PNNL

Abstract

Watershed delineation and flow direction representation are the foundations of stream flow routing in spatially distributed hydrologic modeling. Recent study showed that the hexagon-based watershed discretization has several advantages compared to the traditional cartesian (latitude-longitude) discretization, such as uniform grid adjacency and compatibility with other earth system model components which are usually based on unstructured grid systems (e.g., oceanic models). Despite these advantages, hexagon-based discretization is still not yet widely adopted by the current generation of hydrologic models. One major reason is that there is no existing model that is able to delineate hexagon-based watersheds while maintaining accurate representations of flow direction across various spatial resolutions. In this study, we explored approaches such as spatial resampling and hybrid breaching-filling stream burning techniques to improve watershed delineation and flow direction representation using a newly developed hexagon grid-based watershed delineation model (HexWatershed). We applied these improvements on the Columbia River basin and performed 16 simulations with different configurations. The results show that (1) spatial resampling modulates flow direction around headwaters and provides an opportunity to extract subgrid information; and (2) stream burning corrects the flow directions in mountainous areas with complex terrain features. It is a critical step for accurately representing the river networks, especially in coarse resolutions.