Development of site suitability analysis system for riverbank filtration

SEWater Science and Engineering, 2010, 3(1): 85-94doi:10.382/.issn.1674-2370.2010.01.009htp://ww.waterjournal.cne-mail: wse2008@vip.1 63.comDevelopment of site suitability analysis system forriverbank filtrationSang-il LEE, Sang-sin LEE*Department of Civil and Environmental Engineering, Dongguk University, Seoul100-715, KoreaAbstract: Site selection plays a crucial role in riverbank filtration for sustainable wateravailability and quality. Choosing the most appropriate from among multiple candidate sitesrequires a complex procedure, involving many tangibles and intangibles. In this study, the AnalyticHierarchy Process (AHP), which selects the optimal alternative by hierarchically classifyingvarious attributes and then quantifying the importance of each atribute, was used to prioritizecandidate locations for riverbank filtration. A GIS-based computer program was developed toautomate the assessment process. The developed software was applied to the Han River in Korea.Analysis of four candidate sites reveals that a site that has better water quality and conectivity tothe neighboring purification facility is more suitable than other locations.Key words: riverbank filtration; AHP; site suitabilir; Han River1 IntroductionIn European countries such as Germany and the Netherlands, riverbank filtration (RBF)has been successfully practiced as a way of enhancing the quality of the water supply for over150 years (Grischek et al. 2002; Tufenkji et al. 2002; Eckert and Irmscher 2006). In Germany,RBF is used for 15%-16% of the total drinking water. RBF has also been used for drinkingwater in many cities in the United States. RBF relies on the streambed and aquifer matrixes toimprove source water quality and to reduce pathogens through induced infiltration. Theremoval or degradation of contaminants is achieved through a combination of physicochemicaland biological processes.Tap water in Korea mainly comes from surface water. A more advanced water treatmentprocess is needed due to the risk of accidental spills and the deterioration of surface waterquality. Because of the high cost of water treatment and public concerns, decision makers areturning to RBF as an alternative to the conventional abstraction of surface water. ChangwonCity started supplying domestic water treated through RBF in 2001, the first time in Korea(Office of Waterworks Changwon City 2009). The city continues to expand the facility, and the中国煤化工This work was supported by a grant (3-4-3) from the SustainableMYHCNMHGnterofthe21stCentury Frontier Research Program.*Corresponding author (e-mail: sinslee @ nate.com)Received Sep.28, 2009; accepted Nov. 25, 2009water supply is now 70000 mi /d. A neighboring city, Chil-seo Myeon in Ham-an Gun, has alsobeen supplying riverbank- filtered water (20000 m'/d) since 2003. Seoul, the capital of Korea,is pursuing the introduction of RBF to enhance public trust in tap water. Table 1 shows someexamples of riverbank filtration throughout the world.Table 1 Major examples of riverbank filtrationRiverWell fieldNumber of wellWater production (m/d)Rhine River in GermanyDisseldorf70 vertical wells, 18 clltor wells357 600Llobregat River in SpainCorella26 extraction wells, 7 recharge wells62000Limmat River in SwitzerlandHardhof9 vertical wells, 4 cllctor wells15 000Donau River in AustriaLobau8 clletor wells136000Donau River in HungaryCsepel256 vertical wells, 30 clletor wells150000Missouri River in USAJefferson County5 lateral wells18 900Nearman1 collector well120000Kansas River in USAKansas City1 cllctor well151 200 .Ohio River in USALouisville, Kentucky2 cllector wells75 600Nakdong River in KoreaChangwon50 vertial wells, 1 collector well80000The Analytic Hierarchy Process (AHP), which allows for the selection of the optimalaltermnative by hierarchically classifying the various attributes