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Lake and Stream Hydrology 2009 UJ, UH & TPU

This lecture series explores the hydrological cycle, the role of lakes in the cycle, the morphological characteristics of lakes, and the human impacts on lakes. It provides an overview of lake hydrology in Finland and globally, emphasizing the significance of lakes as water storages and their vulnerability to pollution.

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Lake and Stream Hydrology 2009 UJ, UH & TPU

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  1. Lake and Stream Hydrology 2009 UJ, UH & TPU Timo Huttula UJ/BYTL& SYKE/VTO www.environment.fi

  2. At UJ&UH Lectures 1-6 Video Field period in Konnevesi Examination To be discussed Lecture notes and copies from books Material distributed during field period Web pages: http://users.jyu.fi/~thuttula/Lake&Stream_Hydrology/ At TPU Lectures 1-3 Video Field period in Konnevesi Examination To be discussed Lecture notes Material distributed during field period Webpages: http://users.jyu.fi/~thuttula/Lake&Stream_Hydrology/ Contents Lake and stream hydrology T.Huttula

  3. Lectures Lake and stream hydrology T.Huttula

  4. 1. Lakes as a part of the hydrological cycle • Hydrological cycle and hydrological processes • The importance ot the lakes • What is a lake? • Lake morphology • What is the role of lakes in hydrological cycle? • Lakes in Finland • Basic hydrological statistical parameters • Human impacts on lakes Lake and stream hydrology T.Huttula

  5. Hydrological cycle Lake and stream hydrology T.Huttula

  6. Lake and stream hydrology T.Huttula

  7. Watershed, catchment, river basin… Lake and stream hydrology T.Huttula

  8. Lake and stream hydrology T.Huttula

  9. Units in hydrology • Fluxes are expressed in mm/time or m3/s • Flux= mass or volume /(time*surface area) • One liter of water weights about 1 kg • If we put one liter of water on a surface area of A=1 m* 1m, the water height (h) will be 1 mm Lake and stream hydrology T.Huttula

  10. Hydrological variables and their units Lake and stream hydrology T.Huttula

  11. Why lake hydrology is important in Finland? • In Finland we have 187 888 lakes ( min. size 50 m*10 m) • Sensitive for pollution • More 50 % of Finnish population still drink treated lake water • Important recreational value • Legislative reasons Lake and stream hydrology T.Huttula

  12. In global scale • Lakes contain important amount of fresh water • Water storages • Vulnerable in many ways • Important sources of protein • Recreational value • Preserving of their ecosystem Lake and stream hydrology T.Huttula

  13. What is a lake? • A mass of still water situated in a depression of the ground without direct communication with sea (Encyclopedia of Britannica, 1962) • Baltic Sea is not a a lake, Aral and Caspian Sea are Lake and stream hydrology T.Huttula

  14. Morphological characteristics of lakes • Area, A (km2) • Volume, V (km3) • Mean depth z mean ,(m) • Maximum depth zmax ,(m) • Length of main axis, l long ,(m) • Shore line length l sh ,(m) • Inflow I or outflow O, (m3/s) • Retention time tr=V/O , (years) Lake and stream hydrology T.Huttula

  15. Lake Pääjärvi Area 13.5 km2 Lake and stream hydrology T.Huttula

  16. Morphology… • Shore line length l sh ,(m) • Inflow I or outflow O, (m3/s) • Retention time tr=V/O , (years) • Hypsographic curves • A=f(W) • V=f(W) Lake and stream hydrology T.Huttula

  17. Morphology:Fetch • The wind effect length on the lake: • Lf = the mean length of the lines from the observation site, when lines are taken in 90 0 angle towards wind direction (=direction from where wind is coming from) • Important for wave and erosion calculations Lake and stream hydrology T.Huttula

  18. Lakes in Finland Lake and stream hydrology T.Huttula

  19. Typical for Finnish lakes • Shallow: 95*total volume of Finnish lakes = volume of Lake Baikal • Short retention or renewal time • Cover 32700 km2 (10 %) of Finnish territory • Fragmented and form a river like water course system • Loaded presently by agriculture • Eutrophication is the number one problem • Water budget: • Direct precipitation on lake surface is 14 % of annual water budget • Evaporation from lake surface is 12 % of annual water budget • No ground water flow to lake • Mean annual water level variation is 103 cm (in period of 1961-80) Lake and stream hydrology T.Huttula

  20. Lakes in Finland Mean depth =7.2 m Deepest sites: 1: Lake Päijänne 95.3 m 2: Inari 91.8 m 3: Suvasvesi 89.6 m Lake and stream hydrology T.Huttula

  21. Q An upper lake Downstream lake Lakes in hydrological cycle • Water storages • Smooth out the water level fluctuation in water course • In upper lakes: Rapid water level change and short duration • Downstream lakes: Lagged response and moderate response • Deep lakes act like sedimentation tanks • The rate of change in water quality is related to retention time t Lake and stream hydrology T.Huttula

  22. Mean and extreme values in time series • MQ = mean annual discharge • MHQ=mean high (flood) discharge during the observation period like 30 years • MNQ =mean low (dry) discharge during the observation period like 30 years • MW = mean annual water level • MHW and MLW like for the discharge Lake and stream hydrology T.Huttula

  23. Lake and stream hydrology T.Huttula

  24. Human impacts on lakes • Regulation • Drainage • Sewage input • Construction like embankments, bridges, piers, … • Dredging • Thermal pollution Lake and stream hydrology T.Huttula

  25. Example • Lake area is A=100 km2. A very heavy rain fall occurs and 100 mm precipitation will fall on the lake in six hours. How much that is in m3/s ? We do not consider in and outflows. • Area A=100 km2=100*1000*1000 m2=1*108 m2 • Precipitation P=100 mm=0,1 m . So we put h=0,1 m • Time t=6 h=6*3600s=21600 s • Q=Ah/t=1*108m2*0.1 m/(21600s) = 463 m3/s Lake and stream hydrology T.Huttula

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