FAQ

Why is there a limit on the SHETRAN Grid sizes?

There is a 50x50 limit on the GUI version and a 200x200 limit on the standard version.

What I generally recommend is running with larger grid squares (i.e. change from 100m by 100m to 200m by 200m). From experience I can say it is much better to do any calibration with a coarser grid and faster runtimes. A finer resolution can aways be run at a later stage when most of the calibration has been carried out.

To run a simulation with more than 200x200 grid squares is possible if the total number of grid squares within the catchment is less than 40000. To remove this limitation will require a significant rewritting of the code due to memory limitations.

I use a comma (rather than a full stop) as a decimal mark, this seems to cause problems?

Unfortunately the Shetran GUI and Standard version have been set-up to run with a full stop as a decimal mark. The main restriction is that the DEM, Mask, Soil and Veg maps that are in ASCII format need "." rather than "," as the decimal mark. Using Find and Replace in a text editor will sort out this problem

If there are still problems then the settings on the machine will need changing temporarily. In the Control Panel, select Regional and Language options and Regional Options tab and select English (United Kingdom).

How is it best to view the river channel and elevations that are produced by the program?

The free software HDFView (http://www.hdfgroup.org/hdf-java-html/hdfview/) needs to be installed. Once installed double click on the output_catchmentname_shegraph.h5 file (e.g. output_lise_shegraph.h5) and it will open in HDFView. Double click on "Catchment_Maps" and double click on "SV4_elevation". The river channel network can be viewed in the GUI.

In the standard version in the easy setup a file called river_network_CATCHNAME.txt is produced. This can be opened in a GIS and compared to the actual river network.

How are the positions of the river channels and their elevations calculated?

The position of the channel links is calculated from the DEM by analysing the number of upstream grid squares that flow into a particular grid square. When these reach a certain number (the default is 20) a river channel is produced. The channel elevations are based on the 2 adjacent grid squares. The elevations are then modified so that there is always a downward flow path. Details of the method can be found in the following paper:

Birkinshaw, S. J. (2010) Technical Note: Automatic river network generation for a physically-based river catchment model, Hydrol. Earth Syst. Sci., 14, 1767-1771

In Lise example the data is 23 by 32. In the frd file the data has been modified to 25 by 34, Why is this?

For numerical reasons the Shetran code requires that in the frd input file the entire catchment is surrounded by blank elements. So an extra column is added to the left and right of the catchment and an extra row to the top and bottom. 

In HDFView sometimes the water flow values and the sediment transport values are negative and sometimes positive. Why is this?

For water flow in Shetran: any flow in a northerly or easterly direction is +ve and any flow in a Southerly or westerly direction is -ve.

For sediment transport in Shetran: any flow out of a grid square is +ve and into a grid square is -ve.

This is consistent in the code and in the output.

The result is that if the flow into a grid square is from the south (i.e in a northerly direction) it is positive for water flow but it is into the grid square so negative for sediment transport. Similarly if the flow from a grid  square is from the west (i.e an easterly direction) it is positive for water flow but it is into the grid square so negative for sediment transport.

In the output_catchmnetname_discharge_sim_hourly.txt file the discharge is always set to be positive.

The data is not displaying correctly in HDFView.

On the "data selection" page you select the dimensions for Height, Width and Depth. If the dimension for height is greater than for width you have a choice of "reshape" which is the default or "transpose". Select "Transpose"

In the Shetran GUI how do I view a simulation I have carried out previously?

In the Front-End go to File | Open and select the project file name that you specified previously (e.g lise.xml).

The simulated water discharge at the outlet at the start of the simulation is bad.

Shetran as with other hydrological models needs a run-in period. This is so that the water stored in the catchment reaches an equilibrium. The deeper the soil the longer the run-in period needed. In the GUI one way round this is to have a run-in of say a year with the precipitation and evaporation data repeated in this first year and then only compare the measured and simulated discharge after one years simulation.

In the standard version of Shetran the VSI file is normally used - for more details see the Initial conidtions in Shetran simulations.pdf and Initial conditions video

Send mail to s.j.birkinshaw@ncl.ac.uk with questions or comments about this web site.
Last modified: 26/02/2016