and then measuring theimportance of each attribute, was developed by Saaty (1980). The novelty of AHP lies in thestratification of a decision- making problem with many objectives, evaluation criteria, anddecision-making variables. Due to its simplicity and versatility, AHP has been used in varioussettings to make decisions (Saaty 2008). AHP involves dividing a sophisticated problem intosub-elements, organizing them, forming an orderly hierarchical structure, determining threlative importance of the elements through pairwise comparison, and finally synthesizinghuman judgments to provide a total order (Zhang 2009). There have been some studies relatedto site suitability analysis using AHP. Wu (1998) developed a prototype of a simulation modelbased on cellular automata (CA) and multi- criteria evaluation (MCE) and integrated withgeographic information system (GIS) using the AHP method. Reza (2005) studied the ways inwhich AHP frames the site evaluation problem and can aid in making decisions involvingmultiple criteria, factor diversity, and conditions of uncertainty.2 Suitability analysis using AHPApplying the AHP procedure involves four basic steps (Fig. 1): (1) definition of theproblem; (2) construction of the decision hierarchy; (3) comparative judgment, or datacollection and execution of pairwise comparison for elements in the hierarchical structure; and(4) synthesis of priorities, or evaluation of the overall priority rating.The decision hierarchy is structured from the top, with the goal of the decision, throughthe intermediate levels to the lowest level. Once a hierarchy is established, pairwisecomparison is made. The pairwise comparison makes. the complicated comparison of entireelements easy. The degree of relative importance of ele中国煤化工ccording toa1-9 scale, as shown in Table 2.fYHCNMHG.86Sang-il LEE et al. Water Science and Engineering, Mar. 2010, Vol. 3, No. 1, 85-94J EvaluationDefinitionobjective↓l Hierarchy| Evaluation Evaluation | | Evaluation || Evaluation(1I)2)(3)(4)PairwisecomparisonFinal+[ Ateative1]- -[ Altemative2]synthesisFig. 1 Organized decision-making in AHPTable 2 Fundamental scaleRelative importance of elements i andjDegree of importance ( a,i and j are equally importanti is absolutly more important thanjWhen the number of elements is four, the pairwise comparison matrix can be formedas followsa12ah3a4a2392(1)a34913 a23a4 a24a3The normalized pairwise comparison matrix (or normalized matrix) is obtained from thefollowing equation:aVj=r(2)S;wheres,=之=Iand n is the size of the normalized matrix.The priority is obtained from Eq. (4): .p,=之上司nZP,=1(5)where P; is also called the relative preference or the re中国煤化Iof element j.In other words, priorities are obtained by adding eadYHCNMHGmatrixandSang-il LEE et al. Water Science and Engineering, Mar. 2010, Vol. 3, No. 1, 85-9437dividing by the size of the matrix. The consistency ratio ( CR ) needs to be calculated to checkthe logical consistency of the pairwise comparison. According to Saaty (1980), CR can becalculated by dividing the consistency index (C ) by the random index (R ): .Cp=_C(6)Rwhere C is defined asAmax -nn-1where Amax is the largest eigenvalue of the pairwise comparison matrix, and R is given inTable3.If Cp is less than 0.1, the pairwise comparison can be regarded as reliable.Table 3 R for nxn pairwise comparison matrixn2061.240.58 .1.320.901.411.12Finally, the suitability index can be calculated by accumulating the multiplication ofpriorities obtained from the top to the bottom level for the ith element.3 System development3.1 Analysis frameTo construct a hierarchy and to make pairwise comparisons for the AHP analysis o1riverbank filtration, influential elements and their corresponding degrees of importance must bededuced. Comprehensive investigation of previous development projects provided the initialsetting (Table 4). Of the 28 elements involved in the