Long-term landscape trajectory — Can we make predictions about landscape form and function for post-mining landforms?

• Can computer based Landscape Evolution Models (LEMs) produce meaningful results?
• Here we show that using calibrated parameters different possible landscapes result.
• Choice of parameter results in plausible landscapes over geological time.
• The finding demonstrates that parameter choice is major issue when using LEMs.
• Greater quantitative understanding of soil, vegetation, climate interactions are needed.
• This is a significant issue if these models are to be used for landscape assessment.

A significant issue for the application of numerical Landscape Evolution Models (LEMs) is their calibration/parameterisation and validation. LEMs are now at the stage of development where if calibrated, they can provide meaningful and useful results. However, before use, each LEM requires a set of data and parameter values for it to run reliably and most importantly produce results with some measure of precision and accuracy. This calibration/validation process is largely carried out using parameter values determined from present day, or recent surface conditions which are themselves product of much longer-term geology-soil-climate-vegetation interactions. Here we examine the reliability of an LEM to predict catchment form over geological time (500,000 years) for a potential rehabilitated mine landform using defensible parameters derived from field plots. The findings demonstrate that there is no equifinality in landscape form with different parameter sets producing geomorphically and hydrologically unique landscapes throughout their entire evolution. This shows that parameterisation does matter over geological time scales. However, for shorter time scales (< 10,000 years) the geomorphic differences in hillslope form are minimal as described by the hypsometric curve, area–slope and cumulative area distribution, yet there are large differences in sediment output. Therefore, obtaining reliable and defensible parameters for input to LEMs is essential.