South-‐Eastern European Journal of Earth Observation and Geomatics
Issue Vo1, No1, 2012
The use of temporal remote sensing images and GIS for Aliakmon Delta Coastline Change detection Eugenia Kakogiannou*, Athina Soliopoulou, Anna Maria Feneri Students, School of Urban-‐Regional Planning and Development Engineering, Faculty of Engineering, Aristotle University of Thessaloniki, Greece *Corresponding author:
[email protected] Abstract: The purpose of this study is to investigate the change in delta of the river Aliakmon, which occurs in cases of direct or indirect human intervention in river deltas. To conduct this study there were used aerial photos taken in 1950, 1975 and 2009. With proper processing in the software Erdas Imagine 2011 ® there were created timeless orthophotomaps and in ArcMap 10 ® there was studied the changing of the coastline. Keywords: Aliakmon, river’s deltas change, over time remote sensing data. 1. Introduction The river Aliakmon belongs to the Greek area, having developed a good delta. The delta of Aliakmon river, along with the delta of the rivers Axios and Loudias, has been characterized as a National Park, which contains areas of nature conservation and areas of absolute protection (Official Gazette, 2009; URL1). The National Park, which includes one of the most important wetland systems in Greece and Europe, belongs to the network of protected areas in the European Union Natura 2000, while is protected by the Ramsar Convention on Wetlands, code 3GR007 (Official Gazette, 1974; URL2).
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b. Figure 1. a. Aliakmon position in Greece, b. The study area, Aliakmon’s Delta
Despite the importance of delta areas on the natural environment and the general development, man intervenes directly and / or indirectly in deltas of the rivers, transforming the landscape and disrupting the natural balances. As an indirect intervention on river systems is regarded the intensifying in the creation of agricultural crops, which includes deforestation of large areas of land, resulting in increased transport of sediments in the delta. Moreover, deforestation is responsible for the occurrence of floods. Indirect intervention is also considered to be the construction of dams, which delimiting the delta, 55
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South-‐Eastern European Journal of Earth Observation and Geomatics
Issue Vo1, No1, 2012
reducing its supply and intervening in the natural evolution and flow of the river (Poulos et al., 2000). As direct intervention is regarded the reduction of the riverbed, the building of land reclamation projects, the extensive sand extraction from the riverbed, the uncontrolled grazing, the dried areas, etc. In terms of the coastline, affected by both anthropogenic and natural causes, these changes are made in a variable period, which may range from hours to millennia. Long-‐term changes have visible results within 50 years or more, as the change in sea level. The short-‐term ones can be performed in less than a decade, while instant changes are related with extreme weather events, which can alter the coastline within a few hours. 2. Using Data The data used in the investigation were: -‐ Seven aerial photographs of the year 1950, scale 1:20,000. -‐ Six aerial photographs of the 1975, scale 1:20,000. -‐ Modern 2009 orthophotomap planimetric accuracy of 1m. -‐ Digital Terrain Model of the area (grid 20x20m, elevation accuracy 1.5m). -‐ Data calibration for all cameras. 3. Digital Processing The first stage of data processing was digitized aerial photographs with a resolution of 900 dpi (pixel size 0,028 mm in the level of aerial photography or 0,54 m on the ground). To solve the resection in the software Erdas Imagine 2011® were used 12 Ground Control Point, taken from the modern orthophotomap. The derivative Orthorectified images (Greek Geodetic Reference System 1987, GGRS87) and photomosaics have planimetric accuracy 1,8m for the year of 1950 and 1,7 m for the Year 1975. Then, the shoreline of the river was digitized (Fig. 1) using the software ArcMap 10. 4. The Change of Aliakmon’s coastline through timeless remote sensing data The comparative observation of the coastline and the rivers, are making it clear that Aliakmon delta has undergone significant changes from 1950 till today. The marine processes are visible, shown erosion and retreat of the coastline, while in other parts of the mouth of Aliakmon’s has increased deposition of sediments, resulting in the phenomenon of aggradation. Observing the change of the coastline south of the region, both in digitized form (Fig. 2) and in the photomosaics of longitudinal images (Fig. 3), there are no special changes, only a small aggradation formed gradually over time, probably due to the import of sand and sediment transport through the river. Increased silting observed the period 1950 to 1975. Because the construction of the first dams and their start-‐up was completed on the 1970 (URL3), it is not suffered a significant reduction in the width and the flow of the river, so it continued to supply with sediments the coast. During the next period 1975-‐2009, in the southwestern side, coastline follows the same trends of sedimentation, but the change is less intense because the reducing of the river’s width decreased the transfer of sediments (URL4). Observing the northwestern part of the studied area, the changes are significantly visible during the two examined time periods. Initially, the coastline moved toward the sea, as had also happened in the southwest side of the studied area for the same reasons, but to a greater extent. As seen from the photomosaics of the aerial photographs of 1950 and 1975 (Figure 5), in the region dominated the agriculture, and so, because of the intensification of 56
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South-‐Eastern European Journal of Earth Observation and Geomatics
Issue Vo1, No1, 2012
agricultural crops, a big part of that land has suffered deforestation, resulting in increased transport of sediments in the delta. This phenomenon of aggradation is compensated in the next period 1975-‐2009, where the coastline recedes. That phenomenon of erosion, probably was caused by the agricultural and farming activities along the watercourse. The middle part of the studied area (Fig. 4), which includes the ends of the main body of the river, shows the most intense processes that suffered the coastline. The first reporting period of transition between 1950 and 1975, the phenomenon of sedimentation prevails, confirming the strong flow of the river and the transporting of large amount of sediments. It is observed an intense development of the Aliakmon delta because of the steep slopes of the studied area, the altitudes which prevail in the watersheds, the geology of the area that consists of corrodible materials, and moreover, the climatic conditions.