development of riverbank filtration inprevious projects, we selected the 21 most influential elements for analysis (Fig. 2). Dataavailability and specialists' judgments were taken into consideration.Table 4 Influential elements considered for riverbank filtration projectsPumpAquiferHydraulicStage .RiverProject periodWater intake facilitiesI ayerthicknessconductivitcomonevny(m2/d)(cm/s)ChungnamRiver in10/1994-03/1995Alluvial0.13MinochonFeasibilityKum River in02/1996- 12/1996Sediment10-158studyNakdong River06/1997-12/19985wells(φ250mm,H5 00020-350.893-9.9in Leeyoung=40m)6 wells( ψ 250 mm, Hin' Yongsan03/1995-03/1999= 39-45 m)5000 Alluvial2 pumping wellsIrin Bookmyeon1/199999 present(φ400mm,H=40m)9700operation中国煤化工03/1998- present(φ400mm,H=40mDaesanmyeonMHCNMHG-Sang-il LEE et al. Water Science and Engineering, Mar. 2010, Vol. 3, No. 1, 85-94Decision HierarchyLevel1Level 2Level 3Level 4Level 5. Permeability(D)Geological. Aquifer thickness(D)features(C). River path changeability(D)PossibilityWater. General water quality(D2)二(昌)uality (C- Speial water qulity(D>). NI:/-N(E)”Distribution of pollution source and extent (D)SuitabilityL pollution(C3)- Surface water qulity(Dx)indexUrgencyStreamflow during drought season(D2)(S)(B2)- Water supply deficit(Dno)- Faility area(Du): Housing and residents (D2)Cost(C3). Water Pice(Du)Efficiency. Width of trrce land(D1s)(B)Facilities (Co). Connectivity to existing facilities (D1o). Distance to users(Dnz)Fig. 2 Elements of analysis of site suitability for riverbank filtrationVerification of deduced importance values from previous cases was conducted with anexpert survey. Twenty-five experts currently working in the field of water resourcesparticipated in the survey. There were eighteen respondents. Three of them, who declaredthemselves non- specialists in riverbank filtration and site suitability analysis, were excluded. Inthe final analysis, the scores for the included experts' knowledge of riverbank filtration and sitesuitability analysis were 6.73 and 7.73 out of 10, respectively.Table 5 shows the list of influential elements along with their degree of importance. Thescales derived from previous projects are similar to those derived from the expert survey. Thisfeature confirms the justification of the values used in the analysis.Table 5 Influential elements and scales of importance from previous cases and expert surveyScale of importanceClassificationElementsFromprojectssurveyLevel of understanding of6.73Personal .0expertiseCD。.277.73site suitability analysisTop levelBiD> (m2/d)300 .6003.07B20.0.53factorsB30.49>600.5.60stB22.20Ds (grade)2nd - 3rd20> 4th6.47D、D，D2D;D1o336.67中国煤化工3.20D (cm/s)10*- 10-2.40> 1034.53Y出CNMHG5.73Sang-il LEE et al. Water Science and Engineering, Mar. 2010, Vol. 3, No. 1, 85-9489Table 5 Influential elements and scales of importance from previous cases and expert survey (Continued)Scale of importanceClassificationElementsFromFronprojectsurveysurvey< 15PoorD2 (m) .15- 302.67DA verage93527( jood7.40Good0AverageB:.105.93 .)11)122.60D4 (103 m2/d)50- 100CD133.47> 1006.67D146.870-1cDs5.10D11 (km?)1-22.536.40> 10*D123.67103 -1(33Good .7.67(households)5.531.333.002.475.203.00 .ED14 (Korean750- 1 000Won)6.476.13D1s3.4/D16)1533.53DIs (m) .300 - 600> 600None2.17E.4.607.27B0.33 .0.255.47The pairwise comparison matrix down to the second level is shown along with prioritiesand consistency in Table 6. The same method can be applied to the lower levels.Table 6 Pairwise comparison matrix down to level 2Level ElementPairwise comparison matrixPriorities ConsistencyElementBi32Suitability0.5000indexOK(S)/20.2500C20.3330.6667C3Ca130.7500Cs中国煤化工C。