The Wageningen Lowland Runoff Simulator (WALRUS): a Novel Open Source Rainfall-Runoff Model for Areas with Shallow Groundwater

Abstract:

Recently, we developed the Wageningen Lowland Runoff Simulator (WALRUS) to fill the gap between complex, spatially distributed models which are often used in lowland regions and simple, parametric models which have mostly been developed for mountainous catchments. This parametric rainfall-runoff model can be used all over the world, both in freely draining lowland catchments and polders with controlled water levels. Here, we present the model implementation and our recent experience in training students and practitioners to use the model.

WALRUS has several advantages that facilitate practical application. Firstly, WALRUS is computationally efficient, which allows for operational forecasting and uncertainty estimation by running ensembles. Secondly, the code is set-up such that it can be used by both practitioners and researchers. For direct use by practitioners, defaults are implemented for relations between model variables and for the computation of initial conditions based on discharge only, leaving only four parameters which require calibration. For research purposes, the defaults can easily be changed. Finally, an approach for flexible time steps increases numerical stability and makes model parameter values independent of time step size, which facilitates use of the model with the same parameter set for multi-year water balance studies as well as detailed analyses of individual flood peaks.

The open source model code is currently implemented in R and compiled into a package. This package will be made available through the R CRAN server. A small massive open online course (MOOC) is being developed to give students, researchers and practitioners a step-by-step WALRUS-training. This course contains explanations about model elements and its advantages and limitations, as well as hands-on exercises to learn how to use WALRUS. All code, course, literature and examples will be collected on a dedicated website, which can be found via www.wageningenur.nl/hwm.

References

C.C. Brauer, et al. (2014a). Geosci. Model Dev. Discuss., 7, 1357—1411.

C.C. Brauer, et al. (2014b). Hydrol. Earth Syst. Sci. Discuss., 11, 2091—2148.