lake and stream hydrology 2009 uj,uh, &tpu timo huttula jy/bytl& syke/vto

Lake and Stream Hydrology 2009 UJ,UH, &TPU

Timo Huttula

JY/BYTL& SYKE/VTO

www.environment.fi

19.04.23 Lake and stream hydrology T.Huttula

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Contents

River characteristics River hydraulics

Example from wet temperate region


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River characteristics Water movement is determined by a slope along

the longitudinal axis of the channel In general we limit ourselves to one dimensional

spatial analysis Variables: Length, (m), water level W (m),

cross sectional area A (m2) Cross sectional area can vary significantly Most important variable is the discharge Q (or

flow rate). It’ s unit is m3s-1. For small rivers or creeks it can be expressed as ls-1

Water body is expected fully mixed, incompressible and acting as an ideal fluid

Short retention time as compared to lakes

Lake Päijänne surface level is about 76 m above sea. Distance from Kalkkinen is about 100 km from sea. What is the mean slope of a hypothetical river from lake to sea?

Slope= 76 m/(100*1000 m)=0,00076


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Time and space scales of hydrological phenomena

Note that the storage units are expressed hear as mm over the surface!


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Duration curves


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What determines the discharge duration? Example from Japan


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Examples from humid temperate

region

Temperate: no extremes Humid: abundant water storages, still large varions. Mean annual evaporation

500<E0<1000 mm and precipitation P>E0

Well known ecohydological region, rich in research Long cultural history diverse land use Anthropogenic effects to H-processes are significant locally and also

regionally


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Formation of runoff and discharge in this region

Stream discharge is here a sum of groundwater flow, surface runoff and overland flow

Their share varies in space and time

”Quick flow” , in UK 40 % from precipitation of a certain precipitation event . It can vary from 1% (chalky soil)…77% (clay)


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Annual water balance

In this region run off is R=f( annual precipitation, water vapor deficit in air, soil properties)

Figure: Beult good correlation , Pang bad correlation, because soil is very porous (chalk)


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Monthly Q-duration curves 1(2)

Expresses the duration as % of the time in each month.

The duration curves or surface are expressed as 100, 90, 75, 50,25,10, 5 ja 0%:n


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Monthly Q-duration curves for seasonal studies 2(2)

Comparing the curves we can see the effects of watershed factors on river Q- regime

The two rivers here are only 100 km apart Danube obtains waters from Alps. Watershed

is mainly in regions of permanent snow. This means that rain (P) and melting are important factors forming Q steady duration curves in II…VIII. Dry winter months

Tisza: waters come from North. No permanent snow on watershed => peak and valley in duration curves happens in the same time for each curve tells about the similar repeated behavior of the Q in the years cycle.


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River discharge Several classifications for rivers. Comparisons can be made most

effectively if the homogenous and representative catchments

Left we see the share of monthly discharge about the annual total ( catchments)

most have max during winter In West Europe P max is in winter and

evaporation max in summer large variations in winter and summerQ

In continental regions P max is in summer as evaporation max steady Q over the year

In regions with snow we have spring melting and then also spring flood


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River discharge 2(2) Geological effects can be seen in

figures on left Pang: Catchment soil is chalky

slow changes in hydrographs Kym, clay soil drastic changes Q-Pang (SE UK ) ja Q-Wurm(N

Germany) are comparable different inputs summed up produce similar Q time series


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Substances transported in a river: Sediments transport

Total substance transport=sediment transport + soluble substance transport

Sediment transport or suspended solids transport happens in suspension and as a bottom transport

Bottom transport in the ecohydrolgical region is small: 1….11 % of the sediment total transport

Suspended solids yield is inversely related to watershed area. Load decreases as A increases.

In Germany: yield is mostly 50 t/km2 /y, range 6…300 t/km2 /y

UK: also 50 t/km2, on wet upper lands even 500 t/km2 /y and less than 1 t/km2 great flat watersheds or watersheds with impervious soil

Largest yields: Waipoa/NZ 7000 t/km2 /y


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Suspended solids distribution in a river

u=velocity

C=suspended solids concentration


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Transport of soluble substances, natural streams

The variation is normally less that the suspended solids transport It is a function of atmospheric load, soil chemistry and precipitation In UK the soluble substances yield is : 10…400 t/km2 /y In wet regions soluble substance transport has larger values as the

suspended solids transport In SW UK the solutes consists 55…77 % of the total river substance transport In France 68% of the total river substance transport In Poland 93-95% of the total river substance transport


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Suspended solids transport in River Tornionjoki

lake and stream hydrology 2009 uj,uh, &tpu timo huttula jy/bytl& syke/vto

Documents

stream hydrology t

wet temperate region

discharge duration

monthly qduration curves

q steady duration curves

discharge q

duration curveslake

river q regime