GeoFEST: an integrated GIS and visualization environment for the development of three-dimensional hydrogeological models

Transcription

1 HydrGIS 96: Applicatin f Gegraphic Infrmatin Systems in Hydrlgy and Water Resurces Management (Prceedings f the Vienna Cnference, April 1996). IAHS Publ. n. 235, GeFEST: an integrated GIS and visualizatin envirnment fr the develpment f three-dimensinal hydrgelgical mdels MARK D. WILLIAMS, CHARLES R. COLE, MICHAEL G. FOLEY & SIGNE K. WURSTNER Pacific Nrthwest Natinal Labratry 1, PO Bx 999, Richland, Washingtn 99352, USA Abstract GeFEST prvides an integrated GIS, grundwater flw and transprt mdelling, and scientific visualizatin envirnment t aid in develping three-dimensinal hydrgelgical mdels. A key cncept in the design f GeFEST was t keep characterizatin data (e.g. gelgy) separate frm mdel-specific data (e.g. finite element mesh, hydraulic prperties, bundary cnditins). This minimizes the impact f mdificatins in the mdel and allws characterizatin data t be used fr cnstructing mdels at different scales. A GIS is used t digitize, cntur, and grid maps f characterizatin data and fr cnturing planview results f the numerical mdel. Scientific visualizatin sftware prvides fr interactively viewing and dissecting the three-dimensinal hydrgelgical mdel and fr visualizing mdelling results. GeFEST is currently being used in the develpment f three-dimensinal hydrgelgical mdels at different scales in the West Siberian basin and at the Hanfrd Site in Washingtn State. INTRODUCTION GeFEST (Gelgic Finite Element Synthesis Tl) was develped t aid in cnstructing three-dimensinal hydrgelgical mdels. A key bjective in develping GeFEST was t keep the site characterizatin data independent f the mdel parameters t minimize the impact f changes in the mdel and t use the site characterizatin data fr mdels f different scales. Mdelling is an iterative prcess, therefre the mdel descriptin shuld be easily mdified t prvide fr refinements, feedback frm simulatins calibratin runs and sensitivity analysis. Figure 1 illustrates the main cmpnents and linkages f the GeFEST system. GeFEST prvides the linkages t integrate a gegraphic infrmatin system used in digitizing, cnturing, and gridding site characterizatin data (ARC/INFO a registered trademark f Envirnmental Systems Research Institute, Inc., Redlands, Califrnia); a grundwater flw and slute transprt cde (CFEST - Gupta et al., 1987); and an bject-riented scientific visualizatin prgram (AVS - a registered trademark f Advanced Visual Systems, Inc., Irvine, Califrnia) int a cmplete system fr hydrgelgical mdel develpment. 1 Pacific Nrthwest Natinal Labratry is perated by Battelle Memrial Institute fr the US Department f Energy under Cntract DE-AC06-76RLO 1830.

2 594 Mark D. Williams et al. I Arc/Inf Facies and Ispachs Finite Element Grid Bundary Cnditins / Gelgic Structure Descriptin/ Facies Translatin Table Material Prperties Table Fig. 1 GeFEST data flw diagram shwing majr cmpnents and linkages between the prgrams used in cnstructing, visualizing, and cnducting numerical simulatins f hydrgelgical mdels. This reprt briefly describes the site characterizatin and mdel parameters used in GeFEST (a mre detailed descriptin can be fund in Fley et al, 1995). The examples used t illustrate this system are frm a hydrgelgical mdel f the West Siberian basin, the largest platfrmal basin in the wrld (see Fig. 2) with a ttal area f 3.5 millin km 2. This large-scale mdel was develped t prvide bundary cnditins fr smaller-scale mdels within the basin. GeFEST is als being used fr develping a three-dimensinal hydrgelgical mdel f the US Department f Energy's Hanfrd Site in Washingtn State, USA. SITE CHARACTERIZATION The gelgy f the area being mdelled is identified by a gelgical structure descriptin

