Abstract
Abstract. Representation of flowing water in landscape evolution models (LEMs) is often simplified compared to hydrodynamic models, as LEMs make assumptions reducing physical complexity in favor of computational efficiency. The Landlab modeling framework can be used to bridge the divide between complex runoff models and more traditional LEMs, creating a new type of framework not commonly used in the geomorphology or hydrology communities. 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 simulates a flood wave across a model domain, where water discharge and flow depth are calculated at all locations within a structured (raster) grid. Here, we illustrate how the OverlandFlow component contained within Landlab can be applied as a simplified event-based runoff model and how to couple the runoff model with an incision model operating on decadal timescales. 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 a map of shear stress applied on the land surface by flowing water. The OverlandFlow component can also be coupled with the Landlab DetachmentLtdErosion component to illustrate how the non-steady flow routing regime impacts incision across a watershed. The hydrograph and incision results are compared to simulations driven by steady-state runoff. Results from the coupled runoff and incision model indicate that runoff dynamics can impact landscape relief and channel concavity, suggesting that, on landscape evolution timescales, the OverlandFlow model may lead to differences in simulated topography in comparison with traditional methods. The exploratory test cases described within demonstrate how the OverlandFlow component can be used in both hydrologic and geomorphic applications.
Highlights
Numerical models of overland flow have a variety of applications
We describe the fundamentals of the Landlab modeling framework, the theoretical background of the Landlab OverlandFlow component, based on a two-dimensional flood inundation model (LISFLOOD-FP; Bates and De Roo, 2000; Bates et al, 2010; de Almeida et al, 2012; de Almeida and Bates, 2013) and how this model was adapted to work in coupled geomorphic–hydrologic applications
To illustrate the flexibility of the OverlandFlow component, we present an example in Sect. 7, in which water discharge cwalwcuwla.gteedoscbiy-mthoedeOl-vdeervl.annedtF/1lo0w/1/2c0o1m7p/onent is used in the erosion component
Summary
Numerical models of overland flow have a variety of applications. Examples include mapping urban flooding events (e.g., Dutta et al, 2000; Morrit and Bates, 2002; Maksimovicet al., 2009; Kulkarni et al, 2014; Cea and Bladé, 2015), understanding the interactions between surface and subsurface water by way of soil infiltration (e.g., Esteves et al, 2000; Panday and Huyakorn, 2004; Kollet and Maxwell, 2006; Maxwell and Kollet, 2008; Shrestha et al, 2015), and exploring hydrogeomorphologic processes in natural landscapes Where Qss is the steady-state water discharge (L3 T−1), P is the spatially averaged effective precipitation or runoff rate (L T−1) and A is drainage area (L2). In more physically based models, the steady-state assumption is replaced with non-steady runoff processes that simulate flowing water across a watershed. Whereas many LEMs generalize surface water flow using steady-state assumptions, most physical models of runoff production simulate changing surface water discharge. Coulthard et al (2013) integrated a semi-implicit hydrodynamic model into the CAESAR LEM and noted reduced sediment yields on decadal timescales of landscape evolution when using non-steady runoff In another approach, Sólyom and Tucker (2004) estimated non-steady peak discharge as a function of storm duration, rainfall rate, and the longest flow length in a network. Core nodes and active links make up the computational domain of a Landlab model
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