Timescales of Drainage Network Evolution Revealed: Spatiotemporal Variability in Drainage Density in the Post-Glacial Central Lowlands, USA

Landscape dissection by rivers is a common qualitative measure of surface maturity. Quantitative studies of fluvial development over time indicate that drainage development increases non-linearly and is influenced by lithology, however, these studies typically take place over short timescales (10s of years), cover small areas, and focus on steep landscapes. In this work we use the Central Lowlands physiographic province (CL) as a natural laboratory in which we investigate rates and controls on drainage development in a post-glacial lowland landscape. Portions of the CL have been glaciated repeatedly in the Quaternary, and its topography is dominated by a patchwork of glacial landforms that have been developing drainage for 10 thousand to more than 500 thousand years. We modify the National Hydrography Dataset to estimate pre-agriculture drainage density developed over different amounts of time to reveal rates of drainage development in the CL. We find that drainage density in the CL increases non-linearly, increasing rapidly following glaciation before slowly approaching a maximum value. Much of the development is accomplished by 50 ka, well within a typical interglacial period. The apparent maximum value, ~1.5 km/km², is comparable to the median drainage density measured in regions in the CL that have not experienced Quaternary glaciation. Our study shows that this value is likely influenced by soil sand content and regional precipitation levels. We note that while drainage density increases to an apparent maximum within an interglacial, the fluvial network is unlikely to adjust to post-glacial base level conditions within that same length of time. Our results are most consistent with a model of drainage expansion driven by the connection of closed depressions, or ‘non-contributing area’ (NCA), the portion of a watershed that does not drain to a river. We find that NCA decreases in tandem with increasing drainage density, which implies that NCA could be a measure of landscape integration that is at least as sensitive as drainage density.