3 GeFEST: an integrated GIS and visualizatin envirnment 595 CHELYABINSK \ Fig. 2 CFEST finite element grids fr the West Siberian basin reginal mdel (a) and the Tmsk Lcal mdel (b). file, a text file that lists the GIS files describing the spatial variatins in rck faciès type and thickness r tp-f-layer elevatin (i.e. ispach r structure cnturs) fr each layer in the hydrgelgical system. Figure 3 shws the facies fr the 13 layers used in the West Siberian Basin Mdel. The layering rder is defined by the rder f file names in the gelgical structure descriptin file, starting with the tp layer. An ptin is prvided fr specifying cnstant facies, thickness, r elevatin f a layer. The upper elevatin f the system is described by a digital elevatin mdel (DEM). An ptinal DEM f the water table can als be specified. The facies, ispach, structure cntur, and DEM files are in ARC/INFO gridded ASCII frmat. Althugh currently nt a direct input t the GeFEST system, rivers in the area need t be identified with the spatial crdinates alng with river mile and elevatin using tpgraphic maps r ther surces (DEMs are nt adequate fr cmpiling these data). These data are required fr identifying ndes that are lcated n rivers and fr specifying the apprpriate bundary cnditins. HYDROGEOLOGICAL MODEL PARAMETERS The main hydrgelgical mdel parameters used by GeFEST are the finite element mesh, translatin table, material prperty table, and bundary cnditins. These data are specified in text files and are described belw.

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5 GeFEST: an integrated GIS and visualizatin envirnment 597 The finite element mesh required fr GeFEST is tw-dimensinal and is cmpsed f a nde file and an element file. The nde file cnsists f a list f nde numbers with crrespnding x and y crdinates. The element file cnsists f an element number and a list f nde numbers, in cunterclckwise rder, that make up the surface element. In reginal mdels, the bundaries f the finite element mesh are typically defined by drainage basin bundaries (where practical) and the interir elements and ndes are aligned with rivers. The current apprach fr develping a reginal finite element mdel is iterative. A carse grid is created that is aligned alng the external and internal mdel bundaries, the rivers, and ther imprtant internal features. Next the number f ndes in this riginal grid is dubled (ne element is split int fur elements) thrugh a utility prgram. Newly created ndes near these bundaries, rivers, and features are then interactively aligned t prvide a mre accurate representatin f their gemetry. This re-dubling and interactive alignment prcess is then repeated until the desired mesh size (reslutin) is achieved. This apprach allws large finite element meshes with relatively unifrm element areas t be quickly generated. The Tmsk finite element mesh, shwn in Fig. 2(b), was develped using this methd. Material Prperty Assignment Facies I ' Translatin Table Fig. 4 Cnceptual diagram f the prcess fr translating facies t materials used in the GeFEST prgram.

