Glossary

Topo-bathymetric DEM

A raster modeling the elevation of a river valley’s bare ground topography, whether under water or not. Can typically be constructed from traditional LiDAR data collected for an ephemeral river during a no-flow period, or using topo-bathymetric / ‘green’ LiDAR.

Thalweg

A line following the lowest part of a valley whether under water or not.

Flow stage elevation

The water surface elevation relative to the thalweg’s elevation. Serves as an inverse proxy for water depth.

Nested topography

In the context of fluvial geomorphology, nested topography refers to the additive scales of topography that river flow interacts with across a range of increasing flow stages. The topography controlling hydraulics at a low flow is literally nested within a larger scale of topography that a interacts with higher flows. For example, the topography of an active channel of a low flows exists as a part of a flood flow’s active channel topography, which may also include floodplain, and valley scale elements. In GCS analysis, we study a given cross-section’s relative geometry at different flow stages in order to capture any cross-section nesting trends/patterns across the river area of interest.

Riffle-pool sequences

Riffle-pool sequences refers to channel bed elevation undulations that alternate between shallow, sediment rich, fast flow cross-sections (riffles) and deep, scoured, slow flow cross-sections (pools). Riffle-pool topography has been shown to be vital habitat for a variety of ecologically and societally relevant fish species. Therefore, understanding which processes and flow stages / discharges are involved with the long term maintenance of channel bed undulations remains an important goal of water resource management agencies and is a key aim of GCS research broadly.