The model has been developed since the end of the 1980´s at the Department of Irrigation, Drainage and Land Scape Engineering, Faculty of Civil Engineering, Czech Technical University in Prague. The first version of 1D model, designed in the FORTRAN programming language, was developed in 1989. It included processes influencing surface runoff and erosion. Two basically independent submodels: (i) submodel 1 used for the calculation of admissible slope length and designing of soil conservation measures, (ii) submodel 2 designed for the calculation of runoff characteristics in order to implement technical anti-erosion measures. Other versions of the model, launched particularly between 1996 and 2001, further developed operating systems. However, these versions did not considerably interfere with parameters and relations inside the model.
In 2011, based on laboratory rainfall simulation, a last version of the 1D model with SMODERP 10.01 designation was created. Compared to the previously introduced versions, a change related to runoff parameters in the kinematic wave equation depending on soil types in accordance with the Czech system of soil classification occurred. This system uses for the determination of basic soil types the content of particles up to 0.01 mm of the first size particle category (physical clay). The second modification was introduced by replacement of the current generation in slopes. Previously, the model functioned in particular sections of various lengths which had been initially defined as parts of the slope between two contour lines with identical vegetation and soil types. At the moment, the new model divides the aforesaid sections into individual elements of the same length and forms thus an interphase terminated by testing and comparison to the distributed 2D model.
The 2D model which is developed in last years is prepared as an extension to the widespread GIS software ArcGIS. The actual script to calculate the 2D model was elaborated in Python and used in ArcGIS standard tools. In the future, the most memory and time consuming parts of the script will be overwritten in C++ with the purpose to shorten the runtime script.
Moreover, besides mathematical calculation of surface runoff, the 2D model also includes a submodel implemented for runoff calculation in the rills
Rill runoff is an additional physic process which is implemented in the model. For each soil type a critical value of the tangential stress and velocity was estimated. From this critical value critical height in each cell is calculated. In principle this is a comparison of the current level and its critical value at each time interval. If the critical value is exceeded, the calculation enters the stage at which the rill starts to form. Dimensions of the rills are calculated from volume of the water exceeding the critical value. Sheet surface runoff is then calculated using the critical value level instead of current height in the time step. Once the level has dropped below the critical height value, the calculation returns only in the calculation of surface runoff. The resulting rasters of rill flow and speed in the rill are stored in user-selected directory along with vector shapefile of created rills. Calculation of the flow in the rill is based on Manning equation.