Water as a Medium
- Medium for chemical reactions
- Transports material around plants and animals
- Medium for transporting matter n rivers: sediment, and redistribution of organisms
- Medium for transporting waste
- Water is important because it sustains life IN, ON and NEAR rivers
Natural systems vs. human impact
Disproportionate importance - 6% of world's known species live in freshwater
- When frozen, expands
- Most dense at 4°C
- Buffers variations in temperature due to its high specific heat capacity
- High latent heat of evaporation
- Moderately viscous
- High surface tension
What are Rivers?
'Stream of water which flows in channels from high to low ground and ultimately to a lake or the sea, except in desert areas where they may dwindle away to nothing.'
'Rivers [are] dynamic mosiac of spatial elements and ecological processes arrayed hierarchically' (WARD et.al. 2002)
Open systems that form an integral part of the surrounding landscape with which they are highly interactive (WARD, 1989)
Region - Catchment - Stream - Stream Reach - Patch - Class/Grain (rocks, animals)
The heterogeneity characteristics of natural riverine landscapes have been masked in many regions by a long history of river engineering. This leads to a distorted perception of natural patterns and processes.
Rural rivers vs. Urban rivers which are extremely modified.
Channelisation - very straight. Dredged sediment used for levees
River System Dimensions
Longitudinal dimension: channel - channel
Lateral dimension: channel - floodplain
Vertical dimension: channel - aquifer
Temporal dimension: low flow/high flow, drought/flood
The River Corridor
Animals can move upstream, not just one way movement
PHREATIC: deeper, older water
HYPORTHEIC: newer, with higher turnover of water (fresher)
Special properties of water influence how rivers function (CLOSS et. al., 2004)
Our traditional view of rivers is one dimensional, predominantly reflecting a culture of river engineering.
River systems are actually highly dynamic in four dimensions (WARD, 1989)
Different processes occur across a range of scales (km-mm) (WARD et. al., 2002)
We can envision rivers as corridors, with a range of spatially arrayed geomorphological units (WARD et. al., 2002)