The Landlab OverlandFlow component: a Python library for computing shallow-water flow across watersheds

Abstract

Abstract. Hydrologic models and modeling components are used in a wide range of applications. Rainfall-runoff models are used to investigate the evolution of hydrologic variables, such as soil moisture and surface water discharge, throughout one or more rainfall events. Longer-term landscape evolution models also include aspects of hydrology, albeit in a highly simplified manner, in order to approximate how flowing water shapes landscapes. Here we illustrate how the OverlandFlow hydrologic component contained within Landlab can be applied as either a short-term rainfall-runoff model or a longer-term landscape evolution model. Landlab is a Python-language library that includes tools and process components that can be used to create models of Earth-surface dynamics over a range of temporal and spatial scales. The Landlab OverlandFlow component is based on a simplified inertial approximation of the shallow water equations, following the solution of de Almeida et al. (2012). This explicit two-dimensional hydrodynamic algorithm propagates a flood wave across a terrain, and water discharge and flow depth are calculated at all locations within a structured (raster) grid. Examples of flow routing on both real and synthetic landscapes are shown. Hydrographs from a single storm at multiple locations in the Spring Creek watershed, Colorado, USA, are illustrated, along with maps of water depth and shear stress applied on the surface by the flowing water. Flow routing on two different synthetic watersheds illustrates how network organization impacts hydrograph shape. The OverlandFlow component is also coupled with the Landlab DetachmentLtdErosion component to illustrate how the nonsteady flow routing regime impacts incision across a watershed. The hydrograph and incision results are compared to simulations driven by steady-state runoff, or discharge equal to the product of drainage area and rainfall rate, which is the norm in landscape evolution modeling. Results from the coupled hydrologic and incision model indicate that runoff dynamics can impact landscape relief and channel concavity. Example code is provided that demonstrates how to use the OverlandFlow component and couple it with other components to create a model.