6 598 Mark D. Williams et al. The ispach/structure cntur grids specified in the gelgical structure descriptin file are stacked nt the tw-dimensinal finite element grid (see Figs 2 and 3), creating a three-dimensinal finite element mesh. The gridded files are sampled at the nde lcatins. The variable bundaries f the layers can result in pinched elements, where nt all the ndes in an element exist in a layer. The upper elevatin f the system is specified by the surface elevatin DEM and the layers are stacked frm the tp dwn. If a water table DEM is specified, ndes are nt created within an element until the elevatin f the nde is belw the water table. Hydrstratigraphic interpretatin and hydraulic prperty assignment lgic is shwn in Fig. 4. This prcess is accmplished thrugh the use f tw text files: a translatin table and a material prperty table. The use f these tw separate files prvides the capability t keep the characterizatin data separate frm the hydrstratigraphic interpretatin. The translatin table permits the user t grup similar facies types int a smaller number f znes with the same hydraulic prperties. In the West Siberian basin, fr example, 70 facies znes exist acrss the 13-layer system. These facies are lumped int 17 categries with distinct hydraulic prperties thrugh the translatin table. The material prperty table cntains the hydraulic cnductivity in the x, y, and z directin; prsity; specific strage; and lngitudinal and transverse dispersivity. This prcess allws fr new hydrstratigraphic interpretatins f the facies and easy mdificatin f hydraulic prperties fr calibratin and sensitivity runs. Currently, mst f the lgic fr handling bundary cnditins ccurs utside f the main GeFEST system. Utility prgrams and netwrks within ARC/INFO are used t specify Dirichlet (prescribed head) bundary cnditins n ndes lcated n surface water features. The resulting bundary cnditin file cntains a cmbinatin f characterizatin and mdel data (nde numbers and elevatin), requiring an additinal step t regenerate this file whenever changes in the finite element mesh influence nde lcatins. Other types f bundaries (e.g. recharge and ther surces and sinks) are currently handled utside f the GeFEST system. ANALYSING RESULTS The utput f GeFEST cnsists f an AVS UCD (unstructured cell data) file fr visualizatin, a CFEST input file fr numerical mdelling f grundwater flw and transprt, and files cntaining summary infrmatin n the ndes and elements in the mdels. Additinal prgrams have been develped fr cmbining CFEST results (calculated hydraulic head, fluid velcity, cncentratin, temperature, and fluid density) with the AVS UCD file fr three-dimensinal visualizatin f results and fr building ARC/INFO TINs fr cnturing results in plan view. Figure 5 shws the AVS UCD file fr the West Siberian basin hydrgelgical mdel. The mdel is clur cded based n material prperties. The entire mdel can be dissected interactively fr viewing and individual materials can be viewed selectively r remved within AVS. Crss-sectins and fence diagrams can be extracted using prgrams utside AVS based n a list f surface ndes r by layers. T check ur hydrstratigraphic interpretatin f the West Siberian basin, a crss-sectin was generated alng a similar transect f a Russian hydrstratigraphic interpretatin published in the literature (Nudner, 1970). This cmparisn shwed that ur carse-grained, mre

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9 GeFEST: an integrated GIS and visualizatin envirnment 601 permeable units crrespnded t transmissive layers in the Russian interpretatin and ur finer grained, less permeable units crrespnded t cnfining layers. Streamlines were generated with AVS using the UCD file cmbined with the velcities within the elements calculated frm a numerical simulatin, as shwn in Fig. 6. The velcity field was extracted frm the three-dimensinal mdel alng a crsssectin s the streamlines are als three-dimensinal. Generating numerus streamlines and prjecting them n a tw-dimensinal crss-sectin yields a trace f the flw directins alng the crss-sectin. A number f simulatins were cnducted using different hydraulic prperties in the materials (istrpic, anistrpic, and hmgeneus hydraulic cnductivity) and the resulting streamline patterns were cmpared t each ther fr sensitivity analysis. Velcity vectrs can als be pltted t evaluate flw paths. The three-dimensinal UCD file can be clur-cded and/r cntured within AVS based n calculated hydraulic heads, temperatures, r cncentratins. Acknwledgements This wrk was spnsred by the US Department f Energy, Office f Technlgy Develpment, Characterizatin, Mnitring, and Sensr Technlgy Crss-Cutting Prgram. REFERENCES Fley, M. G., Bradley, D. J., Cle, C. R., Hansn, J. P., Hver, K. A., Perkins, W. A. & Williams, M. D. (1995) Hydrgelgy f the West Siberian basin and Tmsk regin. PNL-10585, Pacific Nrthwest Labratry, Richland, Washingtn. Gupta, S. K., Cle, C. R., Kincaid, C. T. & Mnti, A. M. (1987) Cupled fluid, energy, and slute transprt (CFEST) mdel: frmulatin and user's manual. Battelle Memrial Institute Reprt BMUONWI-660, Clumbus, Ohi. Nudner, V. A. (ed.) (1970) Gidrgelgiya SSSR; trn XVI, Zapadn-Sibirskaya Ravnina (Tyumeskaya, Omskaya, NvsibirskayaiTmskayablasti) (in Russian) (Hydrgelgy f the USSR; vl. 16, West Siberian Plain, including Tuymen, Omsk, Nvsibirsk, and Tmsk regins.) Ministry f Gelgy, Mscw. Petersn, J. A. & Clarke, J. W. (1991) Gelgy and Hydrcarbn Habitat f the West Siberian Basin. AAPG Studies in Gelgy 32, Am. Ass. f Petrleum Gelgists, Tulsa, Oklahma.