Proc.of the gthWSEAS Int. Conf. on Mathematicaland ComputationalMethods in Scienceand Engineering,Trinidad and Tobago, November 5-7, 2007 The influence of hydrological parameters on the stream floods of a mountainous area in Thessaly, Greece P. LOKKASI, S. KOTSOPOULOS2, J. ALEXIOU2, G. GRAVANISI, V. VASSILOGLOUI. S. MAGALIOS3. V. KASSOS4 1: Department of Civil Engineering Infrastructure Works, Technological Educational Institute (TEI) of Larissa, GREECE 2: National Agricultural ResearchFoundation, Institute of Soil Classification and Mapping of Larissa, GREECE 3: MScE Surveyor Eng, Larissa, GREECE 4: Electro-MechanicalEng, Larissa, GREECE p. lokkas @tei lar.gr http ://users.teilar. grI -p. lokkas Abstract: - The sloping area on the North and North-Eastof Mount Ossa,opposite Mount Olympus, in the region of Thessaly,Greece, receives considerable rainfalls. However, despiteits extendednatural vegetation, severeproblems have arisendue to floods. The existenceof theseproblems is mainly basedon two reasons:a) on the peculiarity of rainfall eventscombined with the local conditions(hydrologic, geologic, land use, etc.) and b) on the existing infrastructureworks. In order to analyzeand interpretthe phenomenaof local floods, in 'oArchimedes" the frame of the researchprogram which is materializedby the TEI of Larissaunder the title "Spatial mapping and estimationof hydrological risk, emphasizingthe floods and draughtsin urban and non urban areas of Thessaly and their environmentalimpacts" it is essentialto record, evaluateand validate various hydrologic parametersof the correspondingstudy area.The GeographicInformation Systems(GIS) is utilized to analyzeand validate the information abouttopographic, hydrologic, geologic and soil data, along with land cover and infrastructure.Finally, the GIS are also used to produce and map complex hydrologic parameters,which, in tum consistinput datafor hydrologic modelsas well as presentationof results. Key-Words:- Hydrology, geology,vegetation, stream, flood, infrastructure. 1 Introduction . the particularity of the rainfall events in this The region of the North andNorth East slopesof the region, mount Ossa,in Thessaly,Greece, is coveredby rich r the local conditions, i.e. hydrologic, geologic, and densenatural vegetation, forest trees, shrubs etc, land use.etc and especially chest nut trees, which, locally, is o the lack of the necessaryinfrastructure works. considered a valuable means for agricultural The environmental consequencesof the above development.The level of rainfalls in the area is floods are highly crucial for both the cultivatedareas considerably high; almost three times higher and the local delta of Pinios river. comparedto those taking place on the main part of For recordingand managementof the necessaryfor EasternThessaly. This situation,combined with the this study local data, the Geographic Information local hydrologic conditions and the existing SystemGIS-ArcView has been utilized. The use of infrastructure, has resulted in serious problems GIS [1] is advisable for any presentationof the concemingdamages due to excessiveflood events. spatial variables and for this reason it has been In the frame of the research program treated as the main tool for a large number of "Archimedes - EPEAEK II", co-funded by the applications,like soil-water resourcesmanagement European Social Fund & National Resourcesand L2l,l3l, [4], [5] etc. realizedby the Dept. of Civil Engineeringof TEI of As far as estimation of flood discharge is Larissa, Greece,the above region has been selected concemed,it has to be noted that there are spatial as a study area. The work is aiming at a fluent parameters,that after processing,create input data evaluation of hydrological parameters,which are for flood simulation [6] throughhydrological models relatedto the estimationof flood discharges. [7], [8], like soil data,data ofvegetation cover, land Theseflood discharges,which actually constitute use,relief, streamnetwork characteristicsetc. the main problem,take placeoccasionally during the The processingof the above data,may directly lead winter and are due to the large amount of water in to hydrological parameters, like the area of the streams.The problemtherefore, is originatingto: Proc.of the gthWSEAS Int. Conf. on Mathematicaland ComputationalMethods in Scienceand Engineering,Trinidad and Tobago, November 5-7 ,2007 168 hydrologic basins,the slopesofthe basinsand their position of each work, through GPS, were water streams,runoff coefficientsetc. saved in corresponding files. There were totally kept 46 positions of stream bridges, ranked from very small to very large. Each 2 Procedure one of the correspondingstreams was mainly For recording and plotting both the existing connectedto one or more