Worldwide water gaps: Using relative elevation modelling to identify transverse drainages

Transverse drainages are stream reaches that flow through, rather than around, topographic high grounds. The development of transverse drainage is intimately tied to the tectonic history of an area, but the identification of transverse reaches has historically been a matter of subjective opinion. Here, a GIS-based method is presented that uses relative elevation modelling to identify and quantify transverse stream reaches. The process was used on a set of 6557 streams from the World Wildlife Fund’s RiverATLAS digital dataset to identify over 7000 potential transverse reaches, of which almost 4000 were visually verified, accounting for over three quarters of the total potential transverse drainage length. The results were used to analyze current theories of formation of transverse drainages on the lower Congo River. The database transverse drainages and geomorphologic analysis are more consistent with an overflow origin for the lower Congo than for stream capture. The results are viewable online at watergaps.com and are available by emailed request as geopackage and Google Earth KMZ files, along with a Google Earth Sea Level Rise slider that simulates sea level rise, to help visualize the lower elevations of upstream areas that define transverse drainage. The methodology is easily scalable depending on the resolution desired for analysis, and can be helpful in identifying previously undocumented transverse drainage and in expanding the identification and quantification of transverse reaches in areas where transverse drainage is already known to exist.