Transmissivity and groundwater flow exert a strong influence on drainage density

Abstract

Abstract. The extent to which groundwater flow affects drainage density and erosion has long been debated but is still uncertain. Here, I present a new hybrid analytical and numerical model that simulates groundwater flow, overland flow, hillslope erosion and stream incision. The model is used to explore the relation between groundwater flow and the incision and persistence of streams for a set of parameters that represent average humid climate conditions. The results show that transmissivity and groundwater flow exert a strong control on drainage density. High transmissivity results in low drainage density and high incision rates (and vice versa), with drainage density varying roughly linearly with transmissivity. The model evolves by a process that is defined here as groundwater capture, whereby streams with a higher rate of incision draw the water table below neighbouring streams, which subsequently run dry and stop incising. This process is less efficient in models with low transmissivity due to the association between low transmissivity and high water table gradients. A comparison of different parameters shows that drainage density is most sensitive to transmissivity, followed by parameters that govern the initial slope and base level. The results agree with field data that show a negative correlation between transmissivity and drainage density. These results imply that permeability and transmissivity exert a strong control on drainage density, stream incision and landscape evolution. Thus, models of landscape evolution may need to explicitly include groundwater flow.

Catchment Coevolution and the Geomorphic Origins of Variable Source Area Hydrology

“…However, such models usually simplify hydrology such that feedbacks between topography and runoff dynamics cannot be examined. Recent studies have made progress in representing hydrologic processes more explicitly in LEMs, and show that drainage density scales linearly (Luijendijk, 2022) or non‐linearly (Litwin et al., 2021) with transmissivity when runoff is generated by saturation excess overland flow. Although these studies broke new ground by revealing how runoff generation affects topography, it is still unclear how this coevolution affects hydrological function.…”

Improving calibration of groundwater flow models using headwater streamflow intermittence

“…For a given topography and aquifer geometry, water table elevation and fluctuation are controlled by both the recharge dynamics and the hydraulic properties (Bresciani et al, 2016; Haitjema & Mitchell‐Bruker, 2005). In the context of an unconfined aquifer with a defined thickness $$$ d $$$ [L], the hydraulic head $$$ h $$$ [L] is determined by the dimensionless ratio of hydraulic conductivity $$$ K $$$ [L/T] and recharge rate $$$ R $$$ [L/T], that is, $$$ K/R $$$ [−] (Goderniaux et al, 2013; Luijendijk, 2022). For a given recharge rate, the transmissivity $$$ T $$$ [L 2 /T], that is, the product of $$$ K $$$ and $$$ h $$$, controls the drainage density and the spatial extent of the stream network (Abhervé et al, 2023; Stoll & Weiler, 2010).…”