1.   Purpose and objectives

     ASM (Aquifer Simulation Model) is a complete implementation of a 2-D groundwater model for use on a PC under MS-Windows. It was originally developed as a tool for the education of students in hydrogeology, civil and environmental engineering. The first version of ASM was published in 1989 and ran under MS-DOS. Since then ASM has been continually enhanced and improved. Version 6.0 of ASM runs under the Microsoft Windows operating system and is the latest and most powerful version. A new, practical graphical user-interface is used and the new version allows the manipulation of larger model grids which makes it suitable for professional use.

2.   Description

     Aquifer Simulation Model for Windows (ASMWIN), which is a greatly improved Windows version of ASM 5.0 which runs under MS-DOS (Kinzelbach & Rausch, 1995), implements a complete two-dimensional groundwater flow and transport model. ASMWIN comes with a professional graphical user-interface, a finite-difference flow model, a tool for the automatic calibration of a flow model, a particle tracking model, a random walk transport model, a finite-difference transport model and several other useful modelling tools.

        The graphical user-interface permits the easy creation and simulation of models. It can handle models with up to 150 x 150 cells and 1000 time periods (pumping intervals). ASMWIN can create contour maps or solid fill plots of input data and simulation results. Solid fill can utilize the full range of RGB colours to fill cells with different values. Contours can be added to these plots. Report-quality graphics can be saved in a wide variety of file formats including SURFER, DXF, HPGL and BMP (Windows Bitmap).

        The discretized flow equations are solved by the preconditioned conjugate gradient (PCG) method (module ASMSIM1) with the choice of diagonal and Cholesky preconditioning. For steady state flow fields, an automatic model calibration procedure using the Marquardt-Levenberg algorithm is available in the module ASMOPTI.

        The particle tracking module ASMPATH offers several velocity interpolation methods and uses Euler-Integration to compute flow paths and travel times. Particle tracking with ASMPATH requires just a few mouse clicks. Both forward and backward particle tracking schemes are possible for steady-state and transient flow fields. ASMPATH calculates and shows pathlines or flowlines and travel time marks simultaneously. It provides various on-screen graphical options including head contours, drawdown 
contours and velocity vectors.

        Two transport simulation modules are available. The first uses a finite-difference scheme (Module ASMT2SIM) while the second uses a random- walk method based on the Ito-Fokker-Planck theory (Module ASMWALK).

        The modelling tools include a result extractor, a field interpolator, a field generator, a water budget calculator and a graph viewer.

        The result extractor allows the user to extract simulation results from any period on to a spread sheet. The results can then be viewed or saved in ASCII or SURFER-compatible data files. Simulation results include hydraulic heads, drawdowns, Darcy velocities, leakage terms and concentrations.

        The water budget calculator calculates not only the budget of user- specified zones but also the exchange of flows between such zones. This facility is very useful in many practical cases. It allows the user to determine the flow through a particular boundary.

        The field generator generates fields with heterogeneously distributed transmissivity or hydraulic conductivity values. It allows the user to statistically simulate effects and influences of unknown small-scale heterogeneities. The field generator is based on Mejía's (1974) algorithm.

        The graphic viewer displays temporal development curves of simulation results including hydraulic heads, drawdowns and concentrations.

3.   Input

     Hydraulic conductivities, storage coefficients, initial conditions, boundary conditions (boundary flux, constant head boundary), hydrological data (e.g. river heads, well withdrawal rates, recharge rates), calibration data.

4.   Output

     Simulation results as contour maps, solid fill plots, time series.

5.   Operational requirements and restrictions

     Hardware:
     Personal computer with Microsoft Windows 3.1x/95/98/NT
     8 MB available memory (16 MB or more recommended)
     A CD-ROM drive and a hard disk
     VGA or higher-resolution monitor
     Microsoft mouse or compatible pointing device

     Software:
     A FORTRAN compiler is required if it is intended to modify and compile
     the modules ASM-SIM1, ASMT2SIM, ASMWINMC and ASMOPTI.

     This model should be used only by those with professional experience.

6.   Form of presentation

     Manual (in English) with programme on CD-ROM.

7.   Operational experience

     It as been successfully employed in Germany and South East Asia.

8.   Originator and technical support

     Wen-Hsing Chiang, Wolfgang Kinzelbach, Randolf Rausch.

     Training courses can be arranged by the HOMS NRC of Germany.

9.   Availability

     From the HOMS National Reference Centre for Germany.

10.  Conditions on use

     A small handling fee is requested. Please inquire for information.