104 Per Ryghaug NGU - BU LL 427. 1995

Expanded use of superficial deposit information in localgovernment with geographical information systemsPER RYGHAU G

Per Ryghaug, Norges geofogiske undersokelse, PiO. Box 3006 -Lade, N-7002 Trondheim, Norway.

IntroductionNGU has recently put a great deal of effort intocustomising basic geological data for targetgroups such as local planners and politicians ,aware that such information is vital for high-qual i­ty decision-making within local government.Although many public policy decis ions and com­mercial enterpr ises require earth science infor­mation, exper ience shows that geological mapsand data are not used to their potential due topoor presentation using scientific terms whichare hard to understand for non-geologists.

This article describes working strategies andsome results from a two-year pilot project withinthe Nord-Trondelag og Fosen geological pro­gramme. The focus of the project has been totransform data from NGU's geological map seri­es and databases into digital geological informa­tion (Ryghaug 1992). The object ive has been tosupply Nord-Trondelag county in Central Norwayand its municipal ities with both regional andmore detailed digital geological and environmen ­tal information for use in local governmentresource and areaI planning (Fig. 1). The articlegives some examples as to how thematic infor­mation in connection with superficial depositscan increase the quality of decision-makingwithin local government by using a geographicalinformation system (GIS). The aim of this articleis not to give a full understandi ng of the technicalconcepts relating to GIS. For this it is necessaryto study the abundance of literature on this sub­ject (Bernhardsen 1992 and many others).

Data capture and data qualityGeological maps and databas e information varywidely in deta il and age. To be able to produce acomp lete superf icial depos it map covering wholemunicipalities , it was necessary to use anassembly of map sheets with different origins,scales and quality (Fig.2). Boundaries from thenational series of colour Quaternary maps werescanned using an Intergraph system, and preli­minary maps and script maps were digitised withFYSAK (software from the Norwegian MappingAuthority). Digital Ordnance Survey base maps(coastline, water systems , administrative boun­daries, roads , etc.) were based on the topograp ­hic map series from the Norweg ian Mapping

Authority, and all coordinates were captured inthe same coordinate system (UTM zone 32 anddatum ED50). Together with additional pointsource attribute tables (groundwater wells anddepos its of sand and gravel aggregates) primari­ly stored in databases , all data were transferredto the ARC/INFO geograp hical information sy­stem.

Bringing together datasets from different sour­ces and with potentially different levels of dataquality (varying scale-related data collect ion,maps with different status and age), calls forstringent data quality descr iption and metadata(data about data). It is important to include suchdescriptions in direct connect ion with the spatialcoverag e features themselves in order to satisfymost queries about the reliability and suitabil ityof the information for a particu lar purpose .Looking at the arcs showing the superf icial depo­sit boundar ies for one of the municipalities (Fig.2), it is possible to make drawings based on thedifferent origin of map scale in the dataset. Theright sub-window shows the possibilities of con­trolling/handling the updating of the information.Updated boundaries not equal to the joinedsource maps are drawn in black , and the date ofthe updating is also stored. In the same way, avariety of data qual ity information can be investi­gated. The map data file will increase by approxi­mately 25-30% in this quality control, but it ena­bles a higher standard of GIS analys is, and deci­sions based on the combination of informationwill be more reliable.

Geological informationDue to different grades of data genera lisation, itis important to create data with different mapscale origins (Fig. 1). Whilst the regional view ofthe superfic ial depos its of the Nord-Tronde lagarea is based on data created from theQuaternary map of Norway at a scale of 1:1 milli­on.(Thoresen 1991), the municipal ity map is deri­ved from maps at a larger scale (1:50,000 or1:20,000). From these Quaternary maps, deriva­tions were made of; (1) the effluent (sewage)infiltrat ion capacity of the depos its; (2) the possi­bility of finding groundwater resources and; (3)sand and grave l resources.

An infiltration map is suitable as an aid in fin-

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Nord·TrsndelagCounty

Per Ryghaug 105

Fig, 1. Digital infor­mation on superficialdeposits in Nord­Trondelag Countyhas a regional scalebased on the 1:1 mil­lion Quaternary mapof Norway. For eachmunicipality theinformation is basedon larger scaleQuaternary maps(scales 1:20,000 and1:50,000).

Fig. 2. The digitalversion of a munici­pality map, showingthe distribution ofsuperficial deposits,contains an assem­bly of map sheetswith different scalesand age. Qualitycontrol is built in anddescribes the originof each line (bounda­ry) and can be inve­stigated in ArcViewdisplay windows (redlines from 1:50,000scale maps, bluefrom 1:20,000 scalemaps, and blackshow which line hasbeen updated inrelation to the origi­nal map).

106 Per Ryghaug NGU . BULL 427. 1995

Fig. 3. Built-in deri­vation functionalityin the dataset trans­forms the superficialdeposit map into aninfiltration capacitymap. Such infor­mation aids thederivation of morecost-effective soluti­ons concerning theclean up of effluentin sparsely pollutedareas. Buffer zonesare included aroundstreams andgroundwater wellsfor safety reasons.