Figure 2. Temporal change of the coastline of the delta of the river Aliakmon.
The significant diversion of the river is caused by the completion of the construction of the first two dams in the decade of ‘70, resulting in the displacement at the ends of the delta. The next time surveying the coastline, is observing a small volume of shoreline erosion, which penetrates inward. These changes may be caused by the reduction of transport and the deposition of sediment through the river, due to the completion of another two important dams in the decade of ’80 (double dam placed in Asomata), but mainly because of the agricultural and farming activities and the using of water for irrigation purposes. 57
®Aristotle University of Thessaloniki, Greece
Published online April 2012
South-‐Eastern European Journal of Earth Observation and Geomatics
Issue Vo1, No1, 2012
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c. Figure 3. a. Photomosaic of the aerial photographs of 1950, b. Photomosaic of the aerial photographs of 1975, και c. Photomosaic of the aerial photographs of 2009, southwest of the study area.
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®Aristotle University of Thessaloniki, Greece
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South-‐Eastern European Journal of Earth Observation and Geomatics
Issue Vo1, No1, 2012
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c. Figure 4. a. Photomosaic of the aerial photographs of 1950, b. Photomosaic of the aerial photographs of 1975, και c. Photomosaic of the aerial photographs of 2009, in the center of the study area.
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®Aristotle University of Thessaloniki, Greece
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South-‐Eastern European Journal of Earth Observation and Geomatics
Issue Vo1, No1, 2012
a.
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c. Figure 5. a. Photomosaic of the aerial photographs of 1950, b. Photomosaic of the aerial photographs of 1975, και c. Photomosaic of the aerial photographs of 2009, northeast of the study area.
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®Aristotle University of Thessaloniki, Greece
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South-‐Eastern European Journal of Earth Observation and Geomatics
Issue Vo1, No1, 2012
5. Conclusions The substudy River Delta, has changed dramatically during the considered period, because of human’s interventions. The change of the coastline of the Aliakmon’s delta is expected to be increased during the next years, because of the possible completion of the dams that are already under construction or the creation of new dams, which in turn will exacerbate such phenomena about the delimitation of the delta, the reducing of its supply and in general interventions in the natural evolution of the river. Finally, regarding the assessment of possible changes in this delta system, the future rise in sea level (Poulos et al., 2000), resulting in a global increase in temperature, will considerably alter the mouth of delta, as a significant part of their extent will be flooded with water. Acknowledgement This study was realized under the supervision of Dr. Dimitri Kaimari in the framework of ‘Applications of Geomatics’ course of the School of Urban-‐Regional Planning and Development Engineering of Aristotle University of Thessaloniki in Greece. The authors would like to thank Dr. Kaimari for their useful advices and support towards this project accomplishment. References Poulos S.E., G.Th. Chronis, M.B. Collins, V. Lykousis, 2000. Thermaikos Gulf Coastal System, NW Aegean Sea: an overview of water sediment fluxes in relation to air–land–ocean interactions and human activities, pp. 61-‐72 Official Gazette 220/Δ/14.05.2009, Decision 12966 Official Gazette 350/Α/1974, Legislative Decree 191/74 Useful Links (accessed March 2012): URL1: http://www.ekby.gr/ekby/el/EKBY_PP_el.html URL2: http://www.ypeka.gr URL3: http://www.callisto.gr URL4: http://www.culturnet.net/naussa-‐environmental-‐heritage.aspx
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