WORLD METEOROLOGICAL ORGANIZATION 
HOMS COMPONENT 

Explanation of the criteria for classification and numbering of components  L20.3.13 (JAN 98) 

Explanation of the dates on the component's description  
COMPLETE PROGRAM PACKAGE FOR MODELLING GROUNDWATER FLOW (TRIWACO) 

1. Purpose and objectives A package for modelling saturated and unsaturated groundwater flow,
based on the finite element method. To calculate the heads, fluxes and path lines in heterogeneous anisotropic multiaquifer systems. 2. Description The flow is described by Darcy's law and the mass continuity equation. The Galerkin finite element method is used to approximate the differential equations as a set of algebraic equations, which are then solved by the conjugate gradient method. Both steadystate and transient systems can be modelled. The system can handle the following cases: Multilayered aquiferaquitard system, neglecting vertical resistance within aquifers and assuming vertical flow in aquitards. Fully 3D schematisation by using up to 99 model aquifers as layers and The TRIWACO package consists of several separate programs:  TESNET to generate the finite element grid (triangles including 3. Input Hydrogeologic parameters, wells, rivers, recharge rate, boundary and initial conditions, and finite element grid structure. 4. Output Heads for all aquifers and fluxes through all aquitards, fluxes to rivers, wells, topsystems and through boundaries. All data is stored in standard datasets which are very easy to use in preprocessing programs or for reinputting. Several preprocessing programs can be used for viewing 5. Operational requirements and restrictions IBM compatible personal computer with 640 K memory, mathematical coprocessor and a hard disc. It is recommended having a 80386processor or higher. The Graphical Kernel System for printing results includes drivers for most plotters and printers. The package is available on PC (DOS, WINDOWS and OS/2) as well as on mainframes (UNIX). The userfriendly WINDOWS version is available from the end of 1996. Easy installation according to manual. Requires a short time to
acquire proficiency in handling. As the FORTRAN 77 source code is not supplied, no FORTRAN compiler is needed by the user. 6. Form of presentation Run version of the computer program package on a number of floppy disks. A comprehensive users manual in English. 7. Operational experience The model has been widely used in The Netherlands since 1988. Many water supply companies and regional authorities have TRIWACO
models for (operationally orientated) groundwater investigations.
It has also been used in other countries like Hungary, Egypt, Indonesia, Belgium, Germany. 8. Originator and technical support IWACO B.V., Consultants for water and environment, Rotterdam, The Netherlands. 9. Availability From the HOMS National Reference Centre for The Netherlands. 10. Conditions on use A charge will be made for supplying the model. Updates of the new run versions will be forwarded to users automatically during a certain period of time.


(First entered: 31 JULY 01  Last updated: 19 JAN 98) 