Abstract niet beschikbaar

This report presents the simulation standard SiShell. This standard is aimed at developing modular simulation programs in FORTRAN-77. Sishell simulation programs have the following features: - All modules in a program are independent units. Opening files, reading model parameters and initialisation are carried out within the module. - The modules can be placed in a hierarchical system. On the highest level are so called model modules. These modules in fact are complete simulations programs, but timing is controlled by the calling program. On a lower level are modules that describe a number of processes. Modules that have the same functionality can be inter changed. - The only function of the main program in a SiShell program is calling a number of model modules, reading the vertical discretisation and timers. Emphasis is on modelling transport and behaviour of water and solutes in the unsaturated soil. The report also describes the subroutine library SiShell which is meant as a tool in developing SiShell programs.