Numerical modeling of groundwater‐driven stream network evolution in low‐relief post‐glacial landscapes

Abstract

In the low-relief post-glacial landscapes of the Central Lowlands of the United States, fluvial networks formed and expanded following deglaciation despite the low slopes and large fraction of the land surface occupied by closed depressions.Low relief topography allows for subtle surface water divides and increases the likelihood that groundwater divides do not coincide with surface water divides. We investigate how groundwater transfer across subtle surface water divides facilitates channel network expansion using a numerical model built on the Landlab platform.Our model simulates surface and subsurface water routing and fluvial erosion. We consider two end-member scenarios for surface water routing, one in which surface water in closed depressions is forced to connect to basin outlets (routing) and one in which surface water in closed depressions is lost to evapotranspiration (no routing).Groundwater is modeled as fully saturated flow within a confined aquifer. Groundwater emerges as surface water where the landscape has eroded to a specified depth. We held the total water flux constant and varied the fraction of water introduced as groundwater versus precipitation. Channel growth is significantly faster in routing cases than no-routing cases given identical groundwater fractions. In both routing and no-routing cases, channel expansion is fastest when $30% of the total water enters the system as groundwater. Groundwater contributions also produce distinctive morphology including steepened channel profiles below groundwater seeps. Groundwater head gradients evolve with topography and groundwater-fed channels can grow more quickly than channels with larger surface water catchments. We conclude that rates of channel network growth in low-relief post-glacial areas are sensitive to groundwater contributions. More broadly, our findings suggest that landscape evolution models may benefit from more detailed representation of hydrologic processes.

Introduction to the Women in Geomorphology special issue

“…• numerical model validation (Negreiros et al, 2022) and numerical modelling of groundwater-driven network evolution (Cullen et al, 2022);…”

“…Remote sensing ( 26) Agostini et al, 2022;Atwood & West, 2022;Davies et al, 2022;Davis et al, 2021;Fadul et al, 2022;Gervasi et al, 2021;Hendrickx et al, 2022;Hodge & Buechel, 2022;Hooke, 2022;Hovenga et al, 2021;Konlechner & Hilton, 2022;Lefebvre et al, 2022;Marchetti et al, 2022;McKenzie et al, 2022;Mol & Grenfell, 2022;Opalka et al, 2022;Rabanaque et al, 2022;Regalla et al, 2022;Reitman et al, 2022;Sampietro-Vattuone et al, 2021;Schoch-Baumann et al, 2022;Thompson et al, 2022;Vah et al, 2022;Valentine et al, 2022;Zhang et al, 2022 Physical experiments (8) Bako et al, 2022;Bywater-Reyes et al, 2022;Demiral et al, 2022;Friedrich et al, 2022;Negreiros et al, 2022;Rachelly et al, 2022;Roelofs et al, 2022;Vah et al, 2022 Numerical models ( 11) Agostini et al, 2022;Bywater-Reyes et al, 2022;Cullen et al, 2022;Glover et al, 2022;Hodge & Buechel, 2022;Kooijma...…”

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

“…Larger hydraulic gradients increase seepage forces, which can occur if groundwater recharge is greater or the interface between the surface and subsurface has greater relief (Dunne, 1980(Dunne, , 1990. As channels expand by seepage erosion, groundwater flow further concentrates at the channel heads and begets more erosion by positive feedback (Dunne, 1990;Cullen et al, 2022). Erosion at channel heads introduces asymmetries in the concentrated flow of groundwater, causing the direction of channel growth to adjust towards maintaining symmetrical flow (Cohen et al, 2015).…”

“…The hydrologic subsidy provided by surface and subsurface connections between NCAs and channels can have important implications for the long-term development of drainage networks (Lai and Anders, 2018;Hilgendorf et al, 2020;Cullen et al, 2022). If NCAs are geographically isolated (Tiner, 2003) but not hydrologically isolated, then hydrologic contributions via the surface or subsurface can help to integrate drainage networks.…”

“…An important, unresolved issue is how water routed via the surface or subsurface to varying degrees drives different processes of channel development and how that partitioning affects NCA integration. Cullen et al (2022) explored the partitioning of surface and subsurface connectivity on network growth in low-gradient systems numerically and found that channel network growth was sensitive to groundwater contributions to channel heads. Geology, climate, vegetation, and relief differ throughout postglacial landscapes of the Central Lowlands, which may favor surface or subsurface routing of potential NCA contributions.…”