Preprints
https://doi.org/10.5194/esurf-2021-74
https://doi.org/10.5194/esurf-2021-74

  21 Oct 2021

21 Oct 2021

Review status: this preprint is currently under review for the journal ESurf.

An experimental study of drainage network development by surface and subsurface flow in low-gradient landscapes

Brian G. Sockness and Karen B. Gran Brian G. Sockness and Karen B. Gran
  • Department of Earth and Environmental Sciences, University of Minnesota Duluth, Duluth, MN, USA

Abstract. How do channel networks develop in low-gradient, poorly-drained landscapes? Rivers form elaborate drainage networks with morphologies that express the unique environments in which they developed, yet we lack an understanding of what drives channel development in low-gradient landscapes like those left behind in the wake of continental glaciation. To better understand what controls the erosional processes allowing channel growth and integration of non-contributing areas (NCA) over time, we conducted a series of experiments in a small-scale drainage basin. By varying substrate and precipitation, we could vary the partitioning of flow between the surface and subsurface, impacting erosional processes. Channels developed by overland flow and seepage erosion to varying extents depending on substrate composition, rainfall rate, and drainage basin relief. Seepage-driven erosion was favored in substrates with higher infiltration rates, while overland flow was more dominant in experiments with high precipitation rates. Overland flow channels formed at the onset of experiments and expanded over a majority of the basin area, forming broad dendritic networks. Large surface water contributing areas supported numerous first-order channels, allowing for more rapid integration of NCA than through seepage erosion. When overland flow was the dominant process, channels integrated NCA at a similar, consistent rate under all experimental conditions. Seepage erosion began later in experiments after channels had incised enough for exfiltrating subsurface flow to initiate mass wasting of headwalls. Periodic mass wasting of channel heads caused them to assume an amphitheater-shaped morphology. Seepage allowed for channel heads to expand with smaller surface water contributing areas than overland flow channels, allowing for network expansion to continue even with low CA. Seepage-driven channel heads integrated NCA more slowly than channel heads dominated by overland flow, but average erosion rates in channels extending through seepage erosion were higher. The experimental results provide insight into drainage networks that formed in glacial sediment throughout areas affected by continental glaciation, and highlight the importance of subsurface hydrologic connections in integrating and expanding drainage networks over time in these landscapes.

Brian G. Sockness and Karen B. Gran

Status: open (until 07 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esurf-2021-74', Anonymous Referee #1, 08 Nov 2021 reply

Brian G. Sockness and Karen B. Gran

Brian G. Sockness and Karen B. Gran

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Short summary
To study channel network development following continental glaciation, we ran small physical experiments where networks slowly expanded into flat surfaces. By changing substrate and rainfall, we altered flow pathways between the surface and subsurface. Initially, most channels grew by overland flow. As relief increased, erosion through groundwater sapping occurred, especially in runs with high infiltration and low cohesion, highlighting the importance of groundwater in channel network evolution.