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Lake and Stream Hydrology 2009 UJ, UH & TPU
Timo Huttula
UJ/BYTL& SYKE/VTO
www.environment.fi
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Contents
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/
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Lectures
1. Lakes and rivers 4.9.
2. Basics of hydrological measurements 4.9.
3. Three practical examples of lake and stream hydrology = ”Problem of the day” (Huttula& Krogerus)
15.9. and 16.9.
4. Steady and unsteady river flow 9.9.
5. Material transport in rivers 9.9.
6. River ice 25.9.
7. Reports on field measurement results (students give short presentations) 30.9
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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
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Hydrological cycle
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Watershed, catchment, river basin…
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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
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Hydrological variables and their units
Variable Notation Unit
Precipitation P mm/day, mm/h
Evaporation E mm/day, mm/h
Infiltration I mm/day, mm/h
Runoff R mm/day, mm/h
Discharge Q m3/s, l/s
Water level W m
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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
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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
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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
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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)
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Lake Pääjärvi
Area 13.5 km2
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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)
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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
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Lakes in Finland
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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)
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Lakes in FinlandLake Location of the
outletArea
km2
Saimaa Imatra 1147
Inari Inari 1102
Päijänne Asikkala 1054
Oulunjärvi Vaala 893
Pielinen Eno 868
Kallavesi Leppävirta 513
Keitele Äänekoski 500
Iso-Längelmävesi Kangasala 410
Puulavesi Hirvensalmi 325
Lokka Sodankylä 317
Mean depth =7.2 m
Deepest sites:
1: Lake Päijänne 95.3 m
2: Inari 91.8 m
3: Suvasvesi 89.6 m
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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
Q
Downstream lake
An upper lake
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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
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Annual
Month MQ HQ NQ
Year 1 2 3 4 5 6 7 8 9 10 11 12
1990 11 10 9 10 33 25 16 17 18 19 21 16 17 33 9
1991 13 12 11 13 25 29 30 31 22 25 26 27 22 31 11
1992 8 10 9 11 23 27 28 29 20 23 24 25 20 29 8
1993 7 13 12 13 36 28 19 20 21 22 24 19 20 36 7
1994 6 4 4 4 8 10 10 10 7 8 9 9 7 10 4
1995 3 8 7 6 7 23 18 11 12 13 13 15 11 23 3
1996 13 12 13 43 33 21 22 23 25 27 21 17 22 43 12
1997 7 6 6 17 16 13 13 14 13 14 12 11 12 17 6
1998 4 4 4 8 10 10 10 10 8 9 9 9 8 10 4
1999 3 4 4 5 10 9 7 7 7 7 8 7 6 10 3
2000 2 2 2 3 5 5 4 4 4 4 4 4 4 5 2
For period MQ HQ NQ MHQ MNQ
1990-2000 14 43 2 23 6
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Human impacts on lakes
Regulation Drainage Sewage input Construction like embankments, bridges, piers, … Dredging Thermal pollution
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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