.:~=. ;.-

t*=? 5C-: I . - I - !l

Fig. 4. Views.tables and chartsare opened andqueried simultane­ously. In this decisi­on-making frame­work. it is po ssibleto assemble allrelevant informati­on concerning the

Idemand for betterdrinking water qua­lity.

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ding deposits with a suitably high effluent infiltra­tion capacity. On the infiltration map of Inderoymunicipality (Fig. 3), the superficial deposits aredivided into four classes of infiltration capacity(very good, good, moderate, unsuitable), mainlybased on thickness and permeability of thedeposit. However, no deposits class ified as verygood capacity are shown in this figure. As a largeproport ion of sewage is still released into theenvironment in a raw state (even close to depo­sits suitable for infiltration), the infiltration of efflu­ent into suitable superficial deposits has provedto be a simple and a cost-efficient method inste­ad of the building of expensive cleaning plants.Detailed infiltration capacity mapping on a scaleof 1:5,000 within the municipality of Inderoy(Hilmo & Sveian 1993) shows an acceptableaccordance with the derived map and test soil­cleaning plants show good results . Extrapolatedfor the whole municipality , savings of NOK 5-10million. could be made in this tiny municipalityalone.

A register for sand and gravel aggregates isnow being transformed to an Oracle database(Neeb 1993). During this GIS project , adjust­ments of the sand and gravel database (inclu­ding standard coding and qualitative classificati­on) have been made to satisfy the requirementsof a GIS product. In Fig. 4, some of the sand andgravel resources in the municipality of Levangerare shown in orange. These deposits commonlyrepresent a groundwater resource as evidencedby the location of several groundwater wells(shown as black hydrants).

In the same way as for the infiltration map, aderivation map has been made illustrating thepotential of finding groundwater resources withinthe superficial deposits. The largest abstractionsof groundwater are generally assumed to occurin large fluvial, glaciof luvial and shore deposits,whilst more limited abstractions usually occur insmaller/thinner deposits of lower permeability.

Assembl ing information relevant to a resourceplanning assessment (such as existing watersupply , groundwater wells, streams and sandand gravel resources), the water supply potentialof an area can be estimated. In Fig. 4, factor ieswhich demand better water quality are alsoshown. The environmental impact is illustratedby the marking of features such as waste dispo­sal sites, contaminated ground (Misund et al.1991), traffic routes with hazardous waste andeven deposits earmarked for the infiltration of ef­fluent (not shown on this figure), i.e. all featuresrepresenting a risk to groundwater quality. Thewater quality of a specific well can then be in­vestigated in sub-windows containing tables orcharts (Fig. 4).

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The use-friendly interfaceWhile use of the ARC/INFO system demandsspecialisation, ArcView desktop GIS can be usedby almost anyone after a short introduction.ArcView can be run under MS Windows.Themes can be switched on and off by clickingon the left of the theme name. It is easy to zoomin and customise a map display (layout) for finalpresentation and export it in a wide range of for­mats. All illustrations (figures) shown in this ar­ticle are made in ArcView. Selections can bemade by geographical search and attributesearch. It is possible to display the results in aview, table and chart simultaneously. A dynamiclink can be established between the spatial dataand other databases such as Microsoft Accessor Oracle. One can combine fields from morethan one table and make queries with a one-to­many relationship . ArcView contains a geo­graphic Hot Link capability that allows varioustypes of datasets (pictures, videos) or programsto be attached to geographic features and initia­ted on request. It has essentially become a multi­media approach.

Using a GIS system and a desktop GIS interfa­ce on the geological information has undoubtedlymade raw scientific data more available to non­specialists in local government. It has strengthe­ned strategic decision-making, preventingresource- and land-use conflicts, and contribu­ting to better resource exploitation.

Acknowledgemen tsI am grateful to Janne Grete Wesche and Ase K. Ronningenfor helping me with the digital work (GIS) and providing thedigital geological information. Many thanks to Torunn Carlssonand Morten Thoresen for constructive comments on themanuscript and to David Segar for making improvements onthe English language.

References

Bernhardsen. T. 1992: Geographic Information Systems.Asplan Vlak, 320 pp.

Hilmo, B.O. & Sveian, H. 1993: Losmassekartlegging for infil­trasjon av avlopsvann fra spredt bebyggelse,Granaelvornradet, Inderoy kommune. Unpubl. Nor. geol.unders. Report 93.031,22 pp.

Misund , A., Morland, G., Brunstad, H. & Banks, D. 1991: A sur­vey of hazardious waste disposial in landfills and contarn i­nated soil - Final report. SFT-Report nr. 9 1.01, 36 pp.

Neeb, P.R. 1993: Aggregate Resources in Norway. Unpubl.Nor. geol. unders. Report 93.068,21 pp.

Thoresen, M. 1991: Quarternary map of Norway. GeologicalSurvey of Norway.

Ryghaug, P. 1992: Geografiske informasjonssystemer skapergeologi for samfunnel. Nor. geol. unders., Arsmelding1992,2 pp.