Fill-Spill-Merge

Title of Manuscript:

• Computing water flow through complex landscapes, Part 3: Fill-Spill-Merge: Flow routing in depression hierarchies (doi: TODO)

Previous Manuscripts:

• Computing water flow through complex landscapes, Part 2: Finding hierarchies in depressions and morphological segmentations (doi: 10.5194/esurf-2019-34)
• Computing water flow through complex landscapes – Part 1: Incorporating depressions in flow routing using FlowFill (doi: 10.5194/esurf-7-737-2019)

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.

Abstract

Depressions---inwardly-draining regions---are common to many landscapes, including those shaped by glaciation, compressional and/or extensional tectonics, and cratering. When there is sufficient moisture, depressions take the form of lakes and wetlands; otherwise, they may be dry. Hydrological flow models used in geomorphology, hydrology, planetary science, soil and water conservation, and other fields often eliminate depressions through filling or breaching; however, this can produce unrealistic results. Models that retain depressions, on the other hand, are often undesirably expensive to run. In previous work we began to address this by developing a depression hierarchy data structure to capture the full topographic complexity of depressions in a region. Here, we extend this work by presenting a Fill-Spill-Merge algorithm that utilizes our depression hierarchy to rapidly process and distribute runoff. Runoff fills depressions, which then overflow and spill into their neighbors. If both a depression and its neighbor fill, they merge. We provide a detailed explanation of the algorithm as well as results from two sample study areas. In these case studies, the algorithm runs 90-2,600x faster (with a 2,000-63,000x reduction in compute time) than the commonly-used Jacobi iteration and produces a more accurate output. Complete, well-commented, open-source code is available on Github and Zenodo.

Prerequisites

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

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

Install the prerequisites

Linux

sudo apt install libgdal-dev cmake

Mac

brew install gdal libomp cmake llvm

(GDAL should not be necessary for installation, but is recommended.)

Additional setup

Mac

Here we assume that you are using the Anaconda Python distribution.

These additional possible requirements to compile Fill-Spill-Merge on MacOSX stem from the fact that those users with the Anaconda Python distribution now comes packaged with its own compilers. This issue may exist in Linux as well, though due to the extensive and well-integrated apt repositories, Linux users are less likely to install Anaconda Python.

1. Download MacOSX10.9.sdk from https://github.com/phracker/MacOSX-SDKs and place it in /opt/MacOSX10.9.sdk
2. Point the cmake compiler at this SDK:

export CONDA_BUILD_SYSROOT=/opt/MacOSX10.9.sdk

Compilation

Be sure to acquire submodules either upon initially obtaining the repository:

git clone --recurse-submodules -j8 https://github.com/r-barnes/Barnes2020-FillSpillMerge

Or afterwards by using the following within the repository itself:

git submodule update --init --recursive

Afterwards, compile:

Linux

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release -DUSE_GDAL=ON ..
make -j 4 # Set to number of CPUs for a faster compilation (4 here)

Mac

mkdir build
cd build
# Be sure to repoint the versioning in the following as necessary:
cmake -D CMAKE_C_COMPILER="/usr/local/Cellar/llvm/10.0.0_3/bin/clang" \
      -D CMAKE_CXX_COMPILER="/usr/local/Cellar/llvm/10.0.0_3/bin/clang++" \
      -DUSE_GDAL
      -DCMAKE_BUILD_TYPE=Release ..
make -j 4 # Set to number of CPUs for a faster compilation (4 here)

Additional options

• Use -DCODE_COVERAGE=ON to enable code coverage report generation. When doing a build this will run all the tests and generate a coverage report.

Running Example Program

A test program, fsm.exe is generated by make. This program simulates pouring a given amount of water onto every cell on a landscape and determining where it all ends up. Running the program shows its command-line arguments.

Running Tests

Compiling as above will produce an executable fsm_unittests.exe. Running this will perform all the tests associated with the code. Randomized testing is used to cover a wide range of possible inputs both for individual functions (unit testing) as well as the entirety of FillSpillMerge in an end-to-end fashion.