watersheds. information and the resulted conclusions, the o Topo€traphicdata for plotting the slopes, Geographic Information System GIS-ArcView has along with the correspondingcross - sectional been utilized, so that the spatial variability of areasof the main streamsthat belong to the different parametersmay easily be presented.The study region. GIS is a powerful technology approachableand All the abovecartographic information, related to accessibleto many users.This technologyallows for the study area of mount Ossa is shown in Fig. l, automationin many procedures,therefore working where, the watershedswere drawn with a bold in a complementary way for many analytical contour. The information was then digitized and methods, which are utilized for aquatic resources convertedto GIS-ArcView format file, where, the management[]. inter-correlationsamong the geographic elements, For analysis,estimation and evaluation of flood i.e. their topologicalrelations [1] along with their eventson the study area,the collection and use ofa databaseconnected to them were developed. variety of data is necessary.Some of this data may On the top of them, in GIS files there were concern hydrological, soil and geological createdsecondary information, like: characteristics,use of land, vegetation cover, and o the borders of watersheds of the most terrain, along with the existing infrastructureworks. important water streams, along with their area, The last one may comprisethe road network, the averageslope and database, cross section of natural water streams. technical o the databaseof water streamsaccompanied by works and crucial cross-sections that affect the flow their length, average slope and the corresponding of water. locations of the selectedcross sections,along with For this reason the following tools have been their geometricalcharacteristics, utilized: r the databaseof soil samples,taken out of . Maps of Hellenic Army GeographicalService selectedlocations ofthe study area. (HAGS),scaled at l:5000and l:50,000, All these data were then combined and worked . Geological maps of the Institute of Geology out to give results,which in tum becamenew data and Mineral Exploration (IGME), scaled at necessaryto simulatethe naturalsystem. 1:50,000, The elaborationof elementscomprises: . Soil maps of the Ministry of Agricultural . Topological processing of hydrological and Development and Foods (MADF), scaled at topographicdata, i.e. hydrographicalnetwork, l:50,000, watershedareas, slopes of earth and water . A silviculturalmap scaled at 1:20,000and streams,as well as length and cross sections o A mapof mountOssa's soil cover,i.e. borders of water streams. of forest vegetation species, scaled at . Topological processing of pedologic maps 1:350,000. along with their correspondingdata. Apart from the above official data it was . Topological processingof silvicultural maps necessary to collect data from local held and mapsof vegetationcover. measurements; for this reason the following The averageslope of the watershedshas been activitieswere realized: calculated through the equation of Gregory & r Soil samplestaken from different locationsall Walling,as described by Tsakiris[10]: over the study area.The depthof samplesmay \,L.D ^S^-- . (r, vary in the rangesof 0-30, 30-60 and 60-90 .E cm. Every location of samplingwas recorded whereS" is the averageslope of the watershed,)Z is through a Geographic Positioning System the total length ofthe contour lines, D is the contour (GPS). interval of lines andE is the areaof the watershed. o Elementsof technicalworks, having the form The outflow of the watershedcould be estimated of stream bridges, along the axis-road through the Soil Conservation Service (SCS) Omolion - Stomion- Karitsa, were recorded, method, where, an estimation of the runoff curve i.e. their crosssectional details alons with the number,Cl{ is required[9], [10],[1 1], [12], [13]. proc.of the gthWSEAS Int. Conf. on Mathematicaland ComputationalMethods in Scienceand Engineering,Trinidad and Tobago, November 5-7,2007 169 AN Fig. 1: Topographicmap of the local studyarea with the contoursof watersheds.Scale l:165,000 This coefficient is given in tables and varies The elaborationof cartographicdata, along with according to the land use, to the managementor the data and types of earthy plotting, result in the practise,to the hydrological conditions and to the estimationof: typeofearth [9], [10], [1 1], [12], [13]. o the area along with the averageslope of the In the casethat there are more than one land uses hydrologicwatersheds, within the watershed,then, the so-calledcomposite o the slopes,the lengths and the cross sections curve numberoCN", must be taken into account.This of water streams. number is an areal weighted average of the Figures 2 and