Browsing by Subject "TIR"
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(2020)The two input rivers of Säkylä’s Lake Pyhäjärvi: Pyhäjoki and Yläneenjoki, were studied with aerial thermal infrared imaging (TIR) analysis and baseflow program, in order to estimate the baseflow in the two rivers. From the helicopter- assisted TIR survey made in July 2011, almost 200 groundwater discharge sites were located in the two studied rivers. The groundwater discharge anomalies were categorized in 5 different classes: 1) spring/springs, 2) cold channel connected to the main channel, 3) diffuse discharge to river, 4) wetland/ wide seepage, 5) unknown anomaly. In addition, a temperature analysis was performed from the studied rivers. In both rivers, pattern of increasing river water temperature from headwaters towards river outlet were discovered with temperature analysis. The baseflow share estimate was made with baseflow filtering program which uses recursive digital filter for signal processing. Mean baseflow share estimation from four years: 2010-2013, were 70 % for River Pyhäjoki and 54 %, for River Yläneenjoki. Larger baseflow portion, lower river water temperature and wide diffuse discharge areas of River Pyhäjoki indicate that Pyhäjoki is more groundwater contributed than River Yläneenjoki. Previous studies made from the Lake Pyhäjärvi catchment have signs of higher groundwater share in River Pyhäjoki catchment, as well. However, TIR and baseflow estimation results of this study have to be dealt with caution. TIR results represent momentary circumstances and GWD locations are interpretations. There are also many factors increasing the uncertainty of the temperature analysis and observations of GWD anomalies. The results of baseflow analysis has to be interpreted carefully too because baseflow filtering is pure signal processing. However, this study shows that River Pyhäjoki and River Yläneenjoki have groundwater contribution. There is a difference in groundwater share in the two studied rivers. In River Pyhäjoki the larger groundwater share (70 %) is related to coarser grained glacial deposits in the river catchment. In TIR results, the influence of headwaters of the River Pyhäjoki, fed by two large springs: Myllylähde and Kankaanranta were emphasized. The two feeding springs are connected to the Säkylä-Virttaankangas esker complex. In River Yläneenjoki catchment, where GW portion was estimated to be smaller (54 %) and GW anomalies where mostly discrete, there are only two little till groundwater areas near the river channel and the catchment is characterized by finer sediments than River Pyhäjoki catchment.
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(2020)The condition of Tahmelanlähde spring in city of Tampere has been under discussion for over two decades. Between 1906–1966, the spring was being used for municipal water supply and the water quality was good. The quality of discharging groundwater has since heavily deteriorated, bearing now high concentrations of iron, manganese, nitrogen, phosphorus and very low oxygen. The cause of this deterioration has remained unclear. The aims of this study were to increase the hydrogeological knowledge of Tahmela-Pispala area in order to get a better understanding of the regional groundwater flow patterns and sources of the groundwater discharging at the artesian spring area, to assess the cause for the spring deterioration and to give suggestions to a possible rehabilitation plan. Tahmelanlähde spring is located on a clay or silt soil under artesian circumstances, down the southern slope of Pispalanharju interlobate esker formation. The esker forms a longitudinal neck between Lake Näsijärvi and Lake Pyhäjärvi, rising up to 160 meters above sea level. The water level of Lake Näsijärvi is approx. 95 m a.s.l. and the water level of Lake Pyhäjärvi approx. 77 m a.s.l. Considering the distance of only a few hundred meters between these two lakes, the difference of 18 meters in the lake water levels is quite unusual in Finland’s geological context, especially because the lakes are separated by a major esker formation. For the assessment of the hydrogeological features in the study area we had two field campaigns including ground penetrating radar (GPR) survey, thermal infrared survey using unmanned aerial vehicle (UAV-TIR), measuring of water tables as well as water sampling from springs, surface water bodies, groundwater observation wells and groundwater discharging into the Lake Pyhäjärvi. 23 water samples were analyzed for main ion composition, stable isotopic (δ18O / δD) composition, pH, EC and trace elements such as iron and manganese. 14 samples were additionally analyzed for CODMn, N, P, O and microbial indicators. Some previous studies have suggested infiltration of Lake Näsijärvi water into the esker. Our results reveal that most of the groundwater in the Pispalanharju area contain a variable amount of surface water component. The samples east from the spring present good-quality groundwater and show nonexistent surface water impact. This and the complex sedimentology revealed by the GPR survey indicate that the regional groundwater flow patterns are not simple and there are at least two water components with different origins discharging at Tahmelanlähde spring. The results imply that the primary cause for the spring deterioration could be a major shift in the groundwater – surface water interaction in the northern esker area, probably driven by urbanization and the heavy construction during the last few decades. The study was a collaboration between the City of Tampere, Pirkanmaa Center for Economic Development, Transport and Environment (ELY Center) and University of Helsinki, Department of Geosciences and Geography.
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