelerate dynamic models of hydrological flow. Complete, well-commented, open-source code and correctness tests are available on Github and Zenodo.

Although GDAL is not required to use the library, it is needed to run the example program.

Install the prerequisites

sudo apt install libgdal-dev cmake

brew install gdal libomp cmake

Ensure you have a working compiler.

The following compilers are known to work: GCC7.5.0, GCC8.4.0, GCC9.3.0

The following compilers are known to be too old: GCC5.4.0

Next, be sure to acquire submodules either upon initially obtaining the repository:

git clone --recurse-submodules -j8 https://github.com/r-barnes/Barnes2019-DepressionHierarchy.git

Or afterwards by using the following within the repository itself:

git submodule update --init --recursive

Afterwards, compile:

mkdir build
cd build
# -DUSE_GDAL is optional
cmake -DCMAKE_BUILD_TYPE=Release -DUSE_GDAL=On ..
make -j 4 #Set to number of CPUs for a faster compilation

Run with:

./build/dephier.exe <Input> <Output Prefix> <Ocean Level>

<INPUT> can be any file that GDAL can read.

<Output Prefix> is a name such as temp/out which is used to prefix the following output files:

• temp/out-label.tif: A file showing the depression hierarchy leaf label of each cell in the DEM
• temp/out-graph.csv: A CSV file showing the topological relationships of the depression hierarchy's depressions

<Ocean Level> is the elevation of the ocean within the dataset All cells having this elevation are considered to be part of the ocean.