Surface routing and Silting-up

Starting with WaSiM 8.1.x there are two new model components implemented in WaSiM:

1. Explicit surface runoff routing from cell to cell
2. Silting-up/Sealing of the soil surface

Module "Surface routing"

1. AN application is only feasible when using small cell sizes of e.g. < 10 m
2. explicit (cell-to-cell) routing of surface flow until a flow channel is reached (and then further down the sub-basin until the outlet cell of the subbasin is reached)
3. multiple flow paths per cell possible (up to three)
4. Flow velocity depends on slope, roughness and flow depth
5. Routing is done using a kinematic wave approach (with very short time steps in order to approximate unsteady conditions, too)
6. surface roughness can be parameterized using different methods (depending on land use)
7. Internally, the time step is controlled automatically down to one seconds, if required
8. Tracer and salt transport is fully integrated

Modul "Silting-up"

this module can be used to simulate the changing infiltration capacity of certain soils when exposed to heavy rain events.

1. Infiltration rate is calculated depending on: accumulated kinetic energy (of precipitation), soil type and time since last tillage
2. If precipitation rate exceeds the infiltration rate, the exceeding water is branched out as surface runoff and routed to the surface runoff routing
3. some parameters can be defined per land use (for roughness, soil tillage etc.)

There are three methods for calculating the potential infiltration:

• use conventional parameters (hard coded, see documentation)
• use custom parameters for the hardcoded functions
• use custom functions. To use this feature, a set of functions must be defined and provided with mappings of variables from the land use and/or soil table. An expression parser was implemented into WaSiM allowing the definition of complex methematical formulas.

more details on creating defining the parameters and un using the modules can be found in the documentation on Surface Routing & Silting upor in the WaSiM model documentation.

Flow chart for modelling silting-up and surface-routing