MYHCNMHG90Sang-il LEE et al. Water Science and Engineering, Mar. 2010, Vol. 3, No. 1, 85-943.2 System configurationAn AHP-based computer program analyzing the optimal site for riverbank filtration wasdevised (Fig. 3). Originally, the system was developed for a site suitability analysis system forconjunctive use (SASCU) of surface water and groundwater. It was developed using Avenue (ascript language for the GIS software ArcView) and Visual Basic, based on the MicrosoftWindows environment (Fig. 4). The system accesses the spatial and attribute database, queriesinformation, and computes the suitability. It integrates the information-searching unit and theAHP-modeling unit. With the aid of the information-searching capability, the task of accessingthe database and obtaining the appropriate values for each attribute appearing in the analysisbecomes simple and almost automatic. Meanwhile, the AHP-modeling unit analyzes thesuitability based on the hierarchy and the relative importance of attributes (Lee and Lee 2008).回HCA 0国网月8口09用口囚团DOFig. 3 SASCU sample screenSpatial databaseAttribute database| AHP model systemDatabase searchsystemSite asessment systemFig. 4 SASCU system configuration4 ApplicationThe Han River Basin is the largest basin in the central part of the Korean Peninsula, andconstitutes about 23% of its total area (Fig. 5). The中国煤化工6 km2 and alength of 481.7 km. In some regions of Kyung-gi Prov:YHC N M H Gss complexesSang-il LEE et al. Water Science and Engineering, Mar. 2010, Vol. 3, No. 1, 85-94)1from the pre-Cambria Archeozoic Era are widely distributed. Granites that have intruded onthese complexes in later periods constitute about 36% of the Seoul region. The granite-filledregions are quite water-permeable because their component particles are relatively large, incontrast to the gneiss- and schist-filled regions, where particles are so small that it is hard forthe groundwater to remain in the alluvial layer. This study mainly deals with the Seoul area.Han River BasinKangseo MangwonTukscomKwangnaniYanghwa Ichon 0 JamsilYcouidoBanpoCHINAS s2ROREA二」Fig. 5 Han River Basin and candidate locations for riverbank filtrationThe Seoul area of the Han River Basin is highly urbanized, which makes it hard to findcandidate locations for riverbank filtration. However, eleven terrace areas turned out to beacceptable for initial consideration according to various previously conducted fieldinvestigations. Preliminary analysis ruled out seven of them, leaving four for further analysis(Table 7 and Fig. 5).Table 7 Candidate sites and their characteristicsThickness of alluvial layer (m)SiteLength (km)Width (m)RiverbedTerraceKwangnaru824.5-6.79.0-17.0Jamsil5.41092.3-7.59.6-12.5Ichon8.0521.8-8.710.0-13.0Y anghwa11.7329.0-17.313.7-17.8The site suitability analysis, for selecting the optimal site, was conducted using SASCU.Spatial and attribute databases were established using an online database in the WaterManagement Information System (http://www.wamis.go.kr)， reports from the Office ofWaterworks Seoul Metropolitan Govermment (2006), and numerical maps. Table 8 shows eachinfluential element and suitability index for four candidate locations based on the performanceof SASCU. The Kwangnaru district, which has advantages over other sites in terms of goodwater quality and a close connection to an existing water purification facility, was selected asthe optimal site.中国煤化工YHCNMHG.9Sang-il LEE et al. Water Science and Engineering, Mar. 2010, Vol. 3, No. 1, 85-94Table 8 Suitability index of candidate sitesLevel 1Level 2Level 3Level 4Level 5KwangnaruJamsilIchon YangwhaD0.001 60.00290.002 90.01150.00470.0047 0.01150.03090.01190.0045_D0.01700.0170 0.03870.03720.00490.0049 0.004 9E0.022 70.008 70.0087cE20.02270.0227 0.0087E30.008 7.E40.0087 0.00870.001 50.00390.0102C0.03130.0104 0.0104B0.02720.0272 0.02720.09400.008 00.00800.0080 0.008 00.02100.021 0DI30.0210 0.02100.063 60.0636D1s0.0008 .0.00080.0008 0.0008D160.01210.0121 0.012 1_D10.01870.0169Sum0.48820.39020.3684 0.41105 ConclusionsIn order to determine the optimal site for riverbank filtration, various hydrogeologic, waterquality, and socioeconomic factors should be considered. As for existing riverbank filtrationsites, there has been a focus on the assessment of available water and the well design 01construction. Selecting the appropriate site has been treated as a minor problem and the processhas been carried out in a conventional way, relying on the subjective experience of experts. Asystemic approach to the selection of the most suitable site of several candidates wouldincrease the objectivity of the decision-making process and make complex decision-makingprocedures efficient. This paper developed a site suitability analysis system based on AHP.Twenty-one elements believed to influence the performance of riverbank filtration wereselected and constituted a hierarchy. To enhance the credibility of the AHP analysis, especiallythe pairwise comparison, experts’ opinions were sought out through a survey. A GIS-baseddecision support system (SASCU) incorporating both spatial and attribute data was developed.To verify the applicability, we applied SASCU to four candidate locations along the Han Riverin Korea.The Kwangnaru district was selected from the candidate locations as the optimal site. Theanalysis indicated that a site having high water quality and better connectivity to theneighboring purification facility is more advantageous中国煤化工AHP turned out to be a useful tool for assessirTYHCNMHG)r riverbankSang-il LEE et al. Water Science and Engineering, Mar. 2010, Vol. 3, No. 1, 85-94)3filtration. We believe that the developed system can assist decision makers in finding anappropriate location for riverbank filtration among many candidates, which involves alimmense amount of spatial and attribute data. In addition, the impact of including or omtting acertain factor in the analysis can be easily estimated using the system.ReferencesEckert, P, and Irmscher, R. 2006. Over 130 years of experience with riverbank filtration in Disseldorf,Germany. Journal of Water Supply: Research and Technology-AQUA, 55(4), 283-291. [doi: 10.2166/aqua.2006.040]Grischek, T, Schoenheinz, D., Worch, E., and Hiscock, K. M.2002. Bank filtration in Europe - An overviewof aquifer conditions and hydraulic controls. Dillon, P, ed, Management of Aquifer Recharge forSustainability, 485-488. Rotterdam: Balkema.Lee, S. I, and Lee, S. 2008. Site suitability analysis for riverbank filtration in the Han River, Korea.Proceedings of the IAHR-APD Congress, 236- 239. Beijing: Tsinghua University Press.Office of Waterworks Changwon City. 2009. Introduction of Riverbank Filtration. Changwon City: ChangwonCity Hall. htp:/suo.changwon.go.kr/05/05_ 05_ 05.jsp. (in Korean) [Retrieved March 9, 2010].Office of Waterworks Seoul Metropolitan Government. 2006. Interim Report: Feasibility Study for theIntroduction of Induced Water Abstraction. Seoul: Seoul Metropolitan Government. (in Korean)Reza, B. K. 2005. A new method for site suitability analysis: The analytic hierarchy process. EnvironmentalManagement, 13(6), 685-693. [doi: 10.1007/BF01 868308]Saaty, T. L. 1980. The Analytic Hierarchy Process. New York: McGraw-Hill.Saaty, T. L. 2008. Decision making with the analytic hierarchy process. International Journal of ServicesSciences, 1(1), 83-98. [doi:10.1504/IJSSCI.2008.017590]Tufenkji, N., Ryan, J. N, and Elimelech, M. 2002. The promise of bank filtration. Environmental ScienceTechnology, 36(21), 423-428. [doi: 10.1021/es022441j]Wu, F 1998. SimLand: A prototype to simulate land conversion through the integrated GIS and CA withAHP-derived transition rules. International Journal of Geographical Information Science, 12(1), 63-82.[doi:10.1080/136588 198242012]Zhang, H. 2009. The analysis of the reasonable structure of water conservancy investment of capitalconstruction in China by AHP method. Water Resources Management, 16， 1-18. [doi:10. 1007/s11269-008-9261-9]中国煤化工MHCNMHG94Sang-il LEE et al. Water Science and Engineering, Mar. 2010, Vol. 3, No. 1, 85-94