Ekologie tekoucích vod
Stream Ecology
Jan Helešic, Marie Zhai, Jindřiška Bojková
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References
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Hydrology: History
• rain-water as the source for springs and streams – since the 16th century
Bernard Palissy
(1510-1589)
Pierre Perrault
(1608-1680)
„On the Origin of Springs“
Hydrology
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Water volume
• renewal time: 12-20 days
Total water volume
Inland water 2.80 %
Ice caps, glaciers 2.24 %
Groundwater 0.61 %
Lakes 0.009%
Atmosphere 0.001%
Running waters 0.0001%
Hydrology
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Water cycle
km3/year
Hydrology
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Water balance on continents
Hydrology
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Pathways of water from land to streams
Hydrology
• infiltration capacity of soil
• depression storage capacity
• 1... Overland flow (plošný splach, sklonový odtok)
– a part of surface runoff, Horton’s model (1933)
• 2... Groudwater flow (podzemní odtok) → river’s
baseflow (základní odtok)
• 3... Shallow sub-surface stormflow
(podpovrchový, hypodermický odtok)
• 4... Saturation overland flow or return flow
(Hewlett & Hibbert, 1967)
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Movement of water between channel and
groundwater
• perennial vs. intermittent streams
• a... Gaining or effluent streams
• b... Losing or influent streams
Hydrology
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Streamflow
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Current velocity
• U [m s-1]
• channel slope, sinuosity and obstructions in
the channel, friction with bed, banks, and
atmosphere
• velocity measurement
• mechanical, electromagnetic flowmeters
• acoustic methods
• mean velocity
• float (plovák): × 0.8
• in turbulent waters – at each 0.1× of
depth
Hydrology
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Discharge (= flow)
• Q [m3 s-1] = width × depth × U
Hydrology
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Hydrograph
• wide variation over time, river size and
geographic region (distribution of
precipitation, snow storage, and basin,
soil and vegetation characteristics)
• flashy streams vs. streams in humid
areas
• broader and less sharp flood peaks with
increasing number of tributaries and
downstream
• natural connection with floodplain
Hydrology
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Flow regime
• characteristic of regions
• magnitude of a flow event vs. its probability →
flow duration curve
• daily records
• median flow (Q0.5)
• extremes:
Q0.05 – exceeded in 18 days in a year
Q0.95 – exceeded in 347 days in a year
• comparisons of flow regime stability between
streams - after normalizing flow for drainage area
• indicator of water availability but not timing
Hydrology
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Flood frequency analysis
• timing of flood events
• counting the peaks of the flood
hydrograph (esp. in small streams)
• T (reccurrence interval) = (n+1)/m
n...years of record, m...rank of the
flood magnitude (max.=1)
• probability of a „1-in N-year“ flood
of a given size or larger
= 1/average reccurence
• bankfull flood
Hydrology
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Fluvial geomorphology
• hydraulic processes
• a tendency to reach a dynamic equlibrium between erosion
and deposition
• slope, chanell width and depth, flow velocity, grain size of
sediment load, bed roughness, sinuosity and braiding
• cross section symetrically trapezoidal in straight reaches
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Hydraulic geometry
• power equations – Leopold & Maddock (1953)
w = aQb
d = cQf
v = kQm
Q = w × d × v → a × c × k = 1, b + f + m = 1
• overgeneralization
• after overflowing of banks, „w“ increases rapidly with
increasing „Q“
• „v“ may remain nearly constant at a site
• highest „v“ usually at the lowest and flattest
downstream parts
Geomorphology
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Sinuosity
• sinuosity index (SI)
= channel thalweg (údolnice) distance / downwalley distance
• values: 1-4
• a consistent pattern of bends accross all streams:
wave length 10-14 × w
mean radius of curvature 2-3 × w
Geomorphology
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Sinuosity II
Geomorphology
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Pool-riffle sequence
• usually at moderate and low gradient,
unconfined, poorly sorted gravel
streams
• riffle – shallow, high velocity, gravel-
cobble
• pool – deeper, lower velocities, finer
sediment
• alternating at intervals of ca 5-7× w
• a change in distribution of forces at high
discharge
• the role of log wood in some geographic
regions (Pacific Northwest)
Geomorphology
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Floodplain
• a flat area adjacent to a river, formed mainly of river sediments and subject to flooding
• only less frequent larger flows inundate the floodplain (with a 1.5 year frequency, sometimes
several times annually)
• degradation - river cut downwards, old floodplain → terrace
• aggradation - increase in land elevation due to the deposition of sediment
Geomorphology
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Grain size
Geomorphology
• given by the sizes introduced
from upstream, tributaries and
hillslopes, by abrasion and
sorting
• The canonical definition by
geologist Chester K. Wentworth
(1922): "A Scale of Grade and
Class Terms for Clastic
Sediments„ - The Journal of
Geology.
(1891-1969)
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Grain size analysis
Geomorphology
SD
D50
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