What is "HexWatershed"?
HexWatershed is a mesh independent flow direction model for hydrologic models.
Why do we develop HexWatershed?
Spatial discretization is the cornerstone of all spatially-distributed numerical simulations including watershed hydrology. Traditional square grid spatial discretization has several limitations:
It cannot represent adjacency uniformly;
It leads to the "island effect" and the diagonal travel path issue in D8 scheme;
It cannot provide a spherical coverage without significant spatial distortion;
It cannot be coupled with other unstructured mesh-based models such as the oceanic models.
Therefore, we developed a watershed delineation model (HexWatershed) based on the hexagon mesh spatial discretization.
We further improve HexWatershed to fully unstructured mesh-based to support variable-resolution meshes such as the MPAS mesh.
We propose that spatially distributed hydrologic simulations should consider using a hexagon grid spatial discretization.
How we did it?
We basically rewrote all the core watershed delineation algorithms, just on a completely different data structure.
What is the current status of "HexWatershed"?
We are adding more features to the HexWatershed ecosystem:
The zonal resampling within the unstructured mesh is supported and other geostatistics are supported as well;
HexWatershed is ready for continental and global scale simulation (e.g., through the MPAS mesh);
HexWatershed uses the state-of-art topology method to conduct stream burning and depression filling;
We are evaluating hydrology simulations using the HexWatershed routing maps.
Chang Liao, & Matt Cooper. (2022). Pyflowline a mesh independent river network generator for hydrologic models. (0.1.24). Zenodo. https://doi.org/10.5281/zenodo.6407299
Chang Liao, Tian Zhou, Donghui Xu, Richard Barnes, Gautam Bisht, Hong-Yi Li, Zeli Tan, Teklu Tesfa, Zhuoran Duan, Darren Engwirda, and L. Ruby Leung. Advances in hexagon mesh based flow direction modeling. Advances in Water Resources (2021). https://doi.org/10.1016/j.advwatres.2021.104099
Liao, C., Tesfa, T., Duan, Z., & Leung, L. R. (2020). Watershed delineation on a hexagonal mesh grid. Environmental Modelling & Software, 104702. https://doi.org/10.1016/j.envsoft